JPH0715343Y2 - Power supply output short circuit / open circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an output short circuit / open detection circuit for a power supply device having a constant voltage circuit.

[Conventional technology]

As an output short circuit / open detection circuit of a conventional power supply device, for example, there is one as shown in FIG. In FIG.
Reference numeral 1 is a DC power source such as a battery, 2 is a current for converting an output current of the DC power source 1 into a voltage, for example, a current detection resistor.
A voltage conversion circuit 3, a constant voltage circuit for stabilizing the power supply voltage applied from the DC power supply 1 through the current-voltage conversion circuit 2, 4 is an output terminal of the constant voltage circuit 3, and 5 is a current-voltage conversion circuit 2. A voltage amplifier circuit for amplifying the converted voltage, 6 compares the output voltage V _C of the voltage amplifier circuit 5 with the reference voltage V _A, and outputs an open circuit detection signal S _A when V _C ≤V _A The circuit 7 compares the output voltage V _C with the reference voltage V _B to obtain V _C
This is a comparison circuit that outputs the output short circuit detection signal S _B when ≧ V _B. The reference voltage V _A is the current-voltage conversion circuit 2 during normal operation.
Is selected to be a value lower than the above output voltage V _C according to the minimum current flowing through the current detection resistor. Also, the above reference voltage V _B
Is selected to be a value higher than the output voltage V _C according to the maximum current flowing through the current detection resistor in a normal state.

Therefore, according to the above configuration, under normal conditions, V _C > V _A and V _C <
It becomes V _B , and output open / short circuit detection signals S _A and S _B cannot be obtained. Then, when the output terminal 4 is opened, the output current of the DC power supply 1 becomes the minimum and V _C ≦ V _A , so the comparison circuit 6
The output release detection signal S _A is obtained from the above. Also, output terminal 4
Is short-circuited (including a ground fault), the output current of the DC power supply 1 becomes maximum and V _C ≧ V _B , so that the output short-circuit detection signal S _B is obtained from the comparison circuit 7.

[Problems to be solved by the device]

However, the output short circuit of such a conventional power supply device
In the open circuit detection circuit, the short circuit detection and the open circuit detection are configured to detect the short circuit detection and the open circuit detection by the voltage across both ends of the current detecting resistor in the current-voltage converting circuit 2 according to the current. Comparison circuits 6 and 7 are required to compare the voltage generated across the two resistors with the preset short-circuit detection and open-circuit detection reference voltages V _A and V _B , respectively. As
There was a problem that the cost would increase.

This invention has been made in view of such a conventional problem, in which an output short circuit detection resistor is connected in series with a current detection resistor and a transistor is controlled by the voltage across the current detection resistor. The purpose of this invention is to solve the above problems by detecting an abnormality based on the output of a transistor.

[Means for Solving the Problems]

The output short circuit / open circuit detection circuit of the power supply device according to the present invention is
Two resistors are provided in series between the AC power supply and the constant voltage circuit, and a transistor whose base and emitter are connected is provided at both ends of the resistor on the constant voltage circuit side. The collector output of this transistor is compared with a predetermined value. An abnormality determination circuit for determining abnormality is provided.

[Action]

The transistor in this device is
Since it is turned off and the collector output does not exceed the above specified value, an abnormality detection signal is obtained.It turns on when the output is short-circuited, but since the collector output falls below the normal value and does not exceed the above specified value, the abnormality detection signal Is obtained.

〔Example〕

 The invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention, in which parts corresponding to those in FIG. First, the configuration will be described. 8 is a current detection resistor of the current-voltage conversion circuit 2 described above, 9 is a short circuit detection resistor connected in series with the current detection resistor 8, and 10 is an emitter / base for current detection. A transistor connected to both ends (between a and b) of the resistor 8, 11 is a level securing resistor connected between the collector of the transistor 10 (point c) and ground, and 12 is a collector output voltage V _{D at the} point c and a predetermined value. Is an abnormality determination circuit that outputs an abnormality detection signal S _C when V _D <V _E by comparing the threshold voltage V _E of the above.

