Output overvoltage protection circuit

Abstract

The utility model relates to an output overvoltage protection circuit, which is characterized in that a first voltage division sampling circuit samples output voltage, when the sampled voltage does not reach a first overvoltage point, a first group of overvoltage sampling loops reach a pre-overvoltage state, and when the sampled voltage exceeds the first overvoltage point, a second group of overvoltage sampling loops are triggered; and the second partial voltage sampling circuit samples the output voltage, when the sampled voltage does not reach a second overvoltage point, the second group of overvoltage sampling loops reach a pre-overvoltage state, and when the sampled voltage exceeds the second overvoltage point, the second group of overvoltage sampling loops transmit an overvoltage signal to the main control chip U6 to realize overvoltage protection. The overvoltage points of the first group of overvoltage sampling loops and the second group of overvoltage sampling loops are different and form a progressive relationship, and overvoltage signals are fed back to the main control chip only after the two stages of overvoltage sampling loops are triggered, so that output abnormity caused by false triggering of the overvoltage circuit is avoided, the anti-interference capability of the circuit is enhanced, and the stability of the circuit is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of electronic circuits, in particular to an output overvoltage protection circuit. Background Art

[0002] For AC-DC switching power supplies, in order to protect the safety of their own components, subsequent circuits or electrical appliances, it is generally necessary to limit the output voltage and provide an overvoltage protection circuit.

[0003] Commonly used protection circuits include: the output voltage is detected by the auxiliary winding and then sent to the primary main control chip; a single overvoltage loop composed of a reference chip and an optocoupler, the overvoltage loop feeds back the overvoltage signal to the primary side; or the output voltage is directly sampled and sent to the secondary microcontroller to control the power supply to stop output. The above schemes all have their own disadvantages. The use of auxiliary windings will increase the difficulty of transformer design and is related to the coupling degree problem; the single overvoltage loop is relatively sensitive and prone to false triggering; and the solution of microcontroller sampling is relatively expensive and is usually used in high-power or complex function power supplies. Utility Model Content

[0004] In view of this, it is necessary to provide an output overvoltage protection circuit with strong anti-disturbance capability and simple circuit structure.

[0005] An output overvoltage protection circuit includes two groups of overvoltage sampling loops connected in series and a main control chip U6, the two groups of overvoltage sampling loops have different overvoltage points, the two groups of overvoltage sampling loops include a first group of overvoltage sampling loops and a second group of overvoltage sampling loops, the overvoltage point of the first group of overvoltage sampling loops is lower than the overvoltage point of the second group of overvoltage sampling loops; when both groups of overvoltage sampling loops are triggered, the overvoltage signal is transmitted to the protection pin of the main control chip U6 to realize overvoltage protection of the circuit.

[0006] Preferably, the first group of overvoltage sampling loops includes a first reference chip U1, a first optical coupler OT1 and a first voltage-dividing sampling circuit, the first voltage-dividing sampling circuit is connected to the voltage output end, the first voltage-dividing sampling circuit includes a sixth resistor R6, a twelfth resistor R12 and an eleventh resistor R11 connected in series, and a tenth resistor R10 is connected in parallel with the eleventh resistor R11; both ends of the tenth resistor R10 are also connected to the reference end and the anode end of the first reference chip U1 respectively, the anode end of the first reference chip U1 is grounded SGND, and the cathode end of the first reference chip U1 is connected to the The cathode of the light-emitting diode OT1-B, the anode of the light-emitting diode OT1-B of the first optocoupler OT1 is connected to the voltage output end through the thirteenth resistor R13; the connection point between the cathode end of the first reference chip U1 and the cathode of the light-emitting diode OT1-B of the first optocoupler OT1 is connected to the connection point between the twelfth resistor R12 and the eleventh resistor R11 through the first capacitor C1 and the fifth resistor R5 connected in series; the connection point between the cathode end of the first reference chip U1 and the cathode of the light-emitting diode OT1-B of the first optocoupler OT1 is also connected to the voltage output end through the second resistor R2.

