阅读说明：本技术 开关电源电路及方法 (Switching power supply circuit and method ) 是由 芮利臣 于 2020-04-22 设计创作，主要内容包括：本申请公开了一种开关电源电路及方法。所述开关电源电路包括：原边开关电路、副边开关电路、原边控制电路和副边控制电路,其中当原边电流达到反向电流阈值、或者原边开关电路两端电压的变化速率达到速率阈值时,原边开关电路被导通；在原边开关电路下一周期被导通之前,所述副边开关电路被导通一段时间。本发明的开关电源电路实现了原边开关电路的零电压(ZVS)开通,降低了损耗。(The application discloses a switching power supply circuit and a method. The switching power supply circuit includes: the device comprises a primary side switching circuit, a secondary side switching circuit, a primary side control circuit and a secondary side control circuit, wherein when a primary side current reaches a reverse current threshold value or the change rate of voltage at two ends of the primary side switching circuit reaches a rate threshold value, the primary side switching circuit is conducted; the secondary side switching circuit is turned on for a period of time before the next cycle of the primary side switching circuit is turned on. The switching power supply circuit realizes Zero Voltage (ZVS) switching-on of the primary side switching circuit and reduces loss.)

1. A switching power supply circuit comprising:

a primary side switching circuit coupled to a primary side of the electrical isolation device, the primary side switching circuit being periodically turned on and off to transfer an input voltage to a secondary side of the electrical isolation device;

a secondary side switching circuit coupled to a secondary side of the electrical isolation device, the secondary side switching circuit being periodically turned on and off to provide a desired output voltage;

the primary side control circuit provides a primary side control signal according to primary side current information or change rate information of voltage at two ends of the primary side switching circuit so as to control the primary side switching circuit, wherein: when the primary side current reaches a reverse current threshold value or the change rate of the voltage at two ends of the primary side switch circuit reaches a rate threshold value, the primary side control circuit controls the primary side switch circuit to be conducted;

and the secondary side control circuit controls the secondary side switching circuit to be conducted for a period of time before the primary side switching circuit is conducted according to the output voltage.

2. The switching power supply circuit of claim 1, wherein:

when the primary side current reaches the reverse current threshold value and the voltage at the two ends of the primary side switch circuit is smaller than the zero reference voltage or the change rate of the voltage at the two ends of the primary side switch circuit reaches the rate threshold value, the primary side switch circuit is conducted.

3. The switching power supply circuit of claim 1, wherein the electrical isolation device comprises a transformer, the switching power supply circuit further comprising: a third winding coupled to the primary side of the transformer, wherein:

and when the primary side current reaches the reverse current threshold value and the voltage of the third winding is less than zero reference voltage or the change rate of the voltage at the two ends of the primary side switch circuit reaches a rate threshold value, the primary side switch circuit is conducted.

4. The switching power supply circuit of claim 1, wherein the primary side control circuit comprises:

and the frequency/voltage conversion circuit generates a compensation signal according to the conducted frequency of the primary side switching circuit so as to control the disconnection of the primary side switching circuit.

5. The switching power supply circuit as claimed in claim 4, wherein the frequency/voltage conversion circuit comprises:

the monostable circuit responds to the conduction action of the primary side switch circuit and generates a pulse signal;

and the low-pass filter is used for carrying out low-pass filtering on the pulse signal to obtain the compensation signal.

6. The switching power supply circuit according to claim 1, wherein the secondary side control circuit comprises:

the frequency generation circuit generates a frequency control signal according to the output voltage so as to control the conduction of the secondary side switch circuit;

and the duration controller responds to the frequency control signal and controls the conduction duration of the secondary side switching circuit.

7. The switching power supply circuit of claim 1, wherein the primary side control circuit comprises:

the first edge detector is used for detecting positive jump of a voltage signal representing the voltage at two ends of the primary side switch circuit;

the second edge detector is used for detecting the negative jump of a voltage signal representing the voltage at two ends of the primary side switch circuit;

and the timing circuit starts timing in response to the positive jump of the voltage signal representing the voltage at the two ends of the primary side switching circuit and finishes timing in response to the negative jump of the voltage signal representing the voltage at the two ends of the primary side switching circuit to generate a timing signal for controlling the disconnection of the primary side switching circuit.

8. A method for switching a power supply circuit including an electrical isolation device having a primary side and a secondary side, a primary side switching circuit coupled to the primary side of the electrical isolation device, and a secondary side switching circuit coupled to the secondary side of the electrical isolation device, the method comprising:

receiving an input voltage at a primary side, and generating an output voltage at a secondary side by controlling the on and off of a primary side switching circuit and a secondary side switching circuit;

detecting primary side current information or change rate information of voltages at two ends of a primary side switching circuit, and controlling the primary side switching circuit to be conducted when the primary side current reaches a reverse current threshold value or the change rate of the voltages at two ends of the primary side switching circuit reaches a rate threshold value;

and feeding back the output voltage, and generating a frequency control signal according to the output voltage, so that the frequency control signal controls the secondary side switching circuit to be conducted for a period of time before the primary side switching circuit is conducted.

