JPH0449850A - Self-excited type switching power source - Google Patents

Abstract

PURPOSE:To synchronize a switching power source without disordering the operation of a self-excited oscillation by using an orthogonal coupled transformer as the switching power source, and controlling the permeability of the transformer by a synchronous signal to be externally supplied. CONSTITUTION:The permeability of a core is varied by the value of a control current to be supplied to a control winding LCO of an orthogonal coupled type transformer T11 as an oscillation transformer, and the inductance of a coupling coil can be resultantly varied. When an external synchronous signal SH is supplied after a self-excited oscillation, a phase difference between the own oscillation frequency and the synchronous signal is detected by a phase comparator 11, and this phase difference information is supplied to a driving circuit 13 through a low pass filter 12. The oscillation frequency is so controlled by a control current flowing to the winding LCO as to be smoothly pulled in the period of the signal SH. Thus, the switching period of a self-excited type switching power source can smoothly be synchronized with the synchronous signal of a device.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to a self-excited switching power supply that opens and closes a DC power supply to form an alternating signal, and rectifies the alternating signal to obtain a desired DC power supply. Summary of the Invention 1 The self-excited switching power supply of the present invention has a phase comparator for comparing alternating output signals of an external synchronization signal, and a phase comparator for smoothing the output of the phase comparator, as means for synchronizing its own oscillation frequency with an external signal. By providing a smoothing means and configuring the output of the smoothing means to be supplied as an excitation current to a quadrature-coupled saturable transformer constituting a self-excited switching power supply, the on/off period of the switching transistor can be controlled by an external signal. It was designed to be synchronized with.

[Prior Art] Various switching power supply circuits are known that switch a DC input signal and convert it into a desired constant voltage DC voltage via a power supply ratio quadramp. It is known that the waveform or voltage waveform is sinusoidal and switching is performed near the point where the current or voltage becomes zero.

Such a switching power supply circuit is disclosed in, for example, Japanese Patent Laid-Open No. 61-9
As seen in Japanese Patent Application Laid-open No. 4566 and Japanese Patent Application Laid-open No. 62-64266, by using a resonance type, turn-on,
It is attracting attention because it reduces the switching loss that occurs during turn-off, reduces heat generation due to high efficiency, and reduces size and weight due to higher frequency.

FIG. 3 shows an example of a series resonant type switching power supply circuit, which forms a modified half-bridge type self-excited converter.

This circuit includes a first transformer T for oscillation (hereinafter referred to as an oscillation transformer) and a second transformer T2 for output (hereinafter referred to as a cadence), and two switching transistors Q, Q2 are alternately connected to a predetermined It is controlled so that it is conductive only for a period of .

That is, when the switching transistor Q becomes conductive, the primary coil L0. Capacitor C
8 and the feedback winding L3 of the oscillation transformer T1, and the switching transistor Q2 is controlled to be turned off by the base winding coil L2 of the oscillation transformer. Next, the switching transistor Q is turned off by the time constant of the base winding coil L of the switching transistor Q, the capacitor C1, and the resistor R1, and the base winding coil L2 of the oscillation transformer T and the capacitor C2 are turned off. ,
When the switching transistor Q2 is turned on by the time constant of the resistor R2 and the time constant of the resistor R2, the primary coil of the output transformer T2 is turned on. The current flowing through the capacitor C8 and the switching transistor Q2 flows through a closed circuit formed by the capacitor C8 and the switching transistor Q2, and becomes a current that changes in a sinusoidal manner due to the resonance of the impedance element. Then, the current direction is reversed by this resonant current, and the switching transistor Q is turned off again, and then the switching transistor Q2 is turned on.

The switching transistors Q3 and Q2 generally operate in class D or class E, but their conduction period is set by an impedance element placed on the pace side, and
By setting this conduction period and the switching period in a predetermined relationship, L is applied to the secondary coil of the output transformer T2.
211 L22 can transfer power with high efficiency.

Note that an orthogonally coupled saturable transformer is used for the output transformer T2, and an error amplifier compares the output voltage E obtained by rectifying the alternating signal of the secondary coil Lz+ with the reference voltage E2, and performs control corresponding to the difference voltage. By supplying current to the control coil Lc, the value of the output voltage E1 or E2 can be made constant.

[Problems to be solved by invention C] By the way, when the above-mentioned self-excited switching power supply circuit is used in electrical equipment, for example, when used in a television receiver, switching It is preferable to synchronize the switching period with a specific frequency C (horizontal frequency signal, etc.) so that the power supply noise generated when the circuit is opened and closed by the transistor does not affect the monitor screen.

