WO2018120828A1 - Power supply converter - Google Patents

Abstract

A power supply converter, comprising a branch a, a branch b, a second transformer (T1B), a first transistor (Q1), a second transistor (Q2) and a first transformer (T1A). The power supply converter can not only accelerate the starting of a transistor, but can also improve the conversion efficiency, enhance a capacitive load starting capability, enhance a low temperature starting capability and realize a short-circuit protection function, and can work normally at different environmental temperatures. The power supply converter has a low no-load power consumption and has a long-term short-circuit protection function.

Description

Power converter

The present application claims priority to Chinese Patent Application No. Serial No. No. No. No. No. No. No. No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No No

Technical field

The present invention relates to the field of power electronics, and in particular, to a power converter.

Background technique

The self-excited push-pull oscillation circuit is a well-known technology, and is described in detail on pages 284 to 298 of the "Practical Power Circuit Design" of the Science Press. The circuit equivalent structure is shown in FIG.

The structure of the existing self-excited push-pull oscillation circuit is shown in Figure 2. The working principle can be referred to page 56 of Power Conversion Technology of People's Posts and Telecommunications Press. ISBN: 7-115-04229-2/TN .353.

Further, Japanese Patent No. JPH0847254 discloses a transistor starting circuit and a DC/DC converter to which the starting circuit is applied, and the implementing circuit is as shown in FIG.

In the above circuit, all the schemes use the same input and output conditions for comparison test, as follows: input voltage 12V, output voltage 5V, output current 200mA, that is, the output power is 1W.

Figure 1 circuit resistance R3 is 4.7kΩ, capacitance C5 is 0.047μF; the disadvantage is that the circuit is powered up, there is too much base current, resulting in deep saturation of the transistor, when the base current of the transistor disappears, it will appear due to the transistor In the presence of storage time, the transistor cannot be turned off instantaneously. At this time, the core of the transformer tends to be saturated (as shown in Fig. 14 at the maximum magnetic flux density ± Bm point), and the inductance of the primary winding is very small. Then, the transistors Q1 and Q2 are The instantaneous current of the collector is large. As shown in Figure 7, the oscilloscope channel 4 is the current waveform of the collector of the transistor. There is an impulse current of 3.72A at the turn-on instant (box in the figure), and the maximum collector transient current of the device is selected. For 2A, when power is applied multiple times or in a harsh working environment, the transistor is easily damaged by high current impact multiple times.

Figure 3 (Figure 3 is a simplified circuit diagram of Figure 2) circuit resistance R1 is 4.7kΩ, capacitor C2 is 0.047μF; at the instant of power-up, the problem of instantaneous high current of the transistor collector caused by Figure 1 can be well solved, as shown in Figure 8. As shown, when the circuit is powered up, the input voltage VIN passes through the resistor R1, and a current flows through the branch a1 to charge the capacitor C2, and the current flows to the input power supply terminal, as shown in the box data of FIG. The pole current is only 16mA, which is caused by the collector of the transistor charging the ground junction capacitor.

When working normally, the input voltage VIN passes through the resistor R1, and a current flows through the branch a1 to provide a starting base current for the transistors Q1 and Q2. In this case, in order to satisfy the start of the transistors Q1 and Q2, a large base current is necessary, and then By reducing the resistance R1 to obtain a large driving current, the low-temperature starting capability and the capacitive load capacity are improved. However, in the steady-state operating state, only a small transistor base current is required to meet the output power requirement, but after startup, it is smaller. The large current generated by the resistor R1 causes the transistor to be deeply saturated during normal operation, the storage time is increased, and the transistor turn-off time is prolonged, resulting in large power consumption of the transistor, low overall efficiency, and large heat generation, which is disadvantageous for high temperature environment work; Increasing the resistance R1, the current flowing through the a1 branch must be reduced, which can meet the efficiency and high temperature environment, but it will cause the circuit to start abnormally at low temperature, which will reduce the ability to start with capacitive load, or even meet the output power requirement.

