JPS6149657A - power supply - Google Patents

Abstract

PURPOSE:To remedy the alteration of a stepup transformer without regulation by controlling the transformer by driving a time constant circuit on the basis of the detected value of the flyback voltage of the transformer at zero point passing time and a load current detection value. CONSTITUTION:In a power source circuit for supplying power generated at the secondary side of a step up transformer T to a load RL by interrupting by switching means TR at the primary side of the transformer T, zero cross detecting means 1 for detecting the time when the flyback voltage of the transformer T passes a zero point is provided. Further, means 3 for controlling the voltage conversion efficiency by detecting the load current is provided, and the output is compared with the output of a time constant circuit 2 by comparator 4. The output of the means 1 and the output of the means 4 are input to the circuit 2, and the TR is controlled by the comparison output f.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a power supply device, and particularly to a power supply device that cuts off the primary side of a step-up transformer and supplies power generated on the secondary side to a load.

[Prior art]

Conventionally, this type of device has been widely used as a device for generating high voltage such as a charger for a copying machine or a horizontal deflection voltage for a CRT.

Many of these devices are constructed so that the application of power to the primary side @ line of the step-up transformer is interrupted by a switching means such as a transistor to generate a voltage on the secondary side according to the winding ratio.

When cutting off the application of power to the primary winding among the quasiting pulses of the switching means, f','ll:
! I] Oh, Yogayori, I, Ae p5:yZjyu1.
Therefore, it was determined appropriately for each circuit. Therefore, when manufacturing a power supply device using several different step-up transformers, it is necessary to change the control circuit appropriately depending on the device so as to set an appropriate off time for each transformer. That is, although it is possible to share the circuit base to a certain extent, it is necessary to provide an adjustment means that can appropriately change the off-time depending on the type of transformer. Therefore, this requires a lot of space on the circuit board 7, and the manufacturing time and adjustment time are also increased by a considerable amount.
There was a chase.

〔the purpose〕

The present invention has been made in view of the above problems, and even if the step-up transformer used is changed, the control circuit part can be adapted without adjustment, and a simple and inexpensive power supply device that is easy to manufacture is provided. for the purpose of serving.

〔Example〕

The present invention will be described in detail below based on embodiments shown in the drawings.

FIG. 1 shows an embodiment of the power supply device according to the present invention, which is a Mononoke step-up transformer indicated by T in the figure. One end of the primary winding of the step-up transformer T, rlT1, is connected to a resistor R1. It is connected to the power supply voltage CC through the capacitor C2, and is grounded through the capacitor C2.
The other end of the transistor Tr is connected to the collector of the switching transistor Tr.

The emitter of this switching transistor T' is grounded, and a capacitor C1 is connected between the core ground and the core ground.
and a diode D1 are connected. Here, the capacitor C1 is used together with the primary winding T1 to perform efficient voltage conversion, and is also a diode]]1 primary winding υ'
This is for absorbing the reverse power of r1 and protecting the transistor Tr.

- The application of power to the secondary winding T1 is interrupted by a switching transistor. As a result, a voltage boosted according to the winding ratio is generated in the secondary winding T2. This AC voltage is rectified by diode D2 and capacitor C3,
It is smoothed and supplied to the load RL.

In the present invention, the step-up transformer T is provided with a detection winding T6. One end of the detection winding T3 is grounded, and the other end is grounded via a resistor R5.

The terminal voltage of the resistor R5 is connected to one input of a zero cross detector 1 composed of an operational amplifier or the like.

The other input of the zero cross detector 1 is grounded, and its output signal a is input to a time constant circuit 20 set terminal comprised of a resistor, a capacitor, and the like. The output signal of this time constant circuit 2 is connected to one input of comparator circuits 4 and 5 each comprising an operational amplifier or the like.

On the other hand, a resistor R2 for current detection is connected between one end of the secondary winding T2 and the ground, and the terminal voltage of the resistor R2 is connected to one input of an error amplifier 6 composed of an operational amplifier or the like. . A predetermined reference voltage obtained by dividing the power supply voltage VCC by a resistor R3 and 1<4 is input to the other input of the error amplifier B. The output signal C of the error amplifier B is connected to the remaining input of the comparator 4 mentioned above.

The output signal d of the comparator 4 is connected to the reset input of the time constant circuit 2. A predetermined reference voltage C obtained by dividing a power supply type 1-voltage CC by resistors R6 and R7 is connected to the remaining inputs of the first comparator 5. The output signal f of the comparator 5 is input to a current amplifier 6 composed of an operational amplifier, a transistor, etc.

The output of the current amplifier O is connected to the pace of the switching transistor TR, and the output of the current amplifier 6 controls the switching operation of the transistor Tl.