Therefore, a synchronous winding LB is provided in the oscillation transformer T1,
It is possible to supply the synchronization signal sH from outside, but
For example, when the switching transistor Q is on and the switching transistor Q2 is off, if the switching transistor Q2 is forcibly driven to be on by this synchronization signal sH, the self-oscillation of the switching power supply is disturbed. , there is a risk of burning out the switching transistor.

Means for Solving Problems] The present invention has been made in view of these problems, and
a phase comparison means for comparing a synchronization signal supplied from an external source and a switching period of a self-excited switching power supply;
A smoothing means for smoothing the output of the phase comparison means is provided, and the magnetic permeability of the oscillation transformer is controlled by the output of the smoothing means.

[Effect 1] An orthogonally coupled transformer is used in a switching power supply that self-oscillates using a switching transistor, and the magnetic permeability (magnetic saturation characteristics) of this orthogonally coupled transformer can be controlled by an externally supplied synchronization signal. The switching power supply can be synchronized without disrupting the self-oscillation operation.

[Embodiment] FIG. 1 shows a circuit diagram of a switching power supply showing an embodiment of the present invention, and the same parts as in FIG. 3 are given the same symbols.

However, in the switching power supply of the present invention, the orthogonal coupling type transformer T1 is employed as the oscillation transformer.

This orthogonal coupling type transformer T1 has a three-dimensional core structure as shown in FIG. The magnetic flux Φ in the direction of

A control winding LCD is wound such that the following occurs.

Therefore, the magnetic permeability of the fur is varied depending on the value of the control current supplied to the control winding L co, and as a result, the design is such that the inductance of the coupling coil can be varied.

Reference numeral 11 denotes a phase comparator in which the oscillation output of the switching voltage self-oscillated by the orthogonal coupling transformer T I+ is supplied to one input terminal via the capacitor C, and a synchronizing signal is supplied to the other input terminal. It is a circuit.

Further, 12 indicates a low-pass filter for smoothing the phase difference output of this phase comparator circuit 11, and 13 indicates the orthogonal coupling type transformer T1. A drive circuit that supplies a control current to the control winding Lco of FIG.

Note that the output side of the output transformer T2 is not directly related to the present invention, so a detailed explanation thereof will be omitted.

Since the switching power supply of the present invention has the above-described configuration, when the external synchronization signal Sn is supplied after self-excited oscillation, the phase difference between the self-oscillation frequency and this external synchronization signal is determined by the phase comparator circuit 11. The detected phase difference information is supplied to the drive circuit 13 via the low-pass filter 12.

Here, the control winding L c of the orthogonal coupling type transformer T I I
.

The oscillation frequency (fundamental frequency) when the current flowing in When So has a lower frequency than the synchronization signal SH, the output of the phase comparator circuit, that is, the output of the low-pass filter 12 is designed to be high, so that this control loop becomes a negative feedback circuit.

At this time, the oscillation frequency is controlled to be smoothly drawn into the period of the synchronizing signal 3.4 by the control current flowing through the control winding Lco.

Note that the oscillation frequency f. Even when the frequency of the external synchronization signal SN is twice or three times that of the external synchronization signal SN, it is possible to establish a synchronization relationship.

Further, the present invention can be widely applied to power supplies other than the half-bridge type, such as a full-bridge type and a chopper type.

[Effects of the Invention] As explained above, the self-excited switching power supply of the present invention includes a means for detecting a phase difference between an oscillation output and an external synchronization signal, and a means for detecting a phase difference between an oscillation output and an external synchronization signal, and a magnetic permeability that is effectively changed by this phase difference. Since the self-excited frequency is drawn into the external signal by an oscillation transformer like this, the switching period of the self-excited switching power supply can be smoothly matched with the synchronization signal of the equipment, reducing the effects of switching power supply noise. can be reduced.

Further, although the circuit configuration is simple, the bowing is performed stably, and the reliability of the switching power supply can be improved.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a switching power supply showing an embodiment of the present invention, Fig. 2 is a principle diagram of a quadrature coupling transformer, Fig. 3 is a circuit diagram of a conventional switching power supply, 11 is a phase comparison circuit, 12
13 is a smoothing circuit, 13 is a drive circuit, L and co are control windings, T l + is an orthogonal coupling type transformer, and Q and Q are switching transistors. Lc.

Claims (1)

[Claims] In a self-excited switching power supply circuit that opens and closes a DC power supply using a switching transistor, a phase comparison means that compares an alternating signal output from the switching power supply circuit with an external synchronization signal, and a smoothing means that smoothes a detection signal of the phase comparison means. A self-excited switching power supply, characterized in that the output of the smoothing means is supplied as an excitation current to a cross-coupled transformer constituting the self-excited switching power supply.