JPH02179270A - Power supply device - Google Patents

Abstract

PURPOSE:To turn ON and OFF the primary side of a converter transformer to make it unrelated to the fluctuation of a load, by setting a time constant shorter than that of the circuit where the alternating current generated on the secondary side with the primary side of the converter transformer ON and OFF is rectified and smoothed to supply to the load. CONSTITUTION:The direct current rectified 2 at an AC power source 1 in full wave and smoothed with a capacitor C1 is supplied to the primary winding N1 of a converter transformer T1 and is turned ON and OFF with a switching element Q1. The alternating current generated to the secondary winding N2 of the transformer T1 is rectified D1 and smoothed C2 to supply to a load not illustrated here. The DC voltage obtained by rectifying and smoothing C3 the AC generated on the secondary side with another diode D2 is divided by resistors R1 and R2 to detect the voltage. The detected voltage is electrically insulated with a photocoupler 4 to control the pulse width generated in a PWM circuit 5. The time constant by resistors R1 and R2 and a capacitor C3 is set smaller than that of a load circuit. The influence to a control loop caused by load fluctuation can thereby be removed and the occurrence of ripple prevented accordingly.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a power supply device used as a switching regulator for electronic equipment.

[Conventional technology]

FIG. 4 is a diagram showing this type of conventional power supply device. In the figure, 1 is an AC power supply, 2 is a diode bridge that converts the AC into DC, C1 is a smoothing capacitor, T1 is a converter transformer, and Ql is the primary ff! of the converter transformer TI. MOSFET, D, which is a switching element connected to the 1o line Nl, is a rectifying diode that rectifies the output generated in the secondary winding N2 of the converter transformer T, and C2 is a smoothing capacitor, R+.

R2 is a resistor for dividing the rectified and smoothed secondary output voltage; 3 is a voltage detection circuit that detects the secondary output voltage of the converter transformer T from the divided voltage;
4 is a photocoupler for insulating the detection side and the control side;
5 is a PWM circuit that controls the drive of MOSFET Q+ based on the detection signal from the voltage detection circuit 3 obtained via the photocoupler 4.

In the power supply device configured as described above, the secondary output voltage of the converter transformer T is constantly detected, and this is
Feedback to M circuit 5 and M OS F E T
By driving Q+, a constant voltage is applied to the load connected to the secondary winding N2.

[The invention tries to solve i! Title]

However, in the conventional power supply device as described above, when the load condition changes, the time constant changes due to the relationship with the capacitance of the smoothing capacitor C2, which adversely affects the frequency characteristics of the feedback control loop. was there. In addition, when the output voltage detection signal is sampled using a CPU or a counter, and the output is repeatedly increased and decreased depending on the result to obtain the desired output, it is necessary to use n times the sampling frequency (n is an integer). There was a problem in that the output had a control ripple that went up and down at a cycle of .

The present invention has been made in view of these problems, and aims to provide a power supply device that eliminates the influence of load fluctuations on the control loop and that does not generate control ripples in the output. .

(Means for solving the three problems) The power supply device of the present invention is constructed as follows.

a. In a power supply device that switches and drives the primary side of a converter transformer and supplies the output generated on the secondary side to a load, a first rectifying/smoothing means for rectifying/smoothing the secondary side output; A second rectifying/smoothing means having a time constant different from that of the first rectifying/smoothing means rectifying/smoothing the same secondary side output is provided, and from this second rectifying/smoothing means, the secondary side of the converter transformer is Detects voltage and controls switching drive on the primary side.

b. In the power supply device having the above configuration, switching on/off is controlled by the value of the first counter driven at a frequency sufficiently higher than the switching frequency of the primary side of the converter transformer, and at the same time, driven at a frequency sufficiently lower than the switching frequency. The on/off ratio of switching is determined by the value of the second counter.

[Effect]

In the power supply device of the present invention, the rectification/smoothing means connected to the load side and the rectification/smoothing means connected to the control side are provided separately and have different time constants, so that the control side due to load fluctuations is The shadow behind is removed. Also, control ripples are prevented from occurring in the output.