9. The method of claim 8, further comprising:

and controlling the primary side switching circuit to be disconnected according to the conducted frequency of the primary side switching circuit.

10. A method for switching a power supply circuit including an electrical isolation device having a primary side and a secondary side, a primary side switching circuit coupled to the primary side of the electrical isolation device, and a secondary side switching circuit coupled to the secondary side of the electrical isolation device, the method comprising:

receiving an input voltage at a primary side, and generating an output voltage at a secondary side by controlling the on and off of a primary side switching circuit and a secondary side switching circuit;

detecting primary side current information and voltage information at two ends of a primary side switch circuit at the same time, and controlling the primary side switch circuit to be conducted when the primary side current reaches a reverse current threshold value and the voltage at two ends of the primary side switch circuit is less than zero reference voltage or the change rate of the voltage at two ends of the primary side switch circuit reaches a rate threshold value;

and feeding back the output voltage, and generating a frequency control signal according to the output voltage, so that the frequency control signal controls the secondary side switching circuit to be conducted for a period of time before the primary side switching circuit is conducted.

Technical Field

The present invention relates to electronic circuits, and more particularly, to switching power supply circuits and methods.

Background

With the rapid development of information technology, various electronic devices, such as mobile phones, portable computers, etc., are increasingly widely used. These devices may be powered by an external adapter power supply (or charger). The adapter power supply is usually an ac-to-dc conversion, i.e. the commercial power of the grid, such as domestic 50Hz/220V ac, is converted into a low voltage dc (e.g. 5V dc output) and is electrically isolated. A typical circuit topology of the circuit is a flyback converter. In order to maintain the output voltage stable, the conventional adapter power supply needs to sample and feedback the output voltage on the output side. Due to input and output isolation, the feedback circuit usually needs electrical isolation, such as optical coupling isolation. As the power consumption of electronic devices becomes larger, the capacity of internal batteries also becomes larger. But the battery capacity is limited by the volume of the electronic equipment, the corresponding quick charging technology is developed, and the quick charging of the battery is realized to compensate the inconvenience that the battery capacity is not large enough. The rapid charging technology requires a more powerful adapter power supply, and how to enable the adapter power supply to output more power, i.e. higher power density, under the same volume has become a current major challenge. In order to achieve higher power density, it is necessary to increase the efficiency of the adapter power supply while increasing the switching frequency, and therefore, it is always the direction of effort of those skilled in the art to increase the efficiency of the flyback converter.

Disclosure of Invention

It is therefore an object of the present invention to solve the above-mentioned problems of the prior art and to provide an improved switching power supply circuit and method.

According to an embodiment of the present invention, there is provided a switching power supply circuit including: a primary side switching circuit coupled to a primary side of the electrical isolation device, the primary side switching circuit being periodically turned on and off to transfer an input voltage to a secondary side of the electrical isolation device; a secondary side switching circuit coupled to a secondary side of the electrical isolation device, the secondary side switching circuit being periodically turned on and off to provide a desired output voltage; the primary side control circuit provides a primary side control signal according to primary side current information or change rate information of voltage at two ends of the primary side switching circuit so as to control the primary side switching circuit, wherein: when the primary side current reaches a reverse current threshold value or the change rate of the voltage at two ends of the primary side switch circuit reaches a rate threshold value, the primary side control circuit controls the primary side switch circuit to be conducted; and the secondary side control circuit controls the secondary side switching circuit to be conducted for a period of time before the primary side switching circuit is conducted according to the output voltage.

There is also provided, in accordance with an embodiment of the present invention, a method for a switching power supply circuit including an electrical isolation device having a primary side and a secondary side, a primary side switching circuit coupled to the primary side of the electrical isolation device, and a secondary side switching circuit coupled to the secondary side of the electrical isolation device, the method including: receiving an input voltage at a primary side, and generating an output voltage at a secondary side by controlling the on and off of a primary side switching circuit and a secondary side switching circuit; detecting primary side current information or change rate information of voltages at two ends of a primary side switching circuit, and controlling the primary side switching circuit to be conducted when the primary side current reaches a reverse current threshold value or the change rate of the voltages at two ends of the primary side switching circuit reaches a rate threshold value; and feeding back the output voltage, and generating a frequency control signal according to the output voltage, so that the frequency control signal controls the secondary side switching circuit to be conducted for a period of time before the primary side switching circuit is conducted.

