JPH0221602B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an AC constant voltage power supply device.

[Conventional technology]

Generally, AC constant voltage power supplies are used in various fields. For example, in an electrophotographic copying machine,
While research is progressing on increasing the sensitivity of photoreceptors, there is a growing need for stabilization of the light output of exposure light sources, and a highly accurate AC constant voltage power supply is required in this field as well. ing.

In response to such demands, an AC constant voltage power supply device having the configuration shown in FIG. 1, for example, has been known. That is,
A load 3, such as a halogen incandescent light bulb for exposing an original, is connected to an AC power source 1 via a bidirectional thyristor 2, which is a bidirectional semiconductor switching element.
A full-wave rectifier 4 is connected to the AC power supply 1 via a power transformer 111, and a resistor 5 and a constant voltage diode 6 are connected in series between the positive output terminal a and the negative output terminal b of the full-wave rectifier 4. Connect the circuit. A control circuit 7 for controlling the conduction phase of the bidirectional thyristor 2 is connected to both ends of the constant voltage diode 6.
Connect. This control circuit 7 has a series circuit of a transistor 8 and a capacitor 9 and a series circuit of a resistor 10 and a resistor 11 connected to both ends of the voltage regulator diode 6, respectively.
A series circuit of a PUT (programmable union transistor) 12 and the primary coil of a pulse transformer 13 is connected, and the gate of this PUT 12 is connected to the connection point of the resistor 10 and the resistor 11, and the node of the PUT 12 is connected through a resistor 121. is connected to the positive side output terminal a of the full-wave rectifier 4, and each time the voltage across the capacitor 9 exceeds the gate voltage of the PUT 12 determined by the resistor 10 and the resistor 11, the PUT 12 becomes conductive and the pulse transformer 13 is A trigger pulse is applied to the gate of the bidirectional thyristor 2 through the bidirectional thyristor 2.

On the other hand, a load voltage detection circuit 14 is connected to the load 3. This load voltage detection circuit 14 connects the primary coil of a load voltage detection transformer 15 in parallel to the load 3, and connects the input terminals of a full-wave rectifier 16 to both ends of the secondary coil of the load voltage detection transformer 15. The positive output terminal c of this full-wave rectifier 16
A resistor 17 and a resistor 18 are connected between the
A series circuit is connected, and the negative output terminal d is connected to the negative output terminal b of the full-wave rectifier 4. A capacitor 19 is connected to both ends of the resistor 18, and a resistor 20 and a capacitor 21 are connected to both ends of the capacitor 19.
The capacitor 21 is configured by connecting a series circuit of
A detection voltage corresponding to the voltage across the load 3 is generated across the terminal.

An error amplifier 22 is connected between the connection point e between the resistor 20 and the capacitor 21 and the negative output terminal d of the full-wave rectifier 16. This error amplifier 22 connects the base of one transistor 24 to the connection point e between the resistor 20 and the capacitor 21 via a resistor 23, and connects the emitter of this transistor 24 to the emitter of the other transistor 25. The emitter of the transistor 24 is connected to the negative output terminal d of the full-wave rectifier 16 through the resistor 26, and the negative terminal of the starting DC power supply 27 is connected to the negative output terminal d, and the collector of the transistor 24 is connected to the negative output terminal d of the full-wave rectifier 16. The starting DC power supply 2 is connected to the starting DC power supply 2 via a resistor 28.
7 to the positive side terminal of the transistor 24.
The base of the transistor 25 is connected to the collector of the transistor 24 via the resistor 29 and the capacitor 30, and the collector of the transistor 25 is connected to the positive terminal of the startup DC power source 27, and the base of the transistor 25 is connected to the collector of the transistor 24 through the resistor 29 and the capacitor 30. The collector of the transistor 24 is connected to the base of the transistor 8 via a resistor 32. The negative terminal of the transistor 27 is connected to the connection point between the capacitor 9 and the pulse transformer 13, and the base voltage of the transistor 25 by the potentiometer 31 is used as a reference voltage.
This reference voltage is compared with the base voltage of the transistor 24 corresponding to the detection voltage generated across the capacitor 21, and the error output generated at the collector of the transistor 24, that is, at the Q point, is connected to the resistor 32 according to the difference. It is added to the base of the transistor 8 through the base of the transistor 8.

With such a configuration, the error output of the error amplifier 22 causes the transistor 8 in the control circuit 7 to
By controlling the base voltage of the capacitor 9 and controlling the dv/dt of the voltage across the capacitor 9, the generation phase of the trigger pulse to the gate of the bidirectional thyristor 2 is controlled, and the voltage across the load 3 is made constant. That's what I do. In the figure, 33 is a noise filter capacitor, 34 and 35 are capacitors and inductors that constitute the noise filter, and 36 and 3 are capacitors.
7 is a capacitor and a resistor that constitute a surge absorption circuit.

