JP2000092830A - Power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to prevent an electric shock accident to be caused by carelessly touching any part of human body to the load terminal of a disconnected cable when a power supply is connected to a load with the cable and the like, by controlling an output voltage in such a way that it becomes lower than the original voltage if the disconnection of the connected cable makes a load current zero. SOLUTION: This power supply circuit is provided with a voltage converting circuit 1 which generates an output voltage, an error-voltage generating circuit 2 which detects the fluctuation of the output voltage, a control circuit 3 which controls the output voltage of the voltage converting circuit 1 to a constant value, based on the error voltage generated by the error-voltage generating circuit 2, and a current detecting circuit 4 which detects the output current of the voltage converting circuit 1. The first three circuits constitute a switching regulator. By controlling the error-voltage generating circuit 2 with the current detecting circuit 4, the output voltage of the voltage converting circuit 1 is variably controlled in such a way that, when the output current is equal to or lower than a threshold, the output voltage is lowered than the original output voltage, and when the output current is larger than the threshold, the output voltage is raised to the original one.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a power supply circuit,
In particular, in the power supply circuit, the output current is detected, the output voltage is controlled to be lower than the original output voltage until the output current reaches a certain value, and when the output current exceeds a certain value, the output voltage is changed to the original output voltage The present invention relates to a power supply circuit provided with a function for performing control.

[0002]

2. Description of the Related Art In a conventional power supply, when the power supply is connected to a load by a cable or the like, when the load is disconnected from the cable at the time of abnormality such as disconnection of the cable connected to the load. The output voltage is supplied to the cable as it is.

For this reason, in order to prevent an electric shock accident when a human body touches the load end of the cable, a voltage that is much lower than the original output voltage compared to the operation state is output. Is desirable.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances inherent in the prior art, and accordingly, an object of the present invention is to provide a novel method capable of realizing the above-mentioned conventional needs. A power supply circuit is provided.

[0005]

To achieve the above object, a power supply circuit according to the present invention comprises a voltage conversion circuit for generating an output voltage, an error voltage generation circuit for detecting a change in the output voltage, and A switching circuit having a control circuit for controlling the output voltage of the voltage conversion circuit to be constant based on the error voltage generated by the error voltage generation circuit, comprising a current detection means for detecting an output current of the voltage conversion circuit. Controlling the error voltage generation circuit by the current detection means to control the output voltage of the voltage conversion circuit to be lower than the original output voltage when the output current is lower than a certain threshold, and to be higher than the threshold. In this case, the output voltage is variably controlled to the original output voltage.

The current detecting means includes a current-voltage conversion circuit for converting the output current into a voltage, a detection circuit for detecting a converted voltage of the current-voltage conversion circuit, and a detection voltage and a reference voltage for the detection circuit. A comparison circuit that generates a comparison output signal when the detection voltage is smaller than the reference voltage, and a resistance voltage dividing circuit that is connected to an output of the voltage conversion circuit that forms a detection circuit of the error voltage generation circuit. A conducting circuit connected in parallel with the first resistor and operated by the comparison output signal of the comparison circuit to short-circuit the first resistor.

[0007]

Next, preferred embodiments of the present invention will be described in detail with reference to the drawings.

[First Embodiment] FIG. 1 is a block diagram showing a first embodiment of the present invention.

[Configuration of First Embodiment] Referring to FIG. 1, a first embodiment of a variable output voltage power supply circuit according to the present invention comprises a voltage conversion circuit 1 (input smoothing circuit 11, switching unit). 12, output smoothing circuit 13, output filter 1
4), error voltage generation circuit 2 (arithmetic circuit (error amplification circuit)
21, a reference voltage 22, a detection circuit 23), and a current detection circuit 4 for detecting an output current with respect to a switching regulator configuration including a control circuit 3 (a pulse width modulation circuit 31, a drive circuit 32, and a sawtooth wave generation circuit 33). And the conduction circuit 45 of the current detection circuit 4 is connected to the detection circuit 23 of the error voltage generation circuit 2.

