CN204304785U - By the Switching Power Supply regulating the turn ratio to realize ultra-wide input voltage range - Google Patents

Abstract

The utility model relates to the technical field of switching power supplies, and discloses a switching power supply that realizes an ultra-wide input voltage range by adjusting the turn ratio, which includes a filter circuit, a PWM control circuit, an input voltage monitoring and photoelectric switch control circuit, a transformer, and a turn ratio control circuit. For circuits such as electrical circuits, the primary side winding of the transformer is connected to the first switching tube, and the secondary side of the transformer is composed of a second winding, a third winding, and a fourth winding connected in series in sequence. The utility model detects the input voltage in real time, compares the input voltage with the reference voltage, and then controls the switch of the photoelectric coupler, so that the three windings on the secondary side of the transformer and the turn ratio control circuit form different circuits. The input voltage threshold value of the ratio jump, and then change the turn ratio of the transformer secondary side series winding, so that the pulse duty cycle of the PWM control circuit is controlled within a reasonable range, avoiding the self-excited oscillation of the switching power supply, and making the circuit feedback The control of the loop is more stable.

Description

A switching power supply with an ultra-wide input voltage range realized by adjusting the turn ratio

technical field

The invention relates to the technical field of switching power supplies, in particular to an isolated wide input voltage range switching power supply which utilizes an electronic switch to control the turn ratio of a transformer to realize an ultra-wide input voltage range of the switching power supply.

Background technique

With the continuous development of modern electronic devices, higher requirements are put forward for the input voltage range, efficiency, volume, reliability, etc. of switching power supplies. Voltage or even wider input voltage requirements, the traditional design method to achieve the purpose of wide input voltage is: to solve the isolated wide input voltage range switching power supply is to rely entirely on adjusting the pulse duty cycle of the controller To meet the needs of voltage changes, force the switching power supply to work barely when the pulse duty cycle exceeds the reasonable area, and stabilize the output voltage; the other is to use two-stage or even multi-stage transformers. The front stage first converts the wider input voltage Stable within a small range, and then meet the requirements of a wide voltage input range through the isolation conversion of the latter stage.

There are following deficiencies in these methods:

(1) When the input voltage changes in the full range, especially when the input voltage is at two limit voltage values, the pulse duty cycle reaches the maximum and minimum respectively. In this case, the feedback loop of the circuit will be extremely unstable In some cases, the self-excited oscillation phenomenon occurs in the switching power supply, which will affect the normal operation of the circuit in the slightest, and directly damage the circuit in severe cases, causing serious consequences;

(2) Most of the switching power supplies designed with the technology of fully adjusting the duty cycle work in the input voltage range of 2 times or 4 times the voltage, and there are very few isolated high-power power supplies with 8 times the voltage and a wider input range. switching power supply;

(3) Although the multi-stage working mode of the switching power supply has achieved the purpose of meeting the design requirements, it greatly increases the complexity of the circuit, the volume of the product will become larger, and the overall efficiency of the power supply will be greatly affected. There may be mutual interference between multi-stage operations, affecting the overall performance of the circuit.

Contents of the invention

The purpose of the present invention is to provide a switching power supply that realizes an ultra-wide input voltage range by adjusting the turn ratio, a method for controlling the turn ratio of a transformer by using an electronic switch, setting the input voltage threshold value of the transformer to control the turn ratio jump, and the secondary The turn ratio of the series winding reduces the adjustment range of the pulse duty cycle of the PWM controller, making the feedback loop control more stable. In the case of fewer components added to the circuit, the switching power supply can operate in an ultra-wide input voltage range. work inside.

In order to achieve the above object, the technical scheme adopted in the present invention is:

A switching power supply that realizes an ultra-wide input voltage range by adjusting the turn ratio, which includes a filter circuit connected to the input end of the power supply, an input voltage monitoring and a photoelectric switch control circuit, the output end of the filter circuit is connected to the primary side winding of the transformer, The output end of the filter circuit is connected to the PWM control circuit through the voltage stabilizing circuit, the PWM control circuit is connected to the feedback loop, and the feedback loop is connected to the output end of the switching power supply. The input voltage monitoring and photoelectric switch control circuit includes a photoelectric A coupler, the primary side winding of the transformer is connected to the drain of the first switch tube, the gate of the first switch tube is connected to the PWM control circuit through the switch tube drive circuit, and the first switch tube The source of the first switching tube is connected to the PWM control circuit through the current sampling circuit, the source of the first switching tube is connected to one end of the fourth resistor, the other end of the fourth resistor is grounded, and the transformer’s The secondary side is composed of a second winding, a third winding, and a fourth winding connected in series in sequence, the second winding is connected to the output terminal of the switching power supply through a rectification and filtering circuit, one end of the third winding is connected to the rectification and filtering circuit The circuit is connected, the other end is connected with the turn ratio control circuit, the fourth winding is connected with the photocoupler through the turn ratio control circuit; the input voltage monitoring and photoelectric switch control circuit detects the input voltage in real time, Comparing the input voltage with the reference voltage, and then controlling the switch of the photocoupler, so that the second winding, the third winding, and the fourth winding on the secondary side of the transformer form different loops with the turn ratio control circuit, By setting the input voltage threshold value for controlling the turn ratio jump and changing the turn ratio of the transformer secondary side series winding, the adjustment range of the pulse duty ratio of the PWM control circuit is within a reasonable range, avoiding the switching power supply Self-excited oscillation occurs, making the control of the feedback loop more stable.

