JP3096676B2 - Power supply circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit, and more particularly to a power supply circuit which is applied to, for example, a VCR and drives a clock circuit built in a microcomputer even during a power failure.

[0002]

2. Description of the Related Art In a conventional power supply circuit 1 of this type shown in FIG. 2, when power is supplied to the primary side of a transformer 2, an AC voltage is generated on the secondary side. Smoothed. The terminal voltage of the electrolytic capacitor C1 is directly applied to another circuit 4 including a motor driving circuit and the like, and is applied to a Vcc terminal (power supply terminal) of the microcomputer 5 via a diode D2. Thus, the other circuit 4 and the microcomputer 5 are driven. When the supply of power stops due to the power failure, the terminal voltage of the capacitor C1 decreases, and the terminal voltage of the resistor R2, that is, the input voltage of the power failure detection terminal also decreases. The microcomputer 5 determines that a power failure has occurred when the terminal voltage of the resistor R2 falls below a predetermined threshold, and shifts from the normal mode to the power failure mode. In the power failure mode, the terminal voltage of the electric double layer capacitor C2 is supplied to the microcomputer 5, which drives the microcomputer 5.

[0003]

However, in such a conventional technique, a voltage is applied to the other circuit 4 unless a power failure occurs. In other words, power is consumed by the other circuit 4 even in a standby state where it is not necessary to operate the other circuit 4. In order to suppress the standby power, a switch may be provided before the other circuit 4 and a standby mode may be provided to open the switch during standby.
, The power failure cannot be detected in the standby mode.

[0004] Therefore, a main object of the present invention is to provide a power supply circuit capable of detecting a power failure in both the normal mode and the standby mode.

[0005]

The present invention provides a transformer,
Rectifying and smoothing the secondary voltage of the transformer to
A first rectifying / smoothing means for generating a first DC voltage for driving a load, a second rectifying / smoothing means for rectifying and smoothing the secondary voltage, an intermediate circuit between an output terminal of the second rectifying / smoothing means and a reference potential; An inserted second load, a power failure detection means for detecting a power failure based on a terminal voltage of the second load, a mode setting means for selectively setting a normal mode and a standby mode, and
In a power supply circuit including a disconnecting unit that disconnects the connection between the first load and the first rectifying / smoothing unit when the standby mode is set, the second load is connected in parallel with two different resistance values. Including a resistor, further comprising activation means for activating one of the two resistors according to the mode set by the mode setting means,
Power supply circuit.

[0006]

In the normal mode, the microcomputer and other circuits are driven by the DC voltage output from one rectifying and smoothing circuit. In the standby mode, the connection between the other circuit and the rectifying / smoothing circuit is cut off, and only the microcomputer is driven. In either mode, the microcomputer monitors the value of the DC voltage output from the other rectifying and smoothing circuit. When the supply of the commercial AC power is stopped due to the power failure, the electric charge of the capacitor provided in the other rectifying / smoothing circuit is consumed by the light emitting diode or the resistor. As a result, the terminal voltage of the capacitor, that is, the output voltage of the other rectifying / smoothing circuit decreases, and the power failure is detected by the microcomputer.

[0007]

According to the present invention, the power failure is detected by the second DC voltage whose value is reduced by the second load, so that the power failure can be detected in both the normal mode and the standby mode. The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG.
Includes a transformer 12 provided with a primary coil 12a and a secondary coil 12b. The high frequency switch circuit 22 is connected to the primary coil 12a. One end of the secondary coil 12b is connected to the rectifying and smoothing circuits 14 and 16, and the other end is connected to the ground (reference potential).

The rectifying / smoothing circuit 14 includes a diode D1 and an electrolytic capacitor C1, and the rectifying / smoothing circuit 16 includes a diode D3 and an electrolytic capacitor C3. The anodes of diodes D1 and D3 are commonly connected to one end of secondary coil 12b, and the cathodes are connected to one ends of electrolytic capacitors C1 and C3, respectively. Electrolytic capacitor C
The other ends of 1 and C3 are commonly connected to ground. The cathode of the diode D1 is also connected to a power supply terminal (V _CC terminal) of the microcomputer 18 via a power supply line L1, and the cathode of the diode D3 is connected to the power failure detection terminal of the microcomputer 18 via a power failure detection line L2.

