CN100514817C - Zero voltage switch active clamp positive and negative violent changer - Google Patents

Abstract

The invention relates to a power supply circuit, which discloses a zero-voltage switch active clamp forward and flyback converter, including a transformer, a switch tube, a clamp tube, a clamp capacitor, a rectifier tube, a resonant inductor, an energy storage inductor and output capacitance. The primary side circuit of the converter is an active clamp circuit, in which the switch tube is connected in series with the primary winding of the transformer and connected to both ends of the input voltage; the clamp tube is connected in series with the clamp capacitor and connected in parallel with the primary winding of the transformer or the switch tube. The secondary circuit of the converter is a full-bridge rectification or full-wave rectification circuit. The resonant inductor is connected in series in the secondary circuit of the converter, so that the current of the secondary winding of the transformer flows through the resonant inductance, and the current change of the secondary winding of the transformer becomes a resonant inductance The excitation current changes. The switch tube of the zero-voltage switch active clamp forward-flyback converter can realize zero-voltage turn-on, thereby reducing the turn-on loss of the switch tube and reducing the EMI emission of the converter.

Description

A Zero Voltage Switching Active Clamp Forward and Flyback Converter

technical field

The invention relates to a power supply circuit, in particular to a switching power supply and a power supply circuit for power conversion.

Background technique

The forward and flyback converter combines the advantages of the forward converter and the flyback converter, and has better overall performance. There is a type of forward-flyback converter that uses one transformer to realize the functions of forward transformer and flyback transformer, so that the transformer can be fully utilized, such as the active clamp forward-flyback (FFAC) converter shown in Figure 1 to Figure 4 . When the forward and flyback converter is working, the clamp tube has a natural zero-voltage turn-on condition, but the turn-on of the switch tube is hard turn-on, which will cause a relatively large turn-on loss.

Contents of the invention

The present invention proposes a novel zero-voltage switching (ZVS) active-clamp forward-flyback converter circuit just to solve the above-mentioned technical problems, which is based on the active-clamp forward-flyback (FFAC) converter The secondary resonant inductance is added to realize the zero-voltage turn-on of the switching tube.

The technical solution adopted by the present invention to solve its technical problems is:

A zero-voltage switch active clamp forward and flyback converter includes a transformer, a switch tube, a clamp tube, a clamp capacitor, a rectifier tube, a resonant inductor, an energy storage inductor and an output capacitor. The primary side circuit of the converter is an active clamp circuit, in which the switch tube is connected in series with the primary winding of the transformer and connected to both ends of the input voltage; the clamp tube is connected in series with the clamp capacitor and connected in parallel with the primary winding of the transformer or the switch tube. The secondary circuit of the converter is a rectifier circuit. A resonant inductor is connected in series in the secondary circuit of the converter, so that the current of the secondary winding of the transformer flows through the resonant inductor, and the change of the current of the secondary winding of the transformer becomes the excitation current change of the resonant inductor.

The converter secondary circuit of the zero-voltage switching active clamp forward-flyback converter is composed of a transformer secondary winding and a rectifier tube to form a full-bridge rectifier circuit, and a resonant inductor is connected in series in the converter secondary circuit, and the resonant inductor and the transformer The secondary windings are connected in series, the two output ends of the rectifier circuit are point a and point b respectively, and the energy storage inductor and output capacitor are connected in series to point a and point b.

The converter secondary circuit of the zero-voltage switching active clamp forward-flyback converter is composed of a transformer secondary winding and a rectifier tube to form a full-bridge rectifier circuit, and two resonant inductors are connected in series in the converter secondary circuit, two The resonant inductors are respectively connected in series between the two sets of rectifier tubes of the full-bridge rectifier circuit. The two output terminals of the rectifier circuit are point a and point b respectively, and the energy storage inductor is connected in series with the output capacitor to point a and point b.

