Power supply circuit and power supply device

Abstract

The application provides a power supply circuit and a power supply device, the power supply circuit comprising a rectification filter circuit, a transformer and a control circuit, the transformer comprising an auxiliary winding, the control circuit comprising a primary side control circuit connected with the auxiliary winding, the primary side control circuit comprising a control chip for controlling the power supply circuit, the control chip comprising a first pin and a second pin connected with the auxiliary winding, the auxiliary winding supplying power for the control chip through the first pin, the second pin being used for detecting the voltage of the auxiliary winding, and a compensation resistor being connected between the first pin and the second pin. Compared with the prior art, the application improves the voltage of the second pin when the output is short-circuited, increases the demagnetization time of the control chip, reduces the working frequency and the power consumption when the output is short-circuited, and avoids the damage of the MOS tube of the control chip without short-circuit protection mechanism.

Description

TECHNICAL FIELD

[0001] The present application relates to a power supply circuit and a power supply device, and belongs to the technical field of power supply devices. BACKGROUND

[0002] Output short circuit protection is a basic requirement for independent power supplies, but some chips do not have short circuit protection function, which is to increase the demagnetization time of inductor current when output short circuit to reduce the switching frequency, thereby reducing power consumption. However, in the constant voltage high voltage output environment, the turn ratio of the secondary winding and the auxiliary winding is large, resulting in a low auxiliary winding voltage Vaux, which is easy to reach the chip opening down threshold, at this time the chip will work with the minimum off time Toff_min, and the chip will be damaged due to the high working frequency of the MOS tube.

[0003] Therefore, it is necessary to provide a power supply circuit and a power supply device to solve the above problems. SUMMARY

[0004] The purpose of the present application is to provide a power supply circuit and a power supply device for short circuit protection of the circuit.

[0005] To achieve the above purpose, the present application provides a power supply circuit, which comprises a rectifier filter circuit, a transformer and a control circuit, the transformer comprises an auxiliary winding, the control circuit comprises a primary side control circuit connected with the auxiliary winding, the primary side control circuit comprises a control chip for controlling the power supply circuit, the control chip comprises a first pin and a second pin connected with the auxiliary winding, the auxiliary winding supplies power to the control chip through the first pin, the second pin is used for detecting the voltage of the auxiliary winding, a compensation resistor is connected between the first pin and the second pin, and the compensation resistor is used for increasing the voltage of the second pin to protect the control chip.

[0006] As a further improvement of the present application, the resistance value of the compensation resistor is between 4-5MΩ.

[0007] As a further improvement of the present application, the rectifier filter circuit comprises a bridge rectifier and a filter, and the filter is used for filtering the output voltage of the bridge rectifier.

[0008] As a further improvement of the present application, the bridge rectifier comprises a first capacitor, a second capacitor and an inductor, the first capacitor and the second capacitor are respectively connected in parallel at two output ends of the bridge rectifier, and the inductor is connected with one of the output ends of the bridge rectifier.

[0009] As a further improvement of the present application, an insurance resistor is arranged at the input end of the rectifier filter circuit.

[0010] As a further improvement of the present application, the power supply circuit further comprises a step-down conversion circuit, the step-down conversion circuit comprising a power diode and an output capacitor.

[0011] As a further improvement of the present application, the transformer further comprises a primary winding and a secondary winding, the primary winding being connected to the output of the rectification filter circuit.

[0012] As a further improvement of the present application, the control circuit further comprises a secondary feedback circuit, the secondary feedback circuit being connected to the secondary winding.

[0013] As a further improvement of the present application, the output voltage detection circuit is further provided between the primary control circuit and the secondary feedback circuit, the output voltage detection circuit comprising a controllable precision voltage stabilizing chip and an optoelectronic coupler, the optoelectronic coupler connecting the cathode of the controllable precision voltage stabilizing chip and the primary control circuit.

[0014] To achieve the above object, the present application further provides a power supply device having the power supply circuit as described above.

[0015] The present application has the advantages that the present application increases the voltage of the second pin when the output is short-circuited, increases the demagnetization time of the control chip, reduces the working frequency and the power consumption when the output is short-circuited, and avoids the damage of the MOS tube of the control chip without short-circuit protection mechanism. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a circuit structure schematic diagram of the primary control circuit in the power supply circuit of the present application.

[0017] Figure 2 is a circuit structure schematic diagram of the power supply circuit of the present application. DETAILED DESCRIPTION

[0018] To make the object, technical solutions and advantages of the present application clearer, the present application is described in detail below with reference to the drawings and specific embodiments.

[0019] Here, it should be noted that, in order to avoid the unnecessary details from obscuring the present application, only the structures and / or processing steps closely related to the solutions of the present application are shown in the drawings, and other details not closely related to the present application are omitted.

[0020] In addition, it should be noted that the term "comprise", "include" or any other variant thereof is intended to cover non-exclusive inclusion, so that the process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or device.

