JPH10323044A - Power circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to prevent surge currents and reduce power loss in a power circuit which converts alternating currents into direct currents. SOLUTION: A transistor 2a of a photo relay switch 2 is placed between a bridge diode BD1 and a smoothing capacitor C1. The transistor 2a is turned on by the emitted light of the light emitting diode 2a. When a switch SW1 is turned on, a relay control circuit 3 is synchronized with AC input and PWM (Pulse Width Modulation)-controls the on state of the photo relay switch 2, so that its duty ratio is gradually increased from 0%. As a result, currents are gradually passed through the smoothing capacitor C1, and the production of a surge current is prevented. In addition, since the transistor 2a of the photo relay switch 2 is no more than tens of mΩ in on resistance, its power loss is low.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit for converting an alternating current into a direct current, and more particularly to a power supply circuit for converting a direct current into a DC in synchronization with an AC input.

[0002]

2. Description of the Related Art In a power supply circuit such as an AC / DC converter, a smoothing capacitor is connected across an AC line. However, when the power switch is turned on, the smoothing capacitor is almost in a short-circuit state, so that a so-called surge current flows in the circuit. Conventionally, in order to prevent the surge current, a method using a thyristor or a power thermistor has been adopted.

FIG. 7 is a diagram showing a configuration of a power supply circuit which uses a thyristor to prevent a surge current. The power supply circuit 20 is provided with a bridge diode BD20 for rectifying the AC power from the input side and a smoothing capacitor C20 for smoothing the rectified output. In addition, a line between the bridge diode BD20 and the smoothing capacitor C20 includes:
A thyristor 21 is provided. Thyristor 2
1, a resistor R20 is connected in parallel.

In such a power supply circuit 20, the switch S
When W20 is turned on, the smoothing capacitor C20 is charged for a while, but the current at this time is limited by the resistor R20. This prevents a surge current when the power is turned on. Then, when the charging has progressed to some extent, a gate signal is sent from a control circuit (not shown) to the thyristor 21, and both ends of the resistor R20 are short-circuited.

[0005]

However, the thyristor has a small forward voltage of about 1 V when the forward voltage is small (about 1 A), but has a large voltage of 1.5 V and a large power loss of about 15 W at a large current of about 10 A. Would. For this reason, a large amount of heat is generated, and a rise in the temperature inside the power supply device may cause a reduction in reliability and life. The current limiting resistor R
Since an excessive current flows through the capacitor 20, deterioration is apt to occur, and there are many failures such as disconnection.

On the other hand, when a power thermistor is used in place of the thyristor, the resistance-temperature characteristic of the resistance becomes 1/8 times between 25 ° C. and 80 ° C. For example, 25
If a temperature of 10 Ω at 1 ° C. is used at a current of 1 A, when the temperature rises in the operating state, the temperature becomes about 1.3 Ω, and the power loss is 1.3 W. However, this is for example 10A
When used at a large current, the power loss is 13 W, which is as large as a thyristor.

[0007] The present invention has been made in view of the above points, and an object of the present invention is to provide a power supply circuit capable of preventing surge current and reducing power loss.

[0008]

According to the present invention, in order to solve the above-mentioned problems, in a power supply circuit for converting an alternating current to a direct current, a photorelay switch is provided in a stage preceding a smoothing capacitor and switches on / off of a line current. And the ON state of the photorelay switch is changed so that the duty ratio gradually increases from 0% in synchronization with the AC input.
And a relay control circuit for performing M (Pulse Width Modulation) control.

In such a power supply circuit, the ON state of the photorelay switch provided in the preceding stage of the smoothing capacitor is PWM-controlled so that the duty ratio gradually increases from 0% in synchronization with the AC input. This prevents surge current when the AC power is turned on, and reduces power consumption by using a photorelay switch.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a principle diagram of a power supply circuit according to the present invention. AC line 1L (Live), 1N (neut
ral), a rectifying bridge diode BD1 and a smoothing capacitor C1 are provided. The transistor 2a of the photorelay switch 2 is connected to a line between the bridge diode BD1 and the smoothing capacitor C1. When the light emitting diode 2b integrally formed emits light, a voltage is applied to the gate (G) of the transistor 2a, and the transistor 2a conducts between the drain (D) and the source (S), that is, the photorelay switch 2 is turned on. Become.

The ON / OFF control of the photorelay switch 2 is performed by a relay control circuit 3. When the switch SW1 is turned on, the relay control circuit 3 changes the on state of the photorelay switch 2 to a PWM (Pulse Width Modulati) so that the duty ratio gradually increases from 0% in synchronization with the AC input.
on) to control. Thereby, the smoothing capacitor C1 has:
Since current flows gradually, generation of surge current is prevented. The transistor 2a of the photorelay switch 2
Has a small power loss because its ON resistance is several tens of mΩ.

