JPS6115447B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a constant voltage generator that generates a constant voltage by inserting a phase control device between an AC power source and a load, and controlling the phase of the phase control device according to a feedback signal from the load. Regarding power supplies.

For example, a constant voltage power supply device is generally used as a power source for a halogen lamp, which is a light source for exposure in a copying machine.

Conventionally, there is a constant voltage power supply device of this type constructed as shown in FIG. That is,
Triac 2, which is a phase control device, is added to AC power supply 1.
For example, a load 3 such as a halogen lamp is connected through the terminal. Further, a full-wave rectifier circuit 4 is connected to the AC power supply 1 via a power transformer 114, and a series circuit of a resistor 5 and a Zener diode 6 is connected to the output terminal of the rectifier circuit 4. A relaxation oscillation circuit 7 is connected to both ends of the Zener diode 6 as a gate control circuit. This oscillation circuit 7 has a series circuit of a transistor 8 and a capacitor 9, a series circuit of resistors 10 and 11 connected to both ends of the Zener diode 6, and a series circuit of a PUT 12 and a pulse transformer 13 connected to both ends of the capacitor 9. , PUT12
The gate of the capacitor 9 is connected to the connection point of the resistors 10 and 11, and the anode is connected to the positive terminal of the rectifier circuit 4 via the resistor 121, so that the terminal voltage of the capacitor 9 is changed to the connection point of the resistors 10 and 11.
PUT every time it exceeds the gate voltage of PUT12 determined by
12 is made conductive, and a trigger pulse is applied to the triax 2 through the pulse transformer 13.

On the other hand, a feedback transformer 14 is connected in parallel to the load 3, and a feedback signal circuit is connected to the secondary winding of the transformer 14. In this feedback signal circuit, a series circuit of resistors 16 and 17 is connected between the output terminals of a rectifier circuit 15, and a capacitor 18 is connected across the resistor 17. A series circuit of a resistor 19 and a capacitor 20 is connected across the capacitor 18 so that a feedback signal is generated across the capacitor 20.

A connection point between the resistor 19 and the capacitor 20 is connected to the base of a transistor 22 via a resistor 21. The emitter of this transistor 22 is connected to the emitter of the transistor 23 and also connected to the negative terminal of the rectifier circuit and the negative terminal of the starting control power supply 25 via a resistor 24, and the collector is connected to the positive terminal of the power supply 25 via a resistor 26. The transistor 23 has a collector connected to the positive terminal of the power supply 25 and a base connected between the power supply 25 and the base thereof to the emitter through a resistor 27 and a capacitor 28. It is connected to the movable element of the yometer 29, thereby forming an error amplification circuit. This error amplification circuit is connected to the potentiometer 2 above.
9 is the reference voltage, and this and transistor 2
2 is compared with the base voltage of the transistor 22, an error output is generated between the emitter of the transistor 22, that is, the potential corresponding to the feedback signal generated at the point A, and this output is sent to the transistor 8 of the oscillation circuit 7 via the resistor 30.
I'm trying to give it a base.

Therefore, the base voltage of the transistor 8 of the relaxation oscillation circuit 7 is controlled by the error output of this error amplification circuit, and by controlling the terminal voltage of the capacitor 9, the generation phase of the trigger pulse to the triac 2 is controlled and a constant voltage is maintained. I am trying to generate output. In addition, capacitors 31, 32 and 33 in the figure are a noise filter circuit, and a resistor 34
The capacitors 35 each constitute a surge absorption circuit.

By the way, in such a device, when the control power supply 25 for starting is turned on, the base of the transistor 8 is biased via the resistors 26 and 30 by the voltage at this time. In this case, since the starting voltage is higher than in the steady state, the charging time of the capacitor 9 is short, and the triac 2 is triggered at an early phase. In this state, if feedback control is not being performed, the triac 2 will maintain the conduction phase described above, so if there is no fluctuation in the power supply voltage, the output voltage will rise sharply as shown in FIG. 3a. However, in reality, feedback control is performed to keep the output voltage constant despite fluctuations in the power supply voltage.
The feedback signal at this time causes the feedback voltage to rise as shown in FIG. 2a, and the potential at point A, where this signal is applied to the base of the transistor 22, may drop as shown in FIG. 2b.
The output voltage may exhibit a slow rise as shown in FIG. 3b. This means that when a halogen lamp is used as the load 3, the rise of the lamp's light becomes slow as shown in FIG. 3c.