[0021] As Figure 1 and Figure 2 The present application discloses a power supply device, which comprises a PCB board, and a power supply circuit arranged on the PCB board, wherein the power supply circuit comprises a rectification filter circuit, a transformer and a control circuit, and the transformer is arranged between the rectification filter circuit and the control circuit and is used for connecting the rectification filter circuit and the control circuit respectively.

[0022] As Figure 2 The rectification filter circuit comprises a bridge rectifier DB1, a first capacitor C1, a second capacitor C2 and an inductor L1 which are connected with each other, the first capacitor C1 and the second capacitor C2 are connected in parallel with two output terminals of the bridge rectifier DB1 respectively, one output terminal of the bridge rectifier DB1 is further connected with one end of the inductor L1, and the other end of the second capacitor C2 is grounded. The first capacitor C1 is used for filtering the alternating current signal input into the rectification filter circuit and transmitting the filtered alternating current signal to one side of the input terminal of the inductor L1, i.e. the side connected with the inductor L1, the second capacitor C2 is used for filtering the direct current signal output from the output terminal of the inductor L1, i.e. the side connected with the inductor L1. Of course, the rectification filter circuit can comprise the first capacitor C1 and the second capacitor C2 at the same time, and at this time, the first capacitor C1, the second capacitor C2 and the inductor L1 form a π-type filter which is used for filtering the alternating current signal input into the rectification filter circuit, so that the output voltage of the bridge rectifier is more stable. In other embodiments of the present application, a fuse resistor F1 is further arranged at the input terminal of the rectification filter circuit.

[0023] The power supply circuit further comprises a step-down conversion circuit (BUCK topology circuit) which comprises a power diode and an output capacitor and can realize bidirectional DC / DC conversion.

[0024] The transformer comprises a primary winding Np, a secondary winding Ns and an auxiliary winding Na, and is used for reducing the rectification filter voltage output by the rectification filter circuit, wherein the primary winding Np is connected with the output terminal of the rectification filter circuit. In the embodiment, the number of turns of the primary winding Np is 45T, the number of turns of the secondary winding Ns is 3T, and the number of turns of the auxiliary winding Na is 4T, which can be set according to requirements and is not limited herein.

[0025] The control circuit includes a primary-side control circuit and a secondary-side feedback circuit. The primary-side control circuit is connected to the auxiliary winding, and the secondary-side feedback circuit is connected to the secondary winding. The primary-side control circuit and the secondary-side feedback circuit can be fabricated as integrated circuits and integrated into a chip, or they can be partially or fully integrated, depending on the components and the actual application.

[0026] like Figure 1 As shown, the primary-side control circuit is connected to the auxiliary winding. The primary-side control circuit includes a control chip U2 for controlling the power supply circuit. The auxiliary winding supplies power to the primary-side control circuit and the control chip U2. The control chip U2 includes a first pin and a second pin connected to the auxiliary winding. The first pin and the second pin are connected to the same side of the auxiliary winding, and the other side of the auxiliary winding is grounded, so that the auxiliary winding is coupled to the transformer. The first pin is the power supply pin VCC, through which the auxiliary winding supplies power to the control chip. The second pin is the auxiliary winding detection pin VSD, used to detect the voltage of the auxiliary winding and feed this voltage information back to the control chip U2. It should be noted that the control chip U2 also has an overvoltage protection device connected to the second pin. The overvoltage protection device can be set with an overvoltage threshold to prevent the power supply from inputting excessively high voltage to sensitive devices. If the voltage detected by the second pin exceeds the threshold, the power supply output will be shut off, thereby protecting the device from damage due to excessive voltage.

[0027] When the control chip U2 does not have short-circuit protection, the auxiliary winding voltage gradually decreases as the forward current of the freewheeling diode decreases, thus achieving turn-on. However, when the control chip U2 is under constant high voltage output, taking an output voltage of 220V and an auxiliary winding voltage of 20V as an example, the output winding Ns / auxiliary winding Na = 11. If a Schottky diode is used at this time, the auxiliary winding voltage corresponding to the MOS turn-off moment is 500mV / 11 = 45mV. The chip cannot detect the zero current detection rising edge threshold of 10mV higher than that of the auxiliary winding, and the chip does not switch on or off. If an ultrafast recovery diode is used at this time, the auxiliary winding voltage is 1000mV / 11 = 91mV. 91mV satisfies both the zero-current detection rising edge threshold condition of 55mV + 10mV and the falling edge threshold condition of rapidly decreasing to 55mV. The demagnetization time is very short, and the control chip U2 operates with the minimum turn-off time Toff_min, which is approximately 7.8µs. Adding the 250ns leading-edge blanking TLEB time, the chip's switching frequency fsw is 1 / 8.05µs = 125kHz. At this point, the MOSFET suffers from a high switching frequency and significant cross-loss during switching.

