JPH09289774A - Switching power supply device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To constitute a switching power supply device having a standby output at low cost, by driving a switching circuit in proper frequency and intermittently supplying the primary winding of a converter transformer with an output from a rectifying smoothing circuit. SOLUTION: In this device, a commercial AC power supply E0 is full-wave rectified by a rectifier circuit D1 and smoothed by a capacitor C0, and converted into a DC E1, and a primary winding N1 for a converter transformer T1 is supplied intermittently with the DC E1 through a switching circuit consisting of transistors Q1, Q2 and a capacitor C1. A frequency control circuit 10 as a control circuit on-off drives the transistor Q1 and the transistor Q2 complementarily in sufficiently high proper frequency, and displays operation as a current resonance type switching regulator. Accordingly, a power switching element at high price for switching a large input current or main output current is unnecessitated, and cost can be reduced largely and the device can be miniaturized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching power supply device incorporated in an electric device such as a general television or a home video connected to a commercial AC power supply, and particularly to a large main power supply while utilizing a minute standby output. The present invention relates to a power supply device with a standby output