FIG. 5 (FIG. 5 is a simplified circuit diagram of FIG. 4) is an embodiment of the prior patent. The resistor R1 is 100 Ω, the resistor R3 is 8.2 kΩ, the capacitor C5 is 0.047 μF, the resistor R4 is 10 kΩ, and the diode D3 is a Schottky diode. The solution solves the instantaneous inrush current caused by Figure 1, as shown in the box of Figure 9, the transient current is 1.44A; also solves the shortage of the transistor driving of Figure 2, but the short-circuit protection function can not be realized, and the scheme is introduced. A new problem: when the transistor is working normally, the voltage of the collector and the base has a large peak voltage. As shown in FIG. 10, at the moment when the transistor is switched on and off, due to the leakage inductance of the transformer and the storage time of the transistor, The collector spike current generated by the saturation of the transformer when the transistor is switched on and off causes a large peak voltage at the collector of the transistor, and is coupled to the base of the transistor by the transformer, which results in a large base of the transistor. Reverse spike voltage, the base of the general transistor has a maximum reverse withstand voltage of only 5V, so it is easy to damage the transistor under long-term impact, and a large collector tip Voltage transistor create loss increases, resulting in decreased overall efficiency of the converter, the device surface temperature is too high resulting in poor reliability of the circuit.

Summary of the invention

In order to solve the above technical problem, the present invention provides a power converter capable of accelerating a startup transistor, improving a capacitive load starting capability, improving a low temperature starting capability, and reducing a transistor storage time under normal working conditions, thereby Improve conversion efficiency and achieve short-circuit protection, which can work normally at different ambient temperatures.

The specific scheme of the present invention to achieve the above object is as follows:

The embodiment of the present invention provides a power converter, including a branch a, a branch b, a second transformer T1B, a first transistor Q1, a second transistor Q2, and a first transformer T1A;

One end of the branch a is electrically connected to the voltage input end, the other end is connected in series with the second capacitor C2 of the branch b, and the other end of the second capacitor C2 is grounded; the branch a includes a parallel connection a third resistor R3 and a fifth capacitor C5; the other end of the branch a is also electrically connected to a center tap of the second transformer T1B, and the center tap of the second transformer T1B is composed of a first coil Nb1 and a second coil Nb2 The other ends of the first coil Nb1 and the second coil Nb2 are electrically connected to the bases of the first transistor Q1 and the second transistor Q2, respectively, the first transistor Q1 and the second transistor Q2. The emitter center of the first transformer T1A is electrically connected to the voltage input terminal, and the two ends are electrically connected to the collectors of the first transistor Q1 and the second transistor Q2, respectively, to pass through the branch a and the branch b provides a large current to the base of the first transistor Q1 and the base of the second transistor Q2 when the circuit is started, and provides the base of the first transistor Q1 and the base of the second transistor Q2 when the circuit is in steady state operation. Small current.

Preferably, a fourth capacitor C4 is electrically connected between the collectors of the first transistor Q1 and the second transistor Q2.

Preferably, it further comprises a branch a1 connected between the power input terminal and the branch a, the branch a1 comprising a first resistor R1.

Compared with the prior art, the power converter provided by the invention has the characteristics of high efficiency, low no-load power consumption, strong ability to start with a capacitive load, strong low-temperature starting capability and long-term short-circuit protection.

DRAWINGS

The drawings described herein are provided to provide a further understanding of the invention, and are not a limitation of the invention.

Figure 1 is a schematic diagram of a basic circuit structure of a self-excited push-pull;

2 is an actual circuit diagram of a conventional self-excited push-pull converter;

Figure 3 is an equivalent circuit diagram of Figure 2;

Figure 4 is a patented implementation circuit;

Figure 5 is a simplified circuit diagram of Figure 4;

6 is a schematic circuit diagram of a circuit according to an embodiment of the present invention;

7 is an instantaneous power-on startup waveform of the circuit shown in FIG. 1;

Figure 8 is an instantaneous power-on startup waveform of the circuit shown in Figure 2;

Figure 9 is an instantaneous power-on startup waveform of the circuit shown in Figure 5;

10 is a waveform diagram of a base voltage and a collector voltage of a transistor in the normal operation of the circuit shown in FIG. 5;

11 is an instantaneous power-on startup waveform of a circuit according to an embodiment of the present invention;

12 is a waveform diagram of a base voltage and a collector voltage of a transistor in a normal operation of the circuit of the embodiment of the present invention;

Figure 13 is an overview of the working principle of the present invention;

Figure 14 is a rectangular hysteresis loop of the magnetic core of the present invention;

Figure 15 is a diagram showing the equivalent structure of the primary side of the power-on instant of the present invention;

Figure 16 is a diagram showing the equivalent structure of the normal working primary side of the present invention;

Figure 17 is a full wave rectification circuit;

18 is a comparison diagram of circuit efficiency between the circuit of the present invention and the prior art solution;

Figure 19 is a circuit startup waveform of the present invention;

Figure 20 is a conventional circuit startup waveform;

21 is a schematic circuit diagram of a second embodiment of the present invention;

Figure 22 is a diagram showing the equivalent structure of the primary side of the circuit at the instant of powering in the second embodiment of the present invention;

Figure 23 is a diagram showing the equivalent structure of the normal working side of the circuit of the second embodiment of the present invention.

detailed description

The invention is described in detail below with reference to the accompanying drawings and the accompanying drawings.

