阅读说明：本技术 两端子整流器及电力转换器 (two-terminal rectifier and power converter ) 是由 黄品豪 张振富 刘权德 于 2018-12-10 设计创作，主要内容包括：本申请案涉及一种两端子整流器及一种电力转换器。两端子整流器包含耦合于第一端子与第二端子之间的电力MOSFET、体二极管及肖特基二极管。所述两端子整流器还具有耦合于所述第一端子与所述第二端子之间的电力管理电路、电容器、控制电路及驱动器电路。所述两端子整流器可以两引脚封装来实施且可用于电力转换器中以进行CCM操作。(The application relates to a two-terminal rectifier and a power converter. The two-terminal rectifier includes a power MOSFET, a body diode, and a schottky diode coupled between a first terminal and a second terminal. The two-terminal rectifier also has a power management circuit, a capacitor, a control circuit, and a driver circuit coupled between the first terminal and the second terminal. The two-terminal rectifier may be implemented in a two-pin package and may be used in a power converter for CCM operation.)

1. a two-terminal rectifier, comprising:

a first terminal and a second terminal configured to be coupled between a transformer of a power converter and an output terminal;

a power switch coupled to the first terminal and the second terminal for turning on and off current flow between the first terminal and the second terminal, wherein the power switch comprises a power MOSFET having a source, a drain, a gate, and a body;

a body diode formed by a junction between the body and the drain of the power MOSFET or a junction between the body and the source of the power MOSFET, the body diode coupled in parallel with the source and the drain of the power switch;

a Schottky diode coupled to the first terminal and the second terminal;

A power management circuit and a capacitor coupled between the first terminal and the second terminal and configured to provide operating power to the two-terminal rectifier;

A control circuit coupled to the power management circuit and configured to provide a control signal for controlling an on/off state of the power MOSFET in response to a voltage between the drain and the source of the power switch; and

A driver circuit coupled to the control circuit to receive the control signal and provide a drive signal to the gate of the power MOSFET;

Wherein the two-terminal rectifier is configured to reduce body diode current conduction during dead time in the power converter and to reduce reverse recovery time in the body diode,

Wherein the two-terminal rectifier is configured to conduct continuous conduction mode CCM operation of the power converter without a synchronization signal.

2. The two-terminal rectifier of claim 1, wherein the two-terminal rectifier is coupled to a secondary side of the power converter.

3. The two-terminal rectifier of claim 2, wherein the control circuit is configured to adjust a dead time for Continuous Conduction Mode (CCM) operation of the power converter, wherein during the dead time a power switch on a primary side of the power converter and the power MOSFET in the two-terminal rectifier on the secondary side of the power converter are off.

4. The two-terminal rectifier of claim 1, further comprising:

A first chip mounting pad and a second chip mounting pad;

a first lead segment coupled to the first chip mounting pad;

A second lead segment coupled to the second chip mount pad;

A first semiconductor chip including the power switch attached to the first chip mounting pad, the drain of the power switch being coupled to the first lead segment through the first chip mounting pad;

A second semiconductor chip including the Schottky diode attached to the first chip mounting pad, a cathode of the Schottky diode being coupled to the first lead segment through the first chip mounting pad;

a third semiconductor chip including the power management circuit, the control circuit, and the driver circuit, the third semiconductor chip attached to the second chip mounting pad;

the capacitor attached to the second chip mounting pad, a first end of the capacitor coupled to the second lead segment through the second chip mounting pad, a second end of the capacitor coupled to the power management circuit in the third semiconductor chip;

A first conductive connection coupling an output pin of the third semiconductor chip to the gate of the power switch;

A second conductive connection coupling an anode of the Schottky diode to a first chip source of a power switch; and

a third conductive connection connecting the source of the power switch to the second chip mounting pad.

5. The two-terminal rectifier of claim 4, further comprising an encapsulation of molding material that encapsulates the first semiconductor chip, the second semiconductor chip, the third semiconductor chip and the capacitor, the first and second chip mounting pads, and portions of the first and second lead segments.

6. the two-terminal rectifier of claim 5 wherein the encapsulation exposes a bottom surface of the first chip mounting pad.

7. the two-terminal rectifier of claim 4 wherein the first and second chip mounting pads and the first and second lead segments are part of a lead frame.

8. The two-terminal rectifier of claim 1, wherein the first terminal of the two-terminal rectifier is coupled to an anode of the schottky diode and the second terminal is coupled to a cathode of the schottky diode.

9. a two-terminal rectifier, comprising:

A first terminal and a second terminal configured to be coupled between a transformer of a power converter and an output terminal;

a power switch coupled to the first terminal and the second terminal for turning on and off current flow between the first terminal and the second terminal, wherein the power switch comprises a power MOSFET having a source, a drain, a gate, and a body;

a body diode formed by a junction between the body and the drain of the power MOSFET or a junction between the body and the source of the power MOSFET, the body diode coupled in parallel with the source and the drain of the power switch;

A Schottky diode coupled to the first terminal and the second terminal;

A power management circuit and a capacitor coupled between the first terminal and the second terminal and configured to provide operating power to the two-terminal rectifier;

A control circuit coupled to the power management circuit and configured to provide a control signal for controlling an on/off state of the power MOSFET in response to a voltage between the drain and the source of the power switch; and

A driver circuit coupled to the control circuit to receive the control signal and provide a drive signal to the gate of the power MOSFET;

Wherein the two-terminal rectifier is configured to reduce body diode current conduction during dead time in the power converter and to reduce reverse recovery time in the body diode.