(Embodiment) FIG. 1 is a circuit diagram of a power supply device according to an embodiment of the present invention, and the same reference numerals as in FIG. 4 indicate the same components. The rectifying diode D1 and the smoothing capacitor C2 are
It constitutes a first rectifying/smoothing means that supplies stable DC to the load side, and apart from this, rectifying/smoothing the secondary output of the converter transformer T1 using a rectifying diode D2 and a smoothing capacitor C1. A second rectifying/smoothing means is configured. The time constant of this second rectification/smoothing means is smaller than and different from the time constant of the first rectification/smoothing means. This second rectifying/smoothing means is connected to the control side, and detects the output voltage on the secondary side of the converter transformer T from the output thereof, and detects the output voltage on the secondary side of the converter transformer T.
It is designed to control the drive of ETQ. Further, the voltage detection circuit 3 compares the detection voltage from the connection point of the resistors R, , R2 with the reference voltage and sends a detection signal to the PWM circuit 5, and the PWM circuit 5 outputs an output based on the detection signal. It is designed to generate pulse signals that turn it up and down.

Next, the operation will be explained.

Line input from AC power supply 1 is diode bridge 2
and is rectified and smoothed by capacitor C1. The positive pole of this line is applied to the primary side of the converter transformer T1, where the other end of the converter transformer T is connected to the drain of MOSFET Q+, which is a switching element, and the source of MOSFET Q+ is connected to the negative pole of the above line. Therefore, MOS FET Q
By switching and driving I, an AC output is generated on the secondary side of the converter transformer T. At this time, since the power supply device shown in Fig. 1 is configured as a flyback type switching regulator, M OS F E
The output varies depending on the switching duty of TQl.

On the other hand, one end of the secondary winding N2 of the converter transformer T1 is grounded, and the other end is connected to a diode D1 and a capacitor C2.
It is connected to the. Then, the secondary output of the converter transformer T1 is rectified and smoothed by the diode D and the capacitor C2, and is supplied to the load. Further, this secondary side output is also rectified and smoothed by the diode D2 and the capacitor C5. This rectified and smoothed DC voltage is divided by resistors R, , R2 and input to the voltage detection circuit 3. The voltage detection circuit 3 then compares the manually input voltage with an internal reference voltage and outputs the comparison result. The photocoupler 4 outputs the comparison result to the PWM circuit 5. The PWM circuit 5 changes the duty of the pulse according to the output of the photocoupler 4, and controls the drive of the MOSFET Q+ so that the output to the load is constant.

In this way, since the first rectification/smoothing means connected to the load side and the second rectification/smoothing means connected to the control side are provided separately and have different time constants, control based on load fluctuations is possible. side effects are eliminated, and control ripples on the output are prevented.

FIG. 2 is a diagram showing another embodiment of the present invention.

In this embodiment, the primary winding N1 of the converter transformer T is directly connected to a DC power supply (voltage Vcc), and -
The other end of the next winding Nl is connected to the collector of a transistor Trl, which is a switching element. The emitter of this transistor T1 is grounded, and a capacitor C4 and a diode D are connected between its collector and ground. Here, the capacitor C4 is for resonating with the primary winding N to perform effective voltage conversion, and the diode D3 is for protecting the transistor Trl. By switching the transistor T,1, a desired voltage according to the winding ratio is generated in the secondary winding N2. Further, the converter transformer T1 is provided with a detection winding N3. One end of this detection winding N is grounded, and the other end is connected to the input end of the flyback voltage detection circuit 6. The output of the flyback voltage detection circuit 6 is connected to the load terminal of the first carantuff. This counter 7 is driven by an oscillator that generates a frequency sufficiently higher than the resonance frequency. In addition, a second counter 8 driven by an oscillator that generates a frequency sufficiently smaller than the oscillation frequency is connected to the data input terminal for setting the data manually input when the load signal of Carantuff is input manually.
is connected. This counter 8 connects the output of another secondary winding N4 provided in the converter transformer T1 to a diode D2. Up or down switching is performed by the output of the voltage detection circuit 3 which detects the output rectified and smoothed by the capacitor C3. Further, the output of the above-mentioned Calantuff is inputted to a comparator 9, which compares the values of the counters 7 and 8 and generates a pulse signal. Driver 1
0 drives the transistor Trl with its pulse signal. Note that a rectifier diode D4 with a large time constant and a smoothing capacitor C5 are also connected to the secondary output winding N.