Embodiment 1

As shown in FIG. 6, a power converter includes a branch a, a branch b, a second transformer T1B, a first transistor Q1, a second transistor Q2, and a first transformer T1A; one end of the branch a and a voltage The input terminal VIN is electrically connected, the other end is connected in series with the second capacitor C2 of the branch b, and the other end of the second capacitor C2 is grounded; the branch a includes a third resistor R3 and a fifth capacitor C5 connected in parallel; The other end of the branch circuit a is also electrically connected to the center tap of the second transformer T1B, and the center tap of the second transformer T1B is composed of the connection ends of the first coil Nb1 and the second coil Nb2, the first The other ends of the coil Nb1 and the second coil Nb2 are electrically connected to the bases of the first transistor Q1 and the second transistor Q2, respectively, and the emitters of the first transistor Q1 and the second transistor Q2 are grounded to GND; The primary side center tap of the first transformer T1A is electrically connected to the voltage input terminal, and the two ends of the first transformer T1A are electrically connected to the collectors of the first transistor Q1 and the second transistor Q2, respectively, and the first transistor Q1 and the second transistor A fourth capacitor C4 is also electrically connected between the collectors of the transistors Q2.

When the circuit is electrically conductive and steady-state, due to the leakage inductance of the transformer, the first transistor Q1 and the second transistor Q2 generate a high-frequency spike voltage when turned on or off, and the fourth capacitor C4 functions to effectively suppress the High frequency spike voltage.

The power converter further includes a branch a1 connected between the voltage input terminal VIN and the branch a, the branch a1 including a first resistor R1. The combination of the first resistor R1, the third resistor R3, the fifth capacitor C5 and the second capacitor C2 of the branch b enables acceleration of the startup transistor, lifting of the capacitive load starting capability and low temperature starting capability.

A filter capacitor C1 is further electrically connected between the voltage input terminal VIN and the ground GND. C1 is used to filter the input voltage to reduce the effect of input voltage fluctuations on the circuit.

When the power is turned on, the first transistor Q1 and the second transistor Q2 pass through the first resistor R1, the third resistor R3, the fifth capacitor C5, the second capacitor C2, the first coil Nb1, and the first of the branches a1, a, and b. The two coils Nb2 are both forward biased and tend to conduct current, but due to the structure of the circuit and the unbalanced characteristics of the symmetrical devices, one of the transistors must be turned on preferentially and the other transistor turned off. Assuming that the first transistor Q1 is turned on first, the induced voltage connected to the primary winding Np1 of the first transistor Q1 is positive and negative, and the induced voltage of the first winding Nb1 is positive and negative, as shown in FIG. The base of one transistor Q1 obtains positive feedback energy, the first transistor Q1 quickly enters saturation conduction; and the second transistor Q2 is connected to the base second coil Nb2, the induced voltage is positive and negative, and the base current of the second transistor Q2 The voltage is rapidly reduced so that the second transistor Q2 is turned off. At this time, the transformer secondary winding Ns2 is rectified by the diode D2 and outputs a current to the load R2.

The series branches a1, a and b can solve the deficiencies caused by the circuits of Figs. 1, 2 and 4. The resistance of the first resistor R1 is 100Ω, the resistance of the third resistor R3 is 8.2kΩ, the capacitance of the fifth capacitor C5 is 0.047μF, and the capacitance of the second capacitor C2 is 0.1μF.

11 is an instantaneous power-on startup waveform of the implementation circuit of the present invention. It can be seen from the figure that the collector transient current of the transistor at startup is 1.76A, which is smaller than the transistor collector transient current of the circuit diagram of FIG. 1.96A, which is similar to the startup current of the circuit of FIG. 5; FIG. 12 is a waveform diagram of the base voltage and the collector voltage of the transistor in the normal operation of the implementation circuit of the present invention, which can be seen from the figure in the normal operation, compared with the circuit of FIG. The transistor base voltage waveform is 7.06V, which is 49.6V smaller than the collector voltage waveform of the circuit of Figure 4.

