JPH08272464A - Dc power supply - Google Patents

Abstract

PURPOSE: To provide the rush current preventing circuit which temporarily makes the power supply line high impedance when the power is tuned on so as to limits the rush current to a capacitor when the input power of the DC power supply circuit is turned on, and returns it to low impedance at the constant time and protects the fuse so that no influence is affected on the operation of the DC power supply circuit. CONSTITUTION: A resistance R1 and the parallel circuit of a P-channel FET 4 are inserted into the power supply circuit between a fuse 2 and a DC power supply circuit 3. A resistance R2 is connected between the gate and the source of the P-channel FET 4. A resistance 3 is grounded from the gate of the P- channel FET 4. Further, a diode D2 and the serial circuit of a transistor Q4 are inserted into between the gate and the source of the P-channel FET 4. A resistance R9 is connected between the base and the emitter of the transistor Q4. A resistance R8 is connected between the base of the transistor Q4 and the drain of the P-channel FET 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention proposes a DC power supply device having a function of limiting an inrush current when the power is turned on.

[0002]

2. Description of the Related Art A conventional DC power supply device is shown in FIG. In the figure, 1 is a DC power supply, 2 is a fuse, 3 is a DC power supply circuit, and has a capacitor C0 in the input section.

The conventional DC power supply device is constructed as described above, and for example, in the case of a short circuit failure of the primary side component of the DC power supply circuit, the fuse 2 is blown to separate it from the primary power supply and prevent the spread of the failure. ing.

[0004]

Since the conventional DC power supply device is constructed as described above, the inrush current flowing into the capacitor of the input part of the DC power supply circuit against a rapid rise of the voltage when the power is turned on. There was a risk that the fuse would blow out. In order to prevent this, if the fuse rating is selected so that it will not be blown by the inrush current when the power is turned on, the fuse rating will be unnecessarily high and the optimum fuse cannot be selected for the abnormal current. there were.

The present invention has been made to solve the above problems, and an object thereof is to limit the inrush current with a high impedance when the power is turned on and to operate the DC power supply circuit with a low impedance at the steady state. Another object of the present invention is to provide a DC power supply device configured so as not to interfere with the fuse protection function.

[0006]

A DC power supply device according to a first embodiment of the present invention includes a P-channel field effect transistor (P-channel FET) between a fuse and a DC power supply circuit.
And a current limiting resistor in parallel circuit are inserted, and P channel FE
A capacitor is connected in parallel with the resistor connected between the gate and source terminals of T.

The DC power supply device according to the second embodiment of the present invention is, in addition to the first embodiment, connected with a transistor for positively discharging the electric charge of the capacitor when the input voltage is low.

In the DC power supply device according to the third embodiment of the present invention, a P channel F is provided between the fuse and the DC power supply circuit.
A parallel circuit of ET and a current limiting resistor is inserted, and a PNP transistor that works so as to short-circuit the gate and source of the P-channel FET is connected while the potential difference across the current limiting resistor is large.

In the DC power supply device according to the fourth embodiment of the present invention, a P channel F is provided between the fuse and the DC power supply circuit.
A parallel circuit of ET and a current limiting resistor is inserted, the voltage across the current limiting resistor is detected, and a comparator for controlling the P-channel FET is connected.

[0010]

According to the first embodiment of the present invention, when the power is turned on, the current flows through the current limiting resistor to the capacitor in the DC power supply circuit, so that the rush current is limited. Since the capacitor between the gate and source of the P channel FET is also charged, the P channel F
When the voltage between the gate and source of ET exceeds the threshold value, the P-channel FET becomes conductive and the power supply line becomes low impedance. Therefore, the rush current is limited for a certain period of time when the power is turned on.

According to the second embodiment of the present invention, in addition to the operation of the first embodiment, the electric charge of the capacitor between the gate and the source of the P-channel FET is immediately discharged when the voltage temporarily drops from the steady state, Even after the power is turned on again, the inrush current is limited for a certain period of time.

According to the third embodiment of the present invention, while the current is flowing into the capacitor in the DC power supply circuit through the current limiting resistor, the P-channel is utilized by utilizing the large potential difference between both ends of the current limiting resistor. The gate and source of the FET are short-circuited, the capacitor in the DC power supply circuit is completely charged, and the P-channel FET is made conductive only after the current stops flowing through the current limiting resistor.

