JPS60156213A - Power source circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a power supply circuit for an electronic S unit such as a microcomputer.

[Background technology]

The operating voltage (power supply voltage) of a microcomputer is generally 5V±0.5V, and the microcomputer cannot operate stably outside this range. In such a case, it is necessary to reset the microcomputer by giving a reset signal to the microcomputer when the power supply voltage returns to within the operating voltage range. If this reset signal is not stably input, the microcomputer may run out of control (programs are not processed in the correct order) and become inoperable or malfunction.

As shown in FIG. 1, in a conventional power supply circuit, an AC power supply 1 is stepped down by a power transformer 2, rectified by a full-wave rectifier 3, smoothed by a capacitor 4, and then connected to a transistor 5. Resistance 6. A constant voltage circuit 9 consisting of a Zener diode 7 and a capacitor 8 stabilizes the voltage, and the output voltage of the constant voltage circuit 9 is applied as a power supply voltage to the microcomputer 10. Accordingly, when the output voltage of the constant voltage circuit 9 falls below the threshold voltage, the voltage detection circuit 11 provides a reset signal to the microcomputer 10.

This power supply circuit applies a reset signal to the microcomputer 10 when the power supply voltage applied to the microcomputer IOK goes out of the operating voltage range of the microcomputer 10 and then returns to within the operating voltage range. 'i It operates normally after the voltage is restored.

For example, if the threshold voltage ■TH of the voltage detection circuit 11 is
When the operating voltage of the black computer 10 is set to the lower limit, when the power supply voltage changes as shown in Figure 2 (2), the output of the voltage detection circuit 11 changes as shown in Figure 2 [F]). However, the microcomputer-0 is reset at the rising edge of the waveform shown in FIG.

K is the operating voltage range of the microcomputer-O.

However, when the threshold voltage VTH is set to the lower limit of the operating voltage of microcomputer-0, the reset of microcomputer-0 is unstable (because the operation of microcomputer-0 is unstable). ,
Also, due to the instantaneous voltage drop, the voltage detection circuit 11:
A micropulse P is generated, and this is the micronine computer 1.
Force 0 to 0. There is a problem that the microcomputer 0 may malfunction if the very fine pulse P is not recognized as a reset signal or if the pulse is generated halfway.

Next, when the threshold voltage TE of the voltage detection circuit 11 is set to a value higher than the lower limit of the operating voltage of the microcomputer-0, when the power supply voltage V fluctuates as shown in FIG. 3 (2), , the output of the voltage detection circuit 11 is shown in FIG. 3 [F]
), and the microcomputer 10 is reset at the rising edge of the waveform shown in FIG.

When the threshold voltage VTR is set in this way, when the output of the voltage detection circuit 11 rises, the microcomputer l
Since the operating voltage is reliably applied to IO, the microcomputer IO is stably reset. However, there is still a problem in that the very fine pulse P2 is generated from the voltage detection circuit 11, and the microcomputer 10 is likely to malfunction as described above.

In order to solve this problem, a power supply circuit as shown in FIG. 4 has been proposed. This power supply circuit is
A monostable multivibrator (delay timer of time t) 12 that is triggered by the rise of the voltage detection circuit 11 is attached to the circuit shown in FIG. 1, and the microcomputer 0 is reset by the rise of the output of this monostable multivibrator 12. It is configured as follows.

5(A) shows the waveform of the source voltage ■ at ', FIG. 5I shows the waveform of the output voltage of the voltage detection circuit 11, and FIG.
shows the waveform of the output voltage of the monostable multivibrator 12.

In this way, when the monostable multivibrator 12 is attached, even if the threshold voltage vT□ is set to the lower limit of the operating voltage of the microcomputer IO, the reset of the microcomputer IO can be performed stably and reliably, and moreover, it can be reset using ultrafine pulses. Malfunctions of the microcomputer 10 are prevented.

However, since the monostable multivibrator 12 is required, there is a drawback that the cost is high.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an inexpensive power supply circuit that can reliably reset electronic equipment such as a microcomputer when the AC power supply voltage drops.

