阅读说明：本技术 一种用于超高压汞灯的降压电路及控制方法 (voltage reduction circuit for ultra-high pressure mercury lamp and control method ) 是由 王孝洪 张波 周鑫东 于 2019-09-24 设计创作，主要内容包括：本发明公开了一种用于超高压汞灯的降压电路及控制方法,包括降压电路、补偿电路、软启动电压限幅电路、PFM调制控制电路及谷底检测电路；所述降压电路为BUCK电路,所述软启动电压限幅电路包括两个电阻及三极管,本发明通过简易电路检测电压、电流及开关管谷底电压等信息,实现降压电路的软启动和输出限幅,利用PFM电路快速调制占空比,实现降压电路谷底导通,降低开关损耗及元器件发热。(the invention discloses a voltage reduction circuit and a control method for an ultrahigh-pressure mercury lamp, wherein the voltage reduction circuit comprises a voltage reduction circuit, a compensation circuit, a soft start voltage amplitude limiting circuit, a PFM modulation control circuit and a valley bottom detection circuit; the soft start and output amplitude limiting of the voltage reduction circuit are realized by detecting information such as voltage, current, valley bottom voltage of a switch tube and the like through a simple circuit, the duty ratio is rapidly modulated by utilizing a PFM circuit, valley bottom conduction of the voltage reduction circuit is realized, and switching loss and heating of components are reduced.)

1. A voltage reduction circuit for an ultrahigh-pressure mercury lamp is characterized by comprising a voltage reduction circuit, a compensation circuit, a soft start voltage amplitude limiting circuit, a PFM modulation control circuit and a valley bottom detection circuit;

The voltage reduction circuit is a BUCK circuit and comprises a switching tube Q1, the drain electrode of the switching tube Q1 is connected with a mains supply input signal, the grid electrode of the switching tube Q1 is connected with a PFM modulation control circuit, the source electrode of the switching tube Q1 is respectively connected with a valley bottom detection circuit, the cathode of a diode D1 and one end of an inductor L1, the anode of the diode D1 is connected with one end of a resistor R1, R1 is a current sampling resistor, and the other end of the resistor R1 and the other end of the inductor L1 are connected across two ends of a capacitor C1;

the soft-start voltage amplitude limiting circuit comprises a resistor R2, a resistor R3 and a triode Q2, wherein the resistor R2 and the resistor R3 are connected in series and then bridged at two ends of a capacitor C1, an emitter of the triode Q2 is connected with the resistor R2 and the resistor R3, a base of the triode Q2 is connected with a PFM modulation control circuit, a collector of the triode Q2 is connected with a compensation circuit, and the compensation circuit is connected with the PFM modulation control circuit.

2. the voltage reduction circuit according to claim 1, wherein the valley detection circuit comprises a resistor Rg1, a diode Dg1 and a capacitor Cg1, the resistor Rg1 is connected in parallel with the diode Dg1 and then connected in series with the capacitor Cg1, and the capacitor Cg1 is connected with a cathode of the diode D1.

3. the voltage reduction circuit according to claim 1, wherein the PFM modulation control circuit comprises a single chip microcomputer and a PFM modulation unit, the PFM modulation unit inputs a modulation signal into the single chip microcomputer, the PFM modulation unit comprises a comparator Q5, a capacitor C2, a resistor R7, a resistor R8 and a resistor R10, the resistor R7, the resistor R8 and the resistor R10 are connected in series, one end of the resistor R7 is connected with a voltage of 5V, one end of the resistor R10 is connected with a ground terminal, an inverting terminal of the comparator Q5 is connected with the other end of the resistor R7, an inverting terminal of the comparator Q5 is connected with the ground terminal through the capacitor C2, the other end of the resistor R10 is connected with a base of a switching tube Q1, and an inverting terminal of the comparator Q5 is connected with the compensation circuit.

4. The voltage reduction circuit according to claim 3, wherein the compensation circuit comprises a resistor R9, a capacitor C4, an operational amplifier Q3, a resistor R4, a resistor R5 and a resistor R6;

the resistor R9 and the capacitor C4 are connected in series between the inverting terminal of the operational amplifier Q3 and the inverting terminal of the comparator Q5, one end of the resistor R4 collects the output current of the voltage reduction circuit, the other end of the resistor R4 is connected with the inverting terminal of the operational amplifier Q3 and the collector of the triode Q2, the inverting terminal of the operational amplifier is connected with the resistor R5 and the resistor R6, the other end of the resistor R5 is grounded, and the other end of the resistor R6 is connected with the single chip microcomputer.