Next, the operation of the above configuration will be explained in detail with reference to the timing chart of FIG.

The waveform indicated by the symbol Ii”Bv at the top of FIG.
The voltage across the resistor R5 in the figure corresponds to the flyback voltage of the secondary winding T2 of the step-up transformer T.

When the flybeck voltage FBV passes through the zero point from the positive region to the negative region, the output of the zero cross detector 1 composed of an operational amplifier or the like is inverted to the positive side. It rises to the output signal of zero cross detector 1. The waveform of the output signal of the time constant circuit 2--the power point difference amplifier 3 has a resistor R2 corresponding to the load current as shown at 3-3 in FIG.

It outputs an error signal C between the voltage across the terminal and the reference voltage formed by the resistors R3 and r14. The waveform of this signal is also shown by a broken line in the third row of FIG. A comparator 4 compares the output signal of the time constant circuit 2 with the error signal C, and outputs the output signal of the time constant circuit 2.
When the output signal of the comparator 5 becomes higher than the error signal C, the reference voltage e of the comparator 5 reaches the level shown in the broken line in the third row of FIG. 2, as shown in the fourth row of FIG. ing. The comparator 5 compares the output signal of the time constant circuit 2 with the reference voltage e, and when the output signal of the time constant circuit 2 becomes higher than the reference voltage C, the output is set to high level, and the output signal of the time constant circuit 2 becomes higher than the reference voltage e. The output goes low when the output signal becomes low. As a result, the output signal f of the comparator 5 has a waveform as shown in the bottom row of FIG.

The output signal f of the comparator 5 is current-amplified by the current amplifier 6, and then transmitted to the switching transistor TR, which switches the step-up transformer T.

By repeating the above operation, a voltage boosted from the power supply voltage VCC according to the turns ratio is generated in the secondary winding T2 of the step-up transformer T and supplied to the load.

According to the embodiments described above, the off time of the step-up transformer is automatically determined according to the zero-crossing timing of the flyback voltage and the load current, so even if the transformer T is changed, it is not necessary to change or adjust the circuit part. There is no need to do
Optimal voltage conversion can always be performed without adjustment. Therefore, manufacturing and design changes are greatly facilitated, and space on the circuit board can also be saved.

In the above embodiment, a detection winding was provided on the step-up transformer T to detect the flyback voltage, but even if no detection winding is provided, the collector voltage of the switching transistor Ti corresponding to the flyback voltage can be detected. Zero cross detection may also be performed.Furthermore, although a switching power supply using a step-up transformer has been illustrated in the above embodiment, it may also be applied to an on/off type switching power supply or an on/off type switching power supply. The present invention can be applied.In this case, zero cross detection may be performed by detecting voltage drop, current decrease, etc. instead of detecting flyback voltage.

〔effect〕

As is clear from the above description, according to the present invention, in a power supply device that supplies a voltage-converted output generated on the secondary side of a step-up transformer by switching the primary side of the step-up transformer intermittently to a load, A zero-crossing detection means for detecting when the flybank voltage passes the zero point, a means for controlling voltage conversion efficiency according to the detected load current, and a comparison means for comparing the output of this first efficiency production means with the output of the time constant circuit. The time constant circuit rises at a constant time constant above the output of the zero cross detection means and is reset by the output of the comparison means, and the comparison signal of the output of the time constant circuit and the reference voltage Since a configuration is adopted that controls the switching means, the off time of the step-up transformer is automatically determined according to the zero-crossing timing of the flyback voltage and the load current.
Even if the transformer is changed, the circuit can be adapted without any adjustment, and an excellent power supply device with easy design change, easy manufacturing, and low cost efficiency can be provided.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the circuit configuration of a power supply device according to the present invention, and FIG. 2 is a timing chart showing voltage waveforms at various parts in the configuration of FIG. 1. 1...Zero cross detector 2...Time constant circuit 6...
・Error amplifier 4, 5...Comparator 6...Current amplifier Tft...Switching transistor T...Transformer T1...-Next winding T2
...Secondary winding T3...Detection winding RL...
Load patent applicant Canon Co., Ltd. Figure 2 Figure 1

Claims (1)

[Claims] Zero-cross detection means for detecting when the flyback voltage of the step-up transformer passes the zero point in a power supply device that supplies a voltage-converted output generated on the secondary side of the step-up transformer to a load by intermittent switching on the primary side of the step-up transformer. and,
Means for controlling voltage conversion efficiency according to the detected load current, and comparison means for comparing the output of this efficiency control means and the output of a time constant circuit, and the time constant circuit is fixed by the output of the zero cross detection means. A power supply device characterized in that the power supply device rises with a time constant of 1 and is reset by the output of the comparison means, and the switching means is controlled by a comparison signal of the output of the time constant circuit and a reference voltage.