According to the fourth embodiment of the present invention, the comparator detects that the potential difference between both ends of the current limiting resistor is large while the current is flowing into the capacitor in the DC power supply circuit through the current limiting resistor. The comparator operates so that the P-channel FET becomes conductive only after the charging of the capacitor in the DC power supply circuit is completed and the current stops flowing in the current limiting resistor.

[0014]

【Example】

Example 1. An embodiment of the present invention will be described below with reference to FIG. In FIG. 1, 1 to 3 are the same as the conventional device. Four
Is a P-channel FET, and is inserted in the power supply line in parallel with the resistor R1. R2 and R3 are P channel FE
T is a driving resistance, D1 is a diode, and C1 is a capacitor connected in parallel with R2.

Next, the operation will be described. When the DC power supply 1 is started up, C0 is not charged, so P0
The voltage between the gate and source of the channel FET is sufficiently low and the P channel FET is non-conductive. Therefore, the current is supplied to the DC power supply circuit via R1,
C0 is charged by the current limited by R1. on the other hand,
The capacitor between the gate and source is also charged by R2 and R3, but by setting the time constant to be larger than the time constants of R1 and C0, the gate and source of the P-channel FET after charging to C0 is completed. The voltage between them exceeds the threshold value and the P-channel FET becomes conductive.

Example 2. Second Embodiment FIG. 2 shows a second embodiment of the present invention, which is suitable when there is a possibility that the voltage of the DC power supply may be significantly reduced due to disturbance or the like. That is, in FIG. 2, the pnp transistor Q1 is connected in parallel with C1 of the first embodiment, the npn transistors Q2 and Q3 of the Darlington configuration are connected from the base of Q1, and the Zener diode D1 and the resistor R6 are connected between the base of Q3 and the power supply line. Are connected.

In such a configuration, the operation at power-on is the same as that in the first embodiment, but during normal operation, Q3 is on and Q2 and Q1 are off. When the voltage of the DC power supply drops significantly due to disturbance during normal operation, the Zener diode D1 cuts off, turning off Q3,
Q2 is turned on and the charge of the capacitor C1 is immediately extracted by Q1 to make the P-channel FET non-conductive. As a result, even if the DC power supply is immediately restored, since C1 is not charged, the power-on operation can be performed again to limit the inrush current.

Example 3. FIG. 3 shows a third embodiment of the present invention. In FIG. 3, instead of C1 of the first embodiment, a diode D2 and a pnp transistor Q are provided between the source and the gate.
4 is connected in series, and a resistor R8 is connected from the base of Q4 to the drain terminal.

In such a structure, when the power is turned on, the voltage on the drain terminal side is lower than that on the source terminal side, so that the transistor Q4 becomes conductive and the gate and source of the P-channel FET are short-circuited. Therefore, the P-channel FET becomes non-conductive and the capacitor C0 is charged via R1. When the capacitor C0 is charged and the voltage of the drain terminal becomes sufficiently high, it becomes impossible to supply a sufficient base current to the transistor Q4, so that Q4 is turned off and thereby the P-channel FET is turned on.

Example 4. FIG. 4 shows Embodiment 4 of the present invention. 3 uses the potential difference between the source and drain terminals to control the potential between the gate and the source of the P-channel FET with a transistor, but a comparator 5 is used instead of the transistor, and the potential of the source terminal and the drain are used. Dividing resistors (R10,
R11, R12, R13) are connected.

In such a configuration, the P-channel FET is rendered non-conductive by keeping the output of the comparator 5 open until the capacitor C0 is fully charged after the power is turned on, and the current is limited via R1. The capacitor C0 is charged as it is. Detecting that the voltage at the drain terminal has become sufficiently higher than the voltage at the source terminal, the comparator 5 short-circuits the output and the P-channel FET becomes conductive.

[0022]

According to the first embodiment of the present invention, the resistance inserted in series to the power supply line limits the inrush current to the capacitor when the power is turned on, and after charging to the capacitor is completed, P The channel FET is made conductive so that the power supply line has a low impedance and does not affect steady operation. Therefore, there is no fear that the fuse will be blown by mistake due to the inrush current, and the fuse can be optimally selected in consideration of only the steady current.