The converter secondary circuit of the zero-voltage switching active clamp forward-flyback converter is composed of a transformer secondary winding and a rectifier tube to form a full-bridge rectifier circuit, and a resonant inductance is connected in series in the converter secondary circuit, and the resonant inductance is a coupling Inductance, the two internal inductors are connected in series between the two sets of rectifier tubes of the full-bridge rectifier circuit. The two output terminals of the rectifier circuit are point a and point b respectively. After the energy storage inductor is connected in series with the output capacitor, the points a and Point b is connected.

The converter secondary circuit of the zero-voltage switching active clamp forward-flyback converter is composed of a transformer secondary winding and a rectifier tube to form a full-wave rectifier circuit, and a resonant inductor is connected in series in the converter secondary circuit, and the resonant inductor and rectifier The tubes are connected in series, the two output ends of the rectifier circuit are point a and point b respectively, and the energy storage inductance and the output capacitor are connected in series to point a and point b.

The converter secondary circuit of the zero-voltage switching active clamp forward-flyback converter is composed of a transformer secondary winding and a rectifier tube to form a full-wave rectifier circuit, and two resonant inductors are connected in series in the converter secondary circuit, two The resonant inductor is connected in series with the two rectifier tubes respectively, the two output terminals of the rectifier circuit are point a and point b respectively, and the energy storage inductor is connected in series with the output capacitor to point a and point b.

The converter secondary circuit of the zero-voltage switching active clamp forward-flyback converter is composed of a transformer secondary winding and a rectifier tube to form a full-wave rectifier circuit, and a resonant inductor is connected in series in the converter secondary circuit, and the resonant inductor is a coupling Inductor, the two internal inductors are respectively connected in series with two rectifier tubes, the two output terminals of the rectifier circuit are point a and point b respectively, and the energy storage inductor is connected in series with the output capacitor to point a and point b.

The beneficial effect of the invention is that the switching tube of the zero-voltage switch active clamp forward-flyback converter can realize zero-voltage turn-on, thereby reducing the turn-on loss of the switch tube and reducing the EMI emission of the converter.

Description of drawings

Figure 1 to Figure 4 are four circuit schematic diagrams of single transformer forward and flyback converters.

Fig. 5 is a circuit schematic diagram of a zero voltage switch active clamp forward and flyback converter according to the present invention.

6 to 10 are schematic circuit diagrams of five embodiments of a zero-voltage switch active clamp forward-flyback converter secondary circuit of the present invention, respectively.

Figure 11 is the equivalent circuit diagram of Figure 5

12 to 19 are schematic diagrams of different working modes of the circuit shown in FIG. 11 .

Fig. 20 is a waveform diagram of main electrical parameters when the circuit shown in Fig. 11 is working.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Fig. 1 to Fig. 4 show four circuit schematic diagrams of the single-transformer forward-flyback converter in the prior art.

As shown in Figure 5, a zero-voltage switching active clamp forward and flyback converter includes a transformer, a switch tube, a clamp tube, a clamp capacitor, a rectifier tube, a resonant inductor, an energy storage inductor, and an output capacitor. The primary side circuit of the converter is an active clamping circuit, the switching tube S1 is connected in series with the primary side winding Np of the transformer and then connected to both ends of the input voltage; the clamping tube S2 is connected in parallel with the primary side winding Np of the transformer after being connected in series with the clamping capacitor C1; The secondary circuit of the converter is composed of the secondary winding Ns of the transformer and the rectifier tubes D1, D2, D3 and D4 to form a full-bridge rectifier circuit. The resonant inductor Lr is connected in series in the secondary circuit of the converter, and the resonant inductor Lr is connected in series with the secondary winding Ns of the transformer. The two output terminals of the rectifier circuit are point a and point b respectively, and the energy storage inductor L1 and the output capacitor C2 are connected in series to point a and point b.