[Problem to be solved by the invention]

However, according to such a configuration, since the load voltage detection transformer 15 is used to detect the load voltage of the power transformer 111 and the load 3, the entire device becomes large and heavy, and the transformer is expensive.
The disadvantage is that the manufacturing cost is high.

Based on the above-mentioned circumstances, the inventor of the present invention has conducted extensive research, and as a result, a reverse-blocking three-terminal thyristor is installed between the connection point between the bidirectional semiconductor switching element and the load, and the output terminal of the full-wave rectifier connected to the power supply. discovered that the voltage across the load could be detected by inserting a series circuit consisting of a resistor and a reverse blocking three-terminal thyristor and making it conductive in synchronization with a phase control device.
The present invention has now been completed.

The present invention is a compact, lightweight, low-cost AC that can detect the voltage across the load without using a transformer, does not require a power transformer, and can reliably keep the voltage across the load constant. The purpose is to provide a constant voltage power supply device.

[Means to solve the problem]

The present invention is characterized by an AC power supply, a load supplied with power from the AC power supply, a bidirectional semiconductor switching element inserted between the load and the AC power supply, and an input terminal of the bidirectional semiconductor switching element inserted between the load and the AC power supply. a full-wave rectifier connected to an AC power source; and a control circuit that controls the conduction phase of the bidirectional semiconductor switching element connected between the output terminals of the full-wave rectifier;
a load voltage detection circuit comprising a series circuit of a semiconductor switching element and a load voltage detection resistor, interposed between a connection point between the load and the bidirectional semiconductor switching element and an output terminal of the full-wave rectifier; and an error amplifier that receives a detection voltage obtained at the load voltage detection resistor and generates an error output according to the difference between this detection voltage and a preset reference voltage, and the control circuit includes: The point is that the conduction phases of the bidirectional semiconductor switching element and the semiconductor switching element are synchronously controlled by the error output from the error amplifier.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

A circuit diagram of an embodiment of the present invention is shown in FIG. Components that are the same as those in FIG. 1 are designated by the same reference numerals.
In this example, a load 3 such as a halogen incandescent light bulb for exposing originals is connected to the AC power source 1 via a bidirectional semiconductor switching element, such as a bidirectional thyristor 2, and the AC power source 1 does not use a power transformer. For example, four diodes D1,
Connect the input terminals of a full-wave rectifier 4 consisting of D2, D3, and D4, and connect the positive output terminal a of this full-wave rectifier 4.
A series circuit of a resistor 5 and a constant voltage diode 6 is connected between the output terminal b and the load output terminal b, and a diode 41 and a capacitor 4 are connected across the constant voltage diode 6.
A control circuit 7 for controlling the conduction phase of the bidirectional thyristor 2 and the bidirectional thyristor 2 is connected.

This control circuit 7 has a series circuit of a resistor 43, a transistor 8, and a capacitor 9 connected to both ends of the constant voltage diode 6, and a series circuit of a resistor 10, a diode 44, and a resistor 11, and a PUT 12 connected to both ends of the capacitor 9. Connect the series circuit of the primary coil of the pulse transformer 13, and connect this PUT12
The gate of PUT12 is connected to the connection point of diode 44 and resistor 11, and the anode of PUT12 is connected to resistor 12.
1 to the positive output terminal a of the full-wave rectifier 4, and the base of the transistor 8 is connected to the diode 4.
5 to the connection point between the resistor 10 and the diode 44.

On the other hand, between the connection point f of the bidirectional thyristor 2 and the load 3 and, for example, the negative output terminal b of the full-wave rectifier 4, there is a resistor 46, a semiconductor switching element, for example, a reverse blocking three-terminal thyristor 47, and a load. A series circuit of a voltage detection resistor 48 is inserted, a series circuit of a diode 49 and a resistor 50 is connected to both ends of this resistor 48, and a resistor 5 is connected to both ends of this resistor 50.
A series circuit of 1 and a capacitor 52 is connected, and a resistor 53 and a capacitor 5 are connected across the capacitor 52.
4 are connected in series, and the gate of the reverse blocking 3-terminal thyristor 47 is connected to the connection point between the PUT 12 and the primary coil of the pulse transformer 13 via a resistor 55 and a diode 56. A resistor 57 is connected between the gate and cathode of
The load voltage detection circuit 14 is configured by connecting the two.

