JPS58190276A - Power source - Google Patents

Abstract

PURPOSE:To stabilize an output voltage by employing an oscillator which varies in the output pulse width when an input power voltage varies. CONSTITUTION:An operational amplifier OA1 is composed of a positively fed back CR oscillator, the output of the amplifier OA1 is applied to the base of a transistor Tr1, and the base-drive transformer T1 of a transistor Tr2 is driven. The base of the transistor Tr2 is driven by a current from the output coil of the transformer T1, and an oscillation waveform is obtained at the collector. A resonance circuit is composed of the inductances of a condenser C5 and the collector coil of a transformer T2. With the above configuration, the output pulse width of the CR oscillator varies in response to the variation in the input voltage VE, and the output can be stabilized without any feedback.

Description

[Detailed description of the invention] The present invention relates to a power supply device.

This type of switching type power supply device switches the DC current obtained by rectifying the input AC current or the input DC current and applies it to the primary winding of the transformer, and also outputs the AC voltage induced in the secondary winding. Rectify to obtain the desired DC voltage. With this method, a high-voltage DC power supply can be easily constructed by appropriately setting the switching frequency and winding ratio. In particular, a switching type power supply device is suitable as a power source for a device with a relatively small load power source, such as a high-voltage power source for a copying machine. FIG. 1 is a circuit diagram showing an example of a switching type power supply device. Rather, operational amplifier OA1
, resistor Ro, R4, Rs and capacitor C! The output of this oscillator is connected to a transistor”*
t Amplified and shaped by Tr2 and applied to the primary winding of transformer T. The voltage induced in the secondary winding of the transformer Tt is rectified by diodes Da and Ds, and then smoothed by capacitors C, , C,. In the above circuit, the change in the power supply voltage VB is magnified and the transformer T
! Since it appears in the secondary circuit of , the voltage fluctuation rate is poor. For this reason, it is common practice to detect the secondary voltage and feed it back to the primary circuit to stabilize the output voltage. For example, by changing the width of the pulse supplied to the primary circuit of the transformer,
In a power supply device using known pulse width control that changes the rectified output voltage in the next circuit, the rectified output voltage or its divided voltage is compared with a reference value to form an error voltage. The pulse width in the primary circuit is controlled and stabilized.

In order to control the pulse width using the error voltage, it is sufficient to compare the triangular waveform and the error voltage with a comparator, and control the timing of energization to the writing coil using the output of the comparator. As described above, by controlling the pulse width, that is, the timing of energization to the primary coil, the power source can be stabilized efficiently.

However, the circuit structure configuration becomes complex and reliability decreases.

The present invention has been proposed in order to solve the disadvantages of these conventional examples, and its purpose is to provide a power supply device that is low in friction, highly reliable, and satisfies the characteristics required as a high voltage power supply for copying machines, etc. It is located in a place that provides.

Hereinafter, the actual 4v/4 of the present invention will be explained in detail with reference to the attached 4 negative aspects.

FIG. 2 is a circuit diagram showing an embodiment of the present invention, and components having the same functions as those in FIG. 1 are given the same reference numerals. In FIG. 2, OAI is an operational amplifier, Tr
, ~Trt is a transistor, D+~) is a diode, Z
D, -ZD! are constant voltage diodes, C and -C are capacitors, L to kg are resistors, TI is a pace drive transformer for Trt, and T is a flyback transformer. Also,
LED is an output display LED, and WI is a charging/neutralizing wire.

The operational amplifier OAI is a positive feedback OCR oscillator, and its ←
) A voltage waveform as shown in FIG. 3 is obtained at the input terminal. Input voltage +vg is divided into 1/1 by resistor R1+Rt and charged to capacitor C1.