When the first transistor Q1 is continuously turned on, the primary winding Np1 generates an exciting current, and the magnetic induction intensity in the magnetic core linearly increases with time under the action of the current. When the magnetic core tends to be saturated, the inductance of the primary winding Np1 rapidly decreases, the collector current of the first transistor Q1 rises rapidly, and the rate of change of the magnetic flux of the first coil Nb1 decreases, that is, dφ/dt decreases, resulting in the first The voltage of the coil Nb1 drops. However, due to the storage time of the transistor, when the base current of the first transistor Q1 drops to zero or even reverse current occurs, the first transistor Q1 does not immediately turn off, but remains in an on state. At this time, the collector current of the first transistor Q1 rises rapidly to form a peak current. After a certain storage time, the first transistor Q1 is out of saturation, the collector current begins to decrease, and the instantaneous core flux does not increase any more (as shown in FIG. 14 at the maximum magnetic flux density ± Bm point), that is, dφ/dt=0, then The collector current of one transistor Q1 begins to drop, and each coil will generate an induced voltage in the opposite direction. The induced voltage of the first coil Nb1 becomes upper and lower positive, the induced voltage of the second coil Nb2 becomes upper and lower positive, the induced voltage on Np2 is positive and negative, the second transistor Q2 is turned on, the first transistor Q1 is turned off, and the circuit is realized. Self-oscillation.

The operation characteristics of the third resistor R3 and the fifth capacitor C5 at the time of circuit startup will be described below.

As shown in FIG. 6, the first resistor Q1 and the second transistor Q2 have a third resistor R3 and a fifth capacitor C5 connected in parallel between the first resistor R1 and the second capacitor C2. The fifth capacitor C5 is charged at the time of power-on, which is equivalent to the short-circuit state of the third resistor R3 and the fifth capacitor C5 of the branch a. As shown in FIG. 15, the first resistor R1 is connected between the branch a1 and the branch a. , causing the branches a1, a to have a sufficiently large current Ia1 flowing in a short time after power-on, providing a base current to the first transistor Q1 and the second transistor Q2, accelerating the activation of the first transistor Q1 and the second transistor Q2. Especially at low temperatures, it also has good starting ability.

The characteristics of the third resistor R3 and the fifth capacitor C5 in the normal operation of the circuit will be described below.

When the circuit of FIG. 6 works normally, the fifth capacitor C5 is no longer charged, which is equivalent to an open circuit. As shown in FIG. 16, the first resistor R1 and the third resistor R3 are connected in series between the branch a1 and the branch a, and flow to the first. The bias current Ia2 of the transistor Q1 and the second transistor Q2 is much smaller than the current Ia1 of the branches a1 and a of FIG. 15, and the driving current supplied to the bases of the first transistor Q1 and the second transistor Q2 is small, which reduces the number of The saturation depth and driving power consumption of a transistor Q1 and a second transistor Q2 are reduced when the circuit is flipped The storage time when the transistor is desaturated is reduced, thereby improving the conversion efficiency of the converter and adapting to the working conditions of the high temperature environment.

When the circuit output terminal DC out-1 is short-circuited, the circuit of FIG. 6 enters a high-frequency self-oscillation state, and the first resistor R1 and the third resistor R3 are connected in series to the branches a1 and a, and are supplied to the first transistor Q1. The bias current of the second transistor Q2 is small, and the short-circuit protection function is realized, and the primary side of the short-circuit operation is equivalent as shown in FIG. 16.

The circuit shown in the embodiment of the present invention is the most similar to the circuit shown in FIG. 5. The difference is that the circuit of FIG. 6 replaces the diode D3 and the resistor R4 of FIG. 5 with the second capacitor C2, and the second capacitor C2 of the circuit of FIG. 6 is connected to one end. The ground of the input end, the other end is connected to the tap of the coil T1B, the function is to absorb the peak voltage caused by the leakage inductance of the transformer and the saturation current of the collector (the peak voltage is coupled to the base of the transistor through the transformer, and the tap of the base of the transistor is grounded to the ground. Capacitor C2 absorption), improve circuit conversion efficiency and improve circuit reliability.

2 is a circuit diagram of a conventional self-excited push-pull converter, and FIG. 6 is a circuit diagram provided by an embodiment of the present invention; both FIG. 2 and FIG. 6 are DC-DC with a DC input of 12V, a DC output of 5V, and an output current of 200 mA. The converter, that is, the output power is 1W; the transformer adopts the same material, the same type of magnetic core, and the input and output coils have the same number of turns, and the same process is used to make the transformer. The transformer is coupled to the output terminal, and the full-wave rectification circuit known in FIG. 17 is used, which is composed of diodes D1 and D2, a dummy load resistor R2 and an output filter capacitor C3.