FIG. 6 to FIG. 10 are respectively five embodiments of the secondary side circuit of the present invention, the principle of which is similar to the circuit shown in FIG. 5 . The following is a detailed description of the working principle of the circuit diagram shown in Figure 5 as an example. In order to facilitate the analysis, the equivalent transformation of the circuit is carried out. The transformer is replaced by an equivalent circuit model of an ideal transformer and an excitation inductance in parallel, and the secondary side resonant inductance, etc. The effective transformation is the primary side resonant inductance. Figure 11 is the equivalent circuit diagram of Figure 5. The inductance Lp in Figure 11 is the primary excitation inductance of the transformer, the inductance Lrp is the primary equivalent inductance of the secondary resonant inductance Lr, and the capacitor Cr is the equivalent capacitance, mainly including the switch Tube, clamp tube output capacitance and transformer stray capacitance. In the analysis, it is assumed that the switch tube, clamp tube and rectifier tube are all ideal devices, the forward conduction voltage drop and reverse conduction voltage drop are negligible, and the capacitances of C1 and C2 are large enough, and the voltage change in one switching cycle is negligible , the inductance of the inductor L1 is large enough that the current variation within one switching cycle is negligible.

Analysis of working principle:

A complete working cycle can be divided into eight working modes. Referring to Figure 12 to Figure 19, the waveforms of the main parameters of the circuit are shown in Figure 20.

①Working mode 1 (corresponding to before time t0, its equivalent circuit is shown in Figure 12)

Before time t0, the switching tube S1 is turned on, the clamping tube S2 is turned off, the primary side of the transformer receives the input voltage, the secondary rectifier tubes D1 and D4 are turned on, and D2 and D3 are turned off. The primary side input current includes two parts, one part is the current ip converted from the secondary winding current to the primary side, and the other part is the primary side excitation current im, and the slope of im increases under the action of the input voltage. In this working mode, the primary side transfers energy to the secondary side, while the magnetizing inductor stores energy.

②Working mode 2 (corresponding to t0~t1, its equivalent circuit is shown in Figure 13)

At time t0, the switch tube S1 is turned off, the input current of the primary side charges Cr, and the voltage at both ends of S1 gradually rises. The excitation current im continues to increase during this period, but the speed gradually decreases. Due to the large excitation inductance, im does not change much during this period, the current ip converted from the secondary winding current to the primary side remains unchanged, and the voltage at both ends of the switch tube rises approximately linearly.

③Working mode 3 (corresponding to t1~t2, its equivalent circuit is shown in Figure 14)

At time t1, the voltage across the switch tube S1 rises to the input voltage, and the excitation current im reaches the maximum value. Then the voltage on the primary side of the transformer is reversed, the excitation current im starts to drop, the resonant inductor Lrp bears the voltage up and down, ip gradually decreases, the secondary side rectifier circuit starts to commutate, D1, D2, D3, D4 are turned on at the same time, D1, The current of D4 decreases gradually, the currents of D2 and D3 gradually increase, and the output voltage Vab of the rectifier circuit is clamped to zero. Cr continues to charge, but the charging current gradually decreases. In this working mode, Lp and Lrp are connected in parallel, and resonate with Cr, and the voltage at both ends of the switching tube rises resonantly. Because the initial current of the resonant tank circuit is relatively large (compared with working mode 7), the voltage at both ends of the switch tube rises faster.

④ Working mode 4 (corresponding to t2~t3, its equivalent circuit is shown in Figure 15)

At time t2, the voltage across the switching tube S1 rises to the sum of the input voltage and the voltage of the clamping capacitor, the body diode of the clamping tube is naturally turned on, Cr is charged, and the excitation current im and the converted current ip of the secondary winding flow to the clamping capacitor C1. The voltage on the primary side of the transformer is clamped at the voltage of the clamp capacitor, the slope of the excitation current im decreases under the action of the clamp voltage, the resonant inductance Lrp bears the clamp voltage, and the slope of ip decreases until it decreases to zero and then gradually increases in the opposite direction. The secondary side rectifier circuit continues the commutation process.