The current detection circuit 4 converts a current flowing in the circuit into a voltage in the current / voltage conversion circuit 41 and detects the voltage. The comparator 42 includes a detection circuit 43
The detected voltage is compared with the reference voltage 44, and an operation of outputting a signal for changing the conduction circuit 45 connected to the detection circuit 23 of the error voltage generation circuit 2 to open / short is executed.

Accordingly, by setting the conduction circuit 45 to open / short, a function of varying the output voltage by changing the voltage division ratio of the voltage divider constituting the detection circuit 23 is obtained.

The embodiment according to the present invention is an example in which a current detection circuit 4 is inserted between a load circuit 5 and a switching regulator including a voltage conversion circuit 1, an error voltage generation circuit 2, and a control circuit 3.

Normally, the output voltage is detected by the detection circuit 23 of the error voltage generation circuit 2 formed in a switching regulator.
The output voltage is controlled to be constant by detecting the voltage supplied to the load circuit 5.

That is, the error voltage generation circuit 2 includes a resistor R2,
The output voltage detection circuit 23 comprising a voltage dividing circuit in which R3 and R4 are connected in series detects a change in the output voltage. When the output voltage becomes high, the arithmetic circuit 21 outputs the pulse width modulation circuit of the control circuit 3 31 when the pulse width of the pulse width modulation circuit 31 is reduced and the output voltage is lowered.
And outputs a voltage that causes the pulse width to become wider. The control circuit 3 controls the voltage conversion circuit by using the pulse width modulation circuit to stabilize the output voltage.

The current detection circuit 4 detects the output current, and can open / short the conduction circuit 45 connected in the detection circuit 23 according to the amount of the output current, thereby increasing or decreasing the output voltage. Can be.

The current detection circuit 4 includes a current / voltage conversion circuit 4
1, comparator 42, detection circuit 43, reference voltage 44,
It comprises a conduction circuit 45.

[Operation of the First Embodiment] Next, the operation of the first embodiment will be described in detail with reference to FIG. 1 and FIG.

FIG. 2 shows the output voltage with respect to the output current, the voltage of the current / voltage conversion circuit 41, the reference voltage 44, and the comparator 4.
2 shows output voltage characteristics.

First, the current-voltage conversion circuit 41 generates a voltage proportional to the output current by providing a resistor R1 on the GND line.

The comparator 42 compares the voltage generated from the resistor R1 with the reference voltage 44, and outputs a "high" voltage when the compared voltage is equal to or lower than the reference voltage 44,
When the voltage is equal to or higher than the reference voltage 44, a "low" voltage is output.

The conduction circuit 45 is short-circuited when the output of the comparator 42 is "high", and is open when the output of the comparator 42 is "low".

At this time, the output voltage is obtained when the conduction circuit 45 is short-circuited. [Equation 1] output voltage = ((R3 / R4) × (reference voltage 22)) +
(Reference voltage 22) When the conduction circuit is open [Equation 2] Output voltage = (Equation 1) + ((R2 / R4) × (Reference voltage 2)
2)) is obtained.

By such an operation, control for changing the output voltage by ((R2 / R4) × (reference voltage 22)) by the output current can be performed.

[Other Embodiments of the Invention] Next, other embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 3 is a circuit block diagram showing a second embodiment of the present invention.

The output voltage circuit according to one embodiment of the present invention constitutes a current detection circuit using a comparator and a photocoupler, detects a voltage flowing in a power supply line, and detects a voltage of the detection circuit of the switching regulator. Although the operation of varying the output voltage by changing the pressure ratio is enabled, another embodiment will be described below.

Referring to FIG. 3, the second embodiment has
In this embodiment, a transistor is used as the conduction circuit 45 instead of a photocoupler.