According to the second embodiment of the present invention, in addition to the effect of the first embodiment, inrush current is limited even when the voltage of the DC power supply is significantly reduced due to disturbance or the like and then immediately restored. In addition, there is no fear that the fuse will be accidentally blown by the inrush current, and there is an effect that the fuse can be optimally selected in consideration of only the steady current.

According to the third and fourth embodiments of the present invention, while the inrush current to the capacitor is flowing through the current limiting resistor, the P-channel FET is made non-conductive to limit the current and the charging to the capacitor is completed. After that, the P-channel FET is made conductive, and the power supply line is set to have a low impedance so that the steady operation is not affected. Therefore, there is no risk that the fuse will be accidentally blown due to the inrush current, and the fuse can be optimally selected in consideration of only the steady current.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of a DC power supply device according to the present invention.

FIG. 2 is a diagram showing a second embodiment of the DC power supply device according to the present invention.

FIG. 3 is a diagram showing Embodiment 3 of the DC power supply device according to the present invention.

FIG. 4 is a diagram showing Embodiment 4 of the DC power supply device according to the present invention.

FIG. 5 is a diagram showing a conventional DC power supply device.

[Explanation of symbols]

1 DC power supply, 2 fuses, 3 DC power supply circuit, 4
P-channel FET, 5 comparators, C0, C1 capacitors, R1 to R13 resistors, Q1 to Q4 transistors, D1 Zener diode, D2 diode.

Claims (4)

[Claims] 1. A direct-current power supply device comprising a direct-current power supply and a direct-current power supply circuit having a capacitor, one end of which is connected to the direct-current power supply via a fuse and the other end of which is grounded, in which a source is connected via a fuse. A P-channel field effect transistor having a gate connected to a direct current power source, a drain connected to one end of a capacitor of the direct current power source circuit, and a grounded via a resistor as a control terminal, and the source and the drain. A DC power supply device comprising a resistor, a resistor connected between the source and the gate, and a capacitor connected between the source and the gate. 2. A first transistor having a collector connected to the gate and an emitter connected to the source,
A resistor connected between the base and the emitter of the first transistor, a resistor having one end connected to the base of the first transistor, and a second resistor having a collector connected to the other end of the resistor and a grounded emitter. Transistor, a resistor connected between the base and the source of the second transistor, a third transistor whose collector is connected to the base of the second transistor and whose emitter is grounded, and 2. The DC power supply device according to claim 1, further comprising a resistor grounded from the base of the transistor, a resistor connected in series between the base and the source of the third transistor, and a Zener diode. 3. A direct current power supply device comprising a direct current power supply and a direct current power supply circuit having a capacitor, one end of which is connected to the direct current power supply via a fuse and the other end of which is grounded, in which a source is connected via a fuse. The drain is connected to one end of a capacitor of the DC power supply circuit while being connected to a DC power supply, and is connected between the source and the drain, and a P-channel field effect transistor having a gate which is grounded through a resistor as a control terminal. Resistor, a resistor connected between the source and the gate, a diode whose anode is connected to the source, a transistor whose emitter is connected to the cathode of the diode and whose collector is connected to the gate, and a transistor of the transistor. A resistor connected between the base and the emitter and between the base and the drain of the transistor A direct current power supply device comprising: 4. A direct-current power supply device comprising a direct-current power supply and a direct-current power supply circuit having a capacitor, one end of which is connected to the direct-current power supply via a fuse and the other end of which is grounded, in which a source is connected via a fuse. A P-channel field effect transistor having a drain connected to one end of a capacitor of the DC power supply circuit while being connected to a DC power supply, a resistor connected between the source and the drain, and the source. A resistor connected between the gates, a first resistor divider circuit grounded to divide the voltage from the source, a second resistor divider circuit grounded to divide the voltage from the drain, and The voltage at the division point of the first resistance division circuit is input to the non-inverting input terminal, and the voltage at the division point of the second resistance division circuit is input to the inverting input terminal. A DC power supply device comprising: a continuous comparator; and a resistor inserted between the output terminal of the comparator and the gate.