JPH01216417A - Reset circuit - Google Patents

Abstract

PURPOSE:To stably perform a reset operation at the time of disconnecting a power source by providing a discharge circuit to discharge the electric charge of a smoothing capacitor by the output of a power source monitoring circuit. CONSTITUTION:The discharge circuit 4 to discharge the electric charge of the smoothing capacitor in a rectifier smoothing circuit to supply a voltage in which an AC power source is rectified and smoothed to a regulator 3 by the output RST of the power source monitoring circuit 2 is provided. When the power source is disconnected, the output RST of the power source monitoring circuit 2 goes to a low level, and the reset operation of a system circuit 1 is performed. At this time, since a transistor Q2 is turned OFF and a transistor Q1 is turned ON, a discharge resistor R is connected to the smoothing capacitor, and the electric charge of the smoothing capacitor is discharged through the discharge resistor R. In such a way, it is possible to prevent an operation to recover the output voltage of the regulator 3 from being performed even when the reset operation of the system circuit 1 is performed and a consumption current Isy is reduced, thereby, the reset operation can be performed smoothly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to a reset circuit that switches the system operation of a system circuit to a reset operation when power is cut off.

[Prior Art] As shown in FIG. 2, in a conventional system operating device, a system circuit 1 is operated using the output of a regulator 3, which inputs a voltage obtained by rectifying and smoothing an AC power source, as a power source. In such a device, it is necessary to switch the operation so that only a part of the system circuit 1 that performs system operation is operated when the AC power is cut off (hereinafter, this operation is referred to as a reset operation). A power supply monitoring circuit 2 is provided which occasionally performs the above operation switching. This power supply monitoring circuit 2 detects the output voltage of the regulator 3, and resets the system circuit 1 when the output of the regulator 3 falls below a predetermined value. However, when the system circuit 1 is reset in this way, the current consumption Isy of the system circuit 1 decreases.
The output voltage of the regulator 3 may recover slightly.

In this case, the power supply monitoring circuit 2 switches the system circuit 1 to normal system operation, and when the system starts to operate, resets the system circuit 1, repeating the switching between the system operation and the reset operation, thereby smoothing the reset operation. There was a problem that I couldn't get it to work.

[Problems to be Solved by the Invention J The present invention has been made in view of the above points, and its purpose is to provide a reset circuit that can stably perform a reset operation when the power is cut off. It's about doing.

[? Means for Solving Problem J In order to achieve the above object, the present invention detects the cut-off state of the AC power supply, and when the power supply is cut off, the output of a regulator whose input is the voltage obtained by rectifying and smoothing the AC power supply is used as the power supply. It consists of a power supply monitoring circuit that operates only a part of the system circuit that operates as a power supply monitoring circuit, and a discharging circuit that discharges the charge of a smoothing capacitor using the output of this power supply monitoring circuit.

(Function) As described above, in the present invention, by providing the reset circuit with a discharge circuit that discharges the charge in the smoothing capacitor using the power supply monitoring circuit output, the charge in the smoothing capacitor is discharged by the discharge circuit when the power is cut off. This prevents the regulator output from being restored even if the system circuit enters a reset operation and the current consumption decreases.

(Embodiment) FIG. 1 shows an embodiment of the present invention. In this embodiment, the output R8T of the power supply monitoring circuit 2 is a smoothing capacitor ( A discharge circuit 4 is provided for discharging the charged charges (not shown). The discharge circuit 4 is composed of a discharge resistor R for discharging the charge of the smoothing capacitor, and a switching circuit including transistors Q, , Q, for connecting the discharge resistor R to the smoothing capacitor. Note that the discharge current Id caused by the discharge resistor R may have a value that reduces the output voltage of the regulator 3 by an amount corresponding to the consumption current rsy that decreases when the system circuit 1 enters a reset operation.

In a normal state, the system circuit 1 performs appropriate system operations using the output of the regulator 3 as a power source, and the output -R-3T of the power supply monitoring circuit 2 at this time is at a high level. Therefore, the transistor Q of the discharge circuit 4
2 is on and transistor Q is off, so the discharge resistor R is separated from both ends of the smoothing capacitor.

Now, if the power is cut off, the output R of the power supply monitoring circuit 2
8T becomes low level, and the system circuit 1 enters a reset operation. At this time, transistor Q2 turns off,
Since the transistor Q2 is turned on, the discharge resistor R is connected to the smoothing capacitor, and the charge in the smoothing capacitor is discharged via the discharge resistor R.

Therefore, even if the system circuit 1 performs a reset operation and the current consumption Isy decreases, the output voltage of the regulator 3 does not return to normal, and the reset operation is performed smoothly.

[Effects of the Invention 1] As described above, the present invention is a part of a system circuit that detects a cut-off state of an AC power supply and operates using the output of a regulator that receives as input a voltage obtained by rectifying and smoothing the AC power when the power is cut off. It consists of a power supply monitoring circuit that operates only the circuit, and a discharging circuit that discharges the charge in the smoothing capacitor using the output of this power supply monitoring circuit, so when the power supply is disconnected, the charge in the smoothing capacitor is discharged in the discharge circuit. Even when the system circuit enters a reset operation and the M91 current decreases, the regulator output is not restored, which has the effect of allowing the system circuit to perform a reset operation smoothly.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a circuit diagram of a conventional example. 1 is a system circuit, 2 is a power supply monitoring circuit, 3 is a regulator, and 4 is a discharge circuit. Agent Patent Attorney Ishi 1) Ai Shichi

Claims (1)

[Claims] (1) A power supply monitoring circuit that detects a cutoff state of the AC power supply and operates only a part of the system circuit that operates using the output of a regulator whose input is a voltage obtained by rectifying and smoothing the AC power supply when the power supply is cut off; A reset circuit comprising a discharge circuit that discharges the charge of a smoothing capacitor using the output of the power supply monitoring circuit.