[0028] As a preferred embodiment of the present application, a compensation resistor R60 is arranged between the first pin and the second pin of the control chip U2 to solve the loss problem of the MOS transistor. At this time, the voltage of the second pin is equal to the voltage of the auxiliary winding plus the voltage of the compensation resistor R60. By this arrangement, the voltage of the second pin during demagnetization of the inductor is increased, the demagnetization time of the inductor current is prolonged, and the switching frequency during short circuit is reduced to realize short circuit protection. In the present embodiment, the resistance of the compensation resistor R60 can be 4-5MΩ, and preferably 4.7MΩ. Too large or too small resistance of the compensation resistor R60 will cause a restart problem.

[0029] The output voltage detection circuit is further arranged between the primary side control circuit and the secondary side feedback circuit. The output voltage detection circuit comprises a controllable precision voltage stabilizing chip U3, a resistor R51, a resistor R55 and a photoelectric coupler U4. The photoelectric coupler U4 is connected to one end of the resistor R51. The other end of the resistor R51 is connected to one end of the resistor R55 and the reference electrode of the controllable precision voltage stabilizing chip U3. The other end of the resistor R55 and the anode of the controllable precision voltage stabilizing chip U3 are both grounded. The 2nd pin of the photoelectric coupler U4 is connected to the cathode of the controllable precision voltage stabilizing chip U3. The 3rd pin of the photoelectric coupler U4 is grounded. The 4th pin of the photoelectric coupler U4 is connected to the primary side control circuit. The output voltage is sampled by the resistors R51 and R55, and is fed back to the control chip U2 through the photoelectric coupler U4, so that the output voltage can be effectively adjusted to be constant.

[0030] In summary, by arranging the compensation resistor, the voltage of the second pin during output short circuit is increased, the demagnetization time of the control chip is increased, the working frequency and the power consumption during short circuit are reduced, and the loss of the MOS transistor of the control chip without short circuit protection mechanism is avoided.

[0031] The above embodiments are only used to illustrate the technical solutions of the present application but not limit the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the spirit and scope of the present application.

Claims

1. A power supply circuit, characterized by: The power supply circuit comprises a rectifier filter circuit, a transformer and a control circuit, the transformer comprises an auxiliary winding, the control circuit comprises a primary side control circuit connected with the auxiliary winding, the primary side control circuit comprises a control chip for controlling the power supply circuit, the control chip comprises a first pin and a second pin connected with the auxiliary winding, the first pin is a power supply pin VCC, the auxiliary winding supplies power for the control chip through the first pin, the second pin is an auxiliary winding detection pin VSD, used for detecting the voltage of the auxiliary winding and feeding back voltage information to the control chip, a compensation resistor is connected between the first pin and the second pin, the compensation resistor is used for increasing the voltage of the second pin to protect the control chip; the control circuit further comprises a secondary side feedback circuit, and an output voltage detection circuit is further arranged between the primary side control circuit and the secondary side feedback circuit, the output voltage detection circuit comprises a controllable precision voltage stabilizing chip, a resistor R51, a resistor R55 and an optoelectronic coupler, one end of the resistor R51 is connected with the optoelectronic coupler, the other end of the resistor R51 is connected with one end of the resistor R55 and a reference electrode of the controllable precision voltage stabilizing chip, the other end of the resistor R55 and an anode of the controllable precision voltage stabilizing chip are both grounded, and the optoelectronic coupler is further connected with the primary side control circuit, the output voltage is sampled through the resistor R51 and the resistor R55, and the output voltage is fed back to the control chip through the optoelectronic coupler, so that the output voltage is adjusted to be constant.

2. The power supply circuit of claim 1, wherein: The resistance value of the compensation resistor is between 4-5MΩ.

3. The power supply circuit of claim 1, wherein: The rectifier filter circuit comprises a bridge rectifier and a filter, and the filter is used for filtering the output voltage of the bridge rectifier.

4. The power supply circuit of claim 3, wherein: The filter comprises a first capacitor, a second capacitor and an inductor, the first capacitor and the second capacitor are respectively arranged in parallel at two output ends of the bridge rectifier, and the inductor is connected with one of the output ends of the bridge rectifier.

5. The power supply circuit of claim 1, wherein: An insurance resistor is arranged at the input end of the rectifier filter circuit.

6. The power supply circuit of claim 1, wherein: The power supply circuit further comprises a step-down conversion circuit, and the step-down conversion circuit comprises a power diode and an output capacitor.

7. The power supply circuit of claim 1, wherein: The transformer further comprises a primary winding and a secondary winding, and the primary winding is connected with the output end of the rectifier filter circuit.

8. The power supply circuit of claim 7, wherein: The secondary side feedback circuit is connected with the secondary winding.

9. The power supply circuit of claim 8, wherein: The optoelectronic coupler is further connected with a cathode of the controllable precision voltage stabilizing chip.

10. A power supply device characterized by comprising: The power supply circuit has any one of the power supply circuits in claims 1-9.

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