There is also provided, in accordance with an embodiment of the present invention, a method for a switching power supply circuit including an electrical isolation device having a primary side and a secondary side, a primary side switching circuit coupled to the primary side of the electrical isolation device, and a secondary side switching circuit coupled to the secondary side of the electrical isolation device, the method including: receiving an input voltage at a primary side, and generating an output voltage at a secondary side by controlling the on and off of a primary side switching circuit and a secondary side switching circuit; detecting primary side current information and voltage information at two ends of a primary side switch circuit at the same time, and controlling the primary side switch circuit to be conducted when the primary side current reaches a reverse current threshold value and the voltage at two ends of the primary side switch circuit is less than zero reference voltage or the change rate of the voltage at two ends of the primary side switch circuit reaches a rate threshold value;

and feeding back the output voltage, and generating a frequency control signal according to the output voltage, so that the frequency control signal controls the secondary side switching circuit to be conducted for a period of time before the primary side switching circuit is conducted.

According to the switching power supply circuit and the switching power supply method in the aspects of the invention, the body diode of the primary side switching circuit is conducted before the primary side switching circuit is conducted, so that Zero Voltage (ZVS) turn-on of the primary side switching circuit is realized, and loss is reduced.

Drawings

Fig. 1 shows a circuit configuration schematic diagram of a switching power supply circuit 100 according to an embodiment of the invention;

fig. 2 shows a circuit configuration schematic diagram of the secondary side switch circuit 101 according to an embodiment of the present invention;

fig. 3 is a schematic circuit diagram of a switching power supply circuit 300 according to an embodiment of the invention;

FIG. 4 is a schematic circuit diagram of the frequency generation circuit 21 according to the embodiment of the present invention;

fig. 5 is a circuit diagram of a switching power supply circuit 500 according to an embodiment of the invention;

fig. 6 is a schematic circuit diagram of a switching power supply circuit 600 according to an embodiment of the invention;

fig. 7 is a circuit diagram of a switching power supply circuit 700 according to an embodiment of the invention;

fig. 8 is a circuit diagram of a switching power supply circuit 800 according to an embodiment of the invention;

fig. 9 is a circuit diagram of a switching power supply circuit 900 according to an embodiment of the invention;

fig. 10 is a schematic circuit diagram of a switching power supply circuit 1000 according to an embodiment of the invention;

fig. 11 is a circuit diagram of a switching power supply circuit 1100 according to an embodiment of the invention;

fig. 12 is a schematic circuit diagram of a switching power supply circuit 1200 according to an embodiment of the invention;

fig. 13 schematically illustrates a flow chart 1300 of a method for switching a power supply circuit according to an embodiment of the invention.

Detailed Description

Specific embodiments of the present invention will be described in detail below, and it should be noted that the embodiments described herein are only for illustration and are not intended to limit the present invention. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that: it is not necessary to employ these specific details to practice the present invention. In other instances, well-known circuits, materials, or methods have not been described in detail in order to avoid obscuring the present invention.

Throughout the specification, reference to "one embodiment," "an embodiment," "one example," or "an example" means: the particular features, structures, or characteristics described in connection with the embodiment or example are included in at least one embodiment of the invention. Thus, the appearances of the phrases "in one embodiment," "in an embodiment," "one example" or "an example" in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable combination and/or sub-combination in one or more embodiments or examples. Further, those of ordinary skill in the art will appreciate that the drawings provided herein are for illustrative purposes and are not necessarily drawn to scale. It will be understood that when an element is referred to as being "coupled" or "connected" to another element, it can be directly coupled or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly coupled" or "directly connected" to another element, there are no intervening elements present. Like reference numerals refer to like elements. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

Fig. 1 shows a circuit configuration diagram of a switching power supply circuit 100 according to an embodiment of the invention. In the embodiment shown in fig. 1, the switching power supply circuit 100 includes: a primary side switch circuit Q1 coupled to a primary side T1 of the electrical isolation device T, the primary side switch circuit Q1 being periodically turned on and off to deliver the input voltage Vin to a secondary side T2 of the electrical isolation device T; a secondary switching circuit 101 coupled to a secondary T2 of the electrical isolation device T, the secondary switching circuit 101 being periodically turned on and off to provide the desired output voltage Vo; the primary side control circuit U1 provides a primary side control signal G according to the primary side current information or the change rate information of the voltage at two ends of the primary side switch circuit Q1_Q1The primary side switching circuit Q1 is controlled, wherein when the primary side current reaches a reverse current threshold value or the change rate of the voltage at two ends of the primary side switching circuit Q1 reaches a rate threshold value, the primary side switching circuit Q1 is conducted; the secondary control circuit U2 controls the secondary switch circuit 101 to be turned on for a period of time before the primary switch circuit Q1 is turned on according to the output voltage Vo.