[0007] Preferably, the second group of overvoltage sampling loops includes a second reference chip U2, a second optocoupler OT2 and a second voltage-dividing sampling circuit, the second voltage-dividing sampling circuit is connected to the voltage output end, the second voltage-dividing sampling circuit includes a fourth resistor R4, an eighth resistor R8 and a seventh resistor R7 connected in series, and a ninth resistor R9 is connected in parallel with the seventh resistor R7; the two ends of the ninth resistor R9 are also respectively connected to the reference end and the anode end of the second reference chip U2, the anode end of the second reference chip U2 is grounded SGND, the cathode end of the second reference chip U2 is connected to the emitter of the phototransistor OT1-A of the first optocoupler OT1, the collector of the phototransistor OT1-A of the first optocoupler OT1 is connected to the cathode of the light-emitting diode OT2-B of the second optocoupler OT2, and the anode of the light-emitting diode OT2-B of the second optocoupler OT2 is connected to the voltage output end through the first resistor R1; the connection point between the cathode end of the second reference chip U2 and the emitter of the phototransistor OT1-A of the first optocoupler OT1 is also connected to the voltage output end through the third resistor R3.

[0008] Preferably, the collector and emitter of the phototransistor OT2-A of the second optical coupler OT2 are respectively connected to the twenty-fourth pin and the eighteenth pin of the main control chip U6, and the eighteenth pin of the main control chip U6 is connected to the primary ground PGND.

[0009] In the above-mentioned output overvoltage protection circuit, the first voltage-dividing sampling circuit samples the output voltage. When the sampled voltage does not reach the first overvoltage point, the first group of overvoltage sampling loops reaches the pre-overvoltage state. When the sampled voltage exceeds the first overvoltage point, the second group of overvoltage sampling loops is triggered; the second voltage-dividing sampling circuit samples the output voltage. When the sampled voltage does not reach the second overvoltage point, the second group of overvoltage sampling loops reaches the pre-overvoltage state. When the sampled voltage exceeds the second overvoltage point, the second group of overvoltage sampling loops transmits the overvoltage signal to the main control chip U6 to achieve overvoltage protection. The overvoltage points of the first group of overvoltage sampling loops and the second overvoltage sampling loops are different, and form a progressive relationship. Only after both levels of overvoltage sampling loops are triggered, the overvoltage signal is fed back to the main control chip to avoid output abnormalities caused by false triggering of the overvoltage circuit, enhance the anti-interference ability of the circuit, and improve the stability of the circuit. The circuit structure of the utility model is simple, easy to implement, low cost, and easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a circuit structure diagram of the output overvoltage protection circuit of the embodiment of the utility model. DETAILED DESCRIPTION

[0011] The present invention will be described in detail below with reference to specific embodiments and accompanying drawings.

[0012] See also Figure 1 , shows an output overvoltage protection circuit, including two groups of overvoltage sampling loops connected in series and a main control chip U6, the two groups of overvoltage sampling loops have different overvoltage points, the two groups of overvoltage sampling loops include a first group of overvoltage sampling loops and a second group of overvoltage sampling loops, the overvoltage point of the first group of overvoltage sampling loops is lower than the overvoltage point of the second group of overvoltage sampling loops; when both groups of overvoltage sampling loops are triggered, the overvoltage signal is transmitted to the protection pin of the main control chip U6 to realize overvoltage protection of the circuit.

[0013] Specifically, the first group of overvoltage sampling loops has a first overvoltage point, the second group of overvoltage sampling loops has a second overvoltage point, the first overvoltage point is lower than the second overvoltage point, and the first overvoltage point and the second overvoltage point are in a progressive relationship. When the sampling voltage of the first group of overvoltage sampling loops exceeds the first overvoltage point, the second group of overvoltage sampling loops is triggered, so that the second group of overvoltage sampling loops reaches a pre-overvoltage state, and only when the sampling voltage of the second group of overvoltage sampling loops also exceeds the second overvoltage point, the overvoltage signal is transmitted to the main control chip U6.

[0014] Preferably, the first group of overvoltage sampling loops includes a first reference chip U1, a first optical coupler OT1 and a first voltage-dividing sampling circuit, the first voltage-dividing sampling circuit is connected to the voltage output end, the first voltage-dividing sampling circuit includes a sixth resistor R6, a twelfth resistor R12 and an eleventh resistor R11 connected in series, and a tenth resistor R10 is connected in parallel with the eleventh resistor R11; both ends of the tenth resistor R10 are also connected to the reference end and the anode end of the first reference chip U1 respectively, the anode end of the first reference chip U1 is grounded SGND, and the cathode end of the first reference chip U1 is connected to the The cathode of the light-emitting diode OT1-B, the anode of the light-emitting diode OT1-B of the first optocoupler OT1 is connected to the voltage output end through the thirteenth resistor R13; the connection point between the cathode end of the first reference chip U1 and the cathode of the light-emitting diode OT1-B of the first optocoupler OT1 is connected to the connection point between the twelfth resistor R12 and the eleventh resistor R11 through the first capacitor C1 and the fifth resistor R5 connected in series; the connection point between the cathode end of the first reference chip U1 and the cathode of the light-emitting diode OT1-B of the first optocoupler OT1 is also connected to the voltage output end through the second resistor R2.

