JPH10108358A - Power unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To limit the rush current at recovery of instant break, etc., of an input voltage source, and besides, reduce the conduction loss and the power loss at stationary operation. SOLUTION: Though a rush current flows in a capacitor 14 when a power switch 12 is switched instantaneously from on-state to off.on, the current is limited by a resistor 1. On the other hand, voltage of an input voltage source 11 goes up from roughly zero, and is applied to the gate of an FET2, being delayed for a certain time through diodes 6 and 7, time constant setting resistors 5 and 6, and a capacitor 4, and the FET 2 opens, so the rush current does not flow between the drain and the source of this FET 2. Since the gate of the FET 2 is not controlled by the charge voltage of the capacitor 14, the FET 2 does not open in a short time, which can prevent the rush current from flowing between the drain and the source of the FET2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply, and more particularly to a power supply having an inrush current prevention circuit for preventing an inrush current flowing into a smoothing capacitor when a power switch is turned on.

[0002]

2. Description of the Related Art As a method of suppressing an inrush current generated at the time of turning on a power supply and an instantaneous interruption of the power supply, it is general to insert and connect an inrush current limiting resistor in series with an input line. However, the rush current limiting resistor causes conduction loss during normal operation. A function for eliminating this power loss and preventing an inrush current is an inrush current prevention circuit.

FIG. 3 is a circuit diagram of a first example of a rush current prevention circuit of a conventional power supply device. When the AC input voltage from the commercial input voltage source 11 is turned on to the switch 12, it is rectified and smoothed by the bridge diode 13 and the capacitor 14, the DC voltage is converted into a stable output voltage by the voltage stabilizing circuit 15, and the load is supplied to the load 16. Output.

[0004] An inrush current prevention circuit 17 includes an inrush current limiting resistor 18 for limiting an inrush current due to a current flowing into the capacitor 14 when the switch 12 is turned on, and a conduction power loss caused by the resistor 18 during steady operation. MO for bypass connected in parallel with resistor 18 for blocking
It comprises an SFET 19 and a MOSFET drive circuit that turns on the MOSFET 19 after a predetermined time has elapsed after the switch 12 is turned on.

This MOSFET drive circuit includes a resistor 20,
21 and a capacitor 22.

FIG. 4 is a waveform chart showing the operation of the inrush current prevention circuit. In the figure, Vin is the output voltage (V) of the commercial input voltage source, VC is the terminal voltage (V) of the capacitor 14, Iin is the current (I) flowing into the capacitor 14, and Vg is the gate-source voltage ( V) and VTH are threshold values (V) at which the MOSFET 19 starts operating, and t1, t2, and t3 indicate the passage of time (seconds). The operation of the inrush current prevention circuit will be described with reference to FIG. 4 and FIG.

When the switch 12 is turned on, the AC input voltage of the commercial input voltage source 11 is rectified and smoothed by the bridge diode 13 and the capacitor 14, and the DC voltage is converted to a stable output voltage by the voltage stabilizing circuit 15. Load 16
Output to

In this power supply circuit, an inrush current prevention circuit 17 is provided by an inrush current limiting resistor 18 for limiting an inrush current due to a current flowing into a capacitor 14 when the switch 12 is turned on, and a resistor 18 during steady operation. MOSFET 19 and its M for preventing conduction power loss
Resistors 20 and 2 which are MOSFET drive circuits that turn on the OSFET 19 a predetermined time after the switch 12 is turned on
1 and a capacitor 22, and an input current Iin, which is an inrush current when the switch 12 is turned on, is expressed as Iin ≒ Vin / when the peak value of the input voltage is Vin and the resistance value of the resistor 18 is R.
Limited to R.

Further, the resistors 20 and 21 and the capacitor 2
After the switch 12 is turned on, the MOSFET 19 is turned on when the gate-source voltage Vg of the MOSFET 19 reaches the operation start threshold voltage VTH after the switch 12 is turned on, and the conduction loss caused by the inrush current limiting resistor 8 in the steady state is prevented. ing.

Next, a second example of the inrush current prevention circuit of the conventional power supply device will be described. The second example is disclosed in
44730.

FIG. 5 is a circuit diagram of a second example of the rush current prevention circuit of the conventional power supply device. Note that the same components as those of the inrush current prevention circuit of the first example are denoted by the same reference numerals, and description thereof will be omitted.

The inrush current prevention circuit of the second example is different from the first example in an inrush current prevention circuit 27. Others are first
Is the same as in the example.

A rush current prevention circuit according to a second example includes a MOSF connected to an input line between an input voltage source 11 and an input capacitor 14.
In addition to providing a parallel circuit of ET31 and resistor 32,
A gate drive circuit for the MOSFET 31 is provided.

The gate drive circuit includes a MOSFET 31
A constant voltage diode 33 connected between the gate of the MOSFET 31 and the resistor 32, a resistor 34 connected between the source of the MOSFET 31 and the constant voltage diode 33, and a resistor 35 connected between the gate of the MOSFET 31 and the input capacitor. ,
It comprises a transistor 36 having a gate and a collector of the MOSFET 31 connected to each other, and a resistor 37 and a constant voltage diode 38 connected in series between the base of the transistor 36 and the resistor 32.