10. The two-terminal rectifier of claim 9, wherein the two-terminal rectifier is configured to conduct continuous conduction mode CCM operation of the power converter without a synchronization signal.

11. The two-terminal rectifier of claim 9, wherein the two-terminal rectifier is coupled to a secondary side of the power converter.

12. The two-terminal rectifier of claim 9, wherein the control circuit is configured to adjust the dead-time during which a power switch on a primary side of the power converter and the power MOSFET in the two-terminal rectifier on the secondary side of the power converter are off.

13. The two-terminal rectifier of claim 9, further comprising:

A first chip mounting pad and a second chip mounting pad;

A first lead segment coupled to the first chip mounting pad;

A second lead segment coupled to the second chip mount pad;

A first semiconductor chip including the power switch attached to the first chip mounting pad, the drain of the power switch being coupled to the first lead segment through the first chip mounting pad;

A second semiconductor chip including the Schottky diode attached to the first chip mounting pad, a cathode of the Schottky diode being coupled to the first lead segment through the first chip mounting pad;

A third semiconductor chip including the power management circuit, the control circuit, and the driver circuit, the third semiconductor chip attached to the second chip mounting pad;

the capacitor attached to the second chip mounting pad, a first end of the capacitor coupled to a second lead segment through the second chip mounting pad, a second end of the capacitor coupled to the power management circuit in the third semiconductor chip;

a first conductive connection coupling an output pin of the third semiconductor chip to the gate of the power switch;

A second conductive connection coupling an anode of the Schottky diode to the second chip mount pad; and

a third conductive connection connecting the source of the power switch to the second chip mounting pad.

14. The two-terminal rectifier of claim 13, further comprising an encapsulation of molding material that encapsulates the first semiconductor chip, the second semiconductor chip, the third semiconductor chip and the capacitor, the first and second chip mounting pads, and portions of the first and second lead segments.

15. A power converter having a two-terminal rectifier, the power converter comprising:

A transformer having a primary winding for receiving a DC input voltage and a secondary winding for providing an output to an output capacitor;

a power switch coupled to the primary winding of the transformer;

A primary side controller coupled to the power switch, the primary side controller configured to control the power switch for turning on and off current flow in the primary winding, and

a two-terminal rectifier coupled to the secondary winding of the transformer and the output capacitor, the two-terminal rectifier configured to adjust a dead time for continuous conduction mode CCM operation of the power converter.

16. The power converter of claim 15, wherein the two-terminal rectifier comprises:

a first terminal and a second terminal configured to be coupled between a transformer of a power converter and an output terminal;

A power switch coupled to the first terminal and the second terminal for turning on and off current flow between the first terminal and the second terminal, wherein the power switch comprises a power MOSFET having a source, a drain, a gate, and a body;

A body diode formed by a junction between the body and the drain of the power MOSFET or a junction between the body and the source of the power MOSFET, the body diode coupled in parallel with the source and the drain of the power switch;

A Schottky diode coupled to the first terminal and the second terminal;

a power management circuit and a capacitor coupled between the first terminal and the second terminal and configured to provide operating power to the two-terminal rectifier;

A control circuit coupled to the power management circuit and configured to provide a control signal for controlling an on/off state of the power MOSFET in response to a voltage between the drain and the source of the power switch; and

A driver circuit coupled to the control circuit to receive the control signal and provide a drive signal to the gate of the power MOSFET.

17. The power converter of claim 16, wherein the two-terminal rectifier comprises:

A first chip mounting pad and a second chip mounting pad;

a first lead segment coupled to the first chip mounting pad;

a second lead segment coupled to the second chip mount pad;

A first semiconductor chip including the power switch attached to the first chip mounting pad, the drain of the power switch being coupled to the first lead segment through the first chip mounting pad;

A second semiconductor chip including the Schottky diode attached to the first chip mounting pad, a cathode of the Schottky diode being coupled to the first lead segment through the first chip mounting pad;

A third semiconductor chip including the power management circuit, the control circuit, and the driver circuit, the third semiconductor chip attached to the second chip mounting pad;

The capacitor attached to the second chip mounting pad, a first end of the capacitor coupled to a second lead segment through the second chip mounting pad, a second end of the capacitor coupled to the power management circuit in the third semiconductor chip;

a first conductive connection coupling an output pin of the third semiconductor chip to the gate of the power switch;

A second conductive connection coupling an anode of the Schottky diode to the second chip mount pad; and

a third conductive connection connecting the source of the power switch to the second chip mounting pad.

18. the power converter of claim 17, wherein the two-terminal rectifier further comprises an encapsulation of molding material that encapsulates the first, second, and third semiconductor chips and the capacitor, the first and second chip mounting pads, and portions of the first and second lead segments.

19. the power converter of claim 16, wherein the first terminal of the two-terminal rectifier is coupled to an anode of the schottky diode and the second terminal is coupled to a cathode of the schottky diode.

20. the power converter of claim 16, wherein the two-terminal rectifier is configured to conduct Continuous Conduction Mode (CCM) operation of the power converter without a synchronization signal.

Technical Field

The present invention relates generally to power supply controllers. More particularly, the present disclosure relates to Synchronous Rectifiers (SR) for use in power converters to simplify circuit design and improve power efficiency.

Background

switched mode power control techniques have found widespread use in computer and electronic device power supplies. The popularity of switched-mode power supplies (SMPS) as compared to traditional linear transformer circuits is due in part to their compactness, stability, efficiency, and lower cost.

