Overvoltage protection circuit

Abstract

The invention belongs to the technical field of power supply, and particularly relates to an overvoltage protection circuit. The input end is used for being connected with a power adapter, the output end is used for being connected with a load, the first switching device is connected between the input end and the output end in series, the control unit is connected with the controlled end of the first switching device, and the control unit is used for detecting whether the voltage of the output end of the power adapter exceeds a voltage threshold value or not. The first switching device is controlled to be switched off under the condition that a voltage threshold value is exceeded, the first switching device is controlled to be switched on under the condition that the voltage threshold value is not exceeded, the voltage threshold value is larger than the rated voltage of the load, the difference between the voltage threshold value and the rated voltage of the load is smaller than a voltage difference threshold value, and the voltage difference threshold value is larger than 0. By adopting the overvoltage protection circuit provided by the invention, the connection between the power adapter and the load can be cut off at the first time under the condition that the power adapter of which the output end voltage is greater than the rated voltage of the load is used for charging the load, so that the problem that the load is burnt out due to overvoltage is avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of power supply, and in particular relates to an overvoltage protection circuit. Background Art

[0002] Power adapters are a common way to power electrical equipment in daily life. The power supply voltages of devices powered by adapters are commonly DC12V, DC5V, and fast charging. The power plugs include Type-C, Micro-USB, and DC plugs. For Type-C power supply, after the plug is inserted, a data connection is first established through the most standard USB power supply (5V / 500mA). The two sides determine the charging voltage and charging current capacity through the protocol, so there is generally no problem of power supply mismatch causing equipment damage. However, for conventional DC12V and DC5V chargers, if the DC12V power adapter is accidentally inserted into the DC5V charging port, there is a high probability that the device will be burned out. Summary of the invention

[0003] The object of the present invention is to provide an overvoltage protection circuit to solve the problem that the load is burned out due to overvoltage when a power adapter whose output voltage is greater than the rated voltage of the load is used to power the load.

[0004] In order to solve the above technical problems, the present invention provides an overvoltage protection circuit, including an input end for connecting to a power adapter, an output end for connecting to a load, a first switching device connected in series between the input end and the output end, and a control unit connected to a controlled end of the first switching device, wherein the control unit is used to detect whether the voltage at the output end of the power adapter exceeds a voltage threshold, and control the first switching device to disconnect when the voltage threshold is exceeded, and control the first switching device to close when the voltage threshold is not exceeded, wherein the voltage threshold is greater than the rated voltage of the load and the difference between the voltage threshold and the rated voltage of the load is less than a voltage difference threshold, and the voltage difference threshold is greater than 0.

[0005] The beneficial effect is that by adopting the overvoltage protection circuit of the present invention, when a power adapter with an output voltage greater than the rated voltage of the load is used to charge the load, the connection between the power adapter and the load can be disconnected immediately, thereby avoiding the problem of the load being burned out due to overvoltage.

[0006] Preferably, the control unit includes a first voltage-stabilizing diode, a second switching device and a third switching device; the first voltage-stabilizing diode is connected in series between the input terminal and the ground, its anode is grounded through a grounding resistor and its reverse breakdown voltage is equal to the voltage threshold; the second switching device is connected in series between the controlled terminal of the third switching device and the ground, the controlled terminal of the second switching device is connected to the anode of the first voltage-stabilizing diode, and is used to be turned on when the first voltage-stabilizing diode is broken down, so that the third switching device is turned on, and is also used to be turned off when the first voltage-stabilizing diode is not broken down, so that the third switching device is turned off; the third switching device is connected in series between the input terminal and the controlled terminal of the first switching device, and the controlled terminal of the first switching device is grounded, so that after the first switching device is connected to the power adapter, the first switching device is in the off state when the third switching device is in the on state, and the first switching device is in the on state when the third switching device is in the off state.

[0007] Preferably, the overvoltage protection circuit further includes a first capacitor, which is connected in parallel across two ends of the third switch device.

[0008] Its beneficial effect is: by connecting the first capacitor in parallel at both ends of the third switching device, due to the charging effect of the capacitor, the potential of the controlled end of the first switching device can be gradually reduced from the voltage value of the output end of the power adapter to 0, and the potential of the end of the first switching device connected to the input end is equal to the voltage of the output end of the power adapter, so that the first switching device is delayed in turning on, thereby realizing circuit soft start, and when the voltage level of the power adapter is too high, it can avoid powering on too quickly, causing the subsequent load circuit to be damaged before the control unit is activated.

[0009] Preferably, the output end is grounded through a second voltage stabilizing diode, the anode of the second voltage stabilizing diode is grounded, and the reverse breakdown voltage of the second voltage stabilizing diode is equal to the voltage threshold.