Next, the operation of the inrush current prevention circuit of the second example will be described. The description of the same components as in the first example is omitted.

When an input voltage source is applied by turning on the switch 12, a voltage is applied to the gate of the MOSFET 31 by the resistor 35 and the constant voltage diode 33 and the rush current prevention circuit 27 conducts once. When an inrush current due to the charging current flows, a voltage drop generated across the on-resistance of the MOSFET 31 in series with the resistor 34 and the combined resistance of the resistor 32 connected in parallel with the two resistors causes a Zener voltage of the constant voltage diode 38. Is exceeded, the transistor 36 is turned on and the MOSFET 31 is turned off.

Thereafter, the input capacitor 14 is charged by the current limited by the resistor 32. When the input capacitor is sufficiently charged and the voltage drop in the resistor 32 becomes equal to or less than the Zener voltage of the constant voltage diode 38, the transistor 3 is turned on.
6 turns off, the MOSFET 31 conducts, and a steady current flows.

That is, the rush current is controlled by the constant voltage diode 3
8 is limited by the current obtained by dividing the Zener voltage of 8 by the combined resistance. The same applies to the ON / OFF state of the switch 12 and the instantaneous interruption of the input voltage. At time t = t2 (see FIG. 4), the instantaneous interruption of the input voltage source 11 occurs, and when it returns at t3, the voltage Vc of the input capacitor 14 has dropped, and the rush for charging the input capacitor 14 has occurred. A current flows, but when the voltage drop generated in the combined resistor exceeds the Zener voltage of the constant voltage diode 38, the MOSFET
T31 turns off and the current is limited. Thereafter, the input capacitor 14 is charged by the resistor 32, and when the voltage drop of the resistor 32 becomes less than the constant voltage diode 38, the MOSFET
Numeral 31 is always conductive and allows a steady current to flow.

A technique similar to that of the first example is disclosed in
No. 80829, a technique similar to that of the second example is disclosed in JP-A-63-178725.

[0020]

However, according to the first example, the bypass MOS for preventing the conduction power loss caused by the inrush current limiting resistor 18 in the normal operation.
The on-timing of the FET 19 is determined by the time constants of the resistors 20 and 21 and the capacitor 22. The time t2 to t3 during which the input voltage source is not supplied due to the sharp on / off of the switch 12, the momentary interruption of the input voltage source 11, and the like. (Figure 4
Occurs), the voltage Vc of the input capacitor 14 decreases, and the voltage between the gate and the source of the MOSFET 19 also decreases.

Thereafter, when the supply from the input voltage source 11 starts again, the gate-source voltage Vg of the MOSFET 19 reaches the operation start threshold voltage VTH in a short time, and the MOSFET 19
Is turned on, and an inrush current due to a current flowing into the capacitor 14 flows through the MOSFET 19, so that the inrush current cannot be limited.

To prevent this, the input voltage source 11
It is necessary to sharply decrease the gate-source voltage Vg during the time t2-t3 when the power supply is not supplied.
It is necessary to reduce the value of 21 and shorten the discharge time of the capacitor 14.

However, reducing the resistance values of the resistors 20 and 21 has a problem that excessive power loss due to the resistors 20 and 21 in a steady state occurs.

On the other hand, according to the second example, the resistor 34 for detecting the inrush current due to the charging current to the input capacitor 14 is used.
Are conducting during the steady operation, a conduction loss is caused by the resistor 34. In this circuit, MOSFET
It has been proposed that the resistor 34 is unnecessary if the inrush current due to the combined resistance of the on-resistance 31 and the resistor 32 can be detected. Difficult and feasible.

Therefore, in the present circuit, the detection resistor 34 is required to limit the rush current, and it is inevitable that conduction loss occurs in a steady state.

Further, since a high voltage is applied to the resistor 35, there is a problem that an excessive power loss occurs in the resistor 35.

Accordingly, an object of the present invention is to limit the inrush current when the switch is turned on and off steeply or when the input voltage source is restored from an instantaneous interruption, and to reduce conduction loss and power loss during steady operation. A power supply device is provided.

[0028]

According to the present invention, there is provided a power supply apparatus including inrush current preventing means for preventing an inrush current flowing into a smoothing capacitor when a power switch is turned on. The prevention means is controlled by a current limiting means for limiting an inrush current flowing into the smoothing capacitor, a switching means connected in parallel with the current limiting means, and an input voltage inputted when the power switch is turned on. And control means for closing the switch means with a delay for a time capable of avoiding an inrush current.

According to the present invention, the control means is controlled by the input voltage. Therefore, the terminal voltage of the smoothing capacitor is not applied to the control unit when the input voltage source is restored from the momentary interruption, so that the switch unit can be closed after the timing of the occurrence of the rush current.