⑤ Working mode 5 (corresponding to t3~t5, its equivalent circuit is shown in Figure 16)

At time t3, ip reaches the reverse maximum value, the commutation process of the secondary side rectifier circuit ends, D1 and D4 are turned off, and D2 and D3 are turned on. Then ip remains unchanged, the primary side of the transformer still bears the voltage of the clamping capacitor, and the exciting current im continues to decrease in slope under the action of the clamping voltage. The charging current ic of the clamp capacitor gradually decreases to zero and then gradually increases in reverse. In this working mode, the energy stored in the excitation inductance of the primary side is transferred to the secondary side, and the clamping capacitor C1 buffers the energy of the excitation inductance, so that the energy transferred to the secondary side presents a constant power mode.

⑥Working mode 6 (corresponding to t5~t6, its equivalent circuit is shown in Figure 17)

At time t5, the clamping tube S2 is turned off, the clamping capacitor stops discharging, Cr starts to discharge, and the voltage across the switching tube S1 gradually decreases. The excitation current im continues to drop during this period, but the speed gradually decreases. Due to the large excitation inductance, im does not change much during this period, the output current converted to the current ip of the primary side remains unchanged, and the voltage at both ends of the switch tube decreases approximately linearly.

⑦Working mode 7 (corresponding to t6~t7, its equivalent circuit is shown in Figure 18)

At time t6, the voltage across the switch tube S1 drops to the input voltage, and the excitation current im reaches the minimum value (algebraic value). Then the voltage on the primary side of the transformer is reversed, the excitation current im starts to rise, the resonant inductor Lrp withstands the positive and negative voltage, ip gradually decreases, the secondary side rectifier circuit starts to commutate, D1, D2, D3, D4 are turned on at the same time, D2, The current of D3 decreases gradually, the currents of D1 and D4 increase gradually, and the output voltage Vab of the rectifier circuit is clamped to zero. Cr continues to discharge, but the discharge current gradually decreases. In this working mode, Lp and Lrp are connected in parallel, and resonate with Cr, and the voltage at both ends of the switching tube resonantly drops. Because the initial current of the resonant tank circuit is small (compared with working mode 3), the voltage across the switching tube drops slowly.

⑧Working mode 8 (corresponding to t7~t9, its equivalent circuit is shown in Figure 19)

At time t7, the voltage at both ends of the switch tube S1 drops to zero, and the body diode of the switch tube is naturally turned on, and the switch is turned on (zero-voltage turn-on) after time t7. Cr discharge ends. The voltage on the primary side of the transformer is the input voltage, the excitation current im rises with a slope under the action of the input voltage, the resonant inductor Lrp bears the input voltage, the slope of ip decreases, gradually decreases to zero and then gradually increases in the reverse direction, and the secondary side rectifier circuit continues to commutate process. Until time t9, ip reaches the maximum value, the commutation process of the secondary side rectification circuit ends, and the line enters working mode 1 again.

The conditions for the switching tube to realize zero voltage switching (ZVS):

From the analysis of the working principle, it can be seen that the resonant tank circuit that creates the ZVS condition of the switching tube includes the primary side equivalent capacitance C _r , the primary side excitation inductance L _p and the primary side equivalent inductance L _rp of the secondary side resonant inductance, where L _p and L _rp is a parallel relationship.

Set the parallel equivalent inductance of L _p and L _rp as L _eq , the equivalent current flowing through L _eq is i _eq , and the reference direction is the same as the reference direction of i _p shown in the figure, we can know

${\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; eq</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; rp</span>}}}{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; rp</span>}}}$

i _eq =i _m +i _p

In an actual circuit, the excitation inductance is generally much larger than the resonant inductance, and the parallel equivalent inductance of the two inductors is approximately equal to the resonant inductance. Here, the influence of the excitation inductance on the equivalent inductance is ignored, that is, assuming

L _eq = L _rp (1)

Let the average value of i _m be I _m , the total range of change in one cycle is ΔI _m , let the maximum positive amplitude of i _p be I _p , then its negative maximum amplitude is -I _p

Neglecting the influence of the switching process (t0～t3, t5～t9) on the magnitude of the excitation current, it can be seen that I _m =I _p , and _im obtains its minimum value (algebraic value) at time t6