As a further improvement of the present invention, the filter circuit is composed of a first capacitor, a second capacitor, and a first inductor, one end of the first capacitor is connected to the positive input end of the power supply, and the other end is connected to the negative input end of the power supply, so One end of the first inductor is connected to the positive input end of the power supply, and the other end is connected to one end of the second capacitor, the IN end of the voltage stabilizing integrated circuit, and the No. 1 end of the primary side winding of the first transformer. The other end of the capacitor is connected to the ground wire end of the power supply. The filter circuit is a two-way network, which not only prevents the AC interference components on the input wires from entering the switching power supply, suppresses the adverse effects of high-frequency noise on the switching power supply; but also prevents the electromagnetic interference in the switching power supply from being transmitted to the power grid through the power line, causing damage to the power grid. create pollution.

As a further improvement of the present invention, the PWM control circuit is composed of a PWM control integrated circuit, the voltage stabilizing circuit is composed of a voltage stabilizing integrated circuit, the GND terminal of the voltage stabilizing integrated circuit is connected to the ground terminal of the power supply, and the OUT terminal Connect the VCC terminal of the PWM control integrated circuit and the 8 pin of the voltage comparison integrated circuit; the OUT terminal of the PWM control integrated circuit is connected to one end of the first resistor, and the CS sampling terminal is connected to the third resistor and one end of the third capacitor , the GND terminal is connected to the ground terminal of the power supply, one end of the first resistor is connected to one end of the second resistor, the other end of the second resistor is connected to the other end of the third resistor, the The source poles of the first switch tube are connected, and the other end of the third capacitor is connected to the ground terminal of the power supply; the working process of the PWM control circuit is: the feedback loop sends the monitored output voltage signal to the The PWM control integrated circuit, the PWM control integrated circuit processes the collected signals in real time, adjusts the driving pulse duty ratio of the PWM pulse width modulator, so as to achieve the purpose of stabilizing the output voltage, and the voltage stabilizing integrated circuit is used for the PWM control The integrated circuit provides a stable operating voltage.

As a further improvement of the present invention, the input voltage monitoring and photoelectric switch control circuit is composed of the voltage comparison integrated circuit, photocoupler, seventh resistor, eighth resistor, ninth resistor, tenth resistor, Composed of the seventh capacitor and the fifth diode, the photocoupler contains a light-emitting diode and a phototransistor, one end of the seventh resistor is connected to the positive input end of the power supply, and the other end is connected to the eighth resistor One end of the voltage comparison integrated circuit and pin 3 of the voltage comparison integrated circuit; the other end of the eighth resistor is connected to the ground wire end of the power supply; pin 2 of the voltage comparison integrated circuit is connected to the reference voltage, and pin 4 is connected to the ground wire end of the power supply , pin 8 is connected to the OUT end of the voltage stabilizing integrated circuit and one end of the seventh capacitor, pin 1 is connected to the anode of the fifth diode; the other end of the seventh capacitor is connected to the ground terminal of the power supply ; The cathode of the fifth diode is connected to one end of the ninth resistor; the other end of the ninth resistor is connected to one end of the tenth resistor and pin 1 of the photocoupler; Pin 2 of the photocoupler is connected to the other end of the tenth resistor and the ground wire end of the power supply. The working process of the input voltage monitoring and photoelectric switch control circuit is as follows: first, the input voltage is detected in real time at the same input end of the voltage comparison integrated circuit, and the voltage generated by the seventh resistor is sent to the The voltage comparison integrated circuit formed by the operational amplifier is compared with the reference voltage added to the reverse terminal, and the high and low levels are output from the 1 pin of the voltage comparison integrated circuit to control the switch of the photocoupler; when the input voltage When it is higher, the positive terminal voltage of the voltage comparison integrated circuit is higher than the negative terminal reference voltage, and the voltage comparison integrated circuit outputs a high level, so that the light-emitting diode inside the photocoupler is turned on, and the The triode inside the photocoupler is turned on; when the input voltage is low, the positive terminal voltage of the voltage comparison integrated circuit is lower than the reverse terminal reference voltage, and the voltage comparison integrated circuit outputs a low level, so that the photoelectric The light-emitting diode inside the coupler is not conducting, and the triode inside the photocoupler is also not conducting.