FIG. 2 shows an example of the circuit configuration of the abnormality determination circuit 12, which includes a transistor 12a, a load resistor 12b and a base resistor 12c,
12d, the collector output voltage V _D is higher than the threshold voltage V _E determined by the base resistors 12c and 12d, and when V _D <V _E , the transistor 12a is turned off and the high level abnormality detection signal S _C Is output.

The current detection resistor 8 and the short circuit detection resistor 9 shown in FIG. 1 normally generate a voltage between a and b that exceeds the base-emitter voltage V _BE of the transistor 10 and require the constant voltage circuit 3. It has been selected to have a sufficient electric current. Further, the level securing resistor 11 is selected to have a size capable of generating a collector output voltage V _D equal to or higher than the threshold voltage V _{E at the} point c by normally combining with the short circuit detecting resistor 9.

Further, the configuration of the abnormality determination circuit 12 is not limited to that shown in FIG. 2, but may be a configuration using a threshold voltage of a CMOS gate or the like.

Next, the operation will be described.

First, in normal operation, since the constant voltage circuit 3 outputs a predetermined constant voltage, the constant voltage circuit 3 passes through the short circuit detection resistor 9 and the current detection resistor 8 from the DC power supply 1 to the constant voltage circuit 3 within a predetermined range. Is supplied. At this time, a voltage sufficient to turn on the transistor 10 is generated across both ends of the current detection resistor 8, that is, between a and b, and the transistor 10 is turned on. Therefore, a voltage almost equal to that at point a is generated at point c,
The abnormality determination circuit 12 determines that V _D ≧ V _E and outputs a normal signal.

Next, when the output terminal 4 is opened, since no current flows from the DC power supply 1 to the constant voltage circuit 3, both ends of the current detection resistor 8, that is, a and b, have the same potential, and the transistor 10 is OF.
It becomes F. At this time, since the point c is grounded via the level securing resistor 11, if the transistor 10 is turned off,
Since the level becomes the ground (0 potential) and V _D <V _E , the abnormality determination circuit 12 outputs the abnormality detection signal S _C.

When the output terminal 4 is short-circuited, the DC power supply 1 supplies the constant voltage circuit 3 with the current defined by the short-circuit detection resistor 9 and the current detection resistor 9. At this time, a voltage sufficient to turn on the transistor 10 is generated across the current detection resistor 9, and the transistor 10 is turned on. However, at this time, the potential at point a is the voltage (OV) of the output terminal 4 + the voltage drop of the constant voltage circuit 3 at the time of output short circuit + V _{BE of the} transistor 10.
Therefore, even if the transistor 10 is turned on, the voltage V _{D at} point c is lower than the voltage at point a, so V _D <V _E , and the abnormality determination circuit 12 outputs the abnormality detection signal S _C.

[Effect of device]

As described above, according to the present invention, in addition to the conventional current detection resistor, the configuration is made possible by the short circuit detection resistor.
The level of the current detection signal when the output is short-circuited is reduced, the transistor is controlled by this current detection signal, and an abnormality is detected based on the output signal of this transistor. It is possible to obtain the effect that both the short circuit and the open circuit can be detected in the same manner as in the output open circuit or short circuit detection circuit.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a configuration diagram showing an output short circuit / open detection circuit of a power supply device according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing an embodiment of an abnormality determination circuit of FIG. FIG. 3 is a block diagram showing an output short-circuit / open detection circuit of a conventional power supply device. 1 is a DC power supply, 3 is a constant voltage circuit, 8 is a resistor for current detection,
9 is a short circuit detection resistor, 10 is a transistor, 11 is a level securing resistor, and 12 is an abnormality determination circuit.

Claims (1)

[Scope of utility model registration request] 1. A power supply device comprising a DC power supply 1 and a constant voltage circuit 3 for outputting electric power supplied from the DC power supply at a constant voltage, wherein the DC power supply 1 and the constant voltage circuit 3 are provided.
And the first and second resistors 9 and 8 connected in series between and, and the third resistor having a base / emitter connected to both ends of the second resistor and one end grounded. Anomaly detection transistor 10 whose collector is connected to the other end of resistor 11
And an abnormality determination unit 12 for detecting short circuit and open of the output terminal of the constant voltage circuit 3 based on the collector voltage of the abnormality detection transistor. circuit.