An error amplifier 22 is connected between the connection point g between the resistor 53 and the capacitor 54 and the negative output terminal b of the full-wave rectifier 4. This error amplifier 22 connects one transistor 2 to a connection point g between the resistor 53 and the capacitor 54 via a resistor 23.
4, the emitter of this transistor 24 is connected to the emitter of the other transistor 25, and these emitters are connected to the negative output terminal b of the full-wave rectifier 4 through a resistor 26. The collector of the transistor 25 is connected to the connection point between the diode 41 and the capacitor 42 via a resistor 28, and the collector of the transistor 25 is connected to the connection point between the diode 41 and the capacitor 42 via a resistor 58.
A series circuit consisting of a resistor 59, a potentiometer 31, and a resistor 60 is connected to both ends of the capacitor 42, and the base of the transistor 25 is connected to the movable element of the potentiometer 31. is connected to the base of the transistor 8 via a resistor 32. In the figure,
100 indicates a soft start circuit, 101,1
02 and 103 are resistors, 104 is a photocoupler,
105 is a transistor, 106 is a diode, 1
07 is a capacitor.

According to the above embodiment, when the AC power supply 1 is turned on,
Assume that the voltage waveform of this AC power source 1 starts a positive half cycle from zero voltage at time T1, as shown in FIG. 3 (the direction in which the current flows at this time is indicated by arrow A in FIG. direction).
Then, during the half cycle up to time T2 when the voltage becomes zero, the capacitor 9 is charged via the full-wave rectifier 4, and the voltage across the capacitor 9 reaches the resistor 1.
PUT12 at time Ta when the voltage across both ends of
conducts, the pulse transformer 13 applies a trigger pulse to each gate of the bidirectional thyristor 2 and the reverse blocking three-terminal thyristor 47, and at this time Ta
At this point, the bidirectional thyristor 2 and the reverse blocking three-terminal thyristor 47 become conductive at the same time. bidirectional thyristor 2
When conductive, a voltage having the same waveform as the AC power supply 1 is generated across the load 3 as shown in FIG. On the other hand, when the reverse blocking 3-terminal thyristor 47 conducts, the AC power supply 1, load 3, resistor 46, reverse blocking 3-terminal thyristor 47, load voltage detection resistor 48, diode D
At the same time, since the bidirectional thyristor 2 is conductive, the voltage across the load voltage detection resistor 48 is substantially zero, as shown in FIG.

Next, from time T2, the polarity of the voltage waveform of the AC power source 1 is reversed as shown in FIG. 3, and a negative half cycle is started (at this time, the direction of current flow is the second
The direction is indicated by arrow B in the figure. ), then during the half cycle until time T3 when the voltage becomes zero, the discharged capacitor 9 is charged again via the full-wave rectifier 4, and the voltage across this capacitor 9 is changed to the resistor 1.
PUT12 at time Tb when the voltage at both ends becomes greater than 1.
conducts, the pulse transformer 13 gives a trigger pulse to each gate of the bidirectional thyristor 2 and the reverse blocking three-terminal thyristor 47, and at this time Tb
At this point, the bidirectional thyristor 2 and the reverse blocking three-terminal thyristor 47 become conductive at the same time. bidirectional thyristor 2
When conductive, a voltage having the same waveform as that of the AC power source 1 is generated across the load 3, as shown in FIG. On the other hand, when the reverse blocking 3-terminal thyristor 47 becomes conductive, the series circuit of the resistor 46, the reverse blocking 3-terminal thyristor 47, the load voltage detection resistor 48, and the diode D1 becomes a closed circuit connected in parallel to the load 3. A voltage corresponding to the voltage across the load 3 determined by the resistor 46 is generated across the resistor 48, as shown in FIG. Therefore, in the half cycle from time T2 to time T3, the voltage across the load voltage detection resistor 48 is used as the detection voltage, and a voltage determined according to this detection voltage is applied to the base of the transistor 24 of the error amplifier 22, and the preset voltage is applied to the base of the transistor 24 of the error amplifier 22. The base voltage of the transistor 25 obtained by the potentiometer 31 is used as a reference voltage, and an error output is generated at the collector of the transistor 24, that is, at the Q point, according to the difference between this reference voltage and the base voltage of the transistor 24. This error output is applied to the base of transistor 8 through resistor 32, and PUT 12 is turned on with the proper phase according to this error output, thereby causing the next half cycle, that is, the half from time T3 to time T4 as shown in FIG. The conduction phase of the bidirectional thyristor 2 during the cycle, that is, the timing of the conduction time Tc, is controlled, and as a result, the voltage across the load 3 is controlled to be a constant voltage corresponding to the set reference voltage.

Although the above explanation was limited to one cycle of the AC power supply 1, the above-mentioned effect can be obtained in all cycles of the AC power supply 1, and therefore, even if there is a voltage fluctuation of the AC power supply 1, the voltage at both ends of the load 3 is The voltage can be maintained at a constant voltage corresponding to the set reference voltage.