Therefore, in order to shorten the rise time of this light, it is sufficient to reduce the influence of the feedback signal when the output voltage rises, and for this reason, conventionally, the capacitance of the capacitor 20 is set to a relatively large capacity. (Unexamined Japanese Patent Publication No. 51-90180) However, if the capacitance of the capacitor 20 is set to be large in this way, the time constant for charging and discharging the capacitor 20 becomes large, resulting in poor response characteristics in a steady state. In other words, this slows down the response of the feedback signal to fluctuations in the power supply voltage, which deteriorates the ability to keep the output voltage constant. In addition, unreasonably increasing the capacitance of the capacitor 20 will greatly deviate from the optimal capacitance value required for constant voltage characteristics, which is the original function, so it is extremely difficult to select constants that can obtain ideal constant voltage characteristics in circuit design. It becomes difficult.

This invention was made in view of the above circumstances, and it charges the feedback signal when the output voltage rises, reduces the feedback signal input to the gate circuit, and electrically isolates it from the feedback signal circuit after a predetermined period of time. It is an object of the present invention to provide a constant voltage power supply device that can improve the rise characteristics of an output voltage without impairing constant voltage characteristics and response characteristics by providing a time constant circuit.

An embodiment of the present invention will be described below with reference to the drawings. Figure 4 shows the circuit diagram of this invention.
The same parts as those in the figure are given the same reference numerals. In this case, a time constant circuit consisting of a series circuit of a diode 36 and a capacitor 37 is connected in parallel with the capacitor 20 constituting the feedback signal. Here, the capacitor 37 has a sufficiently large capacity. Also,
The connection point between the diode 36 and the capacitor 37 is connected to the positive terminal of the control power supply 25 via a parallel circuit of a resistor 38 and a diode 39. In this case, the diode 39 is for reducing the time constant of the discharge path of the capacitor 37.

The rest is the same as in FIG. 1, so the explanation thereof will be omitted.

In this way, the control power supply 25 for starting now
When the voltage is turned on, the voltage at this time causes the resistor 2 to
The base of transistor 8 is biased via 6, 30. This charges capacitor 9.
When PUT 12 is turned on, triac 2 is triggered and the output voltage starts to rise. In this process, the feedback signal is transferred to the feedback transformer 1.
When generated at the output end of the rectifier circuit 15 via 4,
This signal is passed through the diode 36 to the capacitor 3.
It will be charged to 7. At this time, capacitor 3
Since the capacitor 7 has a large capacity, the charging time constant with the resistor 19 becomes large. Therefore, the rise of the anode side potential of the diode 36 (the potential across the capacitor 20) is delayed, and since this anode side potential is applied to the base of the transistor 22, the rise of the potential at point A is also delayed. For this reason, the rise of the feedback voltage becomes extremely slow as shown in FIG. 5a, and the drop in the potential at point A becomes small as shown in FIG. 5b, so that virtually no feedback control is performed. As a result, the output voltage rises rapidly as shown in FIG. 6a. In this case, by appropriately selecting the capacitance of the capacitor 37 and the time constant, it is possible to overshoot the output voltage as shown by the broken line in FIG.

Therefore, due to the rapid rise of the output voltage, the rise of the optical output can also be significantly accelerated, as shown in FIG.

Thereafter, in a steady state, the capacitor 37 is charged via the resistor 38 to a voltage sufficiently higher than the feedback signal voltage, so that it is electrically isolated from the feedback control system by the diode 36, and its influence on the constant voltage function is eliminated. Furthermore, if the control power supply 25 is cut off in this state, the electric charge of the capacitor 37 will be transferred from the capacitor 37 → diode 39 → resistor 29 →
It is discharged through the path of the capacitor 37 and the path of the capacitor 37→diode 39→transistor 23→resistance 24→capacitor 37 in preparation for the rise of the next output voltage.