Flyback converters are one of the common topologies among a wide variety of power converters. A typical flyback converter includes a transformer having a primary winding and a secondary winding and sometimes a third or more windings for control purposes. Such a transformer provides galvanic isolation between the input and the output, and is typically used in low-power, low-cost power supplies.

to provide a DC voltage, diode rectification has been used in switched mode power supplies for many years. However, scaling down of semiconductor technology requires lower voltage and larger current power supplies. Although diode forward droop cannot be further scaled down, diode rectification can no longer meet the consumer demand for compactness, thinness, and high efficiency. In addition, diode rectification suffers from excessive losses due to large output currents.

therefore, a synchronous rectification method using a Synchronous Rectifier (SR) having a power MOSFET has been used in place of the diode. Even though widely used, conventional synchronous rectifiers have many limitations. More details of these and other limitations are described below.

accordingly, there is a need for methods and systems for improved synchronous rectifiers.

Disclosure of Invention

The inventors have recognized that conventional synchronous rectifiers typically require separate control ICs and supporting circuit elements, and may still have the disadvantage of conducting and storing charge from the body diode. Even though a Schottky (Schottky) diode may be connected in parallel with a MOSFET, this arrangement still requires several separate ICs, complicating the design and increasing cost. The inventors have also recognized that power controller designs for CCM (continuous conduction mode) operation are more complex than power controller designs for DCM (discontinuous conduction mode) operation and typically require a handshake (hand-shake) signal (e.g., CCM synchronization signal) between the primary and secondary sides. In some cases, an additional pin (e.g., a synchronization pin) in the secondary controller is required for CCM operation. Some controllers may perform CCM operations without synchronization pins, but they require complex controllers and several separate ICs, which may make system design difficult and increase cost.

The present invention teaches a two-terminal rectifier including a power MOSFET, a schottky diode, a capacitor, and a control circuit in a single two-pin package. A two-terminal rectifier may be used as a direct replacement (drop-in replacement) for a conventional diffused diode or a conventional synchronous rectifier in a power converter. A simple control method for CCM operation implemented by a two-terminal rectifier is also described.

for example, an exemplary two-terminal rectifier may include: a first terminal and a second terminal configured to be coupled between a transformer of a power converter and an output terminal. The two-terminal rectifier may further have: a power switch coupled to the first terminal and the second terminal for turning on and off current flow between the first terminal and the second terminal. As an example, the power switch may include a power MOSFET having a source, a drain, a gate, and a body. Further, a body diode is formed by a junction between the body and the drain of the power MOSFET or by a junction between the body and the source of the power MOSFET, and the body diode is coupled in parallel with the source and the drain of the power switch. A schottky diode is coupled to the first terminal and the second terminal. The two-terminal rectifier may further have: a power management circuit and a capacitor coupled between the first terminal and the second terminal for providing operating power to the two-terminal rectifier. A control circuit is coupled to the power management circuit and provides a control signal for controlling an on/off state of the power MOSFET in response to a voltage between the drain and the source of the power switch. A driver circuit is coupled to the control circuit to receive the control signal and provide a drive signal to the gate of the power MOSFET. The two-terminal rectifier is configured to reduce body diode current conduction during dead time in the power converter and to reduce reverse recovery time in the body diode for Continuous Conduction Mode (CCM) operation of the power converter. The two-terminal rectifier includes a control circuit to adjust a dead time for Continuous Conduction Mode (CCM) operation of the power converter for improved efficiency.

the two-terminal rectifier may be implemented in a single two-pin package, which may include a lead frame having: a first chip mounting pad, a second chip mounting pad, a first lead segment coupled to the first chip mounting pad, and a second lead segment coupled to the second chip mounting pad. A first semiconductor chip of the power switch is attached to the first chip mounting pad, wherein the drain of the power switch is coupled to the first lead segment through the first chip mounting pad. A second semiconductor chip of the schottky diode is attached to the first chip mounting pad, wherein a cathode of the schottky diode is coupled to the first lead segment through the first chip mounting pad. A third semiconductor chip, which may include the power management circuit, the control circuit, and the driver circuit, is attached to the second chip mounting pad. The capacitor is attached to the second chip mounting pad, wherein a first end of the capacitor is coupled to a second lead segment through the second chip mounting pad and a second end of the capacitor is coupled to the power management circuit in the third semiconductor chip. The two-pin package may include: a first conductive connection coupling an output pin of the third semiconductor chip to the gate of the power switch; a second conductive connection coupling an anode of the Schottky diode to a first chip source of a power switch; and a third conductive connection connecting the source of the power switch to the second chip mounting pad.

Definition of

the terms used in the present invention generally have their ordinary meaning in the art within the context of the present invention. Specific terminology is discussed below to provide additional guidance to the practitioner regarding the description of the invention. It will be appreciated that the same thing can be illustrated in more than one way. Thus, alternative languages and synonyms may be used.

a power switch as used herein refers to a semiconductor switch, for example, a transistor, designed to handle high power levels.

Power MOSFETs are a particular type of Metal Oxide Semiconductor Field Effect Transistor (MOSFET) designed to handle significant power levels. An example of a power MOSFET for switching operation is known as a double diffused MOS or simply DMOS.

A body diode in a power MOSFET is formed when the body and source are coupled together, and the body diode is formed between the drain and source. The diode is interposed between the drain (cathode) and source (anode) of the MOSFET, enabling blocking of current in only one direction.

A schottky diode is a semiconductor diode formed by the junction of a semiconductor and a metal. Which has a low forward voltage drop and fast switching action.