5. The buck circuit according to claim 1, wherein the switching transistor Q1 is an NMOS transistor, and the transistor Q2 is a PNP transistor.

6. The voltage reduction circuit according to claim 1, wherein the resistor R2 has a resistance of 66K ohms and the resistor R3 has a resistance of 2.4K ohms.

7. the voltage reducing circuit according to claim 1, wherein the commercial power signal is obtained after being processed by a power factor correction circuit.

8. A control method of a step-down circuit for an ultra-high pressure mercury lamp according to claim 4, comprising:

before the ultra-high pressure mercury lamp is lighted, the initial control mode of the voltage reduction circuit is constant current control, the current set value is 2A, the output voltage is limited to 170V by the amplitude limiting circuit, the voltage reduction circuit works in a current discontinuous mode, and the voltage amplitude limiting effect is achieved by adopting double-loop control; the triode Q2 and the compensation circuit realize the soft start function;

When the mercury lamp is lighted, the voltage reduction circuit detects whether the lighting is successful, if so, the low constant power control stage is entered, otherwise, the voltage reduction circuit still works in the constant current mode;

after the mercury lamp is lighted, the mercury lamp firstly enters a low constant power stage, then enters a power-up stage, and the voltage reduction circuit increases the set power according to the sampled information until the power reaches the rated power and maintains the constant power;

When the voltage reduction circuit enters a rated constant power stage, the valley bottom detection circuit starts to work, the PFM modulation control circuit and the single chip microcomputer determine the on and off time of the switching tube Q1 according to the detection result of the valley bottom detection circuit, the switching loss is reduced, and at the moment, the voltage reduction circuit is switched from a current discontinuous mode to a current critical continuous mode.

9. the control method according to claim 8, wherein the voltage limiting is implemented by: when the voltage of the output end of the voltage reduction circuit is divided to the voltage of the emitter of the triode Q2 and is less than 5.7V, the triode Q2 is turned off, and the circuit is in a pure current closed loop; when the voltage of the output end of the voltage reduction circuit is divided to a triode Q2 emitter by more than 57V, the transistor Q2 is conducted to raise the negative terminal of the compensation circuit, and the duty ratio is pulled down, so that the output voltage is limited to:

10. The control method according to claim 8, wherein the soft start function is realized by:

before the voltage reduction circuit is started, the base level of the triode Q2 is 0V, so that the voltage of the inverting terminal of the operational amplifier Q3 is always higher than the voltage of the non-inverting terminal, the PFM modulation unit is in a closed state, the generation of a duty ratio is restrained, when the voltage reduction circuit is started, the base of the triode Q2 is raised to 5V, the triode Q2 is closed, the voltage at a point P7 does not influence a current loop any more, the duty ratio is generated at the moment, the point P7 is a sampling point of the resistor R2 and the resistor R3, and because the closing of the Q2 is not instantaneously completed, the duty ratio can be gradually increased by utilizing the transition process, and the function of soft starting is.

Technical Field

The invention belongs to the field of driving control of ultra-high pressure mercury lamps, and particularly relates to a voltage reduction circuit for an ultra-high pressure mercury lamp and a control method.

Background

the ultra-high pressure mercury lamp is a gas discharge lamp which is conductive by mercury vapor and has negative resistance, the special load has extremely high requirement on a power supply, and meanwhile, in consideration of the practical application requirement, the ballast of the power supply device needs to meet the following requirements: 1. a high-voltage ignition circuit capable of providing an appropriate ignition power is provided. Ignition is difficult to trigger when the ignition voltage and the ignition power are insufficient; and the service life of the bulb is shortened by the excessive ignition power and the too high ignition voltage. 2. The power supply has reliable current limiting measures to prevent current avalanche phenomenon. 3. The discharge instability of the ultra-high pressure mercury lamp under the drive of high frequency energy can be inhibited. 4. The load-balancing circuit has strong nonlinear load-adapting capability and can cope with the transition process from starting to stable operation. The power closed-loop regulating capability is provided, and the light-emitting stability and consistency of the ultra-high pressure mercury lamp can be controlled to meet the production practice requirements. 6. Has certain fault diagnosis and protection measures.

therefore, when the ultra-high pressure mercury lamp starts, the voltage reduction circuit of the electronic ballast is required to provide proper voltage and keep stable, so as to ensure the normal work of the rear-stage resonant circuit, if the voltage is too high, the voltage reduction circuit easily enters an unstable working state, and a power element with a higher voltage level is required to be used, if the voltage is too low, the rear-stage resonant circuit needs to reach higher gain, the working frequency and the element requirements of the rear-stage circuit are also improved, the cathode sputtering of the lamp can be caused by the overhigh pulse voltage output by the rear-stage circuit, the service life of the lamp is influenced, and the lamp is difficult to normally start due to overlow voltage.

