JPS5897720A - Power supply circuit - Google Patents

Abstract

PURPOSE:To reduce the power consumption of an auxiliary power supply, by switching a load to a holding state from an active state with the 1st switching circuit which works when the voltage of a primary power supply becomes lower than a certain level and then switching the primary power supply to an auxiliary power supply when the voltage of the primary power supply drops further. CONSTITUTION:When the constant voltage Vm supplied from a primary power supply battery Bm, a resistance R1 and a Zener diode D2 lowers less than a certain level, a TR1 is turned off. Thus an active/holding switching terminal Run/Halt of a load circuit L is set at a low level, and the load L is set in a holding state regardless of the ON/OFF of a switching SW. As a result, the power consumption is reduced. When the voltage Vm lowers furhter, a TR2 is turned off. At the same time, a TR3 is turned on from off, and the voltage of an auxiliary power supply battery Bb is applied to a terminal Vdd of the load L to maintain the holding state of the load L. This can prevent the waste of the battery Bb. Such a power supply circuit is suited to a power supply of a computer.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a power supply circuit having an auxiliary power supply in addition to the main power supply, and an object of the present invention is to provide an excellent power supply circuit that can prevent the auxiliary power supply from being inadvertently consumed more than necessary. This is the purpose.

In general, for devices with built-in microcomputers, etc., it is necessary to provide a separate auxiliary power source to prevent information stored in the microcomputer from disappearing when replacing the main power supply battery, etc. . Therefore, conventionally, power supply circuits used in devices on the 0th layer have often been configured as shown in FIG. In Figure 1, 1 is a battery for the main power supply, 2.3 is a resistor and constant voltage diode that constitute a constant voltage circuit, 4.6 is a switching diode, 6 is a battery for auxiliary power supply, 7 is a resistor, and 8 is a switching diode. 9 is a load circuit such as a microcomputer, and 9 is a changeover switch for switching the operation of the load circuit 8 between an operating state and a holding state.

Battery 1 for main power supply in the conventional power supply circuit shown in Figure 1
has sufficient power supply capability, a constant voltage appears at the connection point between the resistor 2 and the constant voltage diode 3 by the constant voltage diode 3, the diode 4 is turned on, and the constant voltage is applied to the load circuit 8. Ru. The main power supply battery 1 has a power supply capacity of 3.

When the main power source battery is removed because the system no longer has one, the diode 5 is turned on and a predetermined voltage is applied from the auxiliary power source battery 6 to the load circuit 8.

By the way, in this case, in the conventional power supply circuit, power is supplied from the auxiliary power supply battery 6 to the negative disturbance circuit 8 regardless of the on/off state of the changeover switch 9, that is, the operating state or holding state of the load circuit 8. If you accidentally turn off the changeover switch 9 and remove the main power battery 1 while the load circuit 8 is in operation, the auxiliary power battery 6 will wear out quickly and the information stored in the load circuit 8 will be lost. This was extremely inconvenient, as it could sometimes be erased by mistake.

The present invention eliminates the above-mentioned conventional drawbacks, and is configured so that the load circuit is forcibly switched to the holding state before switching from the main power source to the auxiliary power source. It is.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A power supply circuit according to the present invention will be described below with reference to drawings of an embodiment. FIG. 2 is an electrical wiring diagram of one embodiment of the power supply circuit of the present invention, in which Bm is a main power battery, Bb is an auxiliary power battery, R+ to R7 are resistors, and Dz is a constant voltage diode. , DI, D2 are diodes, TR+~T
R5 is a transistor constituting a switching circuit, and Sw is a changeover switch for switching a load circuit such as a microcomputer between an operating state and a holding state.

