JP3084395U - Power circuit - Google Patents

Abstract

(57) [Problem] To provide an overvoltage protection circuit for suppressing overvoltage from being maintained, the circuit configuration is large, and the overvoltage protection by a latch circuit immediately stops the circuit. SOLUTION: An overvoltage protection circuit 11 for suppressing an output voltage from maintaining an overvoltage, and a latch circuit which operates when an input voltage of the switching element becomes overvoltage, stops the operation of the switching element (by the latch circuit). ) Both overvoltage protection circuits 12 are provided.

Description

[Detailed description of the invention]

[0001]

[Technical field to which the invention belongs]

 The present invention relates to a power supply circuit, and more particularly to a power supply circuit having an overvoltage protection circuit.

[0002]

[Prior art]

 In a power supply circuit configured to apply its output voltage to a load via a switching element, constant voltage control is performed when the input voltage of the switching element rises abnormally or when a major part of the power supply circuit fails. If the circuit fails, the output voltage will jump. When such an overvoltage state occurs, problems such as damage to the output smoothing capacitor, abnormal heating of the switching transistor and the resistor, and damage to the load occur. An overvoltage protection circuit is used in the power supply circuit to prevent the load from being destroyed by such an overvoltage.

A general overvoltage protection circuit used for a power supply circuit configured to apply an output voltage to a load via a switching element controls off the switching element when an overvoltage is applied. When the output voltage decreases and the output voltage decreases, the switching element off control is released and normal constant voltage control is resumed.When the output voltage increases, the switching element off control is restarted again, and this operation is repeated. In this way, it is possible to prevent a phenomenon that a failure occurs in an electrolytic capacitor and an electronic device connected to the output terminal due to an excessive output voltage. Further, when the output voltage becomes excessively higher than a predetermined value, the latch circuit operates and the switching element is turned off to stop the switching operation.

[0004]

[Problems to be solved by the invention]

 When an overvoltage occurs, the switching element is turned off to temporarily lower the output voltage.When the output voltage drops, the off control is released and the control returns to normal constant voltage control. By restarting the off control and repeating this operation, the circuit configuration of the overvoltage protection circuit for protecting the load becomes large. In addition, in the overvoltage protection by the latch circuit, an improvement has been desired, for example, the circuit is immediately stopped and an error mode is entered.

[0005]

[Means for Solving the Problems]

 In order to achieve the above object, the present invention is to control the switching element to be turned off when an output voltage applied to a load via a switching element becomes an excessive voltage up to a first set value. A first overvoltage protection circuit for reducing the output voltage and releasing the off control of the switching element when the output voltage decreases to return to the normal constant voltage control; and a first overvoltage protection circuit for applying the first voltage to the input voltage of the switching element. And a second overvoltage protection circuit for turning off the switching element and stopping the operation of the switching element when an excessive voltage exceeding the set value is applied.

As described above, since both the circuit for suppressing the overvoltage and the circuit for stopping the circuit are provided in the power supply circuit, it is not necessary to stop the circuit unnecessarily depending on the level of the applied overvoltage. You only need to reduce the voltage.

[0007]

[Embodiment of the invention]

 Hereinafter, the present invention will be described with reference to the circuit diagram of FIG. In FIG. 1, terminals B1 and B2 indicate power supply terminals provided on a supply line for a constant DC voltage (+12 V). B3 indicates a power supply terminal for supplying a DC output voltage (+40 V) applied to the load, and G1 and G2 indicate ground terminals. The power supply terminal B3 is connected to the power supply terminal B4 of the load S via the source / drain of the switching element FET1. A resistor R1 is connected between the source and the gate of the switching element FET1. The gate of the switching element FET1 is connected to the collector of the transistor Q1 via the resistor R2. The emitter of the transistor Q1 is grounded, the base of the transistor Q1 is grounded via a resistor R4, and connected to the power supply terminal B1 via resistors R3 and R5. The connection point is the output of the operational amplifier CP1. Terminal and the output terminal of the operational amplifier CP2.