A power converter is an electrical or electromechanical device for converting electrical energy (e.g., converting between AC and DC or changing voltage, current, or frequency, or some combination of these conversions). Power converters typically include voltage regulation.

Regulators or voltage regulators are devices used to automatically maintain a constant voltage level.

switching regulators or Switching Mode Power Supplies (SMPS) use active devices that are switched on and off to maintain an average output value. In contrast, linear regulators are made to function like variable resistors, continuously adjusting the voltage divider network to maintain a constant output voltage, and continuously dissipating power.

A constant current regulator is a regulator that provides a constant output current. A constant current or constant voltage is understood to be a current or voltage that is maintained at a constant value within a certain range of deviation depending on design and manufacturing process variations or within certain limits according to specifications (for example, within ± 10%, ± 5% or ± 1%).

The diode forward voltage is the voltage dropped across the conducting forward biased diode. For example, a silicon P-N junction diode may have a forward voltage of approximately 0.7 volts depending on the doping concentration in the P and N regions.

an operational amplifier (op-amp or opamp) refers to a DC-coupled high-gain electronic voltage amplifier with a differential input and a typically single-ended output. Operational amplifiers can be characterized by high input impedance and low output impedance, and can be used to perform mathematical operations in analog circuits.

a voltage reference is an electronic device that ideally produces a fixed (constant) voltage regardless of the load on the device, power supply variations, temperature changes, and passage of time.

The reference voltage is a voltage value used as a target of the comparison operation.

the leadframe is a thin layer of metal frame to which the semiconductor die is attached during the package assembly process. The lead frame may be encapsulated inside a chip package that carries signals from the die to the outside.

when the term "the same" is used to describe two quantities, it means that the values of the two quantities are determined to be the same within the measurement limits.

drawings

FIG. 1 is a simplified schematic diagram of a power converter, for example, a Switched Mode Power Supply (SMPS), embodying certain aspects of the present disclosure;

FIG. 2 is a simplified block diagram of a two-terminal rectifier 200 of a power converter embodying certain aspects of the present invention;

FIG. 3 is a top layout view and a side cross-sectional view of a two-pin package embodying certain aspects of the present invention;

FIG. 4 is a waveform diagram illustrating operation of a power converter embodying certain aspects of the present disclosure;

FIG. 5 is a waveform diagram 500 illustrating drain-source voltage and current in a rectifier with synchronous MOSFETs in a power converter;

FIG. 6 is a waveform diagram illustrating drain-source voltage and current in a two terminal rectifier with a synchronous MOSFET connected in parallel with a Schottky diode in a power converter;

FIG. 7 is a waveform diagram illustrating drain-source voltage and current in a two-terminal rectifier in a power converter embodying certain aspects of the present disclosure; and is

fig. 8 is a waveform diagram illustrating a method for operating a flyback power converter in CCM operation using a two-terminal rectifier embodying certain aspects of the present invention.

Detailed Description

fig. 1 is a simplified schematic diagram of a power converter, for example, a Switched Mode Power Supply (SMPS), embodying certain aspects of the present invention. As shown in fig. 1, the SMPS 100 is in a flyback converter topology for regulating the output voltage Vout. SMPS 100 includes a transformer T1 having a primary winding Np, a secondary winding Ns, and an auxiliary winding Na coupled in series to a power transistor M1 (which is typically a power MOSFET or power BJT). In fig. 1, Np, Ns, and Na also specify the turn ratios in the respective windings. The primary winding is for coupling to an alternating current power supply AC through a rectifier circuit REC, which includes a diode bridge formed by four diodes and a capacitor C1. The rectification circuit provides rectified DC power VIN to the SMPS. The secondary winding Ns is configured for providing an output Vout to a load device represented by a resistor Rout. A power transistor (also referred to as a power switch) M1 is coupled to the primary winding Np for controlling current flow in the primary winding. The primary side controller circuit QP is configured to receive the detection signal through the DET input terminal and the current sense signal through the CS input terminal. The primary side controller circuit QP is configured to turn the power transistor M1 on and off to regulate the SMPS. When the power transistor M1 is switched on, a primary current Ip builds up in the primary winding Np, which stores energy. The energy stored in the primary winding Np Is transferred to the secondary winding Ns to induce the secondary current Is during the off-time interval of the power transistor M1. A two-terminal rectifier 110 and a buffer capacitor Cout are coupled to the secondary winding Ns and configured to convert the secondary voltage Vs into a DC system voltage Vout for supply to a load device represented by a resistor Rout in fig. 1.

In fig. 1, a two-terminal rectifier 110 includes an anode (a) and a cathode (K) and allows current to flow from the anode to the cathode. The two-terminal rectifier 110 forms a rectifier circuit together with the capacitor Cout to convert the secondary voltage Vs into a DC output Vout.