In the above embodiment, if the voltage of the main power battery Bm is sufficiently high and has sufficient power supply capacity, a constant voltage determined by the constant voltage diode Dz appears at the connection point between the resistor R1 and the constant voltage diode Dz. It is applied to the power supply terminal of the load circuit via the diode Dz. In this case, the connection point of resistors R3 and R4, resistors R4,
Each potential at the connection point of Rs maintains a predetermined value, and both the first and second transistors TR1 and TR2 are in an on state. Therefore, the third transistor TRs
is in the off state, and the auxiliary power supply battery Bb is completely disconnected. Since the first transistor TR+ is in the on state, when the switch Sw is in the OFF state, the operating state of the load circuit and the voltage applied to the holding state switching terminal Run/HOI(i) are changed. is at a high level, it enters an operating state, and when turned on, the switching terminal Run/Ho1d becomes a low level and is switched to a holding state.

Now, if the voltage of the main power supply battery Bm drops below the constant voltage determined by the voltage regulator diode Dz, the voltage at the connection point between the resistor R1 and the voltage regulator diode Dz will similarly drop. Therefore, in this case, first, the voltage applied between the emitter and the emitter of the first transistor TIh becomes less than a certain voltage, and the first transistor TR+ first turns off. When the first transistor TR+ is turned on, the terminal 'R' for switching the operating state of the load circuit
When un/Ho1d is at low level, switch Sw
The load circuit enters the holding state regardless of whether it is on or off.

Then, when the voltage of the main power battery Bm further decreases, the second
The voltage applied between the base and emitter of the transistor R2 also becomes less than a certain voltage, and the second transistor TR2 is similarly turned off. When the second transistor TR2 is turned off, the third transistor TRs, which has been off until now, is turned on, and the power supply voltage is applied to the auxiliary power supply battery Bb and the load circuit.

When the power supply voltage is applied from the auxiliary power supply battery Bb to the load circuit, the first transistor TR+ is off, and the load circuit is forcibly switched to the holding state, so the power consumption by the load circuit is reduced. is extremely small, and consumption of the auxiliary power battery Bb is significantly reduced.

In addition, in the example, the first. Second transistor TR+.

The pace bias of TR2 is connected to resistors R in series with each other.
5. It is obtained from the connection point of Ra and Rs, but the third
As shown in the figure, each transistor TR1, TR2
Separate bias resistors Ra, Rq, Rho
, Ra1 are connected, and these resistors Ra, Ii+9
, Rho, and R++ may be used to obtain the pace bias of the transistors TRI and TR2, respectively.

As is clear from the above embodiments, the seven-vane power supply circuit of the present invention has a main power supply and an auxiliary power supply, and operates when the voltage of the main power supply falls below a certain first constant voltage. The first switching circuit forcibly switches a load circuit such as a microcomputer to a holding state, and the second switching circuit operates when a second constant voltage lower than the first constant voltage is reached. The second switching circuit is configured so that power is supplied to the load circuit from the auxiliary power supply, and when the auxiliary power supply is used, the load circuit is always forced into a holding state.
Therefore, there is no possibility that the auxiliary power source will be consumed prematurely, and even a small capacity auxiliary power source can sufficiently fulfill its role, which is extremely advantageous in practice.

[Brief explanation of the drawing]

FIG. 1 is an electrical wiring diagram of a conventional power supply circuit, and FIG. 2 is an electrical wiring diagram of an embodiment of the power supply circuit of the present invention. FIG. 3 is an electrical wiring diagram of another embodiment. Bm...Battery for main power supply, R1~R1N...
・・Resistance %Dz°−・・・・・・ Constant voltage diode, T
R+~TR3...Transistor, Ih, D
2...Diode, L...Load circuit,
Sw...Switch for switching operating state and holding state,
Bd...Battery for auxiliary power supply.

Claims (1)

[Claims] A first switching circuit that operates when the voltage of the main power source drops below the first constant voltage and a voltage of the main power source
A second switching circuit that operates when the constant voltage drops below a second constant voltage that is lower than the constant voltage b)
The output of the first switching circuit is configured to forcibly switch a load circuit such as a microcomputer from an operating state to a holding state, and the output of a second switching circuit is normally disconnected from the load circuit. A power supply circuit configured such that an auxiliary power supply is connected to the load circuit, and power is supplied from the auxiliary power supply to the load circuit.