JPS601641B2 - High-voltage power supply for charging devices in copying machines - Google Patents

Description

[Detailed Description of the Invention] Conventionally, a ferroresonant type high-voltage power supply device has been used as a power source for a main charger, a transfer charger, etc. of a copying machine (these are collectively referred to as charging devices in this specification). However, only the constant voltage characteristics are considered.

However, in a copying machine, it is desirable to keep the current flowing through the photosensitive drum constant. If this current varies depending on the usage environment or other factors, the charging effect will also directly affect the change in image quality, so it is necessary to readjust the adjustment settings or take a separate compensation means depending on the usage conditions and environment. As high-voltage power supplies having constant current characteristics, inverter-type devices using semiconductors (transistors, triacs, etc.) are known, but they are relatively expensive. SUMMARY OF THE INVENTION An object of the present invention is to provide an inexpensive fero-resonant high-voltage power supply device having constant current characteristics that can be used as a power source for a charging device of a copying machine.

The present invention will be explained below with reference to the illustrated embodiments.

In the figure, 10 is a first iron-resonant transformer, and a parallel capacitor C is connected to its output winding 12. The output winding 1.2 of this transformer 10 is connected to the rectifier bridge 1
3 and a parallel circuit of a capacitor 14 and a resistor 15 connected between the output terminals thereof, the main charger of the copying machine is connected to the rectifier circuit. The impedance of the load circuit including this rectifier circuit is set high. The input winding 11 of the first ferro-resonant transformer 10 is connected to the AC power supply bus line AC, but as it is, the terminal voltage of the input winding 11 will fluctuate due to load fluctuations, power supply voltage fluctuations, etc. The output current will also vary accordingly.

To prevent this, the input winding 11 of the transformer 10 is connected to the power supply bus AC via a second iron-resonant transformer 20. In this case, the input winding of the first ferro-resonant transformer 10 is connected to the second ferro-resonant transformer 20 via the variable resistor VR.
The input winding 2 of the transformer 20 is connected to the output winding 22 of the transformer 20.
1 is connected to a power supply bus AC via a switch SW. C2 is a parallel capacitor for resonance. When the switch SW is closed in the above-mentioned moderation, the second transformer 20
A constant voltage of 0.1 is applied to the first transformer 101.

The output characteristic curve in this case has a current-voltage characteristic as shown in FIG. 2, for example, due to the large impedance of the load seen from the transformer 10. By adjusting the value of the variable resistor VR to change the input voltage of the transformer 10, the characteristics shown in FIG. 2 can be shifted in parallel,
Therefore, a constant current of a desired value can be obtained. However, in a copying machine, it is desirable to operate the charging device as far away as possible when starting the exposure operation, that is, to improve the so-called start-up.
The switch SW is a switch that is turned on at the same time as an exposure lamp (not shown) is turned on during the exposure process, for example, and the rise of the output voltage and current after the switch SW is turned on is a problem. In the above configuration where the load impedance is large, this rise becomes worse. To compensate for this, the first ferro-resonant transformer 101 is provided with a third winding 16. This third winding 16 is connected to a power supply bus AC via a switching circuit 30.

The switching circuit 30 includes a triax 38 inserted into the power supply path of the third winding 16, and a triax 38 that turns the triax ON-O.
It has a transistor 35 for FF control. When the switch SW is turned on to operate the charger, the diode 23
The DC voltage rectified by the capacitor 24 is applied to the resistor 36,
37 to the gate of triac 38. Therefore, at the same time as the switch SW is turned on, the triac 38
becomes 0N, and the third winding 16 is energized through the resistor 39. The energized third winding 16 is connected to the first ferro-resonant transformer 1
A magnetic flux in the same direction as the magnetic flux due to the input winding 11 of zero is generated, and the output voltage of the output winding 12 is increased. On the other hand, at the same time as the switch SW is turned on, the capacitor 34 connected to the base of the transistor 35 via the resistor 33 starts to be charged according to the voltage divided by the resistors 31 and 32. The terminal voltage of the capacitor 34 increases exponentially with the passage of time, and eventually exceeds the threshold value of the transistor 35.
Transistor 35 is made conductive. Therefore, the triator 38, which had been turned on at the same time as the switch was turned on, was turned off.
do. That is, the switching circuit 30 energizes the third winding 16 for a certain period of time after the switch SW is turned on.

Due to the function of this switching circuit, the first transformer 10
The output voltage of the capacitor 14 is increased for a certain period of time after the switch is turned on, and the charging time of the capacitor 14 is shortened. Therefore, the charging device starts operating more quickly. As described above, since the fero-resonant high-voltage generator of the present invention has constant current characteristics, stable copying can be performed without the value of the discharge current to the photosensitive drum of the copying machine fluctuating depending on the usage environment etc. .

Furthermore, due to the function of the third winding, the rise of the charging device does not deteriorate.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a fero-resonant high-voltage power supply device according to the present invention,
FIG. 2 is a graph illustrating the output characteristics. 10...First iron-resonant transformer, 11...
... Input winding, 12 ... Output winding, 13 ... Rectifier bridge, 14 ... Capacitor, 16 ...
...Third winding, 20...Second iron-resonant transformer, 30... ...Switching circuit, 35...
・Transistor, 38...Triack, VR・
...Variable resistor, SW...Switch. Figure 1 Figure 2

Claims (1)

[Claims] 1. The input winding of a first ferro-resonant transformer whose output winding is connected to a charging device via a rectifier circuit is connected to a power source via a second ferro-resonant transformer. A high voltage power supply device for a charging device in a copying machine, characterized in that: 2. Claim 1, in which a variable resistor is inserted in the connection circuit between the first ferro-resonant transformer and the second ferro-resonant transformer.
High-voltage power supply equipment as described in section. 3. A third winding is provided in the first iron-resonant transformer, and this winding is connected to a common power source with the second iron-resonant transformer via a switching circuit, and immediately after this power is turned on, the third winding is 2. The high voltage power supply device according to claim 1, wherein the output voltage of the first iron resonant transformer is increased by activating the switching circuit.