[0015] Specifically, the first voltage-dividing sampling circuit composed of the sixth resistor R6, the twelfth resistor R12 and the eleventh resistor R11 is used for voltage sampling of the first group of overvoltage sampling loops.

[0016] Specifically, the tenth resistor R10 transmits the sampled voltage to the first reference chip U1 for comparison.

[0017] Specifically, the fifth resistor R5 and the first capacitor C1 form a compensation circuit, which can effectively attenuate disturbances and reduce system sensitivity.

[0018] Specifically, the first reference chip U1, the first optical coupler OT1, the thirteenth resistor R13 and the second resistor R2 are connected to realize the current limiting power supply of the first reference chip U1 and the first reference chip U1 to adjust the light emission of the light emitting diode OT1-B of the first optical coupler OT1.

[0019] Preferably, the second group of overvoltage sampling loops includes a second reference chip U2, a second optocoupler OT2 and a second voltage-dividing sampling circuit, the second voltage-dividing sampling circuit is connected to the voltage output end, the second voltage-dividing sampling circuit includes a fourth resistor R4, an eighth resistor R8 and a seventh resistor R7 connected in series, and a ninth resistor R9 is connected in parallel with the seventh resistor R7; the two ends of the ninth resistor R9 are also respectively connected to the reference end and the anode end of the second reference chip U2, the anode end of the second reference chip U2 is grounded SGND, the cathode end of the second reference chip U2 is connected to the emitter of the phototransistor OT1-A of the first optocoupler OT1, the collector of the phototransistor OT1-A of the first optocoupler OT1 is connected to the cathode of the light-emitting diode OT2-B of the second optocoupler OT2, and the anode of the light-emitting diode OT2-B of the second optocoupler OT2 is connected to the voltage output end through the first resistor R1; the connection point between the cathode end of the second reference chip U2 and the emitter of the phototransistor OT1-A of the first optocoupler OT1 is also connected to the voltage output end through the third resistor R3.

[0020] Specifically, the second voltage-dividing sampling circuit composed of the fourth resistor R4, the eighth resistor R8 and the seventh resistor R7 is used for voltage sampling of the second group of overvoltage sampling loops.

[0021] Specifically, the ninth resistor R9 transmits the sampled voltage to the second reference chip U2 for comparison.

[0022] Specifically, the second reference chip U2, the phototransistor OT1-A of the first optocoupler OT1, the light-emitting diode OT2-B of the second optocoupler OT2, the first resistor R1 and the third resistor R3 are connected to realize the following control functions: current-limited power supply of the second reference chip U2, adjustment of the light emission of the second optocoupler OT2 by the second reference chip U2, and control of the second optocoupler OT2 to be turned on or off by the first optocoupler OT1.

[0023] Preferably, the collector and emitter of the phototransistor OT2-A of the second optical coupler OT2 are respectively connected to the twenty-fourth pin and the eighteenth pin of the main control chip U6, and the eighteenth pin of the main control chip U6 is connected to the primary ground PGND.

[0024] Specifically, in this embodiment, the main control chip U6 uses a dedicated power IC chip integrating PFC and LLC. The 24th pin is a boost voltage sampling pin SNSBOOST, which is used to sample the primary PFC output voltage and compare it with the 2.5V reference voltage, and to adjust the stability and abnormal protection of the primary PFC output voltage; the 18th pin is a signal ground potential pin SGND, which is used to provide a reference ground potential for the signal circuit of the main control chip U6.

[0025] To avoid the main control chip U6 operating at a low PFC voltage, when the sampling voltage of the SNSBOOST pin is lower than the set undervoltage point of the main control chip U6, for example, the undervoltage voltage is 1.6V, the undervoltage protection is triggered, the main control chip U6 stops driving the DC-DC circuit, and the power supply stops outputting; when the sampling voltage of the SNSBOOST pin is higher than the set restart point of the main control chip U6, for example, the restart voltage is 2.3V, the main control chip U6 starts driving the DC-DC circuit, and the power supply restarts.

[0026] Specifically, the phototransistor OT2-A of the second optical coupler OT2 transmits the overvoltage signal to the main control chip U6.

