JPH0191619A - Overvoltage protection circuit - Google Patents

Abstract

PURPOSE:To prevent malfunction in gentle voltage variations, by detecting steep overvoltage of a load circuit with a differentiation circuit and by closing an overvoltage generating power consumption circuit through a constant voltage Zener diode. CONSTITUTION:A circuit 10 will work only when the voltage rise is steep and exceeds the set level. If a differentiation circuit 11 detects steep overvoltage of counter-electromotive force when a motor is stopped, a thyristor Q2 is triggered. If this overvoltage is higher than the voltage level set by a constant voltage Zener diode ZD of an overvoltage discrimination circuit 13, a transistor Q1 of a regenerating power consumption circuit 12 is turned ON and the regenerated power is consumed in a short time and a motor control circuit MC is prevented from being applied by excess voltage. Moreover, no malfunction will occur which might be caused by the gentle voltage variations of voltage setting volume, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an overvoltage protection circuit in a multi-output power supply.

[Prior Art] In a multi-output power supply that detects fluctuating voltage on the output side of a master circuit in a multi-output circuit and feeds it back to the primary side of a switching power supply, the output of the master circuit is connected to a motor load, etc. In such cases, there is a risk that the energy of the regenerated power generated when the motor stops enters the feedback circuit and causes the main transistor on the primary side of the switching power supply to stop transmitting, resulting in a loss of power supply to the slave circuit and a voltage drop. There is.

To prevent this, connecting a diode to the output side of the master circuit to prevent the regenerated power from affecting the feedback circuit eliminates the effect on the slave circuit as described above, but it consumes the energy generated by the motor. Since there is no circuit to control the motor, a dangerous voltage will be applied to each motor.

For this reason, in the past, as shown in the second diagram, a circuit for detecting the energy generated by overvoltage and consuming the energy was not provided. That is, in the same figure, 1 is a switching power supply, ■,
■, ■ are the multi-output circuits on the output side, ■ is the master circuit,
■ and ■ indicate slave circuits, Dl, D2, L, and C in master circuit I are rectifying and smoothing circuits on the secondary side of the switching power supply, R1, R2, and circuit 2 are feedback circuits, M is a motor load, and 3 is a This is a motor control circuit. Also, 5 in the slave circuit ■ is a 3-terminal IC.
16 is a load, and slave circuit (2) is an appropriate load circuit.

In the master circuit of such a multi-output circuit, in order to prevent the regenerative power generated when the motor load is stopped from affecting the feedback circuit and to consume the regenerative power, the master circuit engineer is required to perform overvoltage detection and regenerative power consumption. A circuit 4 is provided, in which the Zener diode zD and resistors R3 and R4 detect the occurrence of overvoltage, turn on the transistor Q, and consume the energy generated by the overvoltage through the resistor R5.

[Problems to be solved by the invention] The conventional multi-output circuit switching power supply as described above has the following problems:
The power supply configuration becomes complicated by configuring multiple inverter circuits or using chopper circuits, etc.
is simply an overvoltage detection circuit and is used to start the motor load.
Since it does not determine stoppage, there is a problem in that even slight voltage fluctuations, such as when setting the power supply voltage with a volume control, can cause malfunctions. Also, the purpose of resistor R5,1-transistor Q is to consume regenerative power in a short time, so
These R5 and Q should be kept under excessive load for a long time, e.g. 1 to 2 S.
There is a risk of destruction if exposed to AC voltage, and to prevent this, there is a problem in that large capacitance elements are required for R5 and Q.

SUMMARY OF THE INVENTION Therefore, the present invention provides an overvoltage protection circuit that can quickly consume the energy of regenerated power generated when a motor is stopped in a multi-output circuit, and that does not malfunction due to gradual voltage fluctuations.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a multi-output power supply that supplies power to a motor load, etc., which is connected between the power supply of the multi-output circuit and the load circuit. a differential circuit for detecting a steep overvoltage in a load circuit; a resistor for consuming overvoltage energy when the motor of the load circuit is stopped; and a transistor for connecting the resistor to the load circuit; and an overvoltage determination circuit which includes a constant voltage Zener diode for voltage level setting connected between the differentiating circuit and the base of the transistor, and receives the output signal of the differentiating circuit and closes the transistor when the voltage level is higher than the set voltage level. , only when the differential circuit detects a steep overvoltage in the load circuit when the overvoltage generated in the load circuit is higher than the set voltage level of the overvoltage discrimination circuit, the transistor of the regenerative power consumption circuit is turned on and the resistor connected to its collector is turned on. The system is designed to consume regenerative power.

