JPS5897719A - power circuit - Google Patents

Abstract

PURPOSE:To reduce the consumption of an auxiliary power supply, by switching forcibly a load to a holding state from an active state with a transistor which is turned off when a primary power supply has the voltage less than a certain level and then switching the primary power supply to the auxiliary power supply when the voltage of the primary power supply lowers further. CONSTITUTION:When the constant voltage Vm supplied from a primary power supply battery Bm, a resistance R1 and a Zener diode Dz becomes lower than a certain level, the base voltages of resistances TR1 and TR2 drop. At the same time, the TR1 and TR3 are turned off. As a result, an active/holding state switching terminal Run/Hold of a load circuit L is set at a low level regardless of the ON/OFF of a switch SW. This is equivalent to the fact that the SW is turned on. Thus the load L is set in a holding state to reduce the power consumption. When the voltage of the primary power supply lowers further, both the TR2 and TR4 are turned off whch a TR5 turned on. Then the voltage of an auxiliary power supply battery Bb is applied to a terminal Vdd of the load L. This prevents the waste of the battery Bb. Such a power supply circuit is suited to 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.

Generally, in devices with a built-in microcomputer, etc., it is necessary to provide a separate auxiliary power source in order to prevent information stored in the microcomputer from disappearing when replacing the main power source battery. therefore,
Conventionally, power supply circuits used in this type of equipment have often been configured as shown in FIG. In Figure 1, 1 is a battery for the main power supply, 2 and 3 are resistors and constant voltage diodes that constitute a constant voltage circuit, 4 and 6 are switching diodes, 6 is a battery for auxiliary power supply, 7 is a resistor, and 8 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.

In the conventional power supply circuit shown in Fig. 1, a battery 1 for main power supply is used.
When the voltage regulator has a power supply capability of about 100 volts, a constant voltage appears at the connection point between the resistor 2 and the constant voltage diode 3 by the 3B constant voltage diode 3, the diode 4 is turned on, and the above constant voltage is applied to the load. applied to circuit 8. The main power battery 1 no longer has power supply capacity,
Therefore, when the main power source battery is removed, the diode 6 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 battery 6 to the load 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 the main power battery 1 is removed while the changeover switch 9 is turned off and the load circuit 8 is in operation, the auxiliary power battery 6 will be consumed very 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 drawbacks of the conventional technology.
, when switching from main power to auxiliary power
7719(2) is configured so that the load circuit is forcibly switched to the holding state before that.

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 connection diagram of one embodiment of the power supply circuit of the present invention, in which Bm is the main power battery;
Bb is a battery for auxiliary power supply, R1-R9 are resistors, TR1-T
R5 is a transistor, Dz and D5 are constant voltage diodes, and DI and D2 are switching diodes S.
W is a switch for changing the operating state and holding state of the load circuit.

In the above embodiment, if the main power supply battery Bm has sufficient power supply capacity, the resistor R1 and the constant voltage diode Dz
determined by a constant voltage diode at the connection point with n
A constant voltage appears, which is applied to the power supply terminal Vdd of the load circuit 19 via the diode, Dl. In this case, the base potentials of transistors TR1 and TR20 also maintain a predetermined value, and the first. Second. Third. Fourth transistors TR1, TR2, TR5, and TR4 are all in an on state.

Therefore, the sixth transistor TRs is in an off state, and the auxiliary power supply battery Bb is completely disconnected. Since the third transistor TRs is in the on state, the load circuit is in the operating state when the switch SW is off, and is switched to the holding state when it is on.

Now, assume that the voltage of the main power supply battery Bm has decreased below a certain first constant voltage, that is, the Zener voltage of the voltage regulator diode nz. In this case, since the potential at the connection point between the resistor R1 and the constant voltage diode Dz similarly decreases, the transistor TR1.

The base potential of TR2 similarly decreases; therefore, first the first transistor TR1 is turned off, and the third transistor TRs is turned off. Therefore, regardless of whether the switch SW is on or off, the level of the load circuit switching terminal Run/Ho1d becomes low, and the state is substantially the same as when the switch SW is turned on. That is, in this state, first, the negative circuits are forced into the holding state and switched so that the power consumption by the load circuits is reduced. Suppose that the voltage of the main power supply battery Bm further decreases and the potential at the connection point between the resistor R1 and the constant voltage diode D2 decreases below a predetermined second constant voltage? Transistor TR2 is turned off, and transistor TR4 is turned off. Therefore, in this state, the sixth transistor TRs is turned on, and the voltage of the auxiliary power supply battery Bm is changed to the sixth transistor TRs.
It is applied to the power supply terminal Vdd of the load circuit via Rs.

In this way, according to the above embodiment, when the voltage of the main power supply battery Bm drops below the first constant voltage tl,fc, the load circuit L75E is first forced into the holding state, and the power generated by the load circuit is reduced. It works to reduce consumption. Then, when the voltage of the main power battery Bm further drops below a predetermined second constant voltage, the voltage of the auxiliary power battery Bb is applied to the load circuit for the first time, and the voltage of the auxiliary power battery Bm is applied to the load circuit for the first time. Battery Bb consumption is significantly reduced.

As is clear from the embodiments described above, the power supply circuit of the present invention has a main power supply and an auxiliary power supply, and operates a microcontroller by operating a switching transistor that turns off when the voltage of the main power supply falls below a certain level. It is configured such that a load circuit such as a computer is forcibly switched to a holding state, a separately provided switching transistor is turned on in this state, and power is supplied to the load circuit from the auxiliary power supply through this transistor. When using an auxiliary power supply, the load circuit is always forced into a holding state, so the auxiliary power supply never runs out prematurely, and even a small-capacity auxiliary power supply can fulfill its role. It is extremely advantageous.

[Brief explanation of the drawing]

FIG. 1 is an electrical connection diagram of a conventional power supply circuit, and FIG. 2 is an electrical connection diagram of an embodiment of the power supply circuit of the present invention. Bm...Battery for main power supply, R1-R9...
・Resistance, Dz, Ds... Constant voltage diode, TR1~TRs... Transistor, D
I, D2...Diode, L...Load circuit, SW...Switch for operating state and holding state, Bb...Battery for auxiliary power supply.

Claims (1)

[Claims] A first transistor that turns off when the voltage of the main power supply becomes less than a predetermined first constant voltage; A second transistor that turns off when The load circuit is configured to forcibly switch from an operating state to a holding state, and is turned on by a second transistor. A sixth transistor connected between the auxiliary power supply and the load circuit is controlled to be turned on and off by the fourth transistor, which is controlled to be off, so that the voltage of the main power supply is lower than a predetermined second constant voltage. The power supply circuit is configured such that when the load is turned off, the auxiliary power is applied to the load through the sixth transistor.