[0027] In this embodiment, the normal output voltage of the output voltage network is +15V. When the output voltage reaches 17V, it indicates that the power supply has reached the pre-overvoltage state. The first group of overvoltage sampling loops is activated, and the output voltage is divided by the sixth resistor R6, the twelfth resistor R12 and the eleventh resistor R11 and the tenth resistor R10 in parallel to obtain a 2.5V voltage; after comparison, the internal circuit of the first reference chip U1 reduces the impedance between its cathode and anode from high impedance to low impedance; at the same time, the light-emitting diode OT1-B of the first optical coupler OT1 emits light, driving the phototransistor OT1-A of the first optical coupler OT1 to turn on. The resistance values ​​of the sixth resistor R6 and the twelfth resistor R12 are 10KΩ and 20KΩ respectively, and the resistance values ​​of the tenth resistor R10 and the eleventh resistor R11 are 28KΩ and 6.2KΩ respectively; the first capacitor C1 and the fifth resistor R5 form a loop compensation RC, where the first capacitor C1 is 0.22uF, and the resistance value of the fifth resistor R5 is 2.4KΩ; the thirteenth resistor R13 and the second resistor R2 are current limiting resistors and bias resistors respectively, where 2.4KΩ and 5.1KΩ are selected according to the output voltage.

[0028] At this time, the second set of overvoltage sampling loops has not yet acted, but is only in a pre-conduction state; any unreliable overvoltage signal will be filtered out in the first set of overvoltage sampling loops, and will not cause the second optocoupler OT2 of the second set of loops to turn on, so it will not cause the twenty-fourth pin of the main control chip U6 to fluctuate, and the output will remain stable.

[0029] When the actual output voltage reaches 18V, it indicates that the power supply is in an overvoltage state. The output voltage is divided by the fourth resistor R4, the eighth resistor R8, and the seventh resistor R7 and the ninth resistor R9 in parallel to obtain a 2.5V voltage. After the second reference chip U2 internal reference is compared with it, the impedance between its cathode and anode is reduced from the original high impedance to low impedance; at the same time, the light-emitting diode OT2-B of the second optical coupler OT2 is turned on to emit light, and the photosensitive transistor OT2-A of the second optical coupler OT2 is turned on, and the twenty-fourth pin of the main control chip U6 is set low to achieve overvoltage protection. The resistance values ​​of the fourth resistor R4 and the eighth resistor R8 are 10KΩ and 20KΩ respectively, the resistance values ​​of the seventh resistor R7 and the ninth resistor R9 are 6.2KΩ and 22KΩ respectively, and the first resistor R1 and the third resistor R3 are current limiting resistors and bias resistors respectively, and their resistance values ​​are 2.4KΩ and 5.1KΩ respectively.

[0030] Specifically, in this embodiment, the resistance values ​​of the ninth resistor R9 and the tenth resistor R10 are different, so that the sampling voltages obtained in the voltage-dividing sampling circuit are different, so that the two groups of overvoltage sampling loops have different overvoltage points. At the same time, the conduction of the second group of overvoltage sampling loops is controlled by the first optical coupler OT1 in the first group of overvoltage sampling loops. Thus, a two-stage progressive control of the overvoltage protection circuit is realized.

[0031] Specifically, the output overvoltage protection circuit in this embodiment integrates two groups of control loops composed of reference ICs and optocouplers, sets two progressive overvoltage voltages, and the overvoltage point of the first group of overvoltage sampling loops is lower and has loop compensation to filter out some interference signals. When the first group of overvoltage sampling loops is triggered, the signal is fed back to the second group of overvoltage sampling loops to make it reach a pre-overvoltage state. When the higher overvoltage point of the second group of overvoltage sampling loops is also triggered, the protection signal is fed back to the main control chip to lower its protection pin. Overvoltage protection is achieved only when both groups of overvoltage sampling loops are triggered.

[0032] The first group of overvoltage sampling loops controls whether the optocouplers of the second group of overvoltage sampling loops are turned on or off through optocouplers. The overvoltage point of the first group of overvoltage sampling loops is lower and has loop compensation.

[0033] Only when both sets of overvoltage sampling loops are triggered, the overvoltage signal is fed back to the protection pin of the main control chip U6, setting it low to achieve the purpose of overvoltage protection.

[0034] This technical solution can ensure that the level of the overvoltage pin of the control main control chip is stable when the overvoltage voltage is not actually output, thereby avoiding output abnormality caused by false triggering of the overvoltage circuit.

