JP2000105616A - Electronic equipment protecting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low-priced and high-safety electronic equipment protecting circuit by realizing a short-circuit protecting function of load with a simple circuit. SOLUTION: This electronic equipment protecting circuit is provided with a voltage detecting circuit 5 for detecting a load voltage VCC of electronic equipment, a delay circuit 4 for delaying this output for prescribed time, a timer 2 to be started with a VCCON signal showing the ON/OFF of a power source switch and to output the signal after the lapse of prescribed time, and a register 3 to be reset by the VCCON signal for turning on/off a read power source 8 with the output of an output voltage detecting circuit 5 of delay circuit 4 and the timer 2. Short-circuitting between a load power source and GND is detected during and before the operation of electronic equipment and the power source 8 is turned off.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic device protection circuit against a short circuit such as a load.

[0002]

2. Description of the Related Art A conventional protection circuit for preventing an accident such as destruction of components or overheating due to a load of an electronic device or a short circuit of a power supply employs a power supply IC having the function built in.
Or a dedicated I to protect the electronic device against short circuit
C has to be used, and the circuit design has great restrictions and the cost is high.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electronic equipment protection circuit which solves the above-mentioned problems, realizes this short-circuit protection function with a simple circuit, and can be freely designed at low cost. It is.

[0004]

To solve this problem, an electronic equipment protection circuit according to the present invention comprises a voltage detection circuit for detecting a load voltage of an electronic equipment, and a delay for delaying an output of the voltage detection circuit for a predetermined time. A circuit, a timer which is activated by a power-on signal indicating that the power of the electronic device is turned on and outputs after a predetermined time, and a read / write controllability controlled by the power-on signal, and an output of the delay circuit or an output of the voltage detection circuit by an output of the timer. And a register for outputting a signal for turning on / off the power of the electronic device, detecting a short circuit between the load power supply and the GND during and before the operation of the electronic device, and turning off the power when the short circuit is detected. It is configured as follows. .

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is directed to a voltage detection circuit for detecting a load voltage of an electronic device, a delay circuit for delaying an output of the voltage detection circuit for a predetermined time,
An OR circuit that receives a power-on signal indicating that the power of the electronic device has been turned on and outputs the signal after a predetermined time, and an OR circuit; an output of the delay circuit reset by the power-on signal and the output of the timer; Reads the output of the voltage detection circuit and turns on / off the power of the electronic device.
This is an electronic device protection circuit including a register for outputting a signal to generate an electronic device, and has an effect that an electronic device protection circuit that can be freely designed at low cost can be provided.

According to a second aspect of the present invention, there is provided the electronic device according to the first aspect, further comprising a circuit which receives the output of the register and the power ON signal and outputs a signal for turning ON / OFF the electronic device. This is a device protection circuit, which has an effect of providing a user-friendly electronic device protection circuit while maintaining safety by keeping a power supply in an OFF state in a short-circuit state.

Next, an embodiment of an electronic equipment protection circuit according to the present invention will be described with reference to FIGS.

(Embodiment 1) FIG. 1 is a block diagram of an electronic device protection circuit according to Embodiment 1 of the present invention, FIG. 2 is a timing chart of a normal operation in Embodiment 1 of the electronic device protection circuit of the present invention, FIG. 3 is a timing chart when a short circuit occurs during the operation of the electronic device protection circuit according to the first embodiment of the present invention;
FIG. 4 is a timing chart when a short circuit occurs before the operation of the electronic device protection circuit according to the first embodiment of the present invention.

In FIG. 1, an electronic equipment protection circuit is an OR circuit.
Circuit 1, timer 2, register 3, delay circuit 4
And a voltage detection circuit 5 and an AND circuit 6.

The OR circuit 1 outputs the output signal VC of the delay circuit 4
This is an OR circuit that inputs CRST ′ and the output TIMER signal from the timer 2 and outputs a CLK signal.