When the output of the operational amplifier Om1 becomes O■, a current flows through the constant voltage diode ZD, ~2) and the resistor -, and the (+) input of the operational amplifier OAI becomes Q-ΔE. In addition,
ΔE is the Zener voltage of the constant voltage diodes ZD, ZD2. Also, conversely, the output of operational amplifier 0AIC) is +7
When it becomes m, the (+) input of the operational amplifier OAI becomes T+ΔE. Therefore, the (-) input of the operational amplifier OAI is as shown in FIG.
) and converges to +7m with a time constant C1・ru, and a periodic function curve that starts with (1+ΔE) and converges to Qv with a time constant Ct"Ra are repeated alternately. At this time, the oscillation period is expressed as: Here, the output of the operational amplifier OAI is added to the pace of the transistor Trl, and the output of the transistor Trl is
, the pace drive transformer T, is driven.

Transistor Tr! The pace of is driven by a magnetic current from the output winding of the transformer T, and a switching waveform as shown in FIG. 4 is obtained at the collector. t&, the capacitor Cs, and the inductance of the collector winding of the transformer T constitute a resonant circuit. Therefore, when the transistor Try is off, it resonates at a predetermined frequency, so that the Δ pulse width P of the collector waveform remains constant regardless of the input cycle within a certain tolerance range of the input cycle. The output voltage available at each output terminal is proportional to (T-P) within a certain tolerance range of the repetition period T of the input. In addition, the value of P depends on the design conditions of transformer T and capacitor C.
It is determined by the capacity of 6.

If the output voltage of the output terminal is V, then this output voltage V
Since yg is naturally proportional to the input voltage yg, the following relational expression is obtained.

~91・v!・ (T-P) ・・・・・・・−・・
...(2) In (2), set the output voltage V to a predetermined value, 9
．． In order to stabilize it, the following formula should hold true (in the formula, the subtractor is a constant of proportionality).

On the other hand, the above-mentioned fl) formula is now: ■8〉〉△E, that is, +31, (From formula 41, 2 − = 8 C,・R5@△E ・・・・・・・・・・・・
... (5) q+ When the equation is satisfied, the output is kept constant regardless of fluctuations in the input voltage vEg). Note that if a variable resistor is used instead of the resistor tortoise, the output voltage can be changed continuously.

FIG. 5 shows an embodiment of the present invention in which an astable multivibrator is constructed by using transistors Tr3 and Tr4 in place of the operational amplifier OAI of the embodiment shown in FIG. FIG. 7 is a circuit diagram of an oscillation circuit according to another embodiment.

As described above, since the present invention uses an oscillation circuit whose output pulse width changes with fluctuations in the power supply voltage, it has the effect of stabilizing the output voltage without any feedback. Furthermore, a resonant circuit is formed by a transformer and a capacitor, and the secondary side output voltage of this transformer is rectified to obtain a high voltage, so that a high DC voltage higher than the voltage determined by the step-up ratio of the transformer can be generated.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an example of a conventional switching type power supply device, Fig. 2 is a circuit diagram showing an embodiment of the power supply device according to the present invention, and Fig. 3 is a circuit diagram showing an example of an oscillation circuit in the power supply device of the embodiment. FIG. 4 is a waveform diagram of the collector voltage of the switching transistor in such a power supply device, and FIG. 5 is a circuit diagram showing an example of an oscillation circuit according to another embodiment of the present invention. Here, OAI... operational amplifier, Tr+ = Trt
... Transistor, ZD, ~2) ... Constant voltage diode, D. ~)...Diode, C1~C,...Capacitor,
RI-RI. ...Resistor, T+...Pace drive transformer, T,...
...It is a flyback transformer. Patent Applicant: Canon Co., Ltd. Figure 2 Figure 3 Figure 1 ＼, ＼＼ ＼, 0□

Claims (1)

[Claims] 1. An oscillation circuit whose oscillation period changes with fluctuations in power supply voltage, a transformer which is energized according to the oscillation period of the oscillator circuit, and a resonant circuit coupled to the winding of the scissor transformer. What is claimed is: 1. A power supply device comprising: a capacitor forming a capacitor, the output voltage of the power supply device being stabilized by changing the oscillation cycle. 2. The power supply device 0 according to claim 1, wherein the transformer is a flyback transformer.