[0035] In the above-mentioned output overvoltage protection circuit, the first voltage-dividing sampling circuit samples the output voltage. When the sampled voltage does not reach the first overvoltage point, the first group of overvoltage sampling loops reaches the pre-overvoltage state. When the sampled voltage exceeds the first overvoltage point, the second group of overvoltage sampling loops is triggered; the second voltage-dividing sampling circuit samples the output voltage. When the sampled voltage does not reach the second overvoltage point, the second group of overvoltage sampling loops reaches the pre-overvoltage state. When the sampled voltage exceeds the second overvoltage point, the second group of overvoltage sampling loops transmits the overvoltage signal to the main control chip U6 to achieve overvoltage protection. The overvoltage points of the first group of overvoltage sampling loops and the second overvoltage sampling loops are different, and form a progressive relationship. Only after both levels of overvoltage sampling loops are triggered, the overvoltage signal is fed back to the main control chip to avoid output abnormalities caused by false triggering of the overvoltage circuit, enhance the anti-interference ability of the circuit, and improve the stability of the circuit. The circuit structure of the utility model is simple, easy to implement, low cost, and easy to promote.

[0036] It should be noted that the present invention is not limited to the above-mentioned embodiments. According to the creative spirit of the present invention, those skilled in the art may also make other changes. These changes made according to the creative spirit of the present invention should be included in the scope of protection required by the present invention.

Claims

1. An output overvoltage protection circuit, characterized in that: It includes two groups of overvoltage sampling loops connected in series and a main control chip U6, the two groups of overvoltage sampling loops have different overvoltage points, the two groups of overvoltage sampling loops include a first group of overvoltage sampling loops and a second group of overvoltage sampling loops, the overvoltage point of the first group of overvoltage sampling loops is lower than the overvoltage point of the second group of overvoltage sampling loops; when the two groups of overvoltage sampling loops are triggered, the overvoltage signal is transmitted to the protection pin of the main control chip U6 to realize overvoltage protection of the circuit.

2. The output overvoltage protection circuit according to claim 1, characterized in that: The first group of overvoltage sampling loops includes a first reference chip U1, a first optical coupler OT1 and a first voltage-dividing sampling circuit, the first voltage-dividing sampling circuit is connected to the voltage output terminal, the first voltage-dividing sampling circuit includes a sixth resistor R6, a twelfth resistor R12 and an eleventh resistor R11 connected in series, and a tenth resistor R10 is connected in parallel with the eleventh resistor R11; both ends of the tenth resistor R10 are also connected to the reference terminal and the anode terminal of the first reference chip U1 respectively, the anode terminal of the first reference chip U1 is grounded SGND, and the cathode terminal of the first reference chip U1 is connected to the light-emitting terminal of the first optical coupler OT1 The cathode of the diode OT1-B, the anode of the light-emitting diode OT1-B of the first optocoupler OT1 is connected to the voltage output end through the thirteenth resistor R13; the connection point between the cathode end of the first reference chip U1 and the cathode of the light-emitting diode OT1-B of the first optocoupler OT1 is connected to the connection point between the twelfth resistor R12 and the eleventh resistor R11 through the first capacitor C1 and the fifth resistor R5 connected in series; the connection point between the cathode end of the first reference chip U1 and the cathode of the light-emitting diode OT1-B of the first optocoupler OT1 is also connected to the voltage output end through the second resistor R2.

3. The output overvoltage protection circuit according to claim 2, characterized in that: The second group of overvoltage sampling loops includes a second reference chip U2, a second optocoupler OT2 and a second voltage-dividing sampling circuit, the second voltage-dividing sampling circuit is connected to the voltage output end, the second voltage-dividing sampling circuit includes a fourth resistor R4, an eighth resistor R8 and a seventh resistor R7 connected in series, and a ninth resistor R9 is connected in parallel with the seventh resistor R7; the two ends of the ninth resistor R9 are also respectively connected to the reference end and the anode end of the second reference chip U2, the anode end of the second reference chip U2 is grounded SGND, the cathode end of the second reference chip U2 is connected to the emitter of the phototransistor OT1-A of the first optocoupler OT1, the collector of the phototransistor OT1-A of the first optocoupler OT1 is connected to the cathode of the light-emitting diode OT2-B of the second optocoupler OT2, and the anode of the light-emitting diode OT2-B of the second optocoupler OT2 is connected to the voltage output end through the first resistor R1; the connection point between the cathode end of the second reference chip U2 and the emitter of the phototransistor OT1-A of the first optocoupler OT1 is also connected to the voltage output end through the third resistor R3.

4. The output overvoltage protection circuit according to claim 3, characterized in that: The collector and emitter of the phototransistor OT2-A of the second optical coupler OT2 are respectively connected to the 24th pin and the 18th pin of the main control chip U6, and the 18th pin of the main control chip U6 is connected to the primary ground PGND.

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