[Disclosure of the invention]

The power supply circuit of the present invention includes a rectifying and smoothing circuit that rectifies and smoothes an AC power source, and a constant voltage that connects a capacitor between both output terminals to make the output voltage of the rectifying and smoothing circuit a constant voltage and supplies it as a power supply voltage to electronic equipment. a series circuit of a low impedance resistor and a switching element connected between both output terminals of the constant voltage circuit; and a series circuit of a low impedance resistor and a switching element connected between both output terminals of the constant voltage circuit; (2) a voltage detection circuit that turns off the switching element when the output voltage of the constant voltage circuit is higher and turns on all the switching elements when the output voltage of the constant voltage circuit is lower; , an integrating circuit that sets a large charging time constant and a small discharging time constant, charges through the resistor when the switching element is off, and discharges through the switching element when the switching element is on, and an output voltage level of this integrating circuit. The present invention is characterized in that it is configured to include a level discrimination circuit that discriminates between the two and applies a discrimination output to a reset input terminal of the electronic device.

An embodiment of the present invention will be explained based on FIGS. 6 to 8. In this power supply circuit, as shown in FIG.
The connection point between the resistor 13 and the switching transistor 14 is connected to the reset input terminal 10a of the microcomputer 10 through an integrating circuit 15 and a level discrimination circuit 19. The integration circuit 15 is composed of a capacitor 16, a resistor 17, and an ode 18, and is set to have a large charging time constant and a small discharging time constant. Further, the voltage detection circuit 11 detects the output voltage of the constant voltage circuit 9 through a resistor 20.
The voltage drop across the resistor 21 is compared with the base-emitter voltage VBE of the transistor 22.

In this case, the threshold voltage of the voltage detection circuit 11 is set to a value higher than the lower limit of the operating voltage of the microcomputer 10.

Next, the operation of this power supply circuit will be explained with reference to FIG. Time t. When the AC power supply 1 is turned on, the output voltage of the constant voltage circuit 9, that is, the power supply voltage vl, gradually increases as shown in FIG. 6W. At this time, since the power supply voltage V is lower than the threshold voltage VTH, the output voltage V of the voltage detection circuit 11 is at a high level as shown in FIG.
Therefore, when the switching transistor 14 is on, the voltage 3 at the connection point between the resistor 13 and the switching transistor 14 is at a low level as shown in FIG. Voltage) ■
4 is zero.

At time t, the output voltage of the constant voltage circuit 9 reaches the threshold voltage VT.
When R is exceeded, the output voltage 2 of the voltage detection circuit 11 becomes a low level, and therefore the switching transistor 14
is turned off, the voltage 3 at the connection point between the resistor 13 and the switching transistor 14 becomes high level, and as a result, the capacitor 16 of the integrating circuit 15 is turned off by the resistor 13.17'e.
When the voltage of the lever capacitor 16 reaches a predetermined level, the output voltage v5 of the level discrimination circuit 19 changes from a low level to a high level as shown in FIG. (2) At the rising edge of 5, the microphone C computer 10 is reset. Even after the reset, the capacitor 16 continues to be charged and reaches a constant voltage value.

Thereafter, at time t3, the output voltage of the constant voltage circuit 9 begins to decrease due to an abnormality, and when it falls below the threshold voltage VTH at time t4, the output voltage 2 of the voltage detection circuit 11 becomes a high level, and the switching transistor 14 is turned on, the charge in the capacitor 8 is rapidly discharged through the resistor 13, and the power supply voltage (2) drops rapidly. At the same time, the charge in the capacitor 16 of the integrating circuit 15 is rapidly discharged through the diode 18 and the switching transistor 14, and the voltage 3 becomes a low level, causing the integrating circuit 1
5's output voltage v4 suddenly drops, and the level discrimination circuit 19
The output voltage ■5 also becomes a low level.

Thereafter, when the abnormal state is canceled at time t5, the capacitor 8 of the constant voltage circuit 9 begins to be charged, and the power supply voltage, voltage (2), gradually increases.

