KR850002617Y1 - Constant voltage control circuit of exposure lamp in duplicator - Google Patents

Abstract

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Description

Constant voltage control circuit of copier exposure lamp

1 is an explanatory diagram of a copier exposure lamp constant voltage control method.

2 is an overall system diagram of a copier exposure lamp constant voltage control method.

3 is an output waveform diagram of each part of FIG.

4 is a detailed circuit diagram of a waveform generator which is a main part of the present invention.

5 is a circuit diagram of a conventional waveform generator.

* Explanation of symbols for main parts of the drawings

1: rectifier circuit 2: buffer

3, 6: comparator 4: low bandpass

5 waveform generator 7 triac driving circuit

8: triac 9: exposure lamp

TR ₁ : Transistor IC ₁ : Operational Amplifier

C ₁ : condenser R ₁ -R ₄ : resistance

The present invention relates to an exposure lamp control circuit of an electrophotographic copying machine, and more particularly to a constant voltage control circuit for controlling the amount of light emitted from the exposure lamp.

First, the constant voltage control method of the copier exposure lamp will be described.

The method of controlling the exposure lamp is a phase control method using a triac, which generates a linear waveform (a) as shown in FIG. 1 in the waveform generator every half cycle where trigger voltage and direct current voltage are applied. The linear waveform a is compared with the reference voltage b for which the exposure amount of the exposure lamp is determined, and when the two comparison voltage phase angles are located, the triac driving circuit is driven to control the triac.

2 is a schematic diagram of a control method of the exposure lamp of the electrophotographic photocopier. As shown therein, a secondary side of a transformer T connected to an AC power source AC is connected through a rectifier circuit 1 and a buffer 2. After common connection to the input side of the comparator 3 and the low pass filter 4 comparing with the reference voltage b, their output side is connected to the waveform generator 5, and the waveform generator 5 Is connected to the gate of the triac 8 via a comparator 6 and a triac driving circuit 7 which compares the output side of the circuit with the reference voltage b, and both ends of the triac 8 are exposed to an exposure lamp 9 Above bridge)

In the constant voltage control circuit of the electrophotographic photocopier exposure lamp configured as described above, when the AC power source AC is input as shown in FIG. 3A, the AC power source is full-wave rectified by the rectifier circuit 1, and the buffer 2 A waveform is outputted to the output side d thereof, as shown in FIG. 3 (b), and the waveform output from the buffer 2 is compared with the reference voltage b at the comparator 3 to output the waveform. In (e), a rectangular pulse signal as shown in FIG. 3 (c) is output and applied to the waveform generator 5, and the waveform output from the buffer 2 is connected to the low band pass-through 4. As shown in FIG. 3 (d), a direct current waveform is output to the waveform generator 5, and thus, the output side g of the waveform generator 5 is applied to the output generator g. Since the linear waveform as shown in the figure is output and applied to the comparator 6, the linear waveform is compared with the reference voltage b. The square wave as shown in FIG. 3 (f) is output to the output side h. In this way, the square wave signal output from the comparator 6 is applied to the triac driving circuit 7 so that the third (at the time of inputting the square wave signal is input to the output side i of the triac driving circuit 7. g) as shown in Fig.

By the way, in the system of the copier as described above, since the waveform generator is conventionally composed of the resistor R, the transistor TR, and the capacitor C as shown in FIG. 5, the comparator 3 and the low The output voltage V corresponding to the output signal of the band pass section 4 is as follows.

… … … … … … … … … … … … (One)

Here, Vi is a direct current voltage output from the low band pass (4).

As can be seen from Equation (1), since the output voltage of the conventional waveform generator 5 is changed exponentially, the linearity is bad, and the voltage of the part in the waveform (a) of FIG. As a result, the exposure amount of the exposure lamp is severely changed.

In view of the above, the present invention enables stable control of the exposure voltage of the exposure lamp without being affected by the variation of the input voltage, which will be described in detail with reference to FIG.

As shown in FIG. 4, the output side of the comparator 3 is connected to the base of the transistor TR ₁ and its emitter and collector are connected at both ends of the capacitor C ₁ and the inverting input terminal of the operational amplifier IC ₁ . And an inverting input terminal thereof connected to a power supply terminal V _H through a resistor R ₃ , and the output side f of the low band pass 4 connected to a resistor R ₁ , The waveform generator 4 is configured by connecting (R ₄ ) to the non-inverting input terminal and the inverting input terminal of the operational amplifier IC ₁ , respectively. The operation relationship of the inventive waveform generator 5 configured as described above will be described. As follows.

When the DC voltage output from the output side of the low band pass section 4 is Vi, the voltage V ⁺ applied to the non-inverting input terminal of the flexible amplifier IC ₁ is

… … … … … … … … … … … … … … … … (2)

It becomes However, since the operational amplifier IC ₁ has infinite input resistance and voltage gain due to its characteristics, the voltage V ⁻ applied to the inverting input terminal of the operational amplifier IC ₁ is equal to the voltage V ⁺ applied to the non-inverting input terminal. Become equal.

Therefore, the current I ₄ flowing in the resistor R ₄ is

… … … … … … … … … … … … … … … … … … … (3)

And the current I ₃ flowing through the resistor R ₃ is

… … … … … … … … … … … … … … … … … … … (4)

Becomes

On the other hand, when the low potential signal is output from the comparator 3 and the transistor TR ₁ is turned off, the current IC flowing through the capacitor C ₁ is

… … … (4)

Therefore, the output voltage (V ₀ ) of the operational amplifier (IC ₁ ) is

… … (5)

Where α is to be.

In the above formula (5) Speaking of

… … … … … … … … … … … … … (6)

So that

… … … … … … … … … … … … … (7)

It becomes

In addition, when the high potential signal is output from the comparator 3 and the transistor TR ₁ is turned on, all the charges of the capacitor C ₁ are discharged, so the output voltage V ₀ (t) of the operational amplifier IC ₁ is , V ₀ (t) = V ⁺ = Vi... … (8).

As can be seen from the equations (7) and (8), the voltage V ₀ output from the output terminal of the operational amplifier IC ₁ on the output side of the waveform generator 5 changes linearly, On the output side of the waveform generator 5, a complete linear waveform as shown in FIG. 3 (e) is output.

As described above, the linear waveform of the waveform generator of the present invention has very good linearity, and since the voltage at the portion B of the waveform of FIG. 1 remains constant regardless of the variation of the input voltage, Since the exposure voltage of the exposure lamp changes very little, there is an advantage that the exposure amount of the exposure lamp can be stably controlled.

Claims (1)

(Correction) The output side of the rectifier circuit 1 connected to the secondary side of the transformer T is connected to the comparator 3 and the low band pass section 4 via the buffer 2, and then the output side thereof is connected to the waveform generator 5 And a comparator (6) control circuit of a copier exposure lamp connected to the gate of the driving triac (8) of the exposure lamp (9) via a triac drive circuit (7), on the output side of the comparator (3). The emitter and collector of the transistor TR ₁ with the base connected thereto are connected to both ends of the capacitor C ₁ and the inverting input terminal and the output terminal of the operational amplifier IC ₁ , respectively, and the inverting input terminal thereof is resistor R. ₃ ) is connected to the power supply terminal (V _H ), and the non-inverting and inverting input of the operational amplifier (IC ₁ ) through the resistor (R ₁ ), (R ₄ ) to the output side of the low-band pass-through (5), respectively. A constant voltage control circuit for a copier exposure lamp, characterized in that the waveform generator (5) is connected to each terminal.