As a further improvement of the present invention, the turn ratio control circuit and the rectification and filtering circuit constitute the secondary side control circuit of the transformer; the rectification and filtering circuit consists of a first diode, a fourth capacitor, a fifth capacitor, a Composed of two inductors; the turn ratio control circuit consists of a second switch tube, a first Zener diode, a second diode, a third diode, a fourth diode, a fifth resistor, and a sixth resistor , the sixth capacitor, the No. 3 terminal of the second winding of the transformer is connected to the negative output terminal of the switching power supply and one end of the fourth capacitor and the fifth capacitor, and the No. 4 terminal of the second winding is connected to the The anode of the first diode and the No. 5 terminal of the third winding, the cathode of the first diode are simultaneously connected to one end of the second inductor, the other end of the fourth capacitor, and the fourth pole The cathode of the tube, the 3 pins of the photocoupler, the anode of the first Zener diode, the sixth resistor and one end of the sixth capacitor, the other end of the second inductor is connected to the other end of the fifth capacitor And the positive output terminal of the switching power supply, the source of the second switching tube is connected to the anode of the fourth diode, the drain is connected to the cathode of the second diode, and the gate is connected to the sixth resistor and the other end of the sixth capacitor , the cathode of the first Zener tube, the 4 pins of the photocoupler and one end of the fifth resistor; the other end of the fifth resistor is connected to the cathode of the third diode; the anode of the third diode is connected to the first The No. 8 terminal of the four windings; the No. 7 terminal of the fourth winding is connected to the anode of the second diode and the No. 6 terminal of the third winding; the working process is: when the input voltage is high, The voltage comparison integrated circuit outputs a high level, the light-emitting diodes and triodes inside the photocoupler are all turned on, no voltage is established between the gate and source of the second switch tube, and the second switch tube unable to conduct, no current flows through the loop formed by the third winding of the transformer, and the current works through the loop formed by the second winding of the transformer, the first diode, the second inductor and the load; when the input When the voltage is low, the voltage comparison integrated circuit outputs a low level, the light-emitting diodes and triodes inside the photocoupler are not turned on, and the gate and source of the second switch tube pass through the The fourth winding of the transformer, the rectifying and filtering circuit, and the voltage stabilizing circuit establish a suitable voltage, and the second switching tube is turned on. At this time, the second winding, the third winding, and the second diode of the transformer The voltage of the tube and the fourth diode circuit is higher than the voltage passing through the second winding of the transformer and the first diode circuit, and the first diode is in a reverse cut-off state in the entire circuit, and the current only passes through The loop formed by the second winding, the third winding, the second diode, the fourth diode, the second inductor and the load of the transformer works.

Working principle of the present invention is:

In the present invention, the input voltage is firstly detected in real time, and the voltage divided by the seventh resistor is sent to the positive end of the voltage comparison integrated circuit, and compared with the reference voltage added to the reverse end of the voltage comparison integrated circuit For comparison, the high and low levels are output from pin 1 of the voltage comparison integrated circuit to control the switch of the photocoupler.

When the input voltage is high, the positive terminal voltage of the voltage comparison integrated circuit is higher than the reverse terminal voltage, and the voltage comparison integrated circuit outputs a high level, so that the light-emitting diode inside the photocoupler is turned on, and the The phototransistor inside the photocoupler is also turned on, so that no voltage is established between the gate and the source of the second switch tube, the second switch tube is not turned on, and the third winding on the secondary side of the transformer If there is no current flowing in the loop, the current will work through the loop formed by the second winding of the transformer, the first diode, the second inductor and the load.

When the input voltage is low, the positive terminal voltage of the voltage comparison integrated circuit is lower than the reverse terminal voltage, and the voltage comparison integrated circuit outputs a low level, then the light emitting diode inside the photocoupler is not turned on, The phototransistor inside the photocoupler is also not conducting, and the voltage difference between the grid and the source of the second switch tube is established through the fourth winding of the transformer and the corresponding rectification filter circuit, and the second switch tube conduction, at this moment, the voltage passing through the loop composed of the second winding, the third winding, the second diode and the fourth diode of the transformer is higher than the voltage passing through the second winding and the first diode loop of the transformer, Then the first diode D1 is in the reverse cut-off state in the loop, and the current is formed only through the second winding, the third winding, the second diode, the fourth diode, the second inductor and the load of the transformer. circuit works.

Actually, the PWM control circuit is the feedback signal sent by the real-time feedback loop, and internally compares with the reference to control the duty cycle of the PWM output pulse to realize the stability of the output voltage. For example, assuming that the circuit topology is single-ended flyback, the power input is 8 times the voltage Vin=9V～72V; the output voltage Vo=15V, then the maximum duty cycle of the flyback circuit is designed to be Dmax=42%.

(1) In the case where the second switch tube is usually not used to control the transformer turn ratio:

According to the formula:

                                                

Calculate the transformer turns ratio:

Then calculate the duty cycle of the circuit at the highest input voltage with a fixed transformer turns ratio:

Dmax≈8.3%

In this case, the pulse duty cycle varies between 8.3% and 42%.