Therefore, with such a configuration, the capacitance of the capacitor 20 can be set to an optimum value by providing a time constant circuit for charging the feedback signal when the output voltage rises. This makes it possible to reliably prevent the deterioration of the response during steady state due to the increase in the capacitance of the capacitor 20. Furthermore, since the capacitance of the capacitor 20 can be set to an optimal value, the peripheral circuit constants can also be selected to values that will provide optimal constant voltage characteristics, so that good constant voltage characteristics can be achieved.

By the way, in the constant voltage power supply shown in Fig. 4, the current at the time of rising immediately after the starting input is given has an excessive peak value and effective value over one to two cycles, as shown in Fig. 7a. becomes an electric current. For this reason, it was sometimes necessary to use a triax 2 with a larger capacity than necessary as the phase control device.

Therefore, in Fig. 4, point A and control power supply 2
A series circuit of a diode 40, a voltage regulator diode 41, and a capacitor 42 is connected between the negative terminal of Connect to the positive terminal of the control power supply 25. In this case, the charging time constant of the capacitor 42 is set smaller than the charging time constant of the capacitor 37 described above.

In this way, the potential at point A when the start-up control power supply 25 is initially turned on is regulated by the sum of the potential of the capacitor 42 and the Zener voltage of the voltage regulator diode 41, so as the capacitor 42 rises, the potential at the point A increases. The conduction phase angle is gradually advanced as shown in FIG. 7b. When the potential of this capacitor 42 exceeds the potential at point A, the influence on the control system disappears. In this case, as described above, since the charging time constant of the capacitor 37 is large, the feedback signal is still too small, so that the output voltage can be increased to a steady state. As a result, the rise of the output voltage can be made faster, and the rush current can be kept relatively small, so that the triax 2 can be made smaller and cheaper.

It should be noted that the present invention is not limited to the above-mentioned embodiments, but can be implemented with appropriate modifications within the scope without changing the gist.
For example, in the embodiment described above, a triax was used as the phase control device, but instead of the triax, a thyrist connected in antiparallel may be used.

As described above, according to the present invention, the time constant circuit charges the feedback signal at the rise of the output voltage to reduce the feedback signal input to the gate circuit, and is electrically separated from the feedback signal circuit after a predetermined period of time. By providing this, it is possible to provide a constant voltage power supply device that can improve the rise characteristics of the output voltage without impairing the constant voltage characteristics and response characteristics.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a conventional constant voltage power supply device, FIGS. 2 and 3 are characteristic diagrams for explaining the device, and FIG. 4 is a circuit diagram showing an embodiment of the present invention. 5 and 6 are characteristic diagrams for explaining the same embodiment, and FIG. 7 is a waveform diagram showing the current rise characteristics of the same embodiment. 1... AC power supply, 2... Triack, 3... Load,
114...power transformer, 4,15...rectifier circuit,
5, 10, 11, 16, 17, 19, 21, 2
4, 26, 27, 30, 34, 38, 43... Resistor, 6, 41... Constant voltage diode, 7... Relaxation oscillation circuit, 8, 22, 23... Transistor, 9, 1
8, 20, 28, 31, 32, 35, 37, 42
...Capacitor, 12...PUT, 13...Pulse transformer, 14...Feedback transformer, 25...Control power supply, 29...Potentiometer, 33...Coil.

Claims (1)

[Claims] 1. An AC power supply, a load supplied with power from this power supply, a phase control device interposed between the power supply and the load, and a feedback signal that generates a feedback signal according to the voltage of the load. a gate control circuit that controls the conduction phase of the phase control device in accordance with an error output between the circuit and a reference voltage that is preset by inputting a feedback signal of this circuit; It is characterized by comprising a time constant circuit that charges the feedback signal to reduce the feedback signal input to the gate circuit for a predetermined time at startup, and is electrically separated from the feedback signal circuit after the predetermined time. Constant voltage power supply. 2. The constant voltage power supply device according to claim 1, wherein the time constant circuit has a series circuit of a diode and a capacitor provided between the output terminals of the feedback signal circuit.