CN103780065A - Soft turn-off power supply converter - Google Patents

Abstract

The invention provides a soft-off power converter, which includes a transformer connected between the input power supply and the output power supply. The primary winding of the transformer is connected in series with the negative terminal of the input power supply and a circuit control switch is controlled by the output signal of the PWM control circuit. To control on-off, a branch circuit in which the second capacitor, the rectifier diode and the first capacitor are connected in series is connected between the primary winding of the transformer and the negative terminal of the input power supply, and the voltage control switch is controlled by a soft-off control circuit. The invention solves the problem of It solves the problem of large loss caused by hard turn-off of the switch, realizes soft turn-off, reduces switching loss, improves efficiency, and also solves the problem of power supply when the control circuit is working and the problem of absorbing the turn-off peak voltage of the switch. The power converter does not need to be provided with a power supply circuit and a absorption circuit, and the circuit structure is simplified.

Description

A soft turn-off power converter

technical field

The present invention relates to the technical field of control of electronic circuits, in particular to a power converter that controls a power switch to realize soft shutdown.

Background technique

At present, in the single-ended power converter, due to the leakage inductance of the transformer, a high reverse voltage peak will be generated at both ends of the switch tube when the switch tube in the power converter is turned off, which may exceed the withstand voltage of the switch tube and cause The switch tube is damaged, and in order to improve the conversion efficiency of the single-ended power converter, the switch tube must be soft-switched to reduce the switching loss.

The known quasi-resonant QR mode single-ended power converter can only achieve zero-voltage turn-on, the switch tube is still hard off, the turn-off loss is relatively large, the conversion efficiency of the power converter is low, and the leakage inductance of the transformer still needs to be used for energy storage Commonly used, as shown in Figure 4 of the attached drawing, is an RCD absorption circuit structure diagram with absorption function to absorb, the leakage inductance energy is dumped into the capacitor C and partly consumed by the resistor R, and the electric energy is wasted without benefit .

The existing circuits for reducing the turn-off loss of the switching tube mainly include an active clamping circuit and an RCD snubbing circuit with absorption and soft turn-off functions as shown in Figure 3. The active clamping technology can greatly reduce the switching tube’s loss. The turn-off voltage peak reduces the product of voltage and current when the switch is turned off, thereby reducing the turn-off loss, but the soft turn-off effect of the switch is not obvious, and the turn-off loss of the switch cannot be further reduced; In the RCD snubber circuit shown in Figure 3, during the switch off period, the power supply voltage and leakage inductance peak voltage are superimposed together to charge the capacitor C through the diode D and the primary winding of the transformer, and the voltage across the capacitor C rises slowly. At this time, When the switch tube is turned off, the current drops sharply, so that the overlapping area of voltage and current is very small, that is, the power loss is small, and the switch tube is softly turned off. During the conduction period of the switch tube, the energy storage of capacitor C passes The resistor R and the switch tube are discharged, and the electric energy is consumed in the resistor R, so that the terminal voltage of the capacitor C drops, preparing for the capacitor C to absorb the leakage inductance energy storage in the next cycle. In this mode, the electric energy is still useless. Waste, even the electric energy consumed by the resistor is much more than the electric energy saved by the switch tube due to soft turn-off, which makes this circuit lose its use value in today's advocacy of energy saving.

Moreover, the control circuit in the current power converter needs an external power supply to work. Generally, another independent small power supply or standby power supply is used for power supply, or a power supply winding is set in the transformer to provide auxiliary power supply, which makes the power supply more complicated and wastes electronic materials. high cost.

Contents of the invention

In view of this, the technical problem to be solved by the present invention is to provide a soft turn-off power converter with low switching loss, high efficiency and simple circuit.

In order to solve the above technical problems, the technical solution provided by the present invention is: a soft turn-off power converter, including a transformer connected between the input power supply and the output power supply, the primary winding of the transformer is connected in series with the negative terminal of the input power supply, and a circuit control switch , the circuit control switch is controlled on and off by the output signal of a PWM control circuit, and also includes a soft-off control circuit and a voltage control switch controlled by it, one end of the voltage control switch is connected to the anode of the rectifier diode, and the other end is connected to The negative pole of the input power supply; a branch circuit in which the second capacitor, the rectifier diode and the first capacitor are sequentially connected in series between the primary winding of the transformer and the negative terminal of the input power supply, the first capacitor and the second capacitor are controlled in the circuit Charging during the switch off period provides working voltage for the PWM control circuit and the soft-off control circuit, and at the same time makes the circuit control switch soft-off and suppresses the reverse voltage spike at both ends of the circuit control switch;