Fig. 2 is a simplified block diagram of a two-terminal rectifier 200 of a power converter embodying certain aspects of the present invention. The two-terminal rectifier 200 is an example of a rectifying element that may be used as the two-terminal rectifier 110 in fig. 1. In fig. 2, a two-terminal rectifier 200 includes an anode a and a cathode K, which allow current to flow from the anode to the cathode. In the configuration of fig. 1, the cathode K of the two-terminal rectifier 110 is coupled to the secondary winding of the transformer, and the anode a of the two-terminal rectifier 110 is coupled to the output terminal of the power converter, which in this case is the ground terminal. In another configuration, the two-terminal rectifier 110 may have the cathode K coupled to the Vout terminal and the anode a coupled to the secondary winding of the transformer. In general, the two-terminal rectifier 200 may have a first terminal for coupling to a transformer of a power converter and a second terminal for coupling to an output terminal of the power converter. In fig. 2, terminal 201 is a cathode labeled "K" and terminal 202 is an anode labeled "a".

the two-terminal rectifier 200 also has a power switch 210 coupled to the first and second terminals of the two-terminal rectifier 200. In this example, the power switch 210 is a four terminal MOSFET having a source 211, a drain 212, a gate 213, and a body 214. The two-terminal rectifier 200 also has a body diode 220 formed by the junction between the body and the drain or by the junction between the body and the source. The body diode 220 is coupled in parallel with the source and drain of the power switch. The two-terminal rectifier 200 also has a schottky diode 230 that leads to the first and second terminals of the two-terminal rectifier 200.

To provide the DC voltage, diode rectification has been used in switched mode power supplies (for example on the secondary side of SMPS 100 in fig. 1). A standard diode typically includes a diffused junction between two semiconductor regions. However, scaling down of semiconductor technology requires lower voltage and larger current power supplies. Active or synchronous rectification involves replacing the diffusion diode with an actively controlled switching element (e.g., MOSFET). MOSFETs have a low resistance when conducting, called the on resistance (rds (on)). MOSFETs can be made with on-resistances as low as 10m omega or even lower. The voltage drop across the transistor is much lower, resulting in reduced power loss and increased efficiency. To further reduce the on-resistance, several MOSFETs or parallel combinations of devices with larger active areas may be used.

Control circuits for active rectification typically use comparators to sense the voltage of the input voltage and turn on transistors at the correct time to allow current to flow in the correct direction. Snubber capacitors are commonly used with active rectifiers for rectification operations. Using an active rectifier instead of a standard diode can reduce power dissipation, improve efficiency, and reduce the size and weight of the circuitry required for a heat sink to handle the power dissipation.

in fig. 2, a two terminal rectifier 200 may provide rectification through a power MOSFET 210, a logic control circuit 270, and a driver circuit 280. The power MOSFET 210 also has a built-in body diode 220. In a power MOSFET, if the body and source are coupled together (as shown in fig. 2), the body and drain form a diode between the drain (cathode) and source (anode) of the MOSFET, enabling the blocking of current in only one direction. Similarly, if the body and drain are coupled together, the body and source form a diode, enabling the blocking of current in the other direction.

In the switching cycle of the SMPS 100, when the primary switching device is turned off, current flows through the parasitic body diode of the power MOSFET before the synchronous rectifier circuit responds to turn on the MOSFET, forming a voltage drop of 0.7V to 1.2V across the drain and source terminals of the MOSFET. This voltage difference is sensed by the input of the logic control circuit 270, which turns on the MOSFETs. After turning on the MOSFET, most of the current in the secondary winding will flow through the MOSFET while bypassing the body diode. Due to the small on-resistance rds (on), the voltage drop across the MOSFET may be less than 0.2V. As the current in the secondary winding decreases, the voltage across the MOSFET also decreases. The synchronous control circuit turns off the MOSFETs when the voltage across the MOSFETs has dropped to a certain preset threshold voltage. Thus, the switching cycle can be repeated.

when a sufficient forward voltage is applied, current flows in the forward direction. Silicon diodes have a typical forward voltage of 600mV to 700 mV. When switching from the conducting state to the blocking state, the body diode has stored a charge that must first be discharged before the diode blocks the reverse current. This discharge takes a finite amount of time, called the reverse recovery time or Trr. The body diode forward voltage may cause power loss, and the reverse recovery time may cause a delay in switching speed. These problems can be alleviated by attaching a schottky diode in parallel with the body diode.

as shown in fig. 2, a schottky diode 230 and a body diode 220 are disposed in parallel between terminals 201 and 202 of the two-terminal rectifier 200. Schottky diode 230 (also referred to as a schottky barrier diode) is a semiconductor diode formed by the junction of a semiconductor and a metal. The schottky diode has low forward voltage drop and fast switching action. For example, the schottky diode may have a forward voltage that may be 150mV to 450 mV. This lower forward voltage requirement allows for higher switching speeds and good system efficiency than conventional diffused diodes or body diodes. The difference between a p-n diode (e.g., a body diode) and a schottky diode is the reverse recovery time (Trr) when the diode switches from a conducting state to a non-conducting state. In a p-n diode, the reverse recovery time may be on the order of microseconds to less than 100ns (for fast diodes). Schottky diodes are majority carrier devices and have very little recovery time. The switching time may be on the order of 100ps for small signal diodes and up to tens of nanoseconds for high capacity power diodes. Due to the low forward voltage drop of the schottky diode, less energy is wasted as heat, making it the most efficient choice for efficiency sensitive applications.

As shown in fig. 2, the two-terminal rectifier 200 also has a power management circuit 250 coupled to the first terminal 201 and a capacitor 260 coupled to the power management circuit 250 and the second terminal 202. The power management circuit 250 and the capacitor 260 provide power to circuit components in the two-terminal rectifier 200. The control circuit 270 is coupled to the power management circuit 250 to receive operating power. The control circuit provides a control signal 272 for controlling the on/off state of the power switch 210 in response to voltage conditions of the two terminals of the power switch. The two-terminal rectifier 200 also has a driver circuit 280 coupled to the control circuit 270 to receive the control signal 272 and provide a drive signal 282 to the power switch 210.

