JPS62150910A - Protection circuit - Google Patents

Abstract

PURPOSE:To ensure the circuit protection by detecting a fluctuation of a power voltage, driving a switching transistor (TR), interrupting a signal so as to stop the drive of an output circuit. CONSTITUTION:The circuit is devised to stop the control of a motor drive circuit by detecting the fluctuation of the power voltage. That is, an input amplifier 1 receives a pulse input signal Vin and drives an output 2, and when an output signal of the amplifier 1 is at a high level, an output current Io is obtained by the operation of TRs Q1-Q3 and a TR Q12 is also turned on by an output signal supplied via a resistor R6. A bias voltage fed to a TR Q11 via a resistor R7 is lowered to turn off the TR Q11. While the circuit is operated, the protection circuit 11 is inoperative. Thus, the fluctuation of the power voltage is detected by the comparison with a reference voltage and the protection of a signal transmission path is ensured by interrupting the signal transmission forcibly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a protection circuit suitable for frequent use in protecting audio equipment, motor drive circuits, etc. when surge voltage occurs.

[Background technology]

Taking motor drive circuits as an example, there are circuits that perform forward/reverse rotation control and are used in office automation equipment and the like. An example of the circuit configuration is an rDC brushless motor and control circuit.
(1st edition published on November 30, 1981, published by Sogo Electronic Publishing Co., Ltd., p. 160).

Stabilization of the power supply voltage is important in electronic equipment, but it is not preferable especially in OA equipment because it causes errors in data processing. Furthermore, due to power fluctuations,
It is necessary to avoid damage to the signal processing system.

The present inventor studied protection circuits for electronic devices from the above-mentioned viewpoints.

If a fluctuation occurs in the power supply voltage, detecting this and temporarily disabling the output circuit where particularly large current control is performed ensures the protection of the signal processing circuit and, in turn, the semiconductor integrated circuit. This led us to propose the present invention.

[Purpose of the invention]

An object of the present invention is to provide a protection circuit that can detect fluctuations in power supply voltage and reliably protect the circuit.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Summary of the invention]

A brief summary of typical inventions disclosed in this application is as follows.

That is, the present invention detects fluctuations in the power supply voltage by comparing it with a reference voltage, and upon detection, drives a switching transistor to cut off the signal and stop driving the output circuit, thereby ensuring circuit protection. The goal is to achieve the following objectives.

〔Example〕

Hereinafter, one embodiment of a protection circuit to which the present invention is applied will be described with reference to FIG. Note that FIG. 1 is a circuit diagram of a motor drive circuit to which the protection circuit of the present invention is applied, and is implemented as an IC.

The feature of this embodiment is that the control of the motor drive circuit is stopped by detecting fluctuations in the power supply voltage.

Reference numeral 1 denotes an input amplifier, which drives the output 2 with a pulsed input signal Vin.

The input transistor Q1 performs on/off operation according to the signal supplied via the resistor R1, and the transistor Q1
, is driven similarly. The above operation of transistor Q results in transistor Q.

is driven, and when it is on, the motor coil Li
C output current 0 is supplied.

Since the reference voltage Vref is supplied to the transistor Q, the transistor Q continues to be in the on state due to the fact that power is always supplied through the resistor R1, and the transistor Q is always kept in the on state.

The above circuit configuration is the same for the drive circuit 100 provided at the other end of the motor coil L. Therefore, when the transistor Q3 is in the on state as described above, the current Io flows as shown in the figure, and when the transistor Q is off, the drive circuit 1
When 00 operates as described above, the transistor Qs is held in the on state, so an output current of the opposite polarity flows through the coil L.

The transistor Qu operates in an on state when the transistor Q+t is off, and discharges the charge accumulated in the base of the transistor Q3. The present invention utilizes this discharge transistor QII.

When the output signal of the amplifier 1 is at a high level, the output current I is generated by the above operation of the transistors Q1 to Q.

is obtained, but in this case, the transistor Qu also has a resistance R.

It is turned on by an output signal provided through.

Resistance R? The bias voltage supplied to the transistor Qll via the transistor Qll is reduced, and the transistor QII is turned off.

On the other hand, when the output signal becomes low level, the transistor Q
,! is turned off, output circuit 4 is also inactive, and transistor Q is also turned off. However, since the bias voltage is supplied to the transistor Qo, it is turned on and the charge is discharged as described above.

By the way, while the power supply Vcc is at a normal voltage level and the above circuit operation is being performed, the protection circuit 11 is inactive.

That is, the transistor Q! corresponds to the detection circuit according to the present invention. A constant voltage is supplied to the base of I as a reference voltage by a Zener diode ZD. When the power supply Vcc is at a normal voltage level, the base-emitter voltage Vbe is not supplied to the transistor Q21, and the transistor Q21 is turned off. Since the control signal Vc cannot be obtained, the switching transistor Q2 in the present invention! + Q23 is turned off, and transistor QI2 is not controlled.

However, if the power supply Vcc rises due to surge voltage, etc.
Since the voltage Va divided by the resistors R, .

A control signal Vc is obtained, which is connected to the transistor Q via the resistor R.
! 2 + QH operates in the on state. As a result, transistor Q+g is forcibly turned off regardless of whether it is in operation, whereas transistor Q++ operates in an on state.

The base current supplied from transistor Q2 to transistor Q3 is cut off, and transistor Q3 is forcibly turned off.

That is, the output current IO is cut off, an excessive output current does not flow through the transistor Q3, and its destruction is prevented. Also, if an excessive current flows, the device will be destroyed and the IC will
Although destruction of itself is more likely to occur, such unforeseen situations can also be avoided.

〔effect〕

(1) By detecting fluctuations in the power supply voltage by comparison with a reference voltage and forcibly cutting off signal transmission, it is possible to securely protect the signal transmission path.

(2) Since a transistor provided for the other purpose of discharging the base accumulated charge can be used, the protection operation can be performed with a simple circuit configuration.

(3) The above (2) provides the effect that the load value of the motor drive circuit is improved.

Although the invention made by the present inventor has been specifically explained based on examples above, the present invention is not limited to the above examples (and may be modified in various ways without departing from the gist of the invention). Needless to say, for example, the base current of the transistor Qt may be cut off.

[Application field]

In the above explanation, the invention made by the present inventor was mainly applied to the protection of motor drive circuits, which is the field of application that formed the background of the invention, but the invention is not limited to this, and the invention is not limited to this. It can also be used in circuits.

The present invention can be used in electronic equipment that is susceptible to fluctuations in power supply voltage.

[Brief explanation of drawings]

FIG. 1 shows a circuit diagram showing an embodiment of a storage circuit to which the present invention is applied. 1...Human power amplifier, 2...Output circuit, 11...Host@circuit, Q+"'-Qts...Transistor, V
c...control signal, Io...output current. ,・′

Claims (1)

[Claims] 1. (1) A detection circuit to which a reference voltage is supplied and which obtains a detection signal when the power supply voltage fluctuates; and (2) a detection circuit that interrupts signal transmission when the detection signal is supplied, and disconnects the signal transmission path. What is claimed is: 1. A protection circuit comprising: a switching circuit for operating the signal;