[0030]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a circuit diagram of a power supply device according to a preferred embodiment of the present invention. The same components as those in the conventional example are denoted by the same reference numerals, and description thereof will be omitted.

The power supply device according to the present invention comprises an input voltage source 11
, A switch 12, a bridge rectifier diode 13,
A smoothing input capacitor 14, a voltage stabilizing circuit 15,
A conventional circuit including a load 16 includes an inrush current preventing resistor 1 connected between a bridge rectifier diode 13 and a smoothing input capacitor 14, a MOSFET 2 connected in parallel with the inrush current preventing resistor 1, A resistor 3 and a capacitor 4 connected between the gate and the source of the MOSFET 2, a resistor 5 having one end connected to the gate of the MOSFET 2, and a resistor 5 connected between the other end of the resistor 5 and an output terminal of the switch 12. And a diode 7 connected between the other end of the resistor 5 and one end of the input voltage source 11.

Then, the inrush current prevention resistor 1 and the MOS
The inrush current prevention circuit 8 is constituted by the FET 2, the resistors 3, 5, the capacitor 4, and the diodes 6, 7.

Next, the operation of the power supply device will be described with reference to FIGS. The basic operation of rectifying the AC input and supplying the DC voltage to the load is the same as the conventional operation, so that the description thereof will be omitted, and the operation of the inrush current prevention circuit unique to the present invention will be described.

FIG. 2 is a waveform chart showing the operation of the inrush current prevention circuit of the power supply device according to the present invention.

The input current Iin when the switch 12 is turned on is limited to Iin ≒ Vin / R when the peak value of the input voltage is Vin and the resistance value of the resistor 1 is R. Further, after a predetermined time elapses after the switch 12 is turned on, the MOSFET 2
When the gate-source voltage Vg of the MOSFET 2 reaches the operation start threshold voltage VTH due to the time constant of the resistors 3 and 5 and the capacitor 4 via the diodes 6 and 7, the transistor 2 conducts and the steady operation caused by the rush current limiting resistor 1 occurs. To prevent conduction power loss.

When a time period t2-t3 occurs due to turning on / off of the switch 12 and instantaneous interruption of the input voltage source 11, the MOS transistor
The gate-source voltage Vg of the FET 2 drops sharply because it is not affected by the discharge time of the input capacitor 14.
At time t3 when the switch 12 is turned on again and the input voltage source 11 returns from the instantaneous interruption, the gate-source voltage Vg of the MOSFET 2 after a predetermined time elapses, similarly to when the switch 12 is turned on.
In this case, the input current Iin is limited by the inrush current limiting resistor 1 because the voltage reaches the operation start threshold voltage VTH.

Further, since a sine wave voltage obtained by rectifying the commercial input voltage source 11 is applied to the driving resistor 5 of the bypass MOSFET 2 via the diodes 6 and 7, the power loss is reduced to about 比 compared with the related art. Reduced.

[0038]

According to the present invention, there is provided a power supply device including an inrush current preventing means for preventing an inrush current flowing into a smoothing capacitor when a power switch is turned on, wherein the inrush current preventing means is connected to the smoothing capacitor. Current limiting means for limiting the inrush current flowing thereinto, switch means connected in parallel with the current limiting means, and an input voltage which is controlled when the power switch is turned on and is delayed by a time capable of avoiding the inrush current. And the control means for closing the switch means to limit the inrush current when the switch is steeply turned on and off or when the input voltage source is restored from an instantaneous interruption, and to reduce conduction loss and power loss during steady-state operation. Can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a power supply device according to a preferred embodiment of the present invention.

FIG. 2 is a waveform chart showing an operation of an inrush current prevention circuit of the power supply device.

FIG. 3 is a circuit diagram of a first example of a rush current prevention circuit of a conventional power supply device.

FIG. 4 is a waveform chart showing an operation of the inrush current prevention circuit of the power supply device.

FIG. 5 is a circuit diagram of a second example of the inrush current prevention circuit of the power supply device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Inrush current prevention resistor 2 MOSFET 3, 5 resistor 4 Capacitor 6, 7 diode 8 Inrush current prevention circuit 11 Input voltage source 12 Switch 14 Smoothing input capacitor 16 Load

Claims (3)

[Claims] 1. A power supply device comprising an inrush current preventing means for preventing an inrush current flowing into a smoothing capacitor when a power switch is turned on, wherein the inrush current preventing means limits an inrush current flowing into the smoothing capacitor. Current limiting means, and switch means connected in parallel with the current limiting means, and controlled by an input voltage input when the power switch is turned on,
A power supply device comprising: a control unit that closes the switch unit by delaying the inrush current by a time that can avoid the inrush current. 2. The power supply device according to claim 1, wherein the input voltage is a DC voltage obtained by rectifying an AC voltage input to a power supply. 3. The control means includes a delay circuit comprising a resistor and a capacitor, and the switch circuit is closed by delaying the inrush current by a time capable of avoiding the inrush current. Item 3. The power supply device according to item 1 or 2.