The power management circuit 250 is coupled to the first terminal 201. The power management circuit 250, along with the capacitor 260, provides power to the various circuit blocks in the two-terminal rectifier 200. For example, when the power switch 210 in the two terminal rectifier on the secondary side is turned off, the voltage at terminal 201 is higher than the voltage at terminal 202. The power management circuit 250 may direct current to charge the capacitor 260. When the power switch 210 in the two terminal rectifier on the secondary side is turned on, the capacitor 260 may supply energy to the logic control circuit 270 and the driver circuit 280. The power management circuit 250 may also include voltage control circuitry (not shown) to maintain a desired supply voltage to the circuit blocks.

control circuitry 270 (labeled logic control circuitry in fig. 2) is coupled to the power management circuitry 250 to receive operating power, and provides control signals 272 for controlling the on/off state of the power switch 210 in response to voltage conditions of both terminals (source terminal 211 and drain terminal 212) of the power switch. The control circuit 270 may monitor the voltage difference between the source and drain terminals of the MOSFET and compare the voltage difference to a reference voltage to respond before or after the voltage across the drain and source terminals of the MOSFET drops to zero, thereby preventing current backflow and reducing power loss. The driver circuit 280 may provide a driver circuit to rapidly switch the MOSFETs. The driver circuit 280 may include amplifiers and support components.

the present disclosure teaches a two-terminal rectifier including a power MOSFET, a schottky diode, a capacitor, power management and control circuitry in a single package. The package design may reduce parasitic inductance, capacitance, and resistance between components. Implementing these circuit components in a two terminal device may simplify power converter system design. A two terminal rectifier may be used as a two terminal direct replacement for a conventional diffused diode or a conventional synchronous rectifier in a power converter. As described in more detail in subsequent sections, simple control of CCM operation without a synchronization signal is also described.

fig. 3 is a top layout view and a side cross-sectional view of a two-pin package embodying certain aspects of the present invention. In fig. 3, diagram 310 is a top layout view and diagram 320 is a side cross-sectional view of a two-terminal rectifier 300 in a two-pin package. Drawing 310 shows a portion of leadframe 311 before it is trimmed into individual packages. Drawing 320 is a side cross-sectional view of the package. As shown in fig. 3, a two-terminal rectifier 300 in a package includes an encapsulation 312 of a molding material, and first and second leads 313, 314 protruding from the encapsulation 312. The second pin 314 has two connectors electrically connected together.

Two-terminal rectifier 300 includes a first chip mounting pad 301 and a second chip mounting pad 302. A first lead segment 304 is coupled to first chip mount pad 301 and a second lead segment 305, comprising a two-piece conductor, is coupled to second chip mount pad 302. In this example, the two-terminal rectifier 300 may have similar circuit components as the two-terminal rectifier 200 in fig. 2. The first semiconductor chip 310 includes a power switch, which may be similar to the power switch 210 in fig. 2. As shown in fig. 3, a first semiconductor chip 310 is attached to a first chip mounting pad 301. The drain of the power switch 310, which may be located at the bottom of the power switch chip 310 and not shown in fig. 3, may be coupled to the first lead segment 304 through a first chip mount pad 301. The second semiconductor chip 330 includes a schottky diode, which may be similar to the schottky diode 230 in fig. 2. The second semiconductor chip 330 is attached to the first chip mounting pad 301. The cathode of the schottky diode is connected to a drain, not shown in fig. 3, located at the bottom of the power switch die 310, which may be coupled to the first lead segment 304 through a first die attach pad 301.

A third semiconductor chip 340 may be attached to the second chip mount pad 302. Third semiconductor chip 340 may include power management circuitry, control circuitry, and driver circuitry that may be similar to power management circuitry 250, control circuitry 270, and driver circuitry 280 in fig. 2. A capacitor 360, which may be similar to capacitor 260 in fig. 2, is attached to the second chip mounting pad 302. A first end of the capacitor 360 is coupled to the second lead segment 305 through the second chip mount pad 302 and a second end of the capacitor is coupled to the power management circuitry in the third semiconductor chip 340. The first conductive connector 341 couples the output pin of the third semiconductor chip 340 to the gate 313 of the power switch. A second conductive connection 342 couples the cathode of the schottky diode to the source 311 of the power switch chip 310. A third conductive connection 343, shown in fig. 3 as five conductive elements (connections), connects the source 311 of the power switch 310 to the second chip mount pad 302.

The encapsulation 312 in the two-terminal rectifier 300 encapsulates the first semiconductor chip, the second semiconductor chip, the third semiconductor chip and the capacitor, the first and second chip mounting pads, and portions of the first and second lead segments. In some examples, the encapsulation exposes a bottom surface of first chip mounting pad 301.

a Switched Mode Power Supply (SMPS), such as SMPS 100 illustrated in fig. 1, may operate in a Continuous Conduction Mode (CCM) or a Discontinuous Conduction Mode (DCM). In operation of the SMPS 100, the primary side controller circuit QP is configured to turn the power transistor M1 on and off to regulate the SMPS as described above in connection with fig. 1. When the power transistor M1 is switched on, a primary current Ip builds up in the primary winding Np, which stores energy. The energy stored in the primary winding Np Is transferred to the secondary winding Ns to induce the secondary current Is during the off-time interval of the power transistor M1. In CCM, the system switches on the primary side current before stopping the secondary side current. In DCM, there are discontinuous time periods in which current flow on both the primary and secondary sides is stopped.