The operation of the second embodiment is similar to that of the variable output voltage power supply shown in FIG. 1, in which the comparator 42 compares the voltage detected by the detection circuit 43 with the reference voltage 44 to turn on / off the transistor. The operation of varying the output voltage by turning it off is performed.

FIG. 4 is a circuit block diagram showing a third embodiment of the present invention.

Referring to FIG. 4, a third embodiment according to the present invention is an embodiment in which a relay and a transistor are used as the conduction circuit 45 instead of a photocoupler.

The operation of the third embodiment is similar to that of the variable output voltage power supply shown in FIG. 1 except that the voltage detected by the detection circuit 43 by the comparator 42 is compared with the reference voltage 44, and the transistor and the relay are switched. An operation of varying the output voltage by turning ON / OFF is performed.

FIG. 5 is a circuit block diagram showing a fourth embodiment of the present invention.

Referring to FIG. 5, a fourth embodiment of the present invention is an example in which an operation of varying the output voltage is performed without using a comparator. In the operation of the circuit according to the fourth embodiment, as in the case of the voltage variable circuit in FIG. 2, the photocoupler is controlled to open / short by current so as to vary the output voltage. Is provided on the reference voltage side, the output voltage is obtained when the photocoupler is open.
(Reference voltage 22) Output voltage = (Expression 3) + ((R2 / R4) × (Reference voltage 2)
2)) is obtained.

By such an operation, control for changing the output voltage by the output current by ((R2 / R4) × (reference voltage 22)) can be performed.

As described above, according to the present invention, the output voltage can be varied by providing a circuit for detecting the output current and changing the voltage division ratio of the detection circuit portion of the switching regulator.

[0036]

The present invention is constructed and operates as described above. According to the present invention, the following effects can be obtained.

Since the output voltage is varied according to the output current, when the power supply of the present invention and the load are connected by a cable or the like, the connected cable is disconnected and the load current becomes zero.
In this case, by controlling the output voltage to be lower than the original output voltage, it is possible to prevent an electric shock accident when the human body touches the load end of the cable carelessly.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of the present invention.

FIG. 3 is a circuit block diagram showing a second embodiment according to the present invention.

FIG. 4 is a circuit block diagram showing a third embodiment according to the present invention.

FIG. 5 is a circuit block diagram showing a fourth embodiment according to the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 voltage conversion circuit 2 error voltage generation circuit 3 control circuit 4 current detection circuit 5 load circuit

Claims (5)

[Claims] A voltage conversion circuit for generating an output voltage; an error voltage generation circuit for detecting a change in the output voltage; and an output voltage of the voltage conversion circuit based on an error voltage generated by the error voltage generation circuit. A switching circuit having a control circuit for controlling the voltage conversion circuit to a constant value, comprising: a current detection unit for detecting an output current of the voltage conversion circuit; and controlling the error voltage generation circuit by the current detection unit. The output voltage is controlled to be lower than the original output voltage when the output current is equal to or lower than a certain threshold, and is variably controlled to the original output voltage when the output current is equal to or higher than the threshold. circuit. A current-voltage conversion circuit that converts the output current into a voltage; a detection circuit that detects a converted voltage of the current-voltage conversion circuit; a detection voltage of the detection circuit and a reference voltage. A comparison circuit that generates a comparison output signal when the detection voltage is smaller than the reference voltage, and a resistance voltage divider circuit that is connected to an output of the voltage conversion circuit that constitutes a detection circuit of the error voltage generation circuit. The power supply circuit according to claim 1, further comprising: a conduction circuit that is connected in parallel with the first resistor and operates by a comparison output signal of the comparison circuit to short-circuit the first resistor. . 3. The power supply circuit according to claim 2, wherein said conductive circuit is constituted by a photocoupler. 4. The power supply circuit according to claim 2, wherein said conduction circuit is constituted by two transistors. 5. The power supply circuit according to claim 2, wherein said conduction circuit is constituted by a transistor and a relay.