In one embodiment, the electrical isolation device T comprises a transformer including a primary winding and a secondary winding. In one embodiment, the electrical isolation device comprises a piezoelectric transformer.

In one embodiment, the primary switching circuit Q1 includes a power MOSFET having a body diode and a parasitic capacitance. In other embodiments, the primary side switching circuit Q1 may further include other switching devices, such as BJTs, IGBTs, etc.

In one embodiment, in each on period, when the current switching period (switching frequency) reaches the reference switching period (switching frequency), the frequency control signal is generated to control the secondary side switching circuit 101 to be turned on for a period of time. In one embodiment, the greater the output power, the higher the switching frequency f; the smaller the output power, the lower the switching frequency f. In one embodiment, when the switching frequency drops to a certain frequency (e.g., around 20 kHz), the switching frequency is limited and does not continue to drop.

In one embodiment, when the voltage across the secondary switch circuit 101 reaches the valley threshold, the secondary switch circuit 101 is turned on for a period of time determined by the output voltage Vo. For example, the turn-off time of the secondary side switch circuit 101 is controlled by controlling the peak value of the current flowing through the secondary side switch circuit 101 and the output voltage Vo to be in a specific relationship, so as to control the turn-on time of the secondary side switch circuit 101; or the on period of the secondary side switch circuit 101 is controlled by a constant-period on circuit (constanttime) having a specific relationship with the output voltage Vo.

Since the secondary switching circuit 101 is turned on for a while before the primary switching circuit Q1 is turned on, the reverse charging current generated by the turning on of the secondary switching circuit is coupled to the primary side through the transformer, so that the charge on the parasitic capacitor of the primary switching circuit Q1 is released and the voltage across the parasitic capacitor drops. When the primary current reaches a reverse current threshold or the rate of change of the voltage across the primary switching circuit Q1 reaches a rate threshold, this indicates that the body diode of the primary switching circuit Q1 is conducting. That is, the voltage drop across the primary side switching circuit Q1 at this time is-0.7V or less. At this time, the conduction of the primary side switching circuit Q1 is Zero Voltage (ZVS) conduction, so the switching power supply circuit 100 realizes Zero Voltage (ZVS) conduction to the primary side switching circuit, and reduces loss. The reference positive direction of the primary and secondary side currents is shown as an arrow in FIG. 1 as a reference.

In one embodiment, the secondary side switch circuit 101 includes: a power switching device (e.g., a power MOSFET) having a body diode, as shown in the left diagram (a) of fig. 2; or the secondary side switching circuit 101 comprises two (or more) switching devices connected in parallel, as shown in the middle diagram (b) of fig. 2; or the secondary side switching circuit 101 may further include a diode and a switching device connected in parallel, as shown in the right diagram (c) of fig. 2. In one embodiment, the secondary side switch circuit 101 being turned on indicates that all or a portion of the switching devices of the secondary side switch circuit 101 are turned on (e.g., only the diode or body diode is turned on) and current flows therethrough; the secondary side switch circuit 101 is turned off, which means that all the switching devices of the secondary side switch circuit 101 are turned off and no current flows therethrough. If the secondary side switching circuit 101 performs a freewheeling operation after the primary side switching circuit Q1 is turned off, part or all of the switching devices of the secondary side switching circuit 101 are turned on, and a current having a first current direction flows therethrough; after the freewheeling ends and before the primary switching circuit Q1 is turned on, some or all of the switching devices of the secondary switching circuit 101 are turned on for a period of time and a current having a second current direction flows.

In one embodiment, when the primary side switching circuit Q1 is turned off or when a current is detected flowing through the secondary side switching circuit 101, the secondary side switching circuit 101 freewheels until the freewheel is over (i.e., the current flowing therethrough is zero or near zero); after the secondary switching circuit 101 has freewheeling, the secondary switching circuit 101 is turned on again for a period of time before the primary switching circuit Q1 is turned on for the next switching cycle.

Fig. 3 is a circuit diagram of a switching power supply circuit 300 according to an embodiment of the invention. The embodiment shown in fig. 3 shows a schematic circuit configuration diagram of the primary side control circuit U1 and the secondary side control circuit U2 according to the embodiment of the invention. In the embodiment shown in fig. 3, the primary side control circuit U1 includes: reverse current comparisonThe primary side sampling signal V of the primary side current (such as flowing through the primary side switching circuit Q1) is compared by the device 11_CSPAnd a reverse current threshold V_IRGenerating a Set signal Set; primary side logic circuit 12 based on primary side sampling signal V_CSPAnd a reverse current threshold V_IRIs set to control the primary side switching circuit Q1 to conduct. The secondary side control circuit U2 includes: a frequency generating circuit 21 responsive to the output voltage Vo (e.g., an error signal V indicative of the output voltage Vo)_EA) The frequency control signal fc is generated to control the secondary side switch circuit 101 to be turned on.