CCM operation may have many advantages over DCM operation. For example, the voltage gain is not load dependent, the input current is continuous and not pulsed, and the ripple component of the inductor current may be lower than the average component. Furthermore, in CCM operation, higher efficiency can be achieved compared to DCM. In contrast, in DCM operation, the voltage gain depends on the load and design parameters, the input current is pulsed, the ripple component of the inductor current is high and the RMS value of the inductor current is high. However, the size of the inductor may be reduced compared to CCM.

furthermore, the same converter can operate in both modes. For example, to obtain a regulated output voltage, a mode may be defined by the power load and the input voltage. For example, at low loads, the duty cycle is low, and the power supply may operate in DCM. In contrast, at high loads, the duty cycle is higher and the power supply can operate in CCM. The control function of the DCM may be simpler, having a unipolar transfer function. However, the control function of CCM may be more complex, requiring a bipolar transfer function. Converters with only unipolar transfer function are easier to compensate than converters with bipolar response. Some conventional converters utilize additional communication between the primary side and the secondary side to implement CCM operation. For example, the secondary side may have a synchronization pin for receiving a turn-off signal from the primary side. In another example, the secondary side controller may signal the primary side controller to indicate that the secondary side is off. These additional design considerations may increase system complexity and cost.

The present disclosure teaches a two-terminal rectifier including a power MOSFET, a schottky diode, a capacitor, and a control circuit in a single package. A two terminal rectifier may be used as a two terminal direct replacement for a conventional diffused diode or a conventional synchronous rectifier in a power converter. Simple control of CCM operation is also described. The advantages of using a two terminal rectifier described above are illustrated with reference to fig. 4-7.

Fig. 4 is a waveform diagram illustrating the operation of a power converter embodying certain aspects of the present disclosure. Fig. 4 illustrates waveforms of various parameters during a switching cycle of a power converter (which is similar to power converter 100 in fig. 1). As shown in fig. 4, in graph 410 VGS represents the gate-source voltage of the power MOSFET on the primary side and the secondary side. The solid curve 401 (labeled SW) illustrates the gate-source voltage of the power MOSFET on the primary side as a result of the control signal provided to the gate of the power switch M1 on the primary side in fig. 1. Dashed curve 402 (labeled SR) illustrates the gate-source voltage of the power MOSFET in the two-terminal rectifier 110 on the secondary side.

In diagram 420 of fig. 4, Ipri illustrates the current in the primary winding of the transformer. The two graphs 430 and 440 illustrate the current Isec in the secondary winding of the transformer for two different rectifiers, as explained below. In diagram 450, vds (sw) illustrates the drain-source voltage of the power switch on the primary side (e.g., power switch M1 in fig. 1). In diagram 460, Vsec illustrates a waveform across cathode K (210) and anode a (202).

in fig. 4, the switching cycle is marked by a duration Ts, which includes durations Ton and Toff. During Ton, the control signal to the primary side power switch is on, and during Toff, the control signal to the primary side power switch is off. In Vgs diagram 410, during time Ton, the primary side MOSFET is turned on as shown by Vgs curve 401, and during time Toff, the secondary side MOSFET is turned on as shown by Vgs curve 402. The drive current to the primary side power switch is applied during time Ton. In graph 420, the current Ipri in the primary winding increases linearly from zero to a peak value until the power switch M1 is turned off by the primary side controller. At this time, the secondary winding current Isec abruptly increases.

diagram 430 illustrates the secondary current Isec when the rectifier on the secondary side is a conventional synchronous rectifier. Before the rectifier responds to turn on the power MOSFET, current flows through the parasitic body diode of the power MOSFET, creating a voltage drop across the drain and source terminals of about 0.7V to 1.2V. After the power MOSFET is turned on by the synchronous control circuit, current from the secondary winding flows through the power MOSFET bypassing the body diode. Due to the small on-resistance rds (on), the voltage drop across the power MOSFET is reduced to, for example, about 0.2V or less. As the current decreases linearly in the secondary winding, the voltage across the power MOSFET also decreases. The synchronous control circuit turns off the power MOSFET when the voltage across the power MOSFET drops to the reference voltage. At the start of the next switching cycle, the primary side power switch is turned on again by the primary side power controller, and the switching cycle is repeated.

Note that in Continuous Conduction Mode (CCM) operation, the primary current begins to increase before the secondary current decreases to zero. Furthermore, during durations TDon and TDoff (also referred to as dead times), both the primary and secondary switches are turned off and current flows through the body diodes in the rectifier. In fig. 4, the highlighted areas in diagram 430 indicate the current flow through the body diode in a conventional synchronous rectifier. The stored charge (Qrr) needs to be discharged, which takes a finite amount of time, called the reverse recovery time. These limitations have resulted in complex control circuits in CCM operation in power converters with conventional secondary side synchronous rectifiers. The control circuitry typically involves communicating between the primary side and the secondary side to coordinate the timing of the turning on and off of the primary side power MOSFET and the secondary side power MOSFET.

