JPH04109867A - Switching power source - Google Patents

Abstract

PURPOSE:To process in a wide input range with a simple configuration capable of using a PWM control IC sold in the market by correcting the operating point of a feedback control circuit in response to an input voltage component. CONSTITUTION:A DC/DC converter 1 is driven by a pulse width signal from a pulse width modulation circuit 11 in such a manner that a switching transistor Q1 is turned ON/OFF, A feedback control circuit 2 so varies a feedback control signal Ec as to eliminate a difference between a voltage signal eo corresponding to obtained DC output voltage Eo and a reference voltage ES. The signal Ec is applied to the base of a transistor Q2, and the voltage dividing ratio of the resistors R1, R2 is controlled by the Q2 and a resistor R3. A feedforward control circuit 3 forms a voltage Ei1 corresponding to an input voltage Ei from a winding n3 of a main transformer TR, and the voltage dividing ratio of the resistors R1, R2 is varied in response to an input voltage component.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a switching power supply device that can handle a wide range of input, and more specifically, it is equipped with a DC/DC converter driven by a pulse width modulation circuit, and has an output DC The present invention relates to a switching power supply device that controls pulse width so that the voltage is constant.

<Prior art> Regarding a switching power supply device using a DC/DC converter that can handle a wide range of human power, see, for example, "Nikkei Electronics J, September 28, 1981 issue, pages 164 to 181.
Detailed information is provided on the page.

Switching power supplies that can handle a wide range of human power have many advantages, such as being able to standardize products, being able to operate regardless of the input voltage classification, and being able to handle power inputs where instantaneous voltage drops occur. There is.

In this type of switching power supply, the input terminal range is large, so with the normal feedback control method, the operating point gain of the control system changes depending on the input terminal, so it is difficult to stabilize the control system over the entire range. is difficult, and a wide forward control method is used to compensate for this.

Conventional devices employing this method are configured to manually change the amplitude of the triangular wave signal input to the comparator of the pulse width modulation circuit.

<Problems to be Solved by the Invention> However, such a method cannot be applied to a commercially available pulse width modulation (PWM) control IC with a built-in oscillator.
When implementing this using , it is necessary to stop the internal oscillator and prepare an external oscillator suitable for this purpose.

The present invention has been made in view of these problems, and has a simple configuration that applies a feedforward control method using input voltage, can use a commercially available PWM control IC, and has a wide range of input. The purpose is to provide a switching power supply device that can handle this problem.

<Means for Solving the Problems> FIG. 1 is a block diagram showing the basic configuration of the present invention.

In the figure, reference numeral 1 denotes a DC/DC converter, which includes a pulse width modulation circuit 11 having linear pulse width modulation characteristics, and a switching transistor Q1 that is driven on/off by a pulse width modulation signal from this circuit.

2 is a feedback control circuit for keeping the output voltage Eo of the DC/DC converter constant, and includes an error amplifier 21 that amplifies the difference between the reference voltage ES and the voltage eo corresponding to the output voltage, and its output signal is applied to the feedback input terminal of the pulse width modulation circuit 11.

3 takes the input voltage component from the winding of the main transformer TR of the DC/DC converter 1, and connects it to the pulse width modulation circuit 11.
This is a feedforward control circuit that applies voltage to the feedback input terminal of the oscillator to change its operating point.

Function> The DC/DC converter turns the input DC voltage on and off using a switching transistor, applies it to the primary winding of the main transformer, rectifies and smoothes the voltage obtained at the secondary winding, and outputs the DC voltage Eo. do.

The feedback control circuit feeds back the error signal to the pulse width modulation circuit so that the output voltage of the DC/DC converter becomes a constant voltage corresponding to the reference voltage ES.

The feedforward control circuit applies an input voltage component to a feedback input terminal of the pulse width modulation circuit to correct a control signal fed back to the pulse width modulation circuit.

This changes the operating point of the pulse width modulation circuit and realizes a wide input voltage range.

<Example> Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram showing an embodiment of the present invention. In the figure, the same parts as those in FIG. 1 are designated by the same reference numerals.

In the DC/DC converter 1, co is a smoothing capacitor, TR is a main transformer, and an input DC voltage Ei is applied to its primary winding n1 after being turned on/off by a switching transistor Q1. DI and CI are diodes and smoothing capacitors that rectify and smooth the alternating voltage generated in the secondary winding n2, and an output voltage Eo is obtained across the smoothing capacitor C1.

The switching transistor Q1 is a pulse width modulation circuit 1
It is driven on/off by a pulse width signal output from 1. Here, the pulse width modulation circuit 11 is a commercially available PWM stiffness control IC, and the relationship between the feedback signal applied to the feedback terminal FB and the duty ratio of the output pulse width signal is determined by this block. As shown in the figure, there is a linear relationship.

In the feedback control circuit 2, R], ], , R12 are resistors that divide the output voltage Eo, and the error amplifier 21 divides the output voltage Eo.
The difference between the divided voltage eo corresponding to o and the reference voltage ES is amplified. R13 and R14 are resistors, D2 is a diode, and T
R2 is a signal isolation transformer driven by the output signal from the secondary winding n2 of the main transformer TR.

D3 is a diode for rectifying the signal transmitted through the signal insulating transformer TR2, and c2 is a smoothing capacitor, and a feedback control signal Ec corresponding to the output signal of the error amplifier 21 is obtained across the capacitor C2.