The soft-off control circuit includes a first comparator sequentially connected to compare the voltage value at both ends of the first capacitor after being divided by the third resistor and the fourth resistor with the reference voltage and output an amplified error voltage value; The second comparator that compares the slope voltage generated by a slope generating circuit with the error voltage value and outputs a narrow pulse, the input signal of the slope generating circuit is the output signal of the PWM control circuit, and the narrow pulse passes through a first An inverter and a second inverter are output to the control terminal of the voltage control switch, and quickly control the voltage control switch to be turned on and off; the soft-off control circuit is based on the first detected by the third resistor and the fourth resistor. The voltage of a capacitor is used to control the conduction time of the voltage control switch during the conduction period of the circuit control switch, and the second capacitor connected in series with the voltage control switch is partially discharged during the off period of the circuit control switch to restore the circuit control The soft turn-off function of the switch in the next switching cycle. .

The positive terminal of the input power supply is connected to the connection point of the first capacitor and the rectifier diode through the first resistor, so as to provide the initial start-up working current for the PWM control circuit and the soft-off control circuit.

The voltage control switch is composed of a first field effect transistor, a second field effect transistor and a fifth resistor, and the gate of the first field effect transistor, the gate of the second field effect transistor and one end of the fifth resistor are connected to The output terminal of the second inverter, the source electrode of the first field effect transistor and the source electrode of the second field effect transistor (34) and the other end of the fifth resistor are connected to the power ground terminal of the second inverter, and the The drain of the first field effect transistor is connected to the junction of the second capacitor and the rectifier diode, and the drain of the second field effect transistor is connected to the power supply ground terminal of the soft-off control circuit.

The other end of the circuit control switch is grounded through the second resistor. The PWM control circuit is electrically connected to the circuit control switch through the current detection input terminal and the drive output terminal, and at the same time inputs and outputs the voltage error feedback signal through the FB input terminal.

The pulse signal input to the input terminal of the slope generating circuit is a pulse sequence synchronous with the driving waveform of the circuit control switch.

The circuit control switch is composed of any one of transistors, field effect transistors and insulated gate bipolar transistors.

Compared with prior art, the present invention has following advantage:

The present invention provides a soft-off power converter, which uses a PWM control circuit to control the turn-off of the switch and controls the voltage control switch through the soft-off control circuit, and a series branch pair circuit of the first capacitor, the rectifier diode, and the second capacitor The voltage regulation function solves the problem of large loss caused by the hard turn-off of the switch, realizes soft turn-off, reduces the switching loss, improves the efficiency, and also solves the problem of power supply when the control circuit is working and the turn-off of the switch The peak voltage absorption problem makes it unnecessary for the power converter to set up a power supply circuit and an absorption circuit, which simplifies the circuit structure.

the

Description of drawings

Fig. 1 is a circuit structure block diagram of an embodiment of the present invention;

Fig. 2 is the specific implementation circuit structure block diagram of soft shut-off control circuit among the present invention;

Fig. 3 is a structure diagram of a known RCD snubber circuit with snubber and soft turn-off functions;

Fig. 4 is a structure diagram of a known RCD absorbing circuit with absorbing function.

Detailed ways

In order to facilitate the understanding of those skilled in the art, the present invention will be further described in detail below with reference to the drawings and embodiments.