A diode D2 is provided on the power supply line L1, and the anode and cathode of the diode D2 are
It is connected to the cathode of the diode D1 and the power supply terminal. The cathode of diode D2 is also connected to ground via electric double layer capacitor C2. A resistor R1 is provided on the power failure detection line L2, and one end of the resistance R1 is connected to a cathode of the diode D3 and the other end is connected to a power failure detection terminal. The other end of the resistor R1 and the power failure detection terminal are also connected to the ground via the resistor R2. That is, the terminal voltage of the electrolytic capacitor C3 is
2, divided voltage (terminal voltage of resistor R2)
Is applied to the power failure detection terminal.

The cathode of the diode D1 is further connected to the collector of the transistor Q2 via the resistor R9 and directly to the emitter of the transistor Q1. The emitter of the transistor Q2 is connected to the ground,
A resistor R13 is provided between the emitter and the base of the transistor Q2.
Is inserted. The collector of the transistor Q1 is connected to another circuit 20 including a motor drive circuit, and a resistor R6 is interposed between the emitter and the base of the transistor Q1. The base of transistor Q1 is connected to the collector of transistor Q3 via resistor R7. The emitter and base of transistor Q3 are connected to the ground and the collector of transistor Q2, respectively.
A resistor R10 is interposed between the base 3 and the emitter 3.

The cathode of the diode D3 is connected to the anode of the light emitting diode LED via a resistor R8.
The cathode of ED is connected to the collector of transistor Q4. The emitter of transistor Q4 is connected to the ground and to the base via resistor R12.
The cathode of diode D3 is also connected to the collector of transistor Q5 via resistor R3 and to the collector of transistor Q6 via resistor R4. The collectors of transistors Q5 and Q6 are commonly connected to ground. A resistor R5 is inserted between the emitter and the base of the transistor Q5, and a resistor R15 is inserted between the emitter and the base of the transistor Q6.

A control line L3 is connected to a power save terminal of the microcomputer 18, and the control line L3 is connected to a resistor R11,
Connected to the bases of transistors Q4, Q2 and Q6 via R14 and R16, respectively. The electrolytic capacitor C1 has a capacity of about 1000 μF, the electric double layer capacitor C2 has a capacity of about 0.47F, and the electrolytic capacitor C3 has a capacity of about 10 μF. Also,
The resistors R3 and R8 have a resistance value of about 560Ω, and the resistors R1, R2 and R5 have a resistance value of about 47KΩ.

When the operator operates the power switch 24, the microcomputer 18 is set to one of a normal mode and a power save mode (standby mode). The microcomputer 18 sets the output of the power save terminal to the low level in the normal mode, and sets the output of the power save terminal to the high level in the power save mode. As a result,
In the normal mode, power is supplied to the other circuit 20, but in the power save mode, the supply of power to the other circuit 20 is stopped.

In both the normal mode and the power save mode, the microcomputer 18 is connected to the power line L1.
Through the power failure detection line L2 to determine whether or not a power failure has occurred. When it is determined that a power failure has occurred, the microcomputer 18 shifts to a power failure mode.
Then, the microcomputer 18 drives the clock circuit 18a with the electric power from the electric double layer capacitor C2. Clock circuit 18a
Are driven by so-called thinning oscillation.

When the normal mode is set and a low level signal is output from the power save terminal, the transistor Q
4, Q2 and Q6 are turned off. The DC voltage is output from the rectifying / smoothing circuit 14 based on the commercial AC power supply, while the transistor Q2 is in the off state. Therefore, the output of the rectifying / smoothing circuit 14 turns on the transistor Q3, and further turns on the transistor Q1. Therefore, the other circuit 20 is driven by the output of the rectifying / smoothing circuit 14. In addition, since the DC voltage is output from the rectifying / smoothing circuit 16 and the transistors Q4 and Q6 are off, the LED and the transistor Q5 are turned off and on, respectively. The terminal voltage of the resistor R2 is applied to the power failure detection terminal, and the microcomputer 18 determines whether a power failure has occurred based on the terminal voltage.

When the power save mode is set in the microcomputer 18 and the output of the power save terminal rises, the transistors Q4, Q2 and Q6 are turned on. When transistor Q2 is turned on, transistors Q3 and Q1 are turned off, and power supply line L1 of other circuit 20 is turned off.
The connection to is blocked. As a result, the power supply line L1
Is connected only to the microcomputer 18, and the terminal voltages of the electrolytic capacitor C1 and the electric double layer capacitor C2 decrease to a value at which the microcomputer 18 can be driven. When the transistors Q4 and Q6 are turned on,
The diode LED emits light and the transistor Q5 is turned off. Even in the power save mode, a resistor R is connected to the power failure detection terminal.
2 is applied, and this terminal voltage takes the same value as in the normal mode. The microcomputer 18 determines whether a power failure has occurred based on the terminal voltage.