Q2 is a transistor to which this feedback control signal Ec is applied to the base, R1 is a resistor connected between the reference voltage terminal VREF of the pulse width modulation circuit 1 and the feedback terminal FB, and the transistor Q2 is connected in parallel through the resistor R3. It is connected to the. Further, it is connected in series between the resistor R2 and the common line.

In the feedforward control circuit 3, n3 is an arbitrary winding of the main transformer TR, D4 is a diode, and C3 is a capacitor. These are for extracting the component of the input terminal El, and the capacitor C3 has both ends corresponding to the input terminal Ei. A voltage signal Ei1 is obtained. Dz is a Zener diode, R4 is a resistor, and the voltage signal Eil is connected to the pulse width modulation circuit 1.
1 feedback terminal FB.

The operation of the device configured as described above will be explained as follows.

The DC/DC converter 1 controls the switching transistor Q by the pulse width signal from the pulse width modulation circuit 11.
1 is turned on/off and driven.

The feedback control circuit 2 operates so that there is no difference between the voltage signal eO corresponding to the obtained DC output voltage E0 and the reference voltage ES, that is, so that the DC output voltage EO becomes a constant voltage corresponding to the reference voltage ES. Then, the feedback control signal Ec is changed. This feedback control signal Ec is applied to the base of transistor Q2, and is connected to resistor R by Q2 and resistor R3.
1. Controls the partial pressure ratio of R2.

For this reason, the control voltage applied to the feedback terminal FB of the pulse width modulation circuit 11 changes, and the duty ratio of the pulse width signal can be controlled.

Such a control system was developed by the present applicant in U.S. Patent Application No. 6287396.
No., Utility Application No. 1983-96709 and Utility Application No. 62-967
It has already been proposed as No. 10.

FIG. 3 shows the feedback control signal Ec when the feedforward control circuit 3, which is a feature of the present invention, is not provided.
3 is a diagram showing the relationship between the pulse width signal and the duty ratio (Duty) of the pulse width signal from the pulse width modulation circuit 11. FIG.

When the input voltage Ei is low, the operating point is at a location where the duty ratio is large, but when the input terminal Ei becomes high, the operating point moves to a location where the duty ratio is small, and there is a difference of 11 points.

Returning to FIG. 2, the feedforward control circuit 3 creates a voltage Eil corresponding to the input voltage Ei from the winding n3 of the main transformer TR, and supplies this to the Zener diode Dz,
It is applied to the connection point of the resistors R1 and R2 (feedback terminal FB of the pulse width modulation circuit 11) via the resistor R4, thereby changing the voltage division ratio of the resistors R1 and R2 according to the input voltage component.

FIG. 4 shows the signal E from the feedforward control circuit 3.
The duty ratio of the feedback control signal Ec and the pulse width signal from the pulse width modulation circuit 11 (Du
ty); FIG.

The magnitude of voltage Eil, the voltage of Zener diode Dz,
By adjusting the value of resistor R4, the feedback control signal Ec
The relationship between the input voltage E1 and the duty ratio (Duty) is made into a characteristic that is not affected by the input voltage E1, as shown in FIG.

FIG. 5 is a human output conversion characteristic diagram of a single-stone DC/DC converter. In the on-on type, the conversion ratio Eo/Ei is proportional to the duty ratio (D), but in the on-off type,
The relationship between conversion ratio and duty ratio becomes nonlinear. The control by the feedforward control circuit, which is a feature of the present invention, is linear correction, and in the case of on-off type nonlinear input/output characteristics, it is difficult to completely correct it.
It can be said that the correction effect is greater when an on-on type DC/DC converter is used.

In the embodiment, the primary side of the main transformer is controlled, but the present invention may be applied to a system that controls the secondary side of the main transformer. Further, a buffer or the like may be added to increase the power of the feedforward control circuit.

<Effects of the Invention> As explained in detail above, according to the present invention, the operating point of the feedback control circuit is corrected according to the input voltage component, and it is possible to use a commercially available PWM control IC. By using the present invention, it is possible to provide a switching power supply device that operates stably over a wide range of fluctuations in input terminals.

Further, by extracting the input voltage component from an arbitrary winding of the main transformer, it is easy to comply with safety standards, etc., and the configuration can be the same on the primary and secondary sides.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of the present invention, FIG. 2 is a configuration block diagram showing an embodiment of the present invention, and FIG. 3 is a block diagram showing the basic configuration of the present invention. Figure 4 is a diagram showing the relationship between the duty ratio of the feedback control signal and the pulse width signal from the pulse width modulation circuit when no signal is provided. FIG. 5 is a diagram showing the relationship between the duty ratio of the pulse width signal from the width modulation circuit. ]...DC/DC converter 11...Pulse width modulation circuit Ql...Swiss transition λ/TR...Main transformer 2...Feedback control circuit 21...Error amplifier 3/Feet forward control circuit- ...No Figure 1 I DC/DC converter Figure 3 Duty ratio (Duty)

Claims (1)

[Claims] A pulse width modulation circuit having linear pulse width modulation characteristics, and a D driven by a signal from the pulse width modulation circuit.
a C/DC converter; a feedback control circuit that provides the pulse width modulation circuit with a feedback control signal for keeping the output voltage of the DC/DC converter constant; and a feedback control circuit that receives an input voltage component from a winding of a main transformer of the DC/DC converter. A switching power supply device comprising a feedforward control circuit that takes out a pulse width modulation circuit and feeds it to a pulse width modulation circuit to change its operating point.