JPH0546097Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a current supply circuit that can supply current to a load in accordance with a control signal and prevents excessive current from flowing during overload. The present invention particularly relates to a current supply circuit suitable for use in equipment that uses small capacity batteries as a power source.

(B) Prior Art As a current supply circuit capable of supplying a constant current to a load such as a relay in response to a control signal, a circuit as shown in FIG. 2 can be considered. In FIG. 2, when an "L" level control signal is applied to control terminal 1, transistor 2 is turned off and transistors 3, 4 and 5 are turned on, so that a constant current is supplied from output terminal 6 to relay 7. . Further, when the relay 7 is short-circuited or overloaded, the voltage at the output terminal 6 decreases, so the voltage at point A also decreases, and the transistor 3 turns off. Then,
Transistors 4 and 5 are turned off and current supply is limited.

(c) Problems to be solved by the invention By the way, in the circuit shown in Figure 2, the starting level of the circuit protection operation due to short circuit or overload is set by resistor 8.
and the resistance value of the relay 7. Therefore, the value of the resistor 8 is required to be relatively small. However, this poses a problem in that a large current flows through the transistor 2 while the transistor 2 is on, increasing current consumption. In particular, there is no problem when the power supply terminal 9 is connected to a commercial power source with sufficient capacity, but it becomes a problem when it is connected to a battery or the like with a small capacity.

(d) Means for Solving the Problems The present invention has been made in view of the above points, and includes a first transistor whose emitter is connected to a power supply terminal and whose collector is connected to a load, and which has a common base with the first transistor. a second transistor connected in a current mirror relationship; a starting resistor and a first switching transistor connected in series between a common base of the first and second transistors and ground;
and a constant current circuit that sinks a common base current of the second transistor, a second switching transistor that controls the operation of the constant current circuit, and a detection circuit that detects the current flowing through the first transistor.
and a third switching transistor that controls the operation of the constant current circuit according to the output signal of the detection circuit, and the first and second switching transistors are controlled according to the control signal. Features.

(E) Effect According to the present invention, a short circuit state or an overload state of a load is detected using only the resistance in the current supply circuit,
The base current of the first transistor for current supply is limited in accordance with the detected output.

(F) Embodiment Figure 1 is a circuit diagram showing an embodiment of the present invention.
10 is a first transistor whose emitter is connected to a power supply terminal 11 and its collector is connected to a relay 12; 13 is a second transistor connected to the first transistor 10 in a current mirror relationship; and 14 is a transistor that responds to a control signal from a control terminal 15. 16 is a starting resistor connected between the common base of the first and second transistors 10 and 13 and the collector of the first switching transistor 14; 17 is in a current mirror relationship; A constant current circuit 22 includes third and fourth transistors 18 and 19 connected to each other, a resistor 20, and a diode 21, and sinks current from the base and collector of the second transistor 13; A second switching transistor switches and controls the operation of the circuit 17 , 23 is a voltage dividing resistor that operates as a detection circuit for detecting that an excessive current flows through the first transistor 10, and 24 is the output of the voltage dividing resistor 23. This is a third switching transistor that switches and controls the operation of the constant current circuit 17 according to a signal.

Next, the operation will be explained. "H" from control terminal 15
When a level control signal is applied, the first and second switching transistors 14 and 22 are turned on.
When the first switching transistor 14 is turned on, a base current flows from the common base of the first and second transistors 10 and 13 via the starting resistor 16, so that current is supplied from the collector of the first transistor 10 to the relay 12. . At this time, if the resistance value of the relay 12 as a load is normal, an "H" level voltage is generated at point B of the voltage dividing resistor 23, and the third switching transistor 24 is turned on. When the third switching transistor 24 is turned on, the constant current circuit 17 starts operating, and a constant current flows through the collector-emitter path of the fourth transistor 19. The constant current is reversed by a current mirror circuit consisting of first and second transistors 10 and 13 and supplied to relay 12 . Here, the first
If the emitter area of the transistor 10 is set to be n times larger than that of the second transistor 13, the current flowing through the second transistor 13 will be n times larger than that of the first transistor.
A relay 12 is supplied from the collector of the transistor 10 .

Next, a case will be described in which the relay 12 becomes short-circuited or overloaded in this state. In this case, the first
Since the collector voltage of the transistor 10 becomes zero or a very small value, the voltage at point B of the voltage dividing resistor 23 also decreases, and the third switching transistor 24 is turned off. Then, the constant current circuit 17 stops operating, and the collector current of the second transistor 13 flows to the first switching transistor 14 via the starting resistor 16.
Since the collector current of is determined according to the value of the starting resistor 16, by setting the resistance value appropriately large, the value of the collector current can be reduced, and the current flowing through the first transistor 10 can be limited to a predetermined value. I can do it. As a result, current consumption during short circuit or overload can be minimized.

Further, when an "L" level control signal is applied to the control terminal 15, the first and second switching transistors 14 and 22 are turned off.
The base currents of transistors 10 and 13 are no longer able to flow, and first transistor 10 is turned off.
Therefore, no current is supplied to the relay 12.

(g) Effects of the invention As described above, according to the invention, it is possible to provide a current supply circuit that can supply current to a load in accordance with a control signal and can also limit current in the event of a short circuit or overload. . In particular, when current is limited, current consumption can be kept to a minimum, so even if a battery is used as a power source, the amount of battery consumption can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional current supply circuit. 10...First transistor, 13...Second transistor, 14...First switching transistor, 16...Starting resistor, 17 ...Constant current circuit, 2
2...Second switching transistor, 23...
Voltage dividing resistor, 24...Third switching transistor.

Claims (1)

[Claims for Utility Model Registration] A current supply circuit capable of supplying or cutting off current to a load according to a control signal and limiting current in the event of an overload, the emitter being a power supply terminal and the collector being a load. a first transistor connected to the base; the first transistor and the base are commonly connected;
a second transistor in a current mirror relationship; a starting resistor and a first switching transistor connected in series between the common base of the first and second transistors and ground; and a current of the common base of the first and second transistors. a second switching transistor that controls the operation of the constant current circuit; a detection circuit that detects the current flowing through the first transistor; and a detection circuit that detects the current flowing through the first transistor; a third switching transistor that controls the operation of the current supply circuit, and the current supply circuit is configured to control the first and second switching transistors in accordance with the control signal.