FIG. 2 is a circuit diagram showing the configuration of a power factor correction type AC / DC converter which is an embodiment of the power supply circuit of the present invention. AC line 10L of AC / DC converter 10
(Live) and 10N (neutral), a rectifying bridge diode BD10 and a smoothing capacitor C10 are provided. At the next stage of the smoothing capacitor C10, a chopper circuit 12 for improving a power factor is provided.

The chopper circuit 12 includes a coil 12a, an MO
S (Metal Oxide Semiconductor) type FET (Field
Effect Transistor) 12b, rectifier diode 12
c, and a capacitor 12d. FET12
b is turned on and off by a control circuit (not shown). The energy stored in the coil 12a when the FET 12b is on is superimposed on the input voltage when the FET 12b is off, so that a boosted voltage can be output.

On the other hand, the FET 11a of the photorelay switch 11 is connected to a line preceding the smoothing capacitor C10. The FET 11a is a light emitting diode 11
When the light emitting diode 11b emits light, a voltage is applied to its gate (G) and conduction is established between the drain (D) and the source (S), that is, the photorelay switch 11 is turned on. Becomes

The light emission timing of the light emitting diode 11b is controlled by the relay control circuit 13 as described below.
M is controlled. The relay control circuit 13 includes a diode D1
1. A sub power circuit 131 including a resistor R11, a zener diode D12, and a capacitor C11 obtains a DC sub power supply.

In the relay control circuit 13, the resistance R1
2, R13, R14, capacitor D12, comparator IC1
1 constitutes a delay-on circuit 132. In this delay-on circuit 132, the output of the comparator IC11 is kept at a low level immediately after the power switch SW10 is turned on, and during this time, the capacitor C13 of the PWM circuit 133 at the subsequent stage is grounded. And the capacitor C12
From the time when is charged, the output of the comparator IC11 is set to the high level.

In the PWM circuit 133, the resistors R15 and R1
6, R17 and transistor Q11,
A voltage having a waveform proportional to the full-wave rectified voltage from the bridge diode BD10 is input to the input terminal (+) of the comparator IC12. The terminal voltage of the capacitor C13 is input to the other input terminal (-) of the comparator IC12. The terminal voltage of the capacitor C13 changes with a time constant determined by the resistor R18 and the capacitor C13.

A light emitting diode 11b of the photorelay switch 11 is connected to an output terminal of the comparator IC12. When the output of the comparator IC12 becomes low level, a direct current flows through the light emitting diode 11b via the resistor R19, and emits light. The FET 11a is turned on only while the light emitting diode 11b is emitting light, and the AC / DC
The output of converter 10 is obtained.

The delay-on circuit 132 and P
The DC voltage after the rise of the WM circuit 133 can be supplied from the load side via the diode D13. Next, a specific operation of the AC / DC converter 10 having such a configuration will be described.

FIG. 3 is a diagram showing voltage waveforms at points Tb, Tc, Td and Te on the AC / DC converter 10 of FIG. First, when the switch SW10 shown in FIG. 2 is turned on, the point Tb, that is, the potential of the input terminal (-) of the comparator IC11 rises. And the capacitor C1
2 is started, and after a time tr when the charging is completed, the potential of the input terminal (+) of the comparator IC11 becomes higher than the potential of the input terminal (-), and the output terminal of the comparator IC11 becomes high. Level. Thereby, the capacitor C
13 is started, and the potential at the point Tc gradually increases.

Time t when the potential of the point Tc reaches an appropriate potential
At 1, the output (point Td) of the comparator IC12 goes low intermittently. That is, the photo relay switch 11
Is turned on intermittently. Thereby, the smoothing capacitor C
The potential of 10 (point Te) also gradually rises.

When the potential at the point Tc exceeds a certain value (time t2), the output of the comparator IC12 (point Td) becomes completely low, and the potential of the smoothing capacitor C10 (point Te) becomes a certain value. Lasts.

FIG. 4 is an enlarged view of the waveforms at points Td and Te in FIG. In this figure, it can be seen that the potential of the point Te increases in proportion to the low level width D1 of the point Td (the photorelay switch 11 is on).

FIG. 5 is an enlarged view of the waveform of FIG.
Output of the bridge diode BD10 (point Ta)
It is the figure which superimposed the waveform of FIG. In this figure, it can be seen that the photorelay switch 11 is on when the rectified waveform that has been full-wave rectified by the bridge diode BD10 is at a low voltage. That is, the potential at the point Td becomes a PWM wave whose ON width D1 is proportional to the potential of the capacitor C13 shown in FIG.