The design requirements of the circuit parameters must meet the following requirements: 1. The circuit can be hot-swappable under the same low temperature conditions; 2. It can meet the same capacitive load hot-swap startup.

2, FIG. 6 input filter capacitor C1, first transistor Q1, second transistor Q2, diode D1, D2, capacitor C3, fourth capacitor C4, resistor R2, first transformer T1A, T1B adopt the same parameters, in the comparative example The first resistor R1 and the second capacitor C2 of FIG. 2 and FIG. 6 need to be adjusted to meet the parameter design conditions; the third resistor R3 and the fifth capacitor C5 of the circuit device of the present invention need to meet the design requirements.

The data in Table 1 is obtained by the circuit test of Figure 6. The first resistor R1 is 10Ω, the second capacitor C2 is 680pF, the fourth capacitor C4 is 120pF, the third resistor R3 is 8.9KΩ, and the fifth capacitor C5 is 1000pF. The first transistor Q1, the second transistor Q2 has a magnification of about 200, the collector maximum operating current is 1A, and the maximum Vce voltage is 60V; the diodes D1 and D2 are Schottky rectifier tubes, wherein the transformer T1 The turns ratio of the primary side Np1, Np2 and the secondary side Ns1, Ns2 are: 35:16, the number of turns of the feedback Nb1, Nb2 is 2, and the transformer core uses a high permeability ferrite toroidal core.

Table 1 Test record of the technical solution of the present invention

Input voltage (V)	Input current (mA)	Output voltage (V)	Output current (mA)	Working frequency (kHz)	effectiveness(%)
12	8.1	5.31	No load	78.4	no
12	5.20	5.2	20	77.5	50.68
12	26.20	5.15	40	77.4	65.52
12	35.20	5.11	60	77.1	72.59
12	44.50	5.08	80	77.0	76.10
12	53.60	5.05	100	77.2	78.51
12	62.60	5.01	120	77.1	80.03
12	71.80	4.98	140	77.3	80.92
12	80.70	4.95	160	77.2	81.78
12	89.90	4.92	180	77.4	82.09
12	99.10	4.88	200	77.5	82.07

In order to illustrate the beneficial effects of the present invention, comparing the prior art self-excited push-pull converter, the circuit schematic of FIG. 2 is adopted under the condition that the circuit design parameters are satisfied, the first resistor R1 is 3.9KΩ, and the second capacitor C2 is 0.1μF. The fourth capacitor C4 is 120pF. The transformer design is consistent with the manufacturing process. The actual performance parameters of Table 2 are obtained under normal temperature test.

Table 2 test record of prior art scheme

Input voltage (V)	Input current (mA)	Output voltage (V)	Output current (mA)	Working frequency (kHz)	effectiveness(%)
12	11.2	5.31	No load	74.9	no
12	5.20	5.2	20	74.7	43.33
12	29.10	5.15	40	74.7	58.99
12	38.30	5.11	60	74.6	66.71
12	47.60	5.07	80	74.9	71.01
12	56.80	5.04	100	74.5	73.94
12	65.80	5.00	120	74.8	75.99
12	74.90	4.97	140	74.6	77.41
12	83.90	4.94	160	74.6	78.51
12	93.10	4.9	180	74.5	78.95
12	102.30	4.87	200	74.6	79.34

It can be seen that, at full load output efficiency, the circuit provided by the present invention has an efficiency improvement of 2.63% over the prior art. In the full load range, the circuit provided by the present invention is more efficient than the prior art circuit, as shown in FIG.

At no-load output, the no-load input current of the circuit provided by the present invention is lower than that of the existing scheme. The current is 3.1 mA, which means that the no-load power consumption of the present invention is low.

Table 3 shows the short-circuit protection function in order to embody the solution of the present invention. The following conditions were tested: high temperature +105 ° C, output short circuit, duration 1 hour, and input voltage were 12V. The circuit of the invention can well realize the output short circuit protection function.

Table 3 short circuit protection test performance record

Table 4 is to demonstrate the advantages of the first transistor Q1 and the second transistor Q2 in order to embody the present invention. The following conditions are tested: normal temperature +25 ° C, full power 1 W output, input voltage is 12 V, and the output is detected by an oscilloscope. . The circuit provided by the invention has a strong driving capability and can quickly activate the first transistor Q1 and the second transistor Q2. Figure 19 is a circuit startup waveform of the present invention, and Figure 20 is a conventional circuit startup waveform.