The timer 2 has a VCCO indicating the power switch ON / OFF state of the power switch circuit 7 of the electronic device.
The reset signal is held at a low level (hereinafter abbreviated as L) by an N signal, is activated at a high level (hereinafter abbreviated as H), and outputs a TIMER signal that changes from L to H after a lapse of a predetermined time.

First Embodiment of Electronic Device Protection Circuit of the Present Invention
The components on the electronic device side related to are a power switch circuit 7 for outputting a power ON signal and a power supply 8.

The register 3 is for turning on the power supply of the electronic equipment by H
A storage circuit that outputs a PWROFF signal that is turned off at N and L. As a specific example, a D-type flip-flop having a reset terminal R, a data input terminal D, and a clock terminal CK, and a clock generated at rising and falling edges of an input signal And a circuit for outputting to the clock terminal CK.

When the PWRON signal input to the reset terminal R of the register 3 is L, the PWROFF signal is held at H (the power of the electronic device can be turned on), the reset state is released when the PWRON signal is H, and the data input is performed. The signal is read at the rise of the output signal VCCRST of the voltage detection circuit 5 of the terminal D, and the H or L PWROFF signal is output.

[0015] The delay circuit 4 is connected to the VCCR of the voltage detection circuit 5.
It outputs a VCCRST 'signal obtained by delaying the ST signal by a predetermined time equal to or longer than the setup time of the register 3.

The voltage detection circuit 5 is provided with a load voltage V
CC is monitored, and VCC is a predetermined value, for example, 70% of specified voltage.
When it becomes less than the above, it outputs the VCCRST signal which becomes L.

The AND circuit 6 is a logical product circuit which receives the VCCON signal from the power switch circuit 7 and the PWROFF signal from the register 3 and outputs a signal for turning on / off the power supply 8.

The power switch circuit 7 includes a power supply 8 for the electronic device.
Output a VCCON signal for turning ON / OFF.

The power supply 8 is a power supply for the electronic equipment and supplies power of the load voltage VCC to the additional circuits and the equipment.

First, a normal power ON / OFF operation is shown in FIG.
This will be described with reference to FIG. In FIG. 2, at time T1 when the power switch of the electronic device is turned on, the VCCON signal rises from L to H, and at the same time, the load voltage VCC gradually rises.

When the load voltage VCC reaches a predetermined voltage value or more, the VCCRST signal of the voltage detection circuit 5 rises. At time T2 when this change is delayed by the delay circuit 4 for a predetermined time, VCCRST 'rises. Register 3
The H level of the VCCRST signal at the rising point T2 is read. However, the output PWROFF signal of the register 3 does not change because it is H while being already held at L of the VCCON signal. When the output TIMER signal of the timer 2 rises, the H level of the VCCRST signal is read.
The ROFF signal keeps H without changing.

Since the VCCON signal and the PWROFF signal are both H, the AND circuit 6 becomes H, and the power supply 8 is turned on by turning on the power switch circuit 7.

Next, the power switch circuit of the electronic device is turned off.
At time T3, the PWRON signal falls and the load voltage VCC gradually falls at the same time. When the load voltage VCC falls below a predetermined voltage value, the VCCRS of the voltage detection circuit 5
The T signal becomes L. This change causes the output VCC of the delay circuit 4 to change.
RST ′ becomes L. Then, the register 3 stores the VCCR
When the L of the VCCRST signal is read at the falling point T4 of the ST ′ signal, the output PWROFF signal changes to L.

Since both the VCCON signal and the PWROFF signal are H, the AND circuit 6 becomes H, and the power supply 8 is turned off by turning off the power switch circuit 7.

Next, during the operation of the electronic equipment, the load power supply and the GND
The protection operation in the case where a short circuit occurs between them will be described with reference to FIGS.