As described above, in the present embodiment, the photorelay switch 11 connected on the line is PWM-controlled, so that generation of a surge current can be reliably prevented.

In this embodiment, the delay-on circuit 1
Since the charging of the capacitor C13 of the PWM circuit 133 is delayed by 32, it is possible to prevent the PWM circuit 133 from being transiently turned on immediately after the input of the switch SW10.

Next, a comparison will be made between the power loss of the photorelay switch 11 and the power loss of a generally used thyristor. Assuming that the normal thyristor has a forward voltage of 1.0 V at 1 A and 1.5 V at 10 A, the power loss is 1.0 W and 15 W, respectively. On the other hand, MOS type FET
The ON resistance of the photorelay switch 11 using
Assuming that it is mΩ, the power loss under the same conditions as above is 0.05 W and 5 W, respectively, which indicates that the power loss is sufficiently smaller than that of the thyristor. If the on-resistance of the photorelay switch 11 is reduced, the loss can be further reduced.

In this embodiment, the power factor improving type AC / D
Photorelay switch 11 as an application to C converter
Is provided in the next stage of the bridge diode BD10, but as a circuit for suppressing a surge current of a normal AC / DC converter (including double voltage rectification) and a transformer, FIG.
As shown in (1), the photorelay switch 11 may be provided in a stage preceding the bridge diode BD10. However, in this case, a bridge diode BD11 is added to supply full-wave rectification to the relay control circuit 13.
Other configurations are the same as those in FIG.
The same reference numerals are given and the description is omitted.

[0029]

As described above, according to the present invention, the ON state of the photorelay switch provided in the preceding stage of the smoothing capacitor is PWM-controlled so that the duty ratio gradually increases from 0% in synchronization with the AC input. A
A surge current at the time of turning on the C power can be prevented, and power consumption can be reduced by using a photorelay switch.

[Brief description of the drawings]

FIG. 1 is a principle diagram of a power supply circuit of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a power factor correction type AC / DC converter which is one mode of the power supply circuit of the present invention.

FIG. 3 shows each point Tb, on the AC / DC converter of FIG.
It is a figure which shows the voltage waveform in Tc, Td, and Te.

FIG. 4 is an enlarged view of waveforms at points Td and Te in FIG. 3;

5 is a diagram in which the waveform of FIG. 4 is further enlarged, and the waveform of the output (point Ta) of the bridge diode is superimposed on the waveform of point Td.

FIG. 6 is a circuit diagram showing another embodiment of the AC / DC converter.

FIG. 7 is a diagram showing a configuration of a power supply circuit that uses a thyristor to prevent surge current.

[Explanation of symbols]

1. Power supply circuit 2. Photo relay switch 2.
a: transistor, 2b: light-emitting diode, 3
... Relay control circuit, 10 ... AC / DC converter, 11 ... Photo relay switch, 11a ... F
ET, 11b: light emitting diode, 12: chopper circuit, 13: relay control circuit, 131: sub power circuit, 132: delay on circuit, 133
... PWM circuit, BD ... Bridge diode, C
1, C10: a smoothing capacitor.

Claims (6)

[Claims] 1. A power supply circuit for converting an alternating current to a direct current, comprising: a photorelay switch provided before a smoothing capacitor for switching on / off of a line current; and an on-state of the photorelay switch to the AC input. A power supply circuit, comprising: a relay control circuit that performs PWM (Pulse Width Modulation) control so that the duty ratio gradually increases from 0% in synchronization. 2. The relay control circuit according to claim 1, further comprising: a sub-power circuit that converts a full-wave rectified voltage output from the full-wave rectifier circuit to a predetermined DC voltage; The power supply circuit according to claim 1, further comprising: a PWM circuit that performs the PWM output based on a waveform change of a full-wave rectified voltage. 3. The PWM circuit includes: a transistor that obtains an output proportional to the full-wave rectified voltage; a capacitor provided to charge a DC voltage from the sub-power circuit with a predetermined time constant; And a comparison circuit that compares the output of the capacitor with the output of the capacitor and turns on the photorelay switch when the output of the transistor is smaller than the output of the capacitor. Power circuit. 4. The photorelay switch according to claim 1, wherein the photorelay switch is provided at a stage subsequent to the full-wave rectifier circuit.
Power supply circuit as described. 5. The photorelay switch according to claim 1, wherein the photorelay switch is provided in a stage preceding the full-wave rectifier circuit.
Power supply circuit as described. 6. The power supply circuit according to claim 1, wherein said photorelay switch comprises a MOS transistor and a light emitting diode.