After the ultra-high pressure mercury lamp is started, the impedance between the two poles is suddenly reduced from megaohm level to several ohms to dozens of ohms, the voltage reduction circuit needs to judge whether the ultra-high pressure mercury lamp is lightened or not through circuit current, at the moment, the lamp body has negative resistance characteristics, the equivalent impedance is very small, the ultra-high power cannot be borne, and if the ultra-high pressure mercury lamp runs at rated power, the lamp body can be damaged quickly. During the transition process, the speed of increasing the power and the setting of the lowest power all affect the stable operation and the service life of the ultra-high pressure mercury lamp.

The ultra-high pressure mercury lamp finally works in a constant power state, the mercury lamp is maintained at the rated power of leaving a factory at the moment, under the normal condition, the ultra-high pressure mercury lamp and a ballast circuit are placed in a waterproof and dustproof closed case, so that high requirements are provided for the working loss and the heating condition of a voltage reduction circuit, and under the working environment, the circuit needs to have higher working efficiency and lower working temperature as much as possible. Because the step-down circuit works in the discontinuous mode for a long time, the current of the freewheeling diode is reduced to zero every period, the direct current inductance and the switching tube in the circuit and the parasitic capacitance of the freewheeling diode jointly form an oscillation loop, the circuit generates attenuation oscillation, the oscillation frequency is often far greater than the switching frequency of the step-down circuit, because of the amplitude limiting effect of the freewheeling diode, the amplitude is not too large, but the oscillating fundamental wave and higher harmonic can generate adverse effect on the circuit and peripheral systems, and can generate influence on the efficiency of the converter, the generation of resonance enables the two ends of the switching tube to generate current during the turn-off period, the voltage at the two ends of the switching tube is often large at the moment, and huge loss and heat are caused.

disclosure of Invention

In order to overcome the disadvantages and shortcomings of the prior art, the invention provides a voltage reduction circuit for an ultra-high pressure mercury lamp;

another object of the present invention is to provide a control method of a step-down circuit for an ultra-high pressure mercury lamp.

The invention adopts the following technical scheme:

A voltage reduction circuit for an ultrahigh-pressure mercury lamp comprises a voltage reduction circuit, a compensation circuit, a soft start voltage amplitude limiting circuit, a PFM modulation control circuit and a valley bottom detection circuit;

the voltage reduction circuit is a BUCK circuit and comprises a switching tube Q1, the drain electrode of the switching tube Q1 is connected with a mains supply input signal, the grid electrode of the switching tube Q1 is connected with a PFM modulation control circuit, the source electrode of the switching tube Q1 is respectively connected with a valley bottom detection circuit, the cathode of a diode D1 and one end of an inductor L1, the anode of the diode D1 is connected with one end of a resistor R1, R1 is a current sampling resistor, and the other end of the resistor R1 and the other end of the inductor L1 are connected across two ends of a capacitor C1;

The soft-start voltage amplitude limiting circuit comprises a resistor R2, a resistor R3 and a triode Q2, wherein the resistor R2 and the resistor R3 are connected in series and then bridged at two ends of a capacitor C1, an emitter of the triode Q2 is connected with the resistor R2 and the resistor R3, a base of the triode Q2 is connected with a PFM modulation control circuit, a collector of the triode Q2 is connected with a compensation circuit, and the compensation circuit is connected with the PFM modulation control circuit.

The valley bottom detection circuit comprises a resistor Rg1, a diode Dg1 and a capacitor Cg1, wherein the resistor Rg1 is connected with the diode Dg1 in parallel and then connected with the capacitor Cg1 in series, and the capacitor Cg1 is connected with the cathode of the diode D1.

The PFM modulation control circuit comprises a single chip microcomputer and a PFM modulation unit, the PFM modulation unit inputs a modulation signal into the single chip microcomputer, the PFM modulation unit comprises a comparator Q5, a capacitor C2, a resistor R7, a resistor R8 and a resistor R10, the resistor R7, the resistor R8 and the resistor R10 are connected in series, one end of the resistor R7 is connected with 5V voltage, one end of the resistor R10 is connected with a grounding end, the inverting end of the comparator Q5 is connected with the other end of the resistor R7, the inverting end of the comparator Q5 is connected with the grounding end through the capacitor C2, the other end of the resistor R10 is connected with a base of a switch tube Q1, and the inverting end of the comparator Q5 is connected with a compensation circuit.