(2) In the case of using the second switch tube to control the transformer turn ratio:

Assume that the input voltage threshold for setting the turn ratio jump is 36V; the turns ratio N2:N3=1:1; recalculate:

When Vin=9V～36V, since the secondary side voltage is jointly boosted by the second winding and the third winding of the transformer, therefore:

Calculate the transformer turns ratio:

Then calculate the duty cycle of the circuit under the 36V input voltage with a fixed transformer turn ratio:

Dmax≈15.3%

When the input voltage is greater than 36V and changes from Vin=36V to 72V, since the third winding on the secondary side of the transformer is turned off by the second switching tube, the voltage is only boosted by the N2 winding of the transformer, then the turn ratio of the transformer at this time is:

Then calculate the duty cycle of the circuit under 72V input voltage with a fixed transformer turns ratio:

Dmax≈15.3%

It can be known from the above calculation that the pulse duty cycle is always controlled between 15.3% and 42% within the entire input voltage range (Vin=9V～72V).

It can be seen that in the case of a wide input voltage range, the second switch tube is used to control the transformer turn ratio, and by setting the input voltage threshold value for controlling the turn ratio jump and the turn ratio of the transformer secondary side series winding, the The adjustment range of the pulse duty ratio of the PWM control circuit is widened, the self-excited oscillation phenomenon occurs when the circuit works under larger and smaller pulse duty ratios, and the feedback loop control is more stable. The input voltage range of the switching power supply can be made wider to meet the application requirements of various functions.

Beneficial effects of the present invention:

The present invention abandons the original traditional method of designing an isolated switching power supply with a wide input voltage range, adopts a novel design idea, utilizes an electronic switching circuit, and adjusts the number of turns of the secondary side of the switching power supply transformer during the working process to effectively Reduce the variation range of the pulse duty cycle of the switching power supply, avoid the self-excited oscillation phenomenon when the circuit works under a large and small limit duty cycle, make the circuit feedback loop control more stable, and improve the reliability of the product. At the same time, using this technology, the switching power supply can be designed to work in a wider input voltage range on the original basis with fewer components added to the circuit, and the additional circuit will not generate additional noise. It has a significant impact on other parameters of the circuit.

Compared with switching power supplies designed by other schemes, the present invention has the characteristics of wide input voltage range, simple circuit, good electromagnetic compatibility, small occupied volume, reliable and stable operation, and the like.

Description of drawings

Fig. 1 is a block diagram of the present invention;

Fig. 2 is a schematic circuit diagram of the present invention;

In the figure: 1. Filter circuit, 2. PWM control circuit, 3. Input voltage monitoring and photoelectric switch control circuit, 4. Voltage stabilization circuit, 5. Drive circuit, 6. Current sampling circuit, 7. Turn ratio control circuit, 8 , Rectification filter circuit, 9, feedback loop.

Detailed ways

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

As shown in Figure 1 and Figure 2, a switching power supply that realizes an ultra-wide input voltage range by adjusting the turn ratio, it includes a filter circuit 1 connected to the input end of the power supply, an input voltage monitoring and photoelectric switch control circuit 3, and a filter circuit 1 The output terminal of the filter circuit 1 is connected to the primary side winding N1 of the transformer B1, the output terminal of the filter circuit 1 is connected to the PWM control circuit 2 through the voltage stabilizing circuit 4, the PWM control circuit 2 is connected to the feedback loop 9, and the feedback loop 9 is connected to At the output end of the switching power supply, the input voltage monitoring and photoelectric switch control circuit 3 includes a photocoupler IC4, the primary side winding N1 of the transformer B1 is connected to the drain of the first switching tube T1, and the gate of the first switching tube T1 The switch tube drive circuit 5 is connected to the PWM control circuit 2, the source of the first switch tube T1 is connected to the PWM control circuit 2 through the current sampling circuit 6, and the source of the first switch tube T1 is connected to the fourth resistor R4. One end is connected, the other end of the fourth resistor R4 is grounded, the secondary side of the transformer B1 is composed of the second winding N2, the third winding N3, and the fourth winding N4 in series, and the second winding N2 passes through the rectification filter circuit 8 and the switch The output terminals of the power supply are connected, one end of the third winding N3 is connected to the rectification filter circuit 8, the other end is connected to the turn ratio control circuit 7, and the fourth winding N4 is connected to the photocoupler IC4 through the turn ratio control circuit 7; The input voltage monitoring and photoelectric switch control circuit 3 detects the input voltage in real time, compares the input voltage with the reference voltage, and then controls the switch of the photocoupler IC4 to make the second winding N2 and the third winding N3 on the secondary side of the transformer B1 1. The fourth winding N4 and the turn ratio control circuit 7 form different loops. By setting the input voltage threshold value for controlling the jump of the turn ratio and changing the turn ratio of the secondary side series winding of the transformer B1, the pulse ratio of the PWM control circuit 2 is The adjustment range of the empty ratio is within a reasonable range, which avoids the self-excited oscillation of the switching power supply and makes the control of the feedback loop more stable.