[0010] The beneficial effect is that by setting the second voltage stabilizing diode, when the control unit fails and the voltage level of the voltage adapter connected to the load is too high, the voltage connected to the subsequent load can be clamped to a very small value, thereby protecting the load and further improving the reliability of the overvoltage protection circuit.

[0011] Preferably, a current-limiting resistor is connected in series between the controlled end of the third switching device and the second switching device.

[0012] Preferably, the first switch device is a P-type MOS transistor, the second switch device is an NPN-type transistor, and the third switch device is a PNP-type transistor. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1It is a circuit principle diagram of the overvoltage protection circuit of the present invention. DETAILED DESCRIPTION

[0014] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0015] Overvoltage protection circuit embodiment:

[0016] like Figure 1 As shown, the overvoltage protection circuit of the present invention includes a first switching device Q1 used to be connected in series between the output end of the power adapter and the load, and a control unit connected to the controlled end of the first switching device, the control unit is used to detect whether the voltage at the output end of the power adapter exceeds a voltage threshold, and control the first switching device to be disconnected when the threshold is exceeded, and keep the first switching device closed when the voltage threshold is not exceeded. The voltage threshold is greater than the rated voltage of the load and the difference between the voltage threshold and the rated voltage of the load is less than the voltage difference threshold; the first end of the first switching device is used to connect to the output end of the power adapter, and the second end thereof is used to connect to the load.

[0017] The control unit includes a first voltage zener diode D1, a second switch device Q2, and a third switch device Q3; the reverse breakdown voltage of the first voltage zener diode D1 is equal to the voltage threshold, the cathode of the first voltage zener diode D1 is connected to the first end of the first switch device Q1, and the anode of the first voltage zener diode D3 is grounded through a first resistor R1; the first end of the third switch device is connected to the first end of the first switch device, the second end of the third switch device is connected to the controlled end of the first switch device and grounded, the controlled end of the third switch device is connected in series with a fourth resistor R4 and the second switch device Q2 in sequence and then grounded, and the two ends of the third switch device are connected in parallel with a first capacitor C1; the controlled end of the second switch device Q2 is connected to the anode of the first voltage zener diode D1 through a second resistor R2, and is used to be turned on when the first voltage zener diode D1 is broken down, and the controlled end of the second switch device is grounded through a third resistor R3. The second end of the first switch device Q1 is connected to the cathode of the second voltage zener diode D3, the anode of the second voltage zener diode D3 is grounded, and the reverse breakdown voltage of the second voltage zener diode D3 is equal to the voltage threshold.

[0018] The first switch device, the second switch device and the third switch device can all be transistors or MOS tubes. Preferably, in this embodiment, the first switch device is a P-type MOS tube, the second switch device is an NPN-type transistor, and the third switch device is a PNP-type transistor. At this time, the source of the first switch device is used to connect to the output end of the power adapter, and the drain is used to connect to the load; the emitter of the second switch device is grounded, and its collector is connected to the base of the third switch device through a first resistor, the collector of the third switch device is connected to the gate of the first switch device and is grounded through a fifth resistor, and the emitter of the third switch device is connected to the source of the first switch device.

[0019] In this embodiment, it is assumed that the rated supply voltage of the load is 5V, the voltage threshold can be set to 5.5V, the P-type MOS tube Q1 selects a P-type MOS tube with a turn-on voltage less than 5V, and the reverse breakdown voltages of the first zener diode and the second zener diode are both 5.5V. The resistance values ​​of R2 and R3 need to ensure that after the first zener diode is reversely conducted, the voltage across R3 is greater than the conduction voltage drop of the NPN transistor Q2. The clamping voltage of the second zener diode is 4.8-5.4V.

[0020] The working principle of the overvoltage protection circuit of the present invention is as follows:

[0021] First, the circuit input end is connected to the output end of the power adapter, and the circuit output end is connected to the load to be charged; at this time, the first capacitor C1 is in a charging state, the source potential of the P-type MOS tube is equal to the voltage of the output end of the power adapter, and the gate potential gradually decreases from the voltage value of the output end of the power adapter. When the charging of the capacitor C1 is completed, the gate potential drops to 0. When the gate-source voltage of the P-type MOS tube is greater than its turn-on voltage, the P-type MOS tube is turned on and starts to supply power to the load. By setting the capacitor C1, the power-on control signal is delayed, thereby realizing a soft start of the circuit, thereby preventing the subsequent load circuit from being damaged before the control unit is started due to too fast power-on.