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}$

Then at time t6, i _eq is

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; eq</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Assuming that the switching frequency of the converter is f _s and the conduction duty ratio of the switching tube is D, ΔI _m can be obtained as:

$\mathrm{<span\; class="notranslate">\; \&Delta;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}\mathrm{<span\; class="notranslate">\; D.</span>}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Substituting (3) into (2), we get

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; eq</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}\mathrm{<span\; class="notranslate">\; D.</span>}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

To achieve ZVS for the switching tube, the stored energy of L _eq must be greater than the stored energy of C _r at time t6, namely

$\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; eq</span>}}{{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; eq</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Greater\; Equal;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

Substitute (1), (4) into (5) to get:

$\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; rp</span>}}{<span\; class="notranslate">\; (</span><span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>\frac{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}\mathrm{<span\; class="notranslate">\; D.</span>}}{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Greater\; Equal;</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}$

After simplification:

${\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; rp</span>}}<span\; class="notranslate">\; \&Greater\; Equal;</span>\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; r</span>}}\frac{{{\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; the\; <figure-callout\; id="2"\; label="s"\; filenames="C200710098899E00121.png,C200710098899E00122.png"\; state="\{\{state\}\}">s</figure-callout></span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; D.</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; \&CenterDot;</span>{{\mathrm{<span\; class="notranslate">\; L</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

It can be seen from formula (6) that the conditions for switching tubes to achieve ZVS are not only related to the resonant inductance and resonant capacitor, but also related to the switching frequency, duty cycle, and primary excitation inductance. But it is worth noting that the ZVS condition has nothing to do with i _p , that is, has nothing to do with the load current, so it is easier for the converter to realize ZVS at light load.

Explanation about the time t4 and t8:

Time t4 is the zero-crossing moment of the clamp capacitor current ic, which may occur earlier than time t3 due to different circuit parameters, that is, the current of the clamp capacitor has crossed zero and reversed before the commutation process of the secondary side ends. However, this has no particular influence on the commutation process. The time period from t2 to t4 is the time period when the clamp tube meets the ZVS condition, and the clamp tube is turned on with zero voltage during this time period.

Time t8 is the zero-crossing moment of the input current, and time t7 to t8 is the time period when the switch tube meets the ZVS condition, and the switch tube is turned on at zero voltage during this period. When the line parameters do not meet the ZVS condition of the switch tube, the circuit state at time t7 will not appear, that is, when the input current crosses zero at time t8, the voltage at both ends of the switch tube has not yet dropped to zero and turns to resonant rise after time t8 However, the ZVS condition of the switching tube cannot be realized. In this case, the time t8 becomes the best turn-on time of the switch tube, and turning on the switch tube at t8 can minimize the turn-on loss.

The present invention is not limited to the above-mentioned best implementation mode, and any other products identical or similar to the present invention obtained by anyone under the enlightenment of the present invention all fall within the protection scope of the present invention.

Claims (7)