The filter circuit 1 is composed of a first capacitor C1, a second capacitor C2, and a first inductor L1. One end of the first capacitor C1 is connected to the positive input end P1 of the power supply, and the other end is connected to the negative input end P2 of the power supply. The first inductor L1 One end is connected to the positive input end P1 of the power supply, the other end is connected to one end of the second capacitor C2, the IN end of the voltage stabilizing integrated circuit IC1, and the No. 1 end of the primary side winding N1 of the first transformer B1, and the other end of the second capacitor C2 One end is connected to the ground wire end P2 of the power supply. The filter circuit 1 is a two-way network, which not only prevents the AC interference components on the input wires from entering the switching power supply, suppresses the adverse effects of high-frequency noise on the switching power supply; pollute.

The PWM control circuit 2 is composed of a PWM control integrated circuit IC2, and the voltage stabilizing circuit 4 is composed of a voltage stabilizing integrated circuit IC1. The GND terminal of the voltage stabilizing integrated circuit IC1 is connected to the ground terminal of the power supply, and the OUT terminal is connected to the VCC terminal of the PWM control integrated circuit IC2. And pin 8 of the voltage comparison integrated circuit module IC3; the OUT terminal of the PWM control integrated circuit IC2 is connected to one end of the first resistor R1, the CS sampling terminal is connected to the third resistor R3 and one end of the third capacitor C3, and the GND terminal is connected to the power supply Ground terminal, one end of the first resistor R1 is connected to one end of the second resistor R2, the other end of the second resistor R2 is connected to the other end of the third resistor R3, and the source of the first switch tube T1 , the other terminal of the third capacitor C3 is connected to the ground terminal of the power supply. The working process of the PWM control circuit 2 is: the feedback loop 9 sends the monitored output voltage signal to the PWM control integrated circuit IC2, and the PWM control integrated circuit IC2 processes the collected signals in real time to adjust the driving pulse of the PWM pulse width modulator Duty cycle, so as to achieve the purpose of stabilizing the output voltage, the voltage stabilizing integrated circuit IC1 is to provide a stable working voltage for the PWM control integrated circuit IC2.

The input voltage monitoring and photoelectric switch control circuit 3 is composed of a voltage comparison integrated circuit IC3, a photocoupler IC4, the seventh resistor R7, the eighth resistor R8, the ninth resistor R9, the tenth resistor R10, the seventh capacitor C7, Composed of the fifth diode D5, the photocoupler IC4 contains a light-emitting diode and a phototransistor inside, one end of the seventh resistor R7 is connected to the positive input terminal P1 of the power supply, and the other end is connected to one end of the eighth resistor R8 and the voltage comparison Pin 3 of the integrated circuit IC3; the other end of the eighth resistor R8 is connected to the ground terminal of the power supply; pin 2 of the voltage comparison integrated circuit IC3 is connected to the reference voltage P5, pin 4 is connected to the ground terminal of the power supply, and pin 8 is connected to the integrated voltage regulator The OUT end of the circuit IC1 and one end of the seventh capacitor C7, pin 1 is connected to the anode of the fifth diode D5; the other end of the seventh capacitor C7 is connected to the ground wire of the power supply; the cathode of the fifth diode D5 is connected to the second One end of the nine resistor R9; the other end of the ninth resistor R9 is connected to one end of the tenth resistor R10 and pin 1 of the optocoupler IC4; pin 2 of the optocoupler IC4 is connected to the other end of the tenth resistor R10 and power supply Power ground terminal. The working process of the input voltage monitoring and photoelectric switch control circuit 3 is as follows: first, the input voltage is detected in real time at the same input terminal of the voltage comparison integrated circuit IC3, and the voltage generated by the seventh resistor R7 is sent to the circuit composed of an operational amplifier. The voltage comparison integrated circuit IC3 is compared with the reference voltage P5 added to the reverse terminal, and the high and low levels are output from pin 1 of the voltage comparison integrated circuit IC3 to control the switch of the photocoupler IC4; when the input voltage is high, the voltage The voltage at the forward end of the comparison integrated circuit IC3 is higher than the reference voltage at the reverse end, and the voltage comparison integrated circuit IC3 outputs a high level, so that the light-emitting diode inside the photocoupler IC4 is turned on, and the triode inside the photocoupler IC4 is turned on at the same time; When the input voltage is low, the positive terminal voltage of the voltage comparison integrated circuit IC3 is lower than the negative terminal reference voltage, and the voltage comparison integrated circuit IC3 outputs a low level, so that the light-emitting diode inside the photocoupler IC4 is not conducting, and the photoelectric The triode inside the coupler IC4 is also not conducting.