In one embodiment, the secondary side control circuit U2 further includes: the time length controller 22 controls the on time length of the secondary side switching circuit 101 in response to the frequency control signal fc. In one embodiment, the duration controller 22 may comprise a monostable circuit. The monostable responds to the frequency control signal to generate a pulse of fixed duration to control the secondary switching circuit 101 to conduct for a set duration. In another embodiment, the duration controller 22 may also control the conduction duration by controlling the current flowing through the secondary side switch circuit 101. For example, when the current flowing through the secondary switching circuit 101 reaches a negative current limit value, the secondary switching circuit 101 is turned off. In other embodiments, the duration controller 22 may further control the on duration of the secondary side switch circuit 101 according to the output voltage Vo, where the higher the output voltage Vo is, the shorter the on duration is, and the lower the output voltage Vo is, the longer the on duration is.

In the embodiment shown in fig. 3, the secondary side control circuit U2 further includes: error amplifier EA for feedback voltage V proportional to output voltage Vo_FBAnd a reference voltage V_RIs amplified and integrated to obtain the error signal V_EA。

Fig. 4 is a schematic circuit diagram of the frequency generation circuit 21 according to the embodiment of the present invention. In the embodiment shown in fig. 4, the frequency generation circuit 21 includes: a controlled current source I1 for providing a charging current with a magnitude and an error signal V_EAIs in direct proportion; a charging capacitor C1 coupled in parallel with a reset switch S1, the controlled current flowing when the reset switch S1 is openThe source I1 charges the charging capacitor C1, and when the reset switch S1 is turned on, the voltage across the charging capacitor C1 is reset to zero; a frequency comparator M1 for comparing the voltage across the charging capacitor with a frequency reference value V_FRComparing to generate a frequency control signal fc; short pulse circuit T_PThe short pulse signal is generated according to the frequency control signal fc to control the on and off of the reset switch S1. Those skilled in the art will appreciate that there are many ways of implementing the frequency generation circuit 21, not limited to the one shown in fig. 4, such as various voltage controlled oscillator circuits.

Fig. 5 is a circuit diagram of a switching power supply circuit 500 according to an embodiment of the invention. The switching power supply circuit 500 shown in fig. 5 shows a schematic circuit configuration diagram of a primary side control circuit U1, the primary side control circuit U1 is similar to the primary side control circuit U1 of the switching power supply circuit 300 shown in fig. 3, and in the embodiment shown in fig. 5, the primary side control circuit U1 further includes: a voltage comparator 13 for comparing the voltage V at two ends of the primary side switching circuit Q1_DSQAnd zero reference voltage V_ZWhen the current characteristic of the primary side switching circuit Q1 reaches the reverse current threshold value V_IRAnd the voltage V at the two ends of the primary side switching circuit Q1_DSQLess than zero reference voltage V_ZThe primary side switching circuit Q1 is turned on. I.e. the primary side logic circuit 12 is based on a primary side sampling signal V_CSPAnd a reverse current threshold V_IRAnd the voltage V across the primary side switching circuit Q1_DSQAnd zero reference voltage V_ZIs set to control the conduction of the primary side switching circuit Q1.

In one embodiment, the primary side control circuit U1 further includes: a logic AND circuit 14 for sampling the primary side signal V_CSPAnd a reverse current threshold V_IRAnd the voltage V across the primary side switching circuit Q1_DSQAnd zero reference voltage V_ZAnd performing logical AND operation on the comparison result to obtain the Set signal Set.

Fig. 6 is a schematic circuit diagram of a switching power supply circuit 600 according to an embodiment of the invention. The switching power supply circuit 600 shown in fig. 6 shows a circuit configuration of the primary side control circuit U1It is intended that the primary side control circuit U1 is similar to the primary side control circuit U1 of the switching power supply circuit 300 shown in fig. 3, except that in the embodiment shown in fig. 6, the switching power supply circuit 600 further includes: and a third winding T3 coupled to the primary side T1 of the electrical isolation device T. The primary side control circuit U1 further includes: a voltage comparator 13 for comparing the voltage V of the third winding T3_augAnd zero reference voltage V_ZWhen the current flowing through the primary side switching circuit Q1 reaches the reverse current threshold V_IRAnd the voltage V of the third winding T3_augLess than zero reference voltage V_ZThe primary side switching circuit Q1 is turned on. I.e. the primary side logic circuit 12 is based on a primary side sampling signal V_CSPAnd a reverse current threshold V_IRAnd the voltage V of the third winding T3_augAnd zero reference voltage V_ZIs set to control the conduction of the primary side switching circuit Q1.

