JPS6269310A - Resetting circuit - Google Patents

Abstract

PURPOSE:To effectively use the electric charge stored in a back-up capacitor for holding the memory of a microcomputer, by performing a resetting action after detecting the power supply voltage of the microcomputer only when a commercial power supply is impressed. CONSTITUTION:A voltage detecting circuit 32 consists of resistances 33-37, a constant voltage diode 28 and transistors 39 and 40. The circuit 32 has no actuation in a back-up mode where no commercial power 21 supply is applied. Then the circuit 32 is actuated in response to the power supply voltage VDD of a microcomputer 41 only when the power supply 21 is impressed. In such a way, the electric charge of a back-up capacitor 31 can be effectively used for actuation of the computer 41.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a reset circuit for an electronic circuit or the like that uses a microcomputer and has a backup function.

2. Description of the Related Art A conventional reset circuit of this type connects a commercial power source 1 to a transformer 2, for example, as shown in FIG. diode bridge 3
．． Capacitor 4. Resistance 5. The voltage is regulated by a constant voltage circuit 8 consisting of a constant voltage diode 6 and a transistor 7, and the output of this constant voltage circuit 8 is provided with a back-up function by a backup capacitor 9 and a 1° resistor. The output voltage of 8 was checked by a voltage detection circuit 11, and if the voltage fell below a certain voltage, the voltage detection circuit 11 outputted a "reset" signal to the microcomputer 12.

Problems to be Solved by the Invention However, in such a conventional reset circuit, during backup, the electric charge accumulated in the backup capacitor 9 is transferred to other sources than the microcomputer 12.
Since the voltage detection circuit 11 consumes power, there is a problem that the backup time is shortened and the capacitance of the capacitor 9 is increased.

The present invention has been made in view of these problems, and it is an object of the present invention to effectively utilize the electric charge accumulated in a backup capacitor for memory retention in a microcomputer.

Means for Solving the Problems In order to solve the above problems, the present invention provides a first power supply having a backup function, a second power supply 2 without a bank-up function, detecting voltage, and detecting the voltage. and a voltage detection circuit that outputs a reset signal if the voltage detected is below a certain voltage, and the voltage detection terminal of the voltage detection circuit is connected to a first
and the power supply terminal of the voltage detection circuit is connected to a second power supply.

Effect: With the above configuration, the power supply current for the voltage detection circuit is not supplied from the first power supply having a backup function, so that the backup capability of the first power supply can be effectively used for memory retention of the microcomputer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. In FIG. 1, 21 is a commercial power supply, 22 is a constant voltage circuit, and this constant voltage circuit 22 includes a transformer 23, a diode bridge 24, a capacitor 25, a resistor 26, 27, a transistor 28, 29, a constant voltage diode 30. It is configured with a backup capacitor 31. 32 is a voltage detection circuit, and this voltage detection circuit 32 has resistors 33, 3
4.

35, 36, 37, a constant voltage diode 28, and transistors 39, 40. 41 is a microcomputer.

Next, the operation of the reset circuit configured as described above will be explained. The commercial power supply 21 is depressurized by the transformer 23 and becomes a full-wave rectified waveform by the diode bridge 24. This full-wave rectified waveform is smoothed by a capacitor 25 and becomes a DC voltage.

This DC voltage is applied to the resistor 26. The voltage is made constant by the constant voltage diode 30° transistor 28,29.

Note that a backup capacitor 31 and a resistor 27 are connected to the emitter electrode of the transistor 28, and operates as a bank-up power supply in the event of a power outage. Hereinafter, the emitter electrode of the transistor 28 will be referred to as a first power source (a power source with a backup function), and the emitter electrode of the transistor 29 will be referred to as a second power source (a power source without a backup function).

FIG. 2 shows waveforms of various parts when the commercial power supply 21 is applied with the backup capacitor 31 not being charged. The Zener voltage of the constant voltage diode 38 is Vz, and the voltage of part a is Va.

If the voltage at section d is Vd, the voltage between Vz) and VdO is Vc)
Since the voltage becomes V'd, the transistor 39 is turned off.

Transistor 4o turns on, and as a result, a reset signal is generated in section 6, so microcomputer 41
is reset, (part a is called the voltage detection terminal, this voltage is Va, and the resistance value of resistor 35.37 is R35, respectively.
If Rs ends, transistor 39 turns on and transistor 4 turns off, and as a result, the voltage at section 6 becomes o.
Since the voltage becomes V, the reset of the microcomputer 41 is released. Note that part b is referred to as a power supply terminal of the voltage detection circuit 32.

FIG. 3 shows the waveforms of various parts when the commercial power supply 21 is applied while the backup capacitor 31 has a residual charge. In this case, always Vc(
Vd, so the transistor 40 is always OFF and the 6
The voltage of the microcomputer 41 remains at OV, so the microcomputer 41 is not reset. Note that the guaranteed operation lower limit voltage of the microcomputer 41 is Vddxx.
Then, when Va==”ldm(71), vC=vd
The Zener voltage vz of the constant voltage diode 38 is set so that
If the charging voltage of the backup capacitor 31 is below 'l/dd, the microcomputer 41 will be reset when commercial power is applied;
If it is d4 or more, it will not be reset.

In this way, during backup when commercial power is not applied, the voltage detection circuit 32 is not operated and the commercial power
1 is applied, the voltage detection circuit 32 operates according to the power supply voltage VDD of the microcomputer 41, so that the charge of the backup capacitor 31 can be effectively used to operate the microcomputer 41.

Effects of the Invention As described above, according to the present invention, during backup, the power supply voltage of the microcomputer is not always detected and reset operation is performed, but only when commercial power is applied.
Since the power supply voltage of the microcomputer is detected and the reset operation is performed, the power supply current of the voltage detection circuit is not required during backup, and the charge stored in the backup capacitor is used to maintain the memory of the microcomputer. It can be used for

[Brief explanation of drawings]

Figure 1 is a reset circuit diagram showing one embodiment of the present invention, Figure 2 is a reset circuit diagram showing one embodiment of the present invention.
3 are waveform diagrams of various parts of the reset circuit, and FIG. 4 is a diagram of a conventional reset circuit. 22... Constant voltage circuit, 32... Voltage detection circuit, 28... First power supply, 29...
-Second power supply. Name of agent: Patent attorney Toshio Nakao and 1 other person32
---Ichiden Iwone Retrospective 41 ---Micro Computer Tag Z?

Claims (1)

[Claims] It has a first power supply having a backup function, a second power supply having no backup function, and a voltage detection circuit that detects voltage and outputs a reset signal if the detected voltage is below a certain voltage. . A reset circuit configured by connecting a voltage detection terminal of the voltage detection circuit to a first power supply and a power supply terminal of the voltage detection circuit to a second power supply.