The turn ratio control circuit 7 and the rectification filter circuit 8 constitute the secondary side control circuit of the transformer B1; the rectification filter circuit 8 is composed of the first diode D1, the fourth capacitor R4, the fifth capacitor R5, and the second inductor L2; The ratio control circuit 7 is composed of a second switching tube T2, a first voltage regulator diode DZ1, a second diode D2, a third diode D3, a fourth diode D4, a fifth resistor R5, and a sixth resistor R6 , the sixth capacitor R6, the No. 3 terminal of the second winding N2 of the transformer B1 is connected to the negative output terminal P4 of the switching power supply and one end of the fourth capacitor C4 and the fifth capacitor C5, and the No. 4 terminal of the second winding N2 is connected to the No. 4 terminal of the second winding N2 The anode of a diode D1 and the No. 5 terminal of the third winding N3, the cathode of the first diode D1 are simultaneously connected to one end of the second inductor L2, the other end of the fourth capacitor C4, and the fourth diode D4 The cathode of the photocoupler IC4 pin 3, the anode of the first Zener diode DZ1, the sixth resistor R6 and one end of the sixth capacitor C6, the other end of the second inductor L2 is connected to the other end of the fifth capacitor C5 and The positive output terminal P3 of the switching power supply, the source of the second switching tube T2 is connected to the anode of the fourth diode D4, the drain is connected to the cathode of the second diode D2, and the gate is connected to the sixth resistor R6 and the sixth capacitor C6 The other end of the first regulator tube DZ1, the cathode of the first regulator IC4 pin 4 and one end of the fifth resistor R5; the other end of the fifth resistor R5 is connected to the cathode of the third diode D3; the third two The anode of the diode D3 is connected to the No. 8 terminal of the fourth winding N4; the No. 7 terminal of the fourth winding N4 is connected to the anode of the second diode D2 and the No. 6 terminal of the third winding N3. Its working process is: when the input voltage is high, the voltage comparison integrated circuit IC3 outputs a high level, the light-emitting diodes and triodes inside the photocoupler IC4 are all turned on, and there is no gap between the gate and the source of the second switching tube T2. When the voltage is established, the second switching tube T2 cannot be turned on, and no current flows in the loop formed by the third winding N3 of the transformer B1, and the current passes through the second winding N2 of the transformer B1, the first diode D1, and the second inductor The circuit composed of L2 and load works; when the input voltage is low, the voltage comparison integrated circuit IC3 outputs a low level, the light-emitting diode and triode inside the photocoupler IC4 are not conducting, the gate of the second switching tube T2 is connected to the source Between the poles, a suitable voltage is established through the fourth winding N4 of the transformer B1, the rectification filter circuit 8, and the voltage stabilizing circuit 4, and the second switching tube T2 is turned on. At this time, the second winding N2 and the third winding N3 of the transformer B1 , The voltage of the second diode D2 and the fourth diode D4 circuit is higher than the voltage of the second winding N2 of the transformer B1 and the voltage of the first diode D1 circuit, and the first diode D1 is in reverse in the whole circuit To the cut-off state, the current only works through the loop formed by the second winding N2, the third winding N3, the second diode D2, the fourth diode D4, the second inductor L2 and the load of the transformer B1.

The invention is a technique for realizing the ultra-wide input voltage range of a switching power supply by using an electronic switch to control the turn ratio of a transformer, so that the pulse duty ratio changes within a reasonable range during circuit operation, thereby realizing the purpose of an ultra-wide input voltage range.

The technical solution provided by the present invention is only aimed at illustrating a relatively general circuit UCC2843 in the flyback circuit topology in the field of switching power supplies. This solution can also be directly replaced and applied to other circuit structures, such as forward, push In the circuit topologies such as the pull type, the specific circuit models are also replaceable, and should be regarded as the scope of protection of this patent.

Claims (5)