[Function] The above-mentioned differentiation circuit detects a steep overvoltage that occurs when the motor is stopped, and the overvoltage discrimination circuit drives the base of the transistor of the regenerative power consumption circuit only when the voltage level is higher than the voltage level set by the constant voltage Zener diode. As a result, even if there is a voltage fluctuation in the load circuit, if the voltage does not reach the set voltage level, the transistor in the regenerative power consumption circuit will not be turned on, and even if there is a voltage fluctuation in the load circuit, the transistor in the regenerative power consumption circuit will not be turned on. However, if the voltage fluctuates slowly, there is no detection output from the differentiating circuit, and in this case as well, the transistor of the regenerative power consumption circuit is not turned on.

The transistor in the regenerative power consumption circuit is turned on only when the voltage fluctuation in the load circuit is higher than the set voltage level and a steep overvoltage detected by the differentiating circuit occurs, that is, when the motor is stopped. This occurs only in the case of an overvoltage, and only in this case the regenerative power is consumed by the resistance of the regenerative power consuming circuit. Therefore, a reliable overvoltage protection circuit that does not malfunction due to gradual voltage fluctuations such as when setting the voltage with a volume can be obtained.

[Example] Embodiments of the present invention will be described below with reference to FIG.

FIG. 1 is a diagram showing a circuit that is an improved version of the dotted line circuit 4 in the master circuit shown in FIG. 2, in which terminals a and b are connected to the output circuit of a switching power supply of a multi-output circuit to supply power to a motor load M. be done.

HC is a control I/roll circuit for this motor, and D is a diode that prevents the back electromotive force generated when the motor is stopped from entering the switching power supply side.

The circuit 10 inside the chain line is an overvoltage protection circuit according to the present invention provided between the diode D and the motor control circuit (IC), and in this circuit 10, the capacitor C1 and the resistor R6 in the circuit 11 shown by the dotted line protect against sudden overvoltage. A differential circuit 11 for detection is configured.

The circuit 12 within the dotted line is a regenerative power consuming circuit, which includes a transistor Q1 and a resistor R7 connected to its collector to consume regenerative power. R8 is the base resistance of the l transistor.

Further, the circuit 13 in the dotted line is an overvoltage discrimination circuit that drives the transistor Q1 and closes the regenerative power consumption circuit when the voltage level is higher than the set voltage level. The constant voltage Zener diode 2D is composed of a constant voltage Zener diode zD for setting a voltage level, and this constant voltage Zener diode 2D sets the voltage level before the regenerative power becomes excessive when the motor is stopped and is applied to the motor control circuit HC. C2+R9 is the capacitor and resistor of the gate circuit of thyristor Q2.

The overvoltage protection circuit according to the present invention configured as described above has the following features:
It operates only when the voltage rises rapidly and exceeds the set voltage level.If there is a sudden voltage rise when the motor is stopped, it is detected by the differentiating circuit 11, which is controlled by the power supply voltage setting volume. The signal to turn on the thyristor Q2 is not output when the voltage fluctuates at a peak level, such as during the setting operation.

Differentiator circuit 1 for the steep overvoltage of back electromotive force when the motor is stopped
1 is detected, the thyristor Q2 is triggered, and this overvoltage is detected by the overvoltage discriminator tl? If the voltage level is higher than the voltage level set by the constant voltage Zener diode ZD of r13, the transistor Q1 of the regenerative power consumption circuit 12 is turned on, and the regenerative power when the motor is stopped is consumed by the resistor R7 connected to the collector. .

In this way, the regenerated power is consumed in a short period of time, and as a result, excessive voltage is applied to the motor control circuit H.
It is possible to prevent the voltage from being applied to C, and furthermore, there is no possibility of malfunction due to gradual voltage fluctuations of the voltage setting volume or the like.

[Effects of the Invention] As described above, the present invention detects a steep overvoltage in a load circuit using a differentiating circuit, and closes the overvoltage generation power consumption circuit via a constant voltage Zener diode for setting the voltage level. Therefore, the energy of regenerated power generated when the motor is stopped can be consumed in a short time, there is no risk of malfunction due to gradual voltage fluctuations, and the circuit configuration and elements used can be made smaller.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the present invention, and FIG. 2 is a diagram showing a conventional example. 11: Differential circuit 12: Overvoltage generation power consumption circuit 13
: Overvoltage discrimination circuit Ql: Transistor R7: Resistor
ID: Constant voltage Zener diode Patent applicant Toshiba Electric Materials Co., Ltd. Representative Patent attorney Oka 1) Kikuji Figure 1 Figure 2

Claims (1)

[Claims] An overvoltage circuit that includes a differentiating circuit that is connected between a power source of a multi-output circuit and a load circuit to detect a steep overvoltage in the load circuit, and a transistor that connects a resistor that consumes power generated in the overvoltage of the load circuit to the load circuit. A generating power consumption circuit, and a constant voltage Zener diode for setting a voltage level connected between the differentiating circuit and the base of the transistor, and receiving an output signal of the differentiating circuit and determining an overvoltage that closes the transistor when the voltage level exceeds a set voltage level. An overvoltage protection circuit comprising a circuit.