In one embodiment, the voltage V of the third winding T3_augThe voltage may be divided by a resistor divider circuit (not shown) and then summed with V_ZA comparison is made to achieve the adaptation of the voltage. In one embodiment, zero reference voltage V_ZIs a reference voltage close to zero, e.g. V_Z＝100mV。

Fig. 7 is a circuit diagram of a switching power supply circuit 700 according to an embodiment of the invention. The embodiment shown in fig. 7 shows a schematic circuit configuration diagram of a primary side control circuit U1 according to another embodiment of the present invention. In the embodiment shown in fig. 7, the primary side control circuit U1 includes: a rate comparator 15 for comparing the differential signal dv/dt representing the voltage variation rate across the primary switching circuit 101 with a rate threshold V_TRGenerating a Set signal Set; a primary logic circuit 12 based on the differential signal dv/dt and a rate threshold V_TRIs set to control the primary side switching circuit Q1 to conduct.

In the embodiment shown in fig. 7, the primary side control circuit U1 further includes: a differential circuit 16 receiving the voltage V across the primary switching circuit Q1_DSQOr the voltage V of the third winding T3_augGenerating said differentiated signal dv/dt.

Fig. 8 is a circuit diagram of a switching power supply circuit 800 according to an embodiment of the invention. The embodiment shown in fig. 8 shows a schematic circuit configuration diagram of a primary side control circuit U1 according to another embodiment of the present invention. In the embodiment shown in fig. 8, the primary side control circuit U1 includes the primary side logic circuit 12, and turns on the primary side switch circuit Q1 in response to a Set signal Set, which may be generated in the manner shown in fig. 3 or one of fig. 5 to 7; the primary side control circuit U1 further includes: a peak current comparator 17 for comparing the primary sampling signal V_CSPAnd a reference peak value V_PGenerating a Reset signal Reset; wherein the primary side logic circuit 12 is based on a primary side sampling signal V_CSPAnd a reference peak value V_PIs reset to control the primary side switching circuit Q1 to turn off.

Fig. 9 is a circuit diagram of a switching power supply circuit 900 according to an embodiment of the invention. The embodiment shown in fig. 9 shows a schematic circuit configuration diagram of a primary side control circuit U1 according to another embodiment of the present invention. In the embodiment shown in fig. 9, the primary side control circuit U1 includes the primary side logic circuit 12, and turns on the primary side switch circuit Q1 in response to a Set signal Set, which may be generated in the manner shown in fig. 3 or one of fig. 5 to 7; the primary side control circuit U1 further includes: the constant on-time circuit COT controls the on-time of the primary side switching circuit Q1, and generates a Reset signal Reset to turn off the primary side switching circuit Q1.

Fig. 10 is a schematic circuit diagram of a switching power supply circuit 1000 according to an embodiment of the invention. The embodiment shown in fig. 10 is a schematic circuit diagram of a primary side control circuit U1 according to another embodiment of the present invention. In the embodiment shown in fig. 10, the primary side control circuit U1 includes the primary side logic circuit 12, and turns on the primary side switch circuit Q1 in response to a Set signal Set, which may be generated in the manner shown in fig. 3 or one of fig. 5 to 7; the primary side control circuit U1 further includes: the frequency/voltage conversion circuit 18 generates the compensation signal V according to the frequency of the Set signal Set (i.e., the frequency at which the primary side switching circuit Q1 is turned on)_CFor controlling the turn-off of the primary side switching circuit Q1.

In one embodiment, the primary side control circuit U1 further includes: a disconnection processing circuit 19 for receiving the compensation signal V_CThe disconnection processing circuit 19 may compensate the signal V by_CThe on-time of the primary side switching circuit Q1 is controlled (as shown in FIG. 9) to control the off-time of the primary side switching circuit Q1 or by compensating the signal V_CThe peak current flowing through the primary side switching circuit Q1 (see fig. 8) is controlled to control the turn-off timing of the primary side switching circuit Q1.