1. A switching power supply that realizes an ultra-wide input voltage range by adjusting the turn ratio, which includes a filter circuit (1) connected to the input end of the power supply, an input voltage monitoring and photoelectric switch control circuit (3), and a filter circuit (1) The output end is connected to the primary side winding (N1) of the transformer (B1), the output end of the filter circuit (1) is connected to the PWM control circuit (2) through the voltage stabilizing circuit (4), and the PWM control circuit (2) is connected to the feedback The loops (9) are connected, and the feedback loop (9) is connected to the output end of the switching power supply, which is characterized in that: the input voltage monitoring and photoelectric switch control circuit (3) includes a photocoupler (IC4), the The primary side winding (N1) of the transformer (B1) is connected to the drain of the first switching tube (T1), and the gate of the first switching tube (T1) is controlled by the PWM through the switching tube drive circuit (5) circuit (2), the source of the first switching tube (T1) is connected to the PWM control circuit (2) through a current sampling circuit (6), and the source of the first switching tube (T1) It is connected with one end of the fourth resistor (R4), the other end of the fourth resistor (R4) is grounded, and the secondary side of the transformer (B1) is composed of the second winding (N2), the third winding (N3) and fourth winding (N4), the second winding (N2) is connected to the output terminal of the switching power supply through a rectification and filtering circuit (8), and one end of the third winding (N3) is connected to the The rectification and filtering circuit (8) is connected, and the other end is connected to the turn ratio control circuit (7), and the fourth winding (N4) is connected to the photocoupler (IC4) through the turn ratio control circuit (7); The input voltage monitoring and photoelectric switch control circuit (3) detects the input voltage in real time, compares the input voltage with the reference voltage, and then controls the switch of the photoelectric coupler (IC4), so that the transformer (B1) The second winding (N2), the third winding (N3), and the fourth winding (N4) on the stage side form different loops with the turn ratio control circuit (7). By setting the input voltage threshold for controlling the turn ratio jump value, changing the turn ratio of the secondary side series winding of the transformer (B1), so that the adjustment range of the pulse duty ratio of the PWM control circuit (2) is within a reasonable range, avoiding self-oscillation of the switching power supply, and making The control of the feedback loop is more stable. 2. A switching power supply that realizes an ultra-wide input voltage range by adjusting the turn ratio according to claim 1, characterized in that: the filter circuit (1) is composed of a first capacitor (C1), a second capacitor (C2) , the first inductor (L1), one end of the first capacitor (C1) is connected to the positive input end (P1) of the power supply, and the other end is connected to the negative input end (P2) of the power supply, the first inductor (L1 ) is connected to the positive input terminal (P1) of the power supply, and the other terminal is connected to one terminal of the second capacitor (C2), the IN terminal of the voltage stabilizing integrated circuit (IC1) and the primary side winding (N1) of the first transformer (B1) ), the other end of the second capacitor (C2) is connected to the ground terminal (P2) of the power supply, and the filter circuit (1) is a bidirectional network, which prevents the AC interference components on the input wire from entering the switch Power supply, inhibit high-frequency noise from adversely affecting the switching power supply; and prevent electromagnetic interference in the switching power supply from being transmitted to the power grid through the power line, causing pollution to the power grid. 3. A switching power supply that realizes an ultra-wide input voltage range by adjusting the turn ratio according to claim 1, characterized in that: the PWM control circuit (2) is composed of a PWM control integrated circuit (IC2), and the stable The voltage circuit (4) is composed of a voltage stabilizing integrated circuit (IC1), the GND terminal of the voltage stabilizing integrated circuit (IC1) is connected to the ground terminal of the power supply, the OUT terminal is connected to the VCC terminal of the PWM control integrated circuit (IC2) and Pin 8 of the voltage comparison integrated circuit module (IC3); the OUT terminal of the PWM control integrated circuit (IC2) is connected to one end of the first resistor (R1), and the CS sampling terminal is connected to the third resistor (R3) and the third capacitor One end of (C3), GND is connected to the ground wire end of the power supply, one end of the first resistor (R1) is connected to one end of the second resistor (R2), and the other end of the second resistor (R2) One end is connected to the other end of the third resistor (R3) and the source of the first switch tube (T1), and the other end of the third capacitor (C3) is connected to the ground terminal of the power supply; the The working process of the PWM control circuit (2) is: the feedback loop (9) sends the monitored output voltage signal to the PWM control integrated circuit (IC2), and the PWM control integrated circuit (IC2) processes the collected signal Real-time processing to adjust the driving pulse duty cycle of the PWM pulse width modulator, so as to achieve the purpose of stabilizing the output voltage. The voltage stabilizing integrated circuit (IC1) provides a stable working voltage for the PWM control integrated circuit (IC2). 