An input terminal of the reference voltage of the operational amplifier CP1 is connected to an output terminal via a resistor R6, and the connection of the resistor R6 provides a hysteresis characteristic. Further, a series voltage dividing circuit of the resistor R7 and the resistor R8 is connected between the power supply terminal B1 and the ground terminal G1, and the connection point is connected to the input terminal of the reference voltage of the operational amplifier CP1 and divided by the resistor R7 and the resistor R8. A compressed reference voltage is applied. A series voltage dividing circuit of a resistor R9 and a resistor R10 is connected between the power supply terminal B4 to which the output voltage of the switching element FET1 is applied and the ground terminal G2, and the connection point is connected to another input terminal of the operational amplifier CP1. The output voltage of the switching element FET1 is divided by the resistors R9 and R10 and applied to another input terminal of the operational amplifier CP1. The voltage divider composed of the operational amplifier CP1, the resistor R7 and the resistor R8 and the voltage divider composed of the resistor R9 and the resistor R10 constitute an overvoltage protection circuit 11.

An input terminal of the reference voltage of the operational amplifier CP2 is connected to an output terminal via a resistor R11, and the connection of the resistor R11 provides a hysteresis characteristic. Further, a series voltage dividing circuit of the resistor R12 and the resistor R13 is connected between the power supply terminal B2 and the ground terminal G2, and the connection point is connected to the input terminal of the reference voltage of the operational amplifier CP2. A compressed reference voltage is applied. A series voltage dividing circuit composed of a resistor R14 and a resistor R15 is connected between the power supply terminal B4 and the ground terminal G2, and the connection point is connected to another input terminal of the operational amplifier CP2 so that the input voltage of the switching element FET1 is reduced. The voltage is divided by the resistors R14 and R15 and applied to another input terminal of the operational amplifier CP2. The voltage divider composed of the operational amplifier CP2, the resistor R12 and the resistor R13 and the voltage divider composed of the resistor R14 and the resistor R15 constitute a latch circuit 12.

Next, the operation will be described. Now, when the output voltage of the switching element FET1 becomes an excessive voltage in the range up to the first set value (+50 V), the operational amplifier CP1 controls the switching element to turn off and lowers the output voltage. Then, when the output voltage decreases, the operational amplifier CP1 releases the OFF control of the switching element FET1. When the output voltage of the switching element FET1 becomes excessively high in the range up to the first set value, the operational amplifier CP1 repeats this operation. Next, when the input voltage of the switching element FET1 is applied with an excessive voltage exceeding the first set value, the operational amplifier CP2 turns off the switching element FET1 and stops the operation of the switching element FET1.

[0011]

[Effect of the invention]

 As described above, in the present invention, the overvoltage protection circuit that suppresses the output voltage applied to the load via the switching element from maintaining the overvoltage, and the latch circuit when the input voltage of the switching element becomes overvoltage, are provided. Since both the overvoltage protection circuit that operates and stops the operation of the switching element (by the latch circuit) is installed in the power supply circuit, the circuit can be stopped according to the applied overvoltage level, This is extremely practical, as there is no need to stop the operation and only the voltage needs to be reduced to a certain value.

[Brief description of the drawings]

FIG. 1 is a schematic circuit diagram of an embodiment according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Overvoltage protection circuit 12 Latch circuit B1, B2 Power supply terminal B3, B4 Power supply terminal CP1, CP2 Operational amplifier G1, G2 Ground terminal FET1 Switching element Q1 Transistor R7, R8 Divider R9, R10 Divider R12, R13 Divider R14 , R15 Voltage divider circuit S load

Claims (1)

[Utility model registration claims] When an output voltage applied to a load via a switching element becomes an excessive voltage up to a first set value, the switching element is turned off to lower the output voltage, and the output voltage is reduced. When the voltage drops, a first overvoltage protection circuit that releases the off control of the switching element and returns to the normal constant voltage control, and an excessive voltage exceeding the first set value is applied to the input voltage of the switching element. And a second overvoltage protection circuit for turning off the switching element and stopping the operation of the switching element when the voltage is applied.