Then, at time t6, the power supply voltage V becomes the threshold voltage T8
When the output voltage V of the voltage detection circuit 11 becomes low level, the switching transistor 14 is turned off, and the capacitor 16 of the integrating circuit 15 starts to be charged. When the voltage reaches a predetermined level, the output voltage 5 of the level discrimination circuit 19 becomes high level, and the microcomputer 10 is reset.

In this way, the power supply circuit of this embodiment has a power supply voltage of ■, (
The threshold voltage (output voltage of constant voltage circuit 9) is abnormal due to an abnormality.
When the voltage drops below TH, the switching transistor 14't is turned on by the voltage detection circuit 11, and thereby the constant voltage circuit 9(i')':1'n't8 is rapidly discharged through the resistor 13. When the abnormality is recovered, the output voltage v1 of the constant voltage circuit 9 is suddenly lowered, and the charge in the capacitor 16 of the integrating circuit 15 is rapidly discharged through the diode 18, so that the output voltage v4 of the integrating circuit 15 is rapidly lowered. The capacitor 8 of the constant voltage circuit 9 is gradually charged to gradually increase the output voltage of the constant voltage circuit 9, and when the output voltage V of the constant voltage circuit 9 exceeds the threshold voltage, the voltage detection circuit Switching transistor 1 by 11
4 is turned off and the capacitor 16 of the integrating circuit 15 is gradually charged to gradually increase the voltage v4 of the integrating circuit 15, and when the output voltage 4 of the integrating circuit 15 exceeds the predetermined value L Since the microcomputer IO is reset by the level discrimination circuit 19, even if an instantaneous power failure occurs, the microcomputer IO is given the same reset as when the power is initially turned on, making it possible to reliably reset the microcomputer IO. . Moreover, the integral circuit 15
Since the reset timing is delayed from the voltage recovery of the constant voltage circuit 9, even if the threshold voltage v'ra is set to the lower limit of the operating voltage of the microcomputer 10, the output voltage of the constant voltage circuit 9 is Since the operating voltage is higher than the lower limit of the operating voltage, the reset can be performed stably.Furthermore, since only one switching transistor 14 and the main circuit 15 are added, there is no increase in cost. do not have.

〔Effect of the invention〕

According to the power supply circuit of the present invention, it is possible to stably and reliably reset electronic equipment such as a microcomputer when the power supply voltage drops abnormally, and it is also inexpensive.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of a conventional power supply circuit, Figures 2 and 3 are waveform diagrams of each part, Figure 4 is a circuit diagram of a proposed example, Figure 5 is a waveform diagram of each part, and Figure 6 is a waveform diagram of each part. FIG. 7 is a circuit diagram of an embodiment of the present invention, and FIG. 7 is a specific circuit diagram of its main parts, and FIG. 8 is a waveform diagram of each part thereof. 1...AC power supply, 2...'-position transformer, 3...
Full wave rectifier, 4... Capacitor, 8... Capacitor, 9... Constant pressure DO path, 10... Microcomputer, 11... Voltage detection circuit, 13... Resistor, 14
...Switching transistor, 15...Integrator circuit, 16...Capacitor, 17...Resistor, 18...
Diode, 1919. Level discrimination circuit Figure 4■! 5 Figure 6 1 / Figure 7 C - Figure 8

Claims (1)

[Claims] A rectifying and smoothing circuit that rectifies and smoothes an AC power supply; a constant voltage circuit that connects a capacitor between both output terminals to constant voltage the output voltage of the rectifying and smoothing circuit and supplies it as a power supply voltage to electronic equipment; and this constant voltage circuit. A series circuit of a low impedance resistor and a switching element connected between both output terminals of A voltage detection circuit that turns off the switching element when the output voltage of the voltage circuit is higher and turns on the switching element when the output voltage of the constant voltage circuit is lower, and sets a large charging time constant. At the same time, the discharging time constant is set small, and the output voltage level of this integrating circuit is discriminated from an integrating circuit which is charged through the resistor when the switching element is off and discharged through the switching element when the switching element is on, and the discrimination output is an 'Iit source circuit comprising a level discrimination circuit applied to a reset input terminal of an electronic device;