Example 1

As shown in Figures 1 and 2, a soft-off power converter includes a first capacitor 7, a second capacitor 11, a rectifier diode 10, a circuit control switch 3, a voltage control switch 9, a soft-off control circuit 8, a second A resistor 1, a second resistor 4, a third resistor 5, a fourth resistor 6, a PWM control circuit 2, a transformer 12, a positive terminal and a negative terminal of an input power supply. The positive end of the input power supply is electrically connected to one end of the first resistor 1 and one end of the primary winding 13 of the transformer 12; one end of the second capacitor 11 is electrically connected to the other end of the primary winding 13 of the transformer 12 and one end 21 of the circuit control switch 3 The other end of the second capacitor 11 is electrically connected to the anode of the rectifier diode 10 and the other end 31 of the voltage control switch 9; the positive end of the first capacitor 7 is connected to the other end of the first resistor 1 and the power supply of the PWM control circuit terminal 15, the positive power supply terminal 23 of the soft-off control circuit 8, the cathode of the rectifier diode 10, and one end of the third resistor 5 are electrically connected, and the negative terminal of the first capacitor 7 is respectively connected with the negative terminal of the input power supply and the PWM control circuit 2. The power supply ground terminal 18, the power supply ground terminal 26 of the soft-off control circuit 8, one terminal 32 of the voltage control switch 9, one terminal of the second resistor 4 and one terminal of the fourth resistor 6 are electrically connected, and the other terminal of the third resistor 5 is connected to the first terminal of the fourth resistor 6. The other end of the four resistors 6 is electrically connected to the input end 25 of the soft-off control circuit 8; the control signal output end 27 of the soft-off control circuit 8 is electrically connected to the control end 29 of the voltage control switch 9, and the soft-off control circuit 8 The control signal output ground end 28 of the control signal is electrically connected with the midpoint 30 of the voltage control switch 9; the other end 22 of the circuit control switch 3 is electrically connected with the other end of the second resistor 4 and the current detection input end 19 of the PWM control circuit 2, and the circuit The control terminal 20 of the control switch 3 is electrically connected to the drive output terminal 17 of the PWM control circuit 2; the signal output terminal 16 of the PWM control circuit 2 is electrically connected to the input terminal 24 of the soft-off control circuit 8; the terminal 14 of the PWM control circuit 2 Connecting the FB end is the input end of the output voltage error feedback signal.

The soft-off control circuit 8 includes at least a second comparator 38, a first comparator 39, a second inverter 36, a first inverter 37, and a ramp generating circuit 40; the voltage control switch 9 is composed of Field effect transistor 33, field effect transistor 34 and resistor 35 are composed. The positive power terminal 23 of the soft-off control circuit 8 is respectively connected to the positive power terminal 50 of the second comparator 38, the positive power terminal 44 of the first comparator 39, the positive power terminal 58 of the second inverter 36, the first inverter The positive power terminal 55 of the phase device 37 is electrically connected to the positive power terminal 42 of the slope generating circuit 40, and the power ground terminal 26 of the soft-off control circuit 8 is respectively connected to the power ground terminal 52 of the second comparator 38 and the power ground terminal 52 of the first comparator 39. The power ground terminal 45, the power ground terminal 54 of the first inverter 37, the power ground terminal 43 of the slope generating circuit 40, and the drain terminal 32 of the field effect transistor 34 are electrically connected; one input terminal of the first comparator 39 is soft-off The input terminal 25 of the off control circuit 8, the other input terminal of the first comparator 39 is electrically connected to the reference voltage Vref; the input terminal of the slope generating circuit 40 is the input terminal 24 of the soft off control circuit 8, and the slope generating circuit 40 The output terminal 41 of the second comparator 38 is electrically connected to an input terminal 49 of the second comparator 38, and the other input terminal 48 of the second comparator 38 is electrically connected to the output terminal 47 of the first comparator 39, and the output terminal of the second comparator 38 51 is electrically connected to the input terminal 53 of the first inverter 37; the output terminal 56 of the first inverter 37 is electrically connected to the input terminal 57 of the second inverter 36, and the output terminal of the second inverter 36 is The control signal output terminal 27 of the soft-off control circuit 8, the output ground terminal of the second inverter 36 is the output ground terminal 28 of the soft-off control circuit 8; The connection point between the grid and one end of the resistor 35 is the control terminal 29 of the voltage control switch 9, and the connection point between the source of the field effect transistor 33 and the source of the field effect transistor 34 and the other end of the resistor 35 is the voltage control switch 9 The midpoint of 30.

Wherein the switch 3 is composed of any one of transistors, field effect transistors and insulated gate bipolar transistors.