Next, the operation of the above configuration will be explained with reference to the timing diagram of FIG. The waveform indicated by FBV indicates the flyback voltage generated in the converter transformer T1. First, when the value of the counter 7 at point 0 is sufficiently larger than the value of the counter 8 at point b, the comparator 9 compares the value and the transistor T1. is turned on by the drive signal d of the driver 10, and as a result, the primary winding N1 of the converter transformer T
A voltage of vcc is applied to. Next, when the counter count-up continues and the counter overflows and becomes smaller than the value of the counter 8, the output of the comparator 9 is inverted and the transistor T□ is turned off. As a result, converter transformer T and capacitor CI undergo voltage resonance, and a flyback voltage as shown in the figure is generated in each winding of converter transformer T. This flyback voltage is detected by the flyback voltage detection circuit 6, eight detection signals are generated at the falling edge of the flyback voltage, and the value of the counter 8 is loaded into the counter 7, thereby turning on the transistor T11 again.

The above one cycle is sequentially repeated to perform voltage conversion. At this time, when the value of the counter 8 is small, the on time of the transistors T, , l becomes longer and the output voltage increases, and when the value of the counter 8 is large, the transistor Tr
Since the on-time of l becomes shorter, the output voltage decreases.

Therefore, by detecting the output voltage by the voltage detection circuit 3 and switching the value of the counter 8 up or down based on the signal, it is possible to set the output voltage to a desired value.

That is, the switching on and off is controlled by the first converter transformer T1 driven at a frequency sufficiently higher than the switching frequency of the primary side of the converter transformer T1, and the second transformer driven at a frequency sufficiently lower than the switching frequency. Since the value of the counter 8 is controlled to determine the switching on/off ratio, the output of the converter transformer T is controlled to always oscillate at one time the driving frequency of the counter 8 (n is an integer, undefined). However, since this control ripple enters the human power of the voltage detection circuit 3, the above-mentioned A(I if becomes IIJ function.However, this control ripple gives an adverse 119N to the load, so the transistor T , the output is rectified and smoothed by the !1 current smoothing means of diode D4 and capacitor C5 with a sufficiently large time constant, and the output is rectified and smoothed by diode D2 and capacitor C3, which has a small time constant, and the output is rectified and smoothed by the control side. By inputting the voltage to the voltage detection circuit 3, it is possible to remove ripples from the output.

〔Effect of the invention〕

As described above, according to the present invention, the rectification/smoothing means connected to the load side and the rectification/smoothing means connected to the control side are provided separately, and their time constants are made different, so that control due to load fluctuations is achieved. This has the effect that the influence on the loop is removed and control ripples do not occur due to the output to the load.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing one embodiment of the present invention, FIG. 2 is a circuit configuration diagram showing another embodiment of the invention, FIG. 3 is a signal waveform diagram at each point in FIG. The figure is a circuit configuration diagram of a conventional power supply device. 1...AC power supply 2...Diode bridge 3---Voltage detection circuit 5---PWM circuit 6---Flyback voltage detection circuit 7--- ---
-First counter 8...Second counter 9...Comparator 10-...Driver T,...Converter transformer N, -Primary winding Line N2. N, ...Secondary winding N, ...Detection winding

Claims (2)

[Claims] (1) In a power supply device that switches and drives the primary side of a converter transformer and supplies the output generated on the secondary side to a load, a first rectifying/smoothing means for rectifying/smoothing the secondary side output; A second rectifying/smoothing means having a time constant different from that of the first rectifying/smoothing means rectifying/smoothing the same secondary side output is provided, and from this second rectifying/smoothing means, the secondary side of the converter transformer is A power supply device characterized by detecting voltage and controlling switching drive on the primary side. (2) Controlling on/off of switching by the value of a first counter driven at a frequency sufficiently higher than the switching frequency of the primary side of the converter transformer,
2. The power supply device according to claim 1, wherein the switching on/off ratio is determined by the value of a second counter driven at a frequency sufficiently lower than the switching frequency.