Diagram 440 in fig. 4 illustrates the secondary current Isec when the rectifier on the secondary side is a two-terminal rectifier as described in connection with fig. 1-3. The two terminal rectifier includes, among other components, a power MOSFET and a schottky diode in the same package. It can be seen that the current conduction and reverse recovery charge in the body diode is substantially reduced. These features may enable CCM operation using a two terminal rectifier. In some cases, a simple control method for CCM operation may be implemented without a handshake arrangement (e.g., a CCM synchronization signal) between the primary side and the secondary side. In some conventional systems, the handshake arrangement may involve additional synchronization pins on the secondary side controller, and may increase the complexity and cost of the system.

fig. 5-7 are waveform diagrams illustrating voltages and currents in a two-terminal rectifier embodying certain aspects of the present disclosure.

fig. 5 is a waveform diagram 500 illustrating drain-source voltage and current in a rectifier with synchronous MOSFETs in a power converter, such as power converter 100 in fig. 1. Fig. 5 plots the rectifier's drain-source Voltage (VKA)510 and MOSFET current (IAK)520 during the switching cycle. For example, during time T1, the primary current is on and the secondary current is off. Thus, the secondary side rectifier is turned off and is not conducting. Therefore, VKA is high and IAK is zero. During time T2, the primary current is off and the secondary current is on. Thus, the secondary side rectifier is turned on and conducting. Therefore, VKA is low and IAK is not zero. During the transition (e.g., during times T3 and T4), current flows in the body diode, which may cause voltage ringing and current spikes.

Fig. 6 is a waveform diagram 600 illustrating drain-source voltage and current in a two-terminal rectifier having a synchronous MOSFET connected in parallel with a schottky diode in a power converter, such as power converter 100 in fig. 1. In this example, the rectifier has a synchronous MOSFET connected in parallel with a schottky diode in two separate semiconductor chip packages. The connections include short and thicker wires to reduce parasitic components such as wiring inductance and resistance.

Fig. 6 plots the rectifier's drain-source Voltage (VKA)610 and MOSFET current (IAK)620 during a switching cycle. For example, during time T1, the primary current is on and the secondary current is off. Thus, the secondary side rectifier is turned off and is not conducting. Therefore, VKA is high and IAK is zero. During time T2, the primary current is off and the secondary current is on. Thus, the secondary side rectifier is turned on and conducting. Therefore, VKA is low and IAK is not zero. During the transition (e.g., during times T3 and T4), current flows in the body diode, which may cause voltage ringing and current spikes. It can be seen that the body diode current and reverse current are reduced in time periods T3 and T4 in fig. 6 as compared to the graph in fig. 5.

Fig. 7 is a waveform diagram 700 illustrating drain-source voltage and current in a two-terminal rectifier embodying certain aspects of the present disclosure. In this example, the two-terminal rectifier is similar to the two-terminal rectifier in a power converter (e.g., power converter 100 in fig. 1) described above in connection with fig. 2 and 3. The two terminal rectifier includes the power MOSFET and schottky diode in a single package and the control function circuit described above. Fig. 7 plots the rectifier's drain-source Voltage (VKA)710 and MOSFET current (IAK)720 during the switching cycle. The MOSFET current (IAK)720 is an estimated MOSFET current with the two-terminal rectifier in a single package, as described above and illustrated in fig. 2 and 3. In fig. 7, MOSFET current (IAK)620 from fig. 6 is superimposed on MOSFET current (IAK) 720.

For example, during time T1, the primary current is on and the secondary current is off. Thus, the secondary side rectifier is turned off and is not conducting. Therefore, VKA is high and IAK is zero. During time T2, the primary current is off and the secondary current is on. Thus, the secondary side rectifier is turned on and conducting. Therefore, VKA is low and IAK is not zero. During the transition (e.g., during times T3 and T4), current flows in the body diode, which may cause voltage ringing and current spikes. It can be seen that the body diode current and reverse current are reduced in time periods T3 and T4 in fig. 7 as compared to the graph in fig. 6. In addition, the thermal efficiency of the system may also be improved.

Fig. 8 is a waveform diagram illustrating a method for operating a flyback power converter in CCM operation using the two-terminal rectifier described above. In fig. 8, the waveform labeled "MOSFET gate" illustrates the gate voltage of the power MOSFET in the rectifier during the switching cycle Ts. Waveform 810 illustrates a control signal applied to the gate of a MOSFET in a conventional rectifier. It can be seen that in the switching cycle of a conventional rectifier, the rectifier is turned on during time Ton and turned off during time Toff. The waveform VKA depicts the voltage variation between the cathode (K) and the anode (a) of the secondary rectifier during the switching cycle Ts. As described above, in conventional CCM operation in flyback power supplies, complex control circuitry is required and it involves handshake signal handling between the primary and secondary sides.

In fig. 8, waveform 820 illustrates a control signal on the gate of a power MOSFET in a two terminal rectifier for CCM operation of a flyback power converter. After turning off the primary side current flow, the secondary current flows through the body diode and the schottky diode. When the voltage VKA between the cathode (K) and the anode (a) in the two-terminal rectifier is below a preset value, the two-terminal rectifier is turned on to start a secondary inductor discharge cycle Ton. And when the voltage between the cathode (K) and the anode (A) of the two-terminal rectifier is less than the preset reference voltage, the power MOSFET is turned off. The preset reference voltage is selected to maintain proper current flow. The two-terminal rectifier may reduce body diode current conduction during dead time in the power converter and reduce the reverse recovery time of the body diode. In a two-terminal rectifier, a control circuit may adjust a dead time for Continuous Conduction Mode (CCM) operation of a power converter. During the off-time Toff, the primary side is turned on to enable CCM operation. Thus, the two-terminal rectifier control signal 820 in this embodiment has a shorter on-time and a longer off-time than the conventional control signal 810. Furthermore, CCM operation can be implemented without CCM synchronization signals using a two-terminal rectifier with a simpler DCM control design. In some cases, the on-time and off-time may be determined empirically or using analog techniques.