The power-on operation at the time T1 to T2 is the same as the above-described normal operation. The load voltage VCC decreases due to the short circuit occurring at the time T5, and the output VCCRST of the voltage detection circuit 5 changes to L. Then, at time T6 when the output signal VCCRST ′ of the delay circuit 4 changes to L with a delay of a predetermined time, the register 3 reads the VCCRST signal and sets
The WROFF signal is set to L. The AND circuit 6 has a VCCO
Since the N signal is H but the PWROFF signal is L, L is output and the power supply 8 is turned off, the load voltage VCC is turned off, and the power supply 8 is kept off.

In this OFF holding state, when the power switch is turned off at time T10, the VCCON signal becomes L at time T10, the PWROFF signal becomes H, and the timer 2 changes to the reset state L. AND circuit 6 is connected to VCCON
Since the signal is L and the PWROFF signal is H, the output is L. The power supply 8 remains off.

Further, after the cause of the short circuit is removed, when the power switch is turned on at time T11, the VCCON signal changes to H, and the above-described normal power ON operation is started.

If the power switch is turned on without removing the cause of the short circuit without removing the cause, the protection operation described below is performed.

Finally, a protection operation in the case where a short circuit occurs before the power is turned on will be described with reference to FIGS.

At time T1 when the power is turned on, the VCCON signal goes high.
Is turned on, but the power is turned on.
Since the voltage of C does not rise, the output VC of the voltage detection circuit 5
CRST does not change to H and the delay circuit 4
Output VCCRST 'remains at L. But VCC
After the reset is released by the ON signal, the output TIMER signal of the timer 2 which has been activated rises to H at a time T7 after a predetermined time sufficient for VCC to rise, and sends the VCCRST 'signal to the register 3 through the OR circuit 1. , VCC
After reading L of the RST signal, the PWROFF signal becomes L.
A because the VCCON signal is H and the PWROFF signal is L
The power supply 8 is turned off by the L output of the ND circuit 6.

After removing the cause of the short circuit, if the power switch is turned off at time T10 and turned on again at time T11,
The normal ON operation is performed as described above. If the power is turned off and the power is turned on again without removing the cause of the short circuit, the operation at the above-described time points T1 and T7 is repeated to turn off the power.
To prevent failures caused by short circuits.

In the first embodiment of the present invention, the flip-flop is used as the register. However, the present invention is not limited to this. The same effects as those of the present invention can be obtained if the reset state is released by the power ON signal, the change in the voltage detection signal of the load is read, and the read signal is held and output.

[0034]

As described above, according to the present invention, a special I
Using a general-purpose IC without using C, an inexpensive and simple circuit configuration, an electronic device that detects a short circuit between the power supply and GND in two states before and after operation and turns off the power supply of the electronic device to ensure safety. An equipment protection circuit can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an electronic device protection circuit according to a first embodiment of the present invention.

FIG. 2 is a timing chart of a normal operation in the electronic device protection circuit according to the first embodiment of the present invention;

FIG. 3 is a timing chart when a short circuit occurs during operation of the electronic device protection circuit according to the first embodiment of the present invention;

FIG. 4 is a timing chart in the case where a short circuit has occurred before the operation of the electronic device protection circuit according to the first embodiment of the present invention;

[Explanation of symbols]

 Reference Signs List 1 OR circuit 2 Timer 3 Register 4 Delay circuit 5 Voltage detection circuit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // H02H 7/20 G06F 1/00 341Q

Claims (2)

[Claims] 1. A voltage detecting circuit for detecting a load voltage of an electronic device, a delay circuit for delaying an output of the voltage detecting circuit for a predetermined time, and a power ON signal indicating that the power of the electronic device is turned on. A timer which outputs after a predetermined time, and a read / write control which is controlled by the power ON signal, outputs an output of the voltage detection circuit by an output of the delay circuit or an output of the timer, and outputs a signal for turning on / off the power of the electronic device. Electronic device protection circuit with register 2. The electronic device protection circuit according to claim 1, further comprising a circuit which receives the output of the register and the power ON signal and outputs a signal for turning on / off the power of the electronic device.