Table 4 starts test performance record

Embodiment 2

21, different from the circuit of FIG. 6 of the first embodiment, the circuit of the second embodiment is connected to the branch a1 between the power input terminal and the branch a, and the branch a1 includes The first resistor R1; the principle of self-oscillation and the principle of circuit short-circuit protection of the circuit are basically the same as those of the first embodiment.

The second capacitor C2 is connected in series to the other end of the third resistor R3 and the fifth capacitor C5, so that the problem caused by the circuits of FIG. 1, FIG. 2, and FIG. 4 can be solved. When the circuit is started, a large current is supplied to the bases of the first transistor Q1 and the second transistor Q2; when the circuit is in steady state operation, a small current is supplied to the bases of the first transistor Q1 and the second transistor Q2;

The operating characteristics of the third resistor R3 and the fifth capacitor C5 at the start of the circuit: a third resistor R3 connected in parallel between the first transistor Q1 and the second capacitor C2 of the second transistor Q2 as shown in FIG. The fifth capacitor C5. The fifth capacitor C5 is charged at the time of power-on, which is equivalent to the short-circuit state of the third resistor R3 and the fifth capacitor C5 of the branch a, as shown in FIG. 22; the input terminal voltage is directly applied to the second capacitor C2. Charging, usually the second capacitor C2 takes a value between 0.03uF and 1uF. It can be seen that there is a large enough current Ia3 flowing in the short time of power-on, providing the base of the first transistor Q1 and the second transistor Q2. The current accelerates the activation of the first transistor Q1 and the second transistor Q2, and particularly has a good starting capability at a low temperature;

The characteristics of the third resistor R3 and the fifth capacitor C5 during normal operation of the circuit: when the circuit of Fig. 21 works normally, the fifth capacitor C5 is no longer charged, which is equivalent to an open circuit, as shown in Fig. 23, the third resistor R3 is connected in series with the voltage. Between the positive terminal and the branch b, the bias current Ia4 flowing to the first transistor Q1 and the second transistor Q2 is much smaller than the current Ia3 of the branch a of FIG. 22, and is given to the first transistor Q1 and the second transistor Q2. The driving current provided by the pole is small, which reduces the saturation depth and driving power consumption of the first transistor Q1 and the second transistor Q2, and reduces the storage time when the transistor is desaturated when the circuit is turned over, thereby improving the conversion efficiency of the converter. , to adapt to the working conditions of high temperature environment.

Claims (7)

1. A power converter, comprising: a branch a, a branch b, a first transistor (Q1), a second transistor (Q2), a first transformer (T1A), and a second transformer (T1B);

   One end of the branch a is electrically connected to the voltage input end, the other end is connected in series with the second capacitor (C2) of the branch b, and the other end of the second capacitor (C2) is grounded;

   The branch a includes a third resistor (R3) and a fifth capacitor (C5) connected in parallel;

   The other end of the branch a is also electrically connected to a center tap of the second transformer (T1B), and the center tap of the second transformer (T1B) is composed of a first coil (Nb1) and a second coil (Nb2) a connecting end; the other ends of the first coil (Nb1) and the second coil (Nb2) are electrically connected to the bases of the first transistor (Q1) and the second transistor (Q2), respectively; The emitters of the transistor (Q1) and the second transistor (Q2) are both grounded; the primary center tap of the first transformer (T1A) is electrically connected to the voltage input terminal, and the primary side of the first transformer (T1A) Both ends are electrically connected to the collectors of the first transistor (Q1) and the second transistor (Q2), respectively.
2. The power converter of claim 1 further comprising a fourth capacitor (C4);

   Both ends of the fourth capacitor (C4) are respectively connected to the collectors of the first transistor (Q1) and the second transistor (Q2).
3. The power converter of claim 1 further comprising a branch a1;

   The branch a1 is connected between the voltage input terminal and the branch a, and the branch a1 includes a first resistor (R1).
4. The power converter of claim 1 further comprising: a filter capacitor;

   Both ends of the filter capacitor are respectively connected to the voltage input terminal and the ground.
5. The power converter of claim 1 wherein an input voltage charges said fifth capacitor when said power converter is activated;

   The input voltage stops charging the fifth capacitor when the power converter is operating normally.
6. A power converter according to any one of claims 1 to 5, wherein the power converter is a self-excited push-pull oscillation converter.
7. A power converter according to any one of claims 1 to 5, wherein said second Capacitance values range from 0.03uF to 1uF.

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