In one embodiment, the frequency/voltage conversion circuit comprises a monostable circuit MC for generating a pulse signal in response to a Set signal Set (i.e., the conduction of the primary side switch circuit Q1), and a low pass filter L PF for low pass filtering the pulse signal to obtain the compensation signal V_C。

Fig. 11 is a circuit diagram of a switching power supply circuit 1100 according to an embodiment of the invention. The embodiment shown in fig. 11 shows a schematic circuit structure diagram of the secondary side control circuit U2 according to another embodiment of the present invention. In the embodiment shown in fig. 11, the secondary side control circuit U2 includes: the frequency generation circuit 21 and the time length controller 22 generate a first control signal G_SR1To control the secondary switching circuit 101 to conduct for a period of time before the primary switching circuit Q1 is turned on for the next switching cycle. The secondary side control circuit U2 further includes: a second control signal generator 23 based on a secondary sampling signal V indicative of a secondary current (e.g., a current flowing through the secondary switch circuit 101)_CSRAnd a first threshold value V_th1The comparison result (e.g., -0.1V) is set to turn on the secondary side switch circuit 101; based on secondary side sampling signal V_CSRAnd a second threshold value V_th2The result of the comparison (e.g., -0.01V) is reset to turn off the secondary side switch circuit 101. I.e. the secondary side sampling signal V on which the second control signal generator 23 is based_CSRAnd a first threshold value V_th1And the secondary side sampling signal V_CSRAnd a second threshold value V_th2Generates the second control signal G as a result of the comparison_SR2And controls the secondary side switching circuit 101 to freewheel after the primary side switching circuit Q1 is turned off.

In one embodiment, the secondary side sampled signal V_CSRIs the voltage drop V across the secondary side switching circuit 101_DSR. In one embodiment, the secondary side control circuit U2 further includes: a logic OR circuit 24 for the first control signal G_SR1And a second control signal G_SR2Performing logical OR operation to obtain secondary side control signal G_SRTo control the secondary side switch circuit 101.

In the operation of the switching power supply circuits according to the embodiments of the present invention, the primary side switching circuit Q1 is in the primary side control signal G at the beginning of each cycle_Q1Is turned on, the current flowing through the primary side T1 of the electrical isolation device T rises linearly until the primary side switching circuit Q1 is turned off. The triggering condition for the disconnection can be, for example, that the current flowing through the primary switching circuit reaches a value determined by the compensation signal V_COr reference peak value V_PThe determined setting may be the conduction time of the primary side switching circuit Q1 reaching the set conduction time or the compensation signal V_CDetermined on-time, etc. At this point, the switching power supply circuit begins to enter the freewheeling phase. Due to the transformer coupling and the secondary side switch circuit 101 is not yet turned on, the body diode of the secondary side switch circuit is turned on. At this time, a current is detected in the secondary switch circuit 101 (so that the secondary sampling signal V is detected_CSRLess than a first threshold value V_th1) A second control signal G_SR2The secondary side switch circuit 101 is controlled to be turned on. Accordingly, a current flows through the secondary-side switch circuit 101. At this time, the voltage V across 101_DSRIn proportion to the current flowing therethrough, the voltage V across 101 decreases with decreasing current_DSRGradually rising from a more negative value. When the voltage V is_DSRRises above a second threshold value V_th2When the current flowing through the secondary switch circuit 101 decreases to zero (it is determined at this time), the secondary switch circuit 101 is turned off, and the freewheeling stage ends. The system then enters a current chopping mode or critical current mode.

When the time from the start time of the present switching cycle (i.e., the time when the primary side switching circuit Q1 is turned on) reaches the reference switching cycle, the frequency generation circuit 21 generates the frequency control signal fc, the secondary side switching circuit 101 is turned on again, and the current flowing through the secondary side switching circuit 101 is reversedTowards the increase. After the on-period controlled by the period controller 22 (e.g., the reverse current flowing through the secondary switch circuit 101 reaches the negative current-limiting value or the on-period of the secondary switch circuit 101 reaches the set period), the secondary switch circuit 101 is turned off. When the secondary side switching circuit 101 is turned off, the reverse current is coupled to the primary side due to the coupling of the transformer, the charge on the parasitic capacitor of the primary side switching circuit Q1 is released, the voltage across the parasitic capacitor drops, and the body diode of the primary side switching circuit is turned on. When the current flowing through the primary side switching circuit Q1 reaches the reverse current threshold V_IRThe rate of change of the voltage across the time or primary side switching circuit Q1 reaches a rate threshold V_TRAt this time, the primary side switching circuit Q1 is turned back on and the switching power supply circuit enters the next cycle. In some of these embodiments, when the current flowing through the primary side switching circuit Q1 reaches the reverse current threshold V_IRAnd the voltage V at the two ends of the primary side switching circuit Q1_DSQ(or the third winding T3 voltage V_aug) Less than zero reference voltage V_ZThe rate of change of the voltage across the time or primary side switching circuit Q1 reaches a rate threshold V_TRAt this time, the primary side switching circuit Q1 is turned back on and the switching power supply circuit enters the next cycle.