During circuit work, in the circuit structure block diagram of the power converter of the soft shut-off of the present invention shown in Fig. 1, the first resistor 1 provides the initial start-up operating current of PWM control circuit 2 and soft shut-off control circuit 8; During the off period of the switch 3, the input power voltage plus the reverse voltage generated by the leakage inductance energy storage of the transformer charges the first capacitor 7 through the second capacitor 11, the primary winding of the transformer 12 and the rectifier diode 10, and the voltage of the first capacitor 7 is used as The operating voltage of the PWM control circuit 2 and the soft-off control circuit 8, a part of the leakage inductance energy storage is converted into the working electric energy of the PWM control circuit 2 and the soft-off control circuit 8, and at the same time, the circuit control switch 3 is generated due to the leakage inductance energy storage The reverse peak voltage will also be absorbed by the first capacitor 7 and the second capacitor 11, and the reverse voltage peak at both ends of the circuit control switch 3 is suppressed; during the conduction period of the circuit control switch 3, the voltage control switch 9 is turned on for a short period time, the conduction time will be determined according to the voltage of the first capacitor 7 detected by the soft-off control circuit 8 through the third resistor 5 and the fourth resistor 6, so that the charge stored in the second capacitor 11 is controlled by the circuit switch 3 and the voltage The control switch 9 discharges a part, and the voltage across the second capacitor 11 will drop. When the circuit control switch 3 is turned off again, the voltage across the series branch of the second capacitor 11, the rectifier diode 10, and the first capacitor 7 cannot change abruptly. , the voltage at both ends of the second capacitor 11 can only rise slowly, causing the voltage at both ends of the circuit control switch 3 to rise slowly, so as to realize the purpose of soft-off of the switch. The conduction time of the voltage control switch 9 is determined by the voltage of the first capacitor 7, therefore, the energy consumed by the discharge circuit of the circuit control switch 3, the voltage control switch 9 and the second capacitor 11 is the same as that provided by the first capacitor 7. The operating power of the PWM control circuit 2 and the soft-off control circuit 8 are related, and the first capacitor 7 consumes less power, so the voltage across the first capacitor 7 will rise slightly, and after being processed by the soft-off control circuit 8, the The conduction time of the voltage control switch 9 is reduced, and the energy consumed by the discharge circuit of the circuit control switch 3, the voltage control switch 9 and the second capacitor 11 will also be reduced. In the prior art, the power consumed by the control circuit of the general power converter At the level of tens of milliwatts, therefore, the energy consumed by the discharge circuit of the circuit control switch 3, the voltage control switch 9 and the second capacitor 11 is also maintained at the level of tens of milliwatts, realizing low-loss leakage inductance energy storage and absorption Function.

In the circuit structure block diagram of the soft-off power converter of the present invention shown in Fig. 1, a more specific circuit structure block diagram of the soft-off control circuit 8 and the voltage control switch 9 is shown in Fig. 2, the soft-off The control circuit 8 at least includes a second comparator 38, a first comparator 39, a second inverter 36, a first inverter 37, and a slope generating circuit 40; the voltage control switch 9 is composed of a field effect transistor 33 and a field The effect tube 34 and the resistor 35 are composed. Wherein, what the input terminal 25 of the first comparator 39 inputs is the voltage value after the voltage at both ends of the first capacitor 7 shown in FIG. The reference voltage Vref of an input terminal 46 is compared, and the output terminal 47 of the first comparator 39 outputs the amplified error voltage value and is input to the input terminal 48 of the second comparator 38; It is a pulse sequence output by the output end 16 of the PWM control circuit 2 and the drive waveform synchronous with the drive circuit control switch 3. After being processed by the slope generating circuit 40, the output end 41 generates a slow leading edge and a steep rear edge and is consistent with the drive of the circuit control switch 3. The slope voltage of the same frequency of the pulse, the pulse width of the slope voltage is also the same as the drive pulse of the circuit control switch 3, and this slope voltage is input to the error voltage of the input terminal 49 of the second comparator 38 and the input terminal 48 of the second comparator 38 Value comparison, the output terminal 51 of the second comparator 38 will output a narrow pulse, the pulse width is related to the voltage across the first capacitor 7, when the voltage across the first capacitor 7 is caused by the PWM control circuit 2 and the soft-off control circuit 8 When the operating current is large and drops, the output terminal 47 of the first comparator 39 outputs an amplified error voltage value, and the pulse at the output terminal of the second comparator 38 becomes wider. When the voltage across the first capacitor 7 changes due to the load When it rises lightly, the amplified error voltage value output by the output terminal 47 of the first comparator 39 decreases, and the output pulse of the output terminal 51 of the second comparator 38 becomes narrower. The output terminal 51 output pulse of the second comparator 38 is output to the input terminal 53 of the first inverter 37, the output terminal 56 output pulse of the first inverter 37 is output to the input terminal 57 of the second inverter 36, the second inverter 36 The output terminal 27 of the two inverters 36 outputs pulses to the control terminal 29 of the voltage control switch 9, and the control voltage control switch 9 is turned on for a short period of time and then turned off. The second inverter 36 also has a level shift function except that it has an inverting driving function. The diode will be turned on, and the forward drive voltage will be obtained between the two ends of the resistor 35 and the gate source of the field effect transistor 33 and the field effect transistor 34, and the power supply ground of the second inverter 36 is directly connected to the voltage control switch 9 inside. The connection midpoint of the field effect transistor 33 and the field effect transistor 34, the power ground terminal of the second inverter 36 is raised by the forward conduction voltage of a diode compared with the power ground of the soft-off control circuit 8, and the ground level is shifted so that the second inverter 36 can quickly control the voltage control switch 9 to turn on and off.