1. A zero voltage switching active clamp forward and flyback converter, comprising a transformer, a switch tube, a clamp tube, a clamp capacitor, a rectifier tube, a resonant inductor, an energy storage inductor and an output capacitor; it is characterized in that: the converter The primary side circuit is an active clamp circuit, the switch tube (S1) is connected in series with the primary winding (Np) of the transformer and connected to both ends of the input voltage; the clamp tube (S2) is connected in series with the clamp capacitor (C1) The side winding (Np) or the switching tube (S1) are connected in parallel; the secondary side circuit of the converter is a full-bridge rectification or full-wave rectification circuit, and a resonant inductor is connected in series in the secondary side circuit of the converter, so that the secondary winding current of the transformer flows through the resonant inductor , and make the current change of the secondary winding of the transformer become the excitation current change of the resonant inductance. 2. The zero-voltage switching active clamp forward-flyback converter according to claim 1, characterized in that: the secondary circuit of the converter consists of a transformer secondary winding (Ns) and four rectifier tubes (D1, D2, D3 and D4) form a full-bridge rectifier circuit, the resonant inductance (Lr) is connected in series in the secondary circuit of the converter, the resonant inductance (Lr) is connected in series with the transformer secondary winding (Ns), and the two output terminals of the rectifier circuit are respectively the first point (a) and the second point (b), the energy storage inductor (L1) is connected in series with the output capacitor (C2) and connected to the first point (a) and the second point (b). 3. The zero-voltage switching active clamp forward-flyback converter according to claim 1, characterized in that: the secondary side circuit of the converter consists of a transformer secondary winding (Ns) and four rectifier tubes (D1, D2, D3 , D4) to form a full-bridge rectifier circuit, the resonant inductors (Lr1, Lr2) are connected in series in the secondary circuit of the converter, and the resonant inductors (Lr1, Lr2) are respectively connected in series with the first rectifier tube (D1) and the second rectifier tube of the full-bridge rectifier circuit Between the three rectifier tubes (D3), the second rectifier tube (D2) and the fourth rectifier tube (D4), the two output terminals of the rectifier circuit are respectively the first point (a) and the second point (b), and the energy storage The inductor (L1) is connected in series with the output capacitor (C2) to the first point (a) and the second point (b). 4. The zero-voltage switching active clamp forward-flyback converter according to claim 1, characterized in that: the secondary side circuit of the converter consists of a transformer secondary winding (Ns) and four rectifier tubes (D1, D2, D3 , D4) form a full-bridge rectifier circuit, and the resonant inductors (Lr1, Lr2) are connected in series in the secondary circuit of the converter. The resonant inductors (Lr1, Lr2) are coupling inductors, and the two internal inductors (Lr1, Lr2) are connected in series Between the first rectifier tube (D1) and the third rectifier tube (D3), the second rectifier tube (D2) and the fourth rectifier tube (D4) of the full-bridge rectifier circuit, the two output ends of the rectifier circuit are respectively One point (a) and the second point (b), the energy storage inductor (L1) and the output capacitor (C2) are connected in series to the first point (a) and the second point (b). 5. The zero-voltage switching active clamp forward-flyback converter according to claim 1, characterized in that: the secondary side circuit of the converter consists of transformer secondary windings (Ns1, Ns2) and two rectifier tubes (D1, D2 ) to form a full-wave rectifier circuit, the resonant inductance (Lr) is connected in series in the secondary circuit of the converter, the resonant inductance (Lr) is connected in series with the first rectifier tube (D1) or the second rectifier tube (D2), and the two rectifier circuits The output terminals are respectively the first point (a) and the second point (b), and the energy storage inductance (L1) and the output capacitor (C2) are connected in series to the first point (a) and the second point (b). 6. The zero-voltage switching active clamp forward-flyback converter according to claim 1, characterized in that: the secondary side circuit of the converter consists of a transformer secondary winding (Ns1, Ns2) and two rectifier tubes (D1, D2 ) to form a full-wave rectifier circuit, the resonant inductors (Lr1, Lr2) are connected in series in the secondary side circuit of the converter, and the resonant inductors (Lr1, Lr2) are respectively connected in series with the first rectifier tube (D1) and the second rectifier tube (D2), The two output ends of the rectifier circuit are the first point (a) and the second point (b), and the energy storage inductor (L1) and the output capacitor (C2) are connected in series with the first point (a) and the second point (b) ) connected. 7. The zero-voltage switching active clamp forward-flyback converter according to claim 1, characterized in that: the secondary circuit of the converter is composed of the transformer secondary winding (Ns1, Ns2) and two rectifier tubes (D1, D2 ) constitutes a full-wave rectifier circuit, the resonant inductors (Lr1, Lr2) are connected in series in the secondary side circuit of the converter, and the resonant inductors (Lr1, Lr2) are coupling inductors, and the two internal inductors (Lr1, Lr2) are respectively connected to the first The rectifier tube (D1) and the second rectifier tube (D2) are connected in series, the two output terminals of the rectifier circuit are the first point (a) and the second point (b), respectively, the energy storage inductor (L1) and the output capacitor (C2) Connect with the first point (a) and the second point (b) in series.

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