JPS6219057Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a power supply circuit that supplies voltage to a load, etc., which is an electronic device, and particularly when a separate power supply is used to supply power to parts that require high reliability. The present invention relates to a power supply circuit that enables voltage to be supplied from another power supply (for example, a general power supply) in the event of a failure.

Conventionally, there is a power supply circuit as shown in FIG. 1 as a dual power supply system. This circuit has two power supplies E1 and E2, and the positive polarity sides of these power supplies E1 and E2 are connected to a load L via diodes D1 and D2, respectively, and the negative polarity sides of the power supplies E1 and E2 are connected to a load L through diodes D1 and D2, respectively. The other end of the load L is connected to the common return wire. In this circuit, two power supplies E1 and E2 perform an OR operation using respective diodes D1 and D to supply a power supply voltage to a load L.

By the way, if the load L1 is installed in parallel to one power source E2 as shown in FIG. 2, and each power source voltage is about +5V, for example, both diodes D
The voltage E appearing at the common part of 1 and D2 is E=E2-V _D2 . However, V _D2 is a voltage drop across diode D2. Therefore, when the load L is TTL/IC and D2 is a silicon diode, the voltage E drops to E4, about 3V by the diode D2, and the load L
There is a problem that the voltage drops below the operating voltage.

Therefore, in order to compensate for this drawback, a control transistor is used instead of the diode D2 as shown in Figure 3.
A resistor R is provided between the base side of TR and the common return line.
A possible configuration is to insert . In this circuit configuration, if the base resistance R is made small enough to bring the control transistor TR into the saturation region,
The voltage drop VTR of the transistor TR is about 0.2V even if it is a silicon transistor, so the voltage supplied to the load L can be set to E4.8V.

However, with this circuit configuration, if the power supply E2 fails or the power switch (not shown) of the power supply E2 is turned off, the control transistor
A situation occurs in which the transistor operation of TR is such that the emitter and collector are reversed, and the voltage of the power source E1 is supplied to the load L1 side. Therefore, it is necessary to make the capacity of the power source E1 larger than necessary, and this causes inconvenience when maintaining the load L1 itself.

The present invention has been developed in view of the above-mentioned circumstances, and is designed to operate the control transistor in the reverse direction using a simple circuit configuration even if one of the power supplies fails in an electronic device that uses dual power supplies. The present invention provides a power supply circuit that can supply power to a load without blocking the power supply and increasing the power supply capacity.

Embodiments of the present invention will be described below with reference to the drawings. In addition, in the circuit of the present invention, the same parts as in FIG. 3 are given the same reference numerals, and some explanations are omitted.
First, FIG. 4 shows an example of the configuration of a power supply circuit, which includes a field effect transistor for controlling the base current between the control transistor TR and the base resistor R.
A comparator circuit COM is provided in which a FET is inserted, and a positive and negative input section is connected to the collector and emitter of a control transistor TR, and an output section is connected to the field effect transistor FET.

For example, when power supply E2 fails or this power supply E
Comparator circuit when power switch 2 is turned off.
COM detects the voltage difference between the emitter and collector of the control transistor TR, and controls the base current of the transistor TR so that the voltage of the power supply E1 is not supplied to the load L1 side via the control transistor TR, thereby reducing the base voltage. Set approximately equal to the collector voltage.

Further, in the event of a failure of the power source E1, as described above, since the voltage drop across the control transistor TR is small, the voltage of the power source E2 can be supplied to the load L almost unchanged.

Next, FIG. 5 shows another embodiment of the power supply circuit of the present invention, which is a comparator circuit shown in FIG.
A similar purpose is achieved using a single diode D3 in place of the COM and field effect transistor FET. That is, a diode D3 is inserted between the positive polarity side of the power source E1 and the base of the control transistor TR, and when the power source E1 is normal, the diode D3 maintains the base voltage of the control transistor TR at E1-V _D3 . The same transistor
Prevents complete saturation of TR. In other words, as described above, the diode D is connected to the base of the transistor TR.
By connecting 3, the current flowing through the diode D3 is reduced to several tenths of the current flowing through the diode D1, and by adding this to the base of the control transistor TR, the transistor TR is completely saturated. It is set so that it does not occur.

Therefore, in the above circuit configuration, the power source E
2 is destroyed or turned off, the base voltage of the control transistor TR becomes E1-V _D3 as described above, which is equal to the collector voltage E (=
E1-V _D1 ) or higher, the control transistor TR becomes non-conductive.

Next, when the power source E1 is destroyed or turned off, the diode D3 is cut off, and the voltage E is supplied from the power source E2 to the load L by saturation of the control transistor TR.

FIG. 6 shows another example of the circuit of the present invention,
This has a dual configuration in which a power source E1 is supplied to the collector side of the control transistor TR via a diode D1.

Now, assuming that these power supplies are E11 and E12, diodes D11 and D11 are connected from the positive polarity sides of these power supplies E11 and E12 to the collector of the transistor TR, respectively.
Similarly, diodes D31 and D32 are connected to the base of the transistor TR from the positive polarity sides of the power supplies E11 and E12, respectively.

In this circuit configuration, when the power supplies E11, E12 or E2 are destroyed or in an off state, the operation is similar to that described above, and a predetermined voltage can be supplied to the load L.

As detailed above, according to the present invention, in a device having a first and second power supply and supplying these power supply voltages to an electronic device that is a load, the load is connected to the second power supply via a control transistor. Since the second power supply voltage is configured to supply power to the load, even if there is a failure or the like in the first power supply, the second power supply voltage can be supplied to the load with a small voltage drop. Further, since a base voltage control circuit is provided that maintains the base voltage of the control transistor at a predetermined voltage to prevent conduction in the event of a failure or the like in the second power supply, the second power supply is connected to the base voltage of the control transistor. Even if another load unrelated to the load is provided in parallel, the first power supply voltage is not supplied to the other load, and therefore a power supply failure can be dealt with without particularly increasing the power supply capacity.

[Brief explanation of the drawing]

Figures 1 and 2 are configuration diagrams of conventional circuits;
The figure is a circuit configuration diagram that can be considered as an improvement of Figure 2.
4 to 6 are configuration diagrams showing one embodiment of the power supply circuit according to the present invention, respectively. E1, E11, E12...first power supply, E2...
...power supply, L, L1...load, D1...diode, TR...control transistor, COM...comparator circuit, FET...field effect transistor, D3...base voltage control diode.

Claims (1)

[Claims for Utility Model Registration] (1) A vehicle having a first and second power supply, capable of supplying the voltage of these power supplies to the first load, and providing a second load in parallel with the second power supply. In a power supply circuit comprising: a diode and a control transistor inserted between the first load and the first and second power sources to prevent interference between the power sources; A power supply circuit comprising: a base voltage control circuit that maintains a base voltage at a predetermined voltage and makes the control transistor non-conductive. (2) The base voltage control circuit detects the differential voltage between the emitter and collector of a control transistor using a comparator circuit, controls the base current, and sets the base voltage of the transistor to a predetermined voltage. The power supply circuit described in item 1. (3) The base voltage control circuit is a utility model in which a base voltage control diode is provided between the first power supply and the base of the control transistor in a forward direction from the first power supply to the base of the control transistor. A power supply circuit according to claim 1. (4) If multiple power supplies serve as the first power supply,
A utility model according to claim 3, wherein base voltage control diodes are provided between these power supplies and the base of the control transistor in a forward direction from each power supply to the base of the control transistor. Power supply circuit.