[0022] If the connected power supply voltage value is greater than the reverse breakdown voltage of the first voltage regulator diode, the first voltage regulator diode is broken down and reversely conducted, a high-level signal flows into the base of the second switch device Q2, the potential difference between the base and the emitter of the second switch device Q2 is equal to the voltage across R3, and the second switch device Q2 changes from the off state to the on state, so that the base of the third switch device Q3 is grounded and the potential becomes 0. Since the emitter potential of the third switch device Q3 is equal to the voltage at the output end of the power adapter, the third switch device Q3 changes to the on state, so that the gate potential of the first switch device is equal to the voltage value of the output end of the power adapter, so that the gate-source voltage of the first switch device is equal to 0, and the first switch device changes from the on state to the off state, thereby disconnecting the connection between the load to be charged and the output end of the power adapter, thereby avoiding the situation where the load to be charged is burned out due to excessive voltage at the output end of the power adapter. If the voltage value at the output terminal of the connected power adapter is less than the reverse breakdown voltage of the first voltage regulator diode, the signal received by the base of the second switch device Q2 is a low-level signal, the second switch device Q2 and the third switch device Q3 both remain in the off state, and the first switch device remains in the on state.

[0023] If a control unit fails and the first switching device cannot be turned off, at this time, if the power supply voltage is too large, the third voltage regulator tube is reversely broken down, and the voltage across it is clamped at a very small value, thereby reducing the potential at the output end of the overvoltage protection circuit, thereby protecting the load to be charged.

[0024] The voltage input and output relationship of this circuit measured on the product sample is shown in Table 1:

[0025] Table 1

[0026] Input voltage(V) Load current(A) Output voltage(V) 5 0 5.247 5 0.2 5.122 5 0.4 5.081 5 0.6 5.026 5 0.8 4.954 5 1 4.884 5 1.2 4.824 5 1.4 4.752 5 1.6 4.671 5 1.8 4.579 5 (The measured adapter voltage is 4.7V at this time) 2 4.477 5.5-6.4 2 0

[0027] Combined with the test data in the above table, this design meets the demand of directly plugging in the adapter for power adaptation when the power supply voltage of the power adapter is unknown.

[0028] By adopting the power adapter circuit of the present invention, when a power adapter with an output voltage greater than the rated voltage of the load is used to charge the load, the connection between the power adapter and the load can be disconnected immediately, thereby avoiding the problem of the load being burned out due to overvoltage.

Claims

1. An overvoltage protection circuit, characterized in that: It includes an input end for connecting to a power adapter, an output end for connecting to a load, a first switch device connected in series between the input end and the output end, and a control unit connected to a controlled end of the first switch device, wherein the control unit is used to detect whether the voltage at the output end of the power adapter exceeds a voltage threshold, and control the first switch device to be disconnected when the voltage threshold is exceeded, and control the first switch device to be closed when the voltage threshold is not exceeded, wherein the voltage threshold is greater than the rated voltage of the load and the difference between the voltage threshold and the rated voltage of the load is less than a voltage difference threshold, and the voltage difference threshold is greater than 0.

2. The overvoltage protection circuit according to claim 1, characterized in that: The control unit includes a first voltage-stabilizing diode, a second switching device and a third switching device; the first voltage-stabilizing diode is connected in series between the input terminal and the ground, the anode of the first voltage-stabilizing diode is grounded through a grounding resistor and the reverse breakdown voltage of the first voltage-stabilizing diode is equal to the voltage threshold; the second switching device is connected in series between the controlled terminal of the third switching device and the ground, the controlled terminal of the second switching device is connected to the anode of the first voltage-stabilizing diode, and is used to be turned on when the first voltage-stabilizing diode is broken down, so that the third switching device is turned on, and is also used to be turned off when the first voltage-stabilizing diode is not broken down, so that the third switching device is turned off; the third switching device is connected in series between the input terminal and the controlled terminal of the first switching device, and the controlled terminal of the first switching device is grounded, so that after the first switching device is connected to the power adapter, the first switching device is in the off state when the third switching device is in the on state, and the first switching device is in the on state when the third switching device is in the off state.

3. The overvoltage protection circuit according to claim 2, characterized in that: The overvoltage protection circuit further includes a first capacitor, which is connected in parallel across two ends of the third switch device.

4. The overvoltage protection circuit according to claim 1, characterized in that: The output end is grounded through a second voltage stabilizing diode, the anode of the second voltage stabilizing diode is grounded, and the reverse breakdown voltage of the second voltage stabilizing diode is equal to the voltage threshold.

5. The overvoltage protection circuit according to claim 2, characterized in that: A current-limiting resistor is connected in series between the controlled end of the third switch device and the second switch device.

6. The overvoltage protection circuit according to any one of claims 2, 3 or 5, characterized in that: The first switch device adopts a P-type MOS tube, the second switch device adopts an NPN-type transistor, and the third switch device adopts a PNP-type transistor.

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