According to the embodiment described above, a series circuit of the resistor 46, the reverse blocking three-terminal thyristor 47, and the load voltage detection resistor 48 is connected to the connection point between the load 3 and the bidirectional thyristor 2 and the input terminal of the AC power supply 1. In order to make the reverse blocking three-terminal thyristor 47 conductive in synchronization with the bidirectional thyristor 2, the series circuit is A closed circuit connected in parallel to the load 3 via the wave rectifier is formed, and the load 3 is connected to both ends of the load voltage detection resistor 48.
Since a voltage that directly corresponds to the voltage across the load 3 is generated, by using this voltage as the detection voltage, the voltage across the load 3 can be detected without using a transformer, and a power transformer is not required.
As a result, it is possible to obtain an AC constant voltage power supply device that is small, lightweight, and has low manufacturing costs.

The soft start circuit 100 is provided as necessary to prevent rush current when the load 3 starts up.

In the above, the configuration of the error amplifier 22 and the control circuit 7 is not limited to this embodiment, but may be any other known configuration. In addition, in the load voltage detection circuit 14, the voltage across the load voltage detection resistor 48 is input to the error amplifier 2.
The circuit configuration for providing the signal to the signal 2 can be changed as appropriate. As the semiconductor switching element, it is sufficient that it has the same function as the reverse blocking three-terminal thyristor, and other elements may be selected as appropriate. The resistor 46 is provided as necessary and may be omitted. Further, if necessary, various bias circuits, noise filters, etc. may be added to the reverse blocking three-terminal thyristor 47 so that the reverse blocking three-terminal thyristor 47 operates satisfactorily.

[Function and effect of the invention]

According to the present invention, a series circuit of a semiconductor switching element and a resistor for detecting load voltage is connected to a connection point between a load and a bidirectional semiconductor switching element, and to an output terminal of a full-wave rectifier whose input terminal is connected to an AC power source. In order to make the semiconductor switching element conductive in synchronization with the bidirectional semiconductor switching element, a series circuit of the semiconductor switching element and the load voltage detection resistor is inserted through the full-wave rectifier every cycle of the AC power supply. A closed circuit connected in parallel to the load is formed, and a voltage that directly corresponds to the voltage across the load is generated across the load voltage detection resistor. By using this voltage as the detection voltage, a transformer can be used. In addition, the voltage across the load can be detected without the need for a power transformer, and the detected voltage obtained at the load is added to an error amplifier, which calculates the difference between the reference voltage set in advance and the detected voltage. An error output corresponding to The voltage at both ends can be stably maintained at a constant voltage corresponding to the set reference voltage, and as a result, it is possible to obtain an AC constant voltage power supply device that is small, lightweight, and low in manufacturing cost.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an example of a conventional AC constant voltage power supply device, Fig. 2 is a circuit diagram showing an embodiment of the present invention, Fig. 3 is a waveform diagram showing the voltage of the AC power supply, and Fig. 4 is a circuit diagram showing an example of a conventional AC constant voltage power supply.
The figure is a waveform diagram showing the voltage across the load, and FIG. 5 is the waveform diagram showing the voltage across the load voltage detection resistor. DESCRIPTION OF SYMBOLS 1... AC power supply, 2... Bidirectional thyristor (bidirectional semiconductor switching element), 3... Load, 11
1...Power transformer, 4...Full-wave rectifier, 7...Control circuit, 8...Transistor, 9...Capacitor, 12...
PUT, 13...Pulse transformer, 14...Load voltage detection circuit, 15...Load voltage detection transformer, 16...
Full wave rectifier, 19, 21... Capacitor, 17, 1
8, 20...Resistor, 22...Error amplifier, 24, 25
...Transistor, 27...Starting DC power supply, 31...
Potentiometer, D1, D2, D3, D4, 4
4, 45, 49, 56... Diode, 47... Reverse blocking 3-terminal thyristor (semiconductor switching element),
48...Resistance for load voltage detection, 100...Soft start circuit.

Claims (1)

[Claims] 1. An AC power supply, a load supplied with power from this AC power supply, a bidirectional semiconductor switching element inserted between this load and the AC power supply, and a full-wave switching element whose input terminal is connected to the AC power supply. rectifier and
a control circuit for controlling the conduction phase of the bidirectional semiconductor switching device connected between the output terminals of the full-wave rectifier; a connection point between the load and the bidirectional semiconductor switching device; and an output of the full-wave rectifier; a load voltage detection circuit comprising a series circuit of a semiconductor switching element and a load voltage detection resistor inserted between the terminal and the load voltage detection circuit; and an error amplifier that generates an error output according to a difference from a set reference voltage, and the control circuit controls the bidirectional semiconductor switching element and the semiconductor switching element by the error output from the error amplifier. An AC constant voltage power supply device characterized in that the conduction phase of the two is controlled in synchronization.