Since the charge on the parasitic capacitor of the primary side switch circuit Q1 is released during the second conduction phase of the secondary side switch circuit 101, and the body diode of the primary side switch circuit Q1 is already turned on before the primary side switch circuit Q1 is turned on, the aforementioned switching power supply circuit according to various embodiments of the present invention achieves zero voltage conduction to the primary side switch circuit Q1.

Fig. 12 is a schematic circuit diagram of a switching power supply circuit 1200 according to an embodiment of the invention. The embodiment shown in fig. 12 is a schematic circuit diagram of the primary side control circuit U1 and the secondary side control circuit U2 according to another embodiment of the present invention. In the embodiment shown in fig. 12, the primary side control circuit U1 includes: the first edge detector 31 detects a voltage signal indicative of a voltage across the primary side switching circuit (e.g., a voltage V across the primary side switching circuit Q1)_DSQOr the voltage V of the third winding T3_aug) Positive jump of; a second edge detector 32 for detecting a negative transition of a voltage signal representing a voltage across the primary side switching circuit; timing electricityCircuit 33 responsive to voltage V across primary switching circuit Q1_DSQPositive transition or the voltage V of the third winding T3_augBegins timing in response to the voltage V across the primary switching circuit Q1_DSQNegative transition or the voltage V of the third winding T3_augThe timing is finished by the negative transition of (a), and a timing signal Ti is generated to control the turn-off of the primary side switching circuit Q1.

In one embodiment, the primary side control circuit U1 further includes: and the disconnection processing circuit 19 receives the timing signal Ti, and the disconnection processing circuit 19 may control the disconnection time of the primary side switch circuit Q1 by controlling the on-time of the primary side switch circuit Q1 (as shown in fig. 9) through the timing signal Ti, or control the disconnection time of the primary side switch circuit Q1 by controlling the peak value of the current flowing through the primary side switch circuit Q1 (as shown in fig. 8) through the timing signal Ti.

The secondary side control circuit U2 includes: a valley bottom detector 25 for comparing the voltage V across the secondary side switching circuit 101_DSRAnd valley bottom threshold V_thGenerating a frequency control signal fc; the time length controller 22 controls the secondary side switching circuit 101 to be turned on in response to the frequency control signal fc, and controls the secondary side switching circuit 101 to be turned off in response to the output voltage Vo. In one embodiment, the output voltage Vo controls the negative current peak flowing through the secondary switching circuit 101. If the block 26 includes a secondary current comparator, the duration controller 22 is reset to turn off the secondary switching circuit 101 when the current flowing through the secondary switching circuit 101 reaches the negative current limit value corresponding to the output voltage Vo. In another embodiment, the output voltage Vo (e.g., an error signal indicative of the output voltage Vo) controls the turn-on duration of the secondary side switching circuit 101. If the block 26 comprises an on-time controller, the error signal V_EAThe larger the error signal V, the longer the on-time_EAThe smaller the conduction period. When the on-time of the secondary side switch circuit 101 reaches the error signal V_EAAt the set value, the duration controller 22 is reset to turn off the secondary side switch circuit 101.

Fig. 13 schematically illustrates a flow chart 1300 of a method for switching a power supply circuit according to an embodiment of the invention. The switching power supply circuit includes: an electrical isolation device having a primary side and a secondary side, a primary side switching circuit coupled to the primary side of the electrical isolation device, and a secondary side switching circuit coupled to the secondary side of the electrical isolation device, the method comprising:

step 1301, receiving an input voltage on a primary side, and generating an output voltage on a secondary side by controlling the on and off of a primary side switching circuit and a secondary side switching circuit.

Step 1302, detecting information of a primary side current or information of a rate of change of a voltage across the primary side switching circuit, and controlling the primary side switching circuit to be turned on when the primary side current reaches a reverse current threshold or the rate of change of the voltage across the primary side switching circuit reaches a rate threshold.

And step 1303, feeding back the output voltage, and generating a frequency control signal according to the output voltage, so that the frequency control signal controls the secondary side switching circuit to be turned on for a period of time before the primary side switching circuit is turned on.

In one embodiment, the primary side current information and the voltage information at two ends of the primary side switch circuit are detected simultaneously, and when the primary side current reaches a reverse current threshold value and the voltage at two ends of the primary side switch circuit is smaller than a zero reference voltage, or the change rate of the voltage at two ends of the primary side switch circuit reaches a rate threshold value, the primary side switch circuit is controlled to be conducted.

In one embodiment, the method further comprises: and controlling the primary side switching circuit to be disconnected according to the conducted frequency of the primary side switching circuit.

While the present invention has been described with reference to several exemplary embodiments, it is understood that the terminology used is intended to be in the nature of words of description and illustration, rather than of limitation. As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the meets and bounds of the claims, or equivalences of such meets and bounds are therefore intended to be embraced by the appended claims.