4. A switching power supply that realizes an ultra-wide input voltage range by adjusting the turn ratio according to claim 2, characterized in that: the input voltage monitoring and photoelectric switch control circuit (3) is composed of a voltage comparison integrated circuit (IC3) , photocoupler (IC4), seventh resistor (R7), eighth resistor (R8), ninth resistor (R9), tenth resistor (R10), seventh capacitor (C7), fifth and second Diode (D5), the photocoupler (IC4) contains a light-emitting diode and a phototransistor, one end of the seventh resistor (R7) is connected to the positive input end (P1) of the power supply, and the other end is connected to the One end of the eighth resistor (R8) and pin 3 of the voltage comparison integrated circuit (IC3); the other end of the eighth resistor (R8) is connected to the ground terminal of the power supply; the voltage comparison integrated circuit ( Pin 2 of IC3) is connected to the reference voltage (P5), pin 4 is connected to the ground terminal of the power supply, pin 8 is connected to the OUT terminal of the voltage stabilizing integrated circuit (IC1) and one end of the seventh capacitor (C7), and pin 1 Connect the anode of the fifth diode (D5); the other end of the seventh capacitor (C7) is connected to the ground terminal of the power supply; the cathode of the fifth diode (D5) is connected to the ninth One end of the resistor (R9); the other end of the ninth resistor (R9) is connected to one end of the tenth resistor (R10) and pin 1 of the optocoupler (IC4); the optocoupler Pin 2 of (IC4) is connected to the other end of the tenth resistor (R10) and the ground wire end of the power supply; the working process of the input voltage monitoring and photoelectric switch control circuit (3) is: firstly, compare the voltage The non-inverting input terminal of the integrated circuit (IC3) detects the input voltage in real time, and the voltage generated by the seventh resistor (R7) is sent to the voltage comparison integrated circuit (IC3) composed of an operational amplifier, and Compared with the reference voltage (P5) applied to the reverse terminal, output high and low levels from pin 1 of the voltage comparison integrated circuit (IC3) to control the switch of the photocoupler (IC4); when the input voltage is high , the positive terminal voltage of the voltage comparison integrated circuit (IC3) is higher than the reference voltage of the reverse terminal, and the voltage comparison integrated circuit (IC3) outputs a high level, so that the light-emitting diode inside the photocoupler (IC4) At the same time, the triode inside the optocoupler (IC4) is turned on; when the input voltage is low, the positive terminal voltage of the voltage comparison integrated circuit (IC3) is lower than the negative terminal reference voltage, and the voltage The comparison integrated circuit (IC3) outputs a low level, so that the light-emitting diode inside the photocoupler (IC4) is not conducting, and at the same time, the triode inside the photocoupler (IC4) is also not conducting. 5. A switching power supply that realizes an ultra-wide input voltage range by adjusting the turn ratio according to claim 3, characterized in that: the turn ratio control circuit (7) and the rectification and filtering circuit (8) constitute the transformer (B1) a secondary side control circuit; the rectification and filtering circuit (8) is composed of a first diode (D1), a fourth capacitor (R4), a fifth capacitor (R5), and a second inductor (L2); The turn ratio control circuit (7) consists of a second switch tube (T2), a first Zener diode (DZ1), a second diode (D2), a third diode (D3), a fourth diode (D4), the fifth resistor (R5), the sixth resistor (R6), and the sixth capacitor (R6), the No. 3 terminal of the second winding (N2) of the transformer (B1) is connected to the switching power supply negative The output terminal (P4) and one terminal of the fourth capacitor (C4) and the fifth capacitor (C5), the No. 4 terminal of the second winding (N2) is connected to the anode of the first diode (D1) and the No. 5 end of the third winding (N3), the cathode of the first diode (D1) is connected to one end of the second inductor (L2) and the other end of the fourth capacitor (C4) at the same time , the cathode of the fourth diode (D4), the 3 pin of the optocoupler (IC4), the anode of the first Zener diode (DZ1), the sixth resistor (R6) and the sixth capacitor (C6) One end, the other end of the second inductor (L2) is connected to the other end of the fifth capacitor (C5) and the positive output end (P3) of the switching power supply, and the source of the second switching tube (T2) is connected to the first The anode of the four diodes (D4), the drain is connected to the cathode of the second diode (D2), the grid is connected to the sixth resistor (R6), the other end of the sixth capacitor (C6), the first regulator tube (DZ1) cathode, pin 4 of the photocoupler (IC4) and one end of the fifth resistor (R5); the other end of the fifth resistor (R5) is connected to the cathode of the third diode (D3); The anode of the third diode (D3) is connected to the No. 8 terminal of the fourth winding (N4); the No. 7 terminal of the fourth winding (N4) is connected to the anode of the second diode (D2) and the The No. 6 terminal of the third winding (N3); its working process is: when the input voltage is high, the voltage comparison integrated circuit (IC3) outputs a high level, and the light-emitting diode inside the photocoupler (IC4) , triodes are all turned on, no voltage is established between the gate and source of the second switching tube (T2), the second switching tube (T2) cannot be turned on, the third winding of the transformer (B1) No current flows in the loop formed by (N3), and the current passes through the loop formed by the second winding (N2), the first diode (D1), the second inductor (L2) and the load of the transformer (B1) work; when the input voltage is low, the voltage comparison integrated circuit (IC3) outputs a low level, the light-emitting diodes and triodes inside the photocoupler (IC4) are not turned on, and the second switch tube (T2 ) between the gate and the source goes through the transformer (B1) The fourth winding (N4), the rectifying and filtering circuit (8), and the voltage stabilizing circuit (4) establish a suitable voltage, and the second switching tube (T2) is turned on. At this time, the transformer (B1 ), the voltage of the second winding (N2), third winding (N3), second diode (D2), fourth diode (D4) circuit is higher than that through the second winding (B1) of the transformer (B1) N2), the voltage of the first diode (D1) loop, the first diode (D1) is in the reverse cut-off state in the whole loop, and the current only passes through the second winding (N2) of the transformer (B1) ), the third winding (N3), the second diode (D2), the fourth diode (D4), the second inductor (L2) and the load constitute a loop.