As can be seen from the above description, LE
D turns off in the normal mode and turns on in the power save mode. When a power failure occurs in the normal mode, the power stored in the electrolytic capacitor C1 is consumed by the other circuit 20, and as a result, the terminal voltage of the electrolytic capacitor C1 decreases rapidly. On the other hand, the electric charge of the electrolytic capacitor C3 is consumed by the resistor R3. As described above, in the normal mode, the transistor Q4 is turned off while the transistor Q5 is turned off, and the resistance value of the resistor R3 is equal to the resistors R1 and R2.
And considerably smaller than R4. Therefore, most of the current flows through the resistor R3, and the terminal voltage of the capacitor C3 gradually decreases. When the terminal voltage of the resistor R2 falls below a predetermined threshold, the microcomputer 18 detects a power failure,
Move to power failure mode. When shifting to the power failure mode, the microcomputer 18 drives the clock circuit 18a by thinning out oscillation based on the terminal voltage of the electric double layer capacitor C2.

In the power save mode, the power stored in the electrolytic capacitor C3 is consumed by the resistor R8 and the LED. As a result, the terminal voltage of the capacitor C3 and the terminal voltage of the resistor R2 gradually decrease, and the power failure mode is set when the terminal voltage of the resistor R2 falls below the threshold. The microcomputer 18 drives the clock circuit 18a with the electric power of the electric double layer capacitor C2 as described above.

As can be seen from the above description, the power stored in the electrolytic capacitor C3 is supplied by the resistor R3 when a power failure occurs in the normal mode, and by the resistor R8 and the LED when a power failure occurs in the power save mode. Consumed. When a power failure occurs in any of the modes, the terminal voltage of the electrolytic capacitor C3 decreases at substantially the same rate from the same value, and it is determined that the power failure has occurred when the terminal voltage of the resistor R2 falls below a predetermined threshold. For this reason, a power failure can be detected regardless of the mode at the time of the power failure occurrence.

In the power save mode, the transistor Q2 is turned on. As a result, the power supply line L of the other circuit 20 is turned on.
1 is disconnected. Therefore, power consumption can be suppressed in a standby state in which it is not necessary to drive the other circuit 20. In this embodiment, a resistor and a light emitting diode are used as loads for consuming the power of the electrolytic capacitor C3 when a power failure occurs, but other loads may be used as long as electric charges are consumed. .

The electrolytic capacitor C1 is a first capacitor, and the electrolytic capacitor C3 is a second capacitor.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional technique.

[Explanation of symbols]

 10 Power supply circuit 14, 16 Rectifying and smoothing circuit 18 Microcomputer LED Light emitting diode

Continuation of the front page (56) References JP-A-60-176417 (JP, A) JP-A-7-298488 (JP, A) JP-A-8-263973 (JP, A) JP-A-9-308136 (JP, A) JP-A-11-281681 (JP, A) JP-A-58-147041 (JP, U) JP-A-61-143284 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB) G01R 19/145-19/165 G06F 1/26-1/32 H02J 1/00-1/16 H02J 9/00-9/08

Claims (3)

(57) [Claims] A transformer for rectifying and smoothing a secondary voltage of the transformer to obtain a first voltage;
A first rectifying / smoothing means for generating a first DC voltage for driving a load; a second rectifying / smoothing means for rectifying and smoothing the secondary voltage; an intermediate circuit between an output terminal of the second rectifying / smoothing means and a reference potential; A second load inserted, a power failure detection means for detecting a power failure based on a terminal voltage of the second load, a mode setting means for selectively setting a normal mode and a standby mode, and when the standby mode is set. A power supply circuit having a disconnection means for disconnecting the connection between the first load and the first rectifying / smoothing means, wherein the second loads are connected in parallel and have different resistance values.
A power supply circuit, comprising: one resistor; and an activation unit that activates one of the two resistors in accordance with a mode set by the mode setting unit. 2. The first rectifying / smoothing means has one end connected to the first rectifying / smoothing means.
A first capacitor connected to a load; the second rectifying / smoothing means includes a second capacitor having one end connected to the second load; and a second capacitance of the second capacitor is equal to a first capacitance of the first capacitor. The power supply circuit according to claim 1, wherein the power supply circuit has less than one capacity. 3. The power supply circuit according to claim 1, wherein one of said two resistors is a light emitting diode.