The above is one of the specific implementations of the present invention, and the description thereof is relatively specific and detailed, but it should not be construed as limiting the patent scope of the present invention. It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these obvious replacement forms all belong to the protection scope of the present invention.

Claims (6)

1. a soft power cutoff converter, comprise the transformer (12) being connected between input power and out-put supply, the armature winding of transformer (12) circuit controling switch (3) of connecting with input power negative terminal, described circuit controling switch (3) is by the output signal control break-make of a pwm control circuit (2), it is characterized in that: also comprise a soft voltage cut-out that switches off control circuit (8) and control (9), described voltage cut-out (9) one end connects the positive pole of rectifier diode (10), and the other end connects input power negative pole; Between the armature winding of described transformer (12) and input power negative terminal, be also connected a branch road of being connected successively by the second electric capacity (11), rectifier diode (10) and the first electric capacity (7); described the first electric capacity (7) and the second electric capacity (11) charge within circuit controling switch (3) the shutoff phase; for pwm control circuit (2) and soft switch off control circuit (8) provide operating voltage, make the soft shutoff of circuit controling switch (3) simultaneously and suppress the reverse voltage spike at circuit controling switch (3) two ends;

Described soft switch off control circuit (8) comprise the magnitude of voltage after the 3rd resistance (5) and the 4th resistance (6) dividing potential drop by the first electric capacity (7) two ends of connection successively and first comparator (39) of the error voltage value of reference voltage relatively and after output amplification, by the ramp voltage producing from a slope generating circuit (40) and described error voltage value relatively and export second comparator (38) of burst pulse, the input end signal of described slope generating circuit (40) is the output signal of pwm control circuit (2), described burst pulse exports the control end of described voltage cut-out (9) to after one first inverter (37) and one second inverter (36), and control fast voltage cut-out (9) conducting and close, soft switch off control circuit (8) are controlled at the ON time of voltage cut-out (9) in circuit controling switch (3) conduction period according to the voltage of first electric capacity (7) of the 3rd resistance (5) and the detection of the 4th resistance (6), and the second electric capacity (11) lotus of charging within circuit controling switch (3) the shutoff phase of voltage cut-out (9) series connection part of being released, restore circuit control switch (3) is at the soft turn-off function of next switch periods.

2. soft power cutoff converter according to claim 1, it is characterized in that: described input power anode connects the first electric capacity (7) and the tie point of rectifier diode (10) by the first resistance (1), for pwm control circuit (2) and soft switch off control circuit (8) provide the operating current of initial start.

3. soft power cutoff converter according to claim 1, it is characterized in that: described voltage cut-out (9) is made up of the first field effect transistor (33) and the second field effect transistor (34) and the 5th resistance (35), one end of the grid of the grid of described the first field effect transistor (33) and the second field effect transistor (34) and the 5th resistance (35) is connected in the output of the second inverter (36), the other end of the source electrode of the source electrode of the first field effect transistor (33) and the second field effect transistor (34) and the 5th resistance (35) is connected in the power supply ground end (28) of the second inverter (36), the drain electrode of described the first field effect transistor (33) connects the node of the second electric capacity (11) and rectifier diode (10), the drain electrode of the second field effect transistor (34) connects the power supply ground end of soft switch off control circuit (8).

4. soft power cutoff converter according to claim 1, it is characterized in that: the other end of circuit controling switch (3) is by the second resistance (4) ground connection, described pwm control circuit (2) is electrically connected with circuit controling switch (3) by current detecting input (19) and drive output (17), simultaneously by FB input input and output voltage error feedback signal.

5. soft power cutoff converter according to claim 1, is characterized in that: the pulse signal of the input (24) of slope generating circuit (40) input is and the synchronous pulse train of drive waveforms of circuit controling switch (3).

6. soft power cutoff converter according to claim 5, is characterized in that: described circuit controling switch (3) is transistor and field effect transistor and wherein any composition of igbt.

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