The compensation circuit comprises a resistor R9, a capacitor C4, an operational amplifier Q3, a resistor R4, a resistor R5 and a resistor R6;

The resistor R9 and the capacitor C4 are connected in series between the inverting terminal of the operational amplifier Q3 and the inverting terminal of the comparator Q5, one end of the resistor R4 collects the output current of the voltage reduction circuit, the other end of the resistor R4 is connected with the inverting terminal of the operational amplifier Q3 and the collector of the triode Q2, the inverting terminal of the operational amplifier is connected with the resistor R5 and the resistor R6, the other end of the resistor R5 is grounded, and the other end of the resistor R6 is connected with the single chip microcomputer.

The switching tube Q1 is an NMOS tube, and the triode Q2 is a PNP tube.

the resistance value of the resistor R2 is 66K ohm, and the resistance value of the resistor R3 is 2.4K ohm.

And the commercial power signal is obtained after being processed by a power factor correction circuit.

A control method of a voltage reduction circuit of an ultrahigh-pressure mercury lamp specifically comprises the steps that before the ultrahigh-pressure mercury lamp is lightened, the initial control mode of the voltage reduction circuit is constant current control, the current set value is 2A, the output voltage is limited to 170V by an amplitude limiting circuit, the voltage reduction circuit works in a current discontinuous mode, and at the moment, the voltage amplitude limiting effect is achieved by adopting double-loop control; the triode Q2 and the compensation circuit realize the soft start function;

When the mercury lamp is lighted, the voltage reduction circuit detects whether the lighting is successful, if so, the low constant power control stage is entered, otherwise, the voltage reduction circuit still works in the constant current mode;

After the mercury lamp is lighted, the mercury lamp firstly enters a low constant power stage, then enters a power-up stage, and the voltage reduction circuit increases the set power according to the sampled information until the power reaches the rated power and maintains the constant power;

When the voltage reduction circuit enters a rated constant power stage, the valley bottom detection circuit starts to work, the PFM modulation control circuit and the single chip microcomputer determine the on and off time of the switching tube Q1 according to the detection result of the valley bottom detection circuit, the switching loss is reduced, and at the moment, the voltage reduction circuit is switched from a current discontinuous mode to a current critical continuous mode.

The voltage amplitude limiting implementation process is as follows: when the voltage of the output end of the voltage reduction circuit is divided to the voltage of the emitter of the triode Q2 and is less than 5.7V, the triode Q2 is turned off, and the circuit is in a pure current closed loop; when the voltage of the output end of the voltage reduction circuit is divided to the emitter of the triode Q2 and is more than 5.7V, the triode Q2 is conducted, so that the negative end of the compensation circuit is increased, the duty ratio is reduced, and the output voltage is limited as follows:The soft start function implementation process comprises the following steps:

Before the voltage reduction circuit is started, the base level of the triode Q2 is 0V, so that the voltage of the inverting terminal of the operational amplifier Q3 is always higher than the voltage of the non-inverting terminal, the PFM modulation unit is in a closed state, the generation of a duty ratio is restrained, when the voltage reduction circuit is started, the base of the triode Q2 is raised to 5V, the triode Q2 is closed, the voltage at a point P7 does not influence a current loop any more, the duty ratio is generated at the moment, and the point P7 is sampling points of a resistor R2 and a resistor R3. Since the turn-off of Q2 is not instantaneous, the duty cycle can be gradually increased using this transition to function as a soft start.

the invention has the beneficial effects that:

(1) the voltage reduction circuit collects information such as voltage and current and performs circuit compensation, and soft start, output amplitude limiting and power control of the voltage reduction circuit are realized;

(2) the PFM circuit is used for rapidly modulating the duty ratio, a valley bottom detection circuit is built for detecting a differential signal of a switching tube, valley bottom conduction of a voltage reduction circuit is realized, and switching loss and component heating are reduced;

(3) The invention realizes the voltage-limiting constant-current control in the ignition stage, the power-rising control in the transition stage and the constant-power control in normal operation, and has good heating performance and stable light brightness.

Drawings

FIG. 1 is a circuit schematic of the present invention;

FIG. 2 is a schematic diagram of the power variation of the voltage step-down circuit of the present invention;

FIG. 3 is an equivalent topology of the voltage step-down circuit of the present invention;

FIG. 4 is a signal flow diagram of the present invention;

FIG. 5 is a comparison graph of the operating waveforms of the valley-enabled and non-enabled circuits according to the present invention.

Detailed Description

The present invention will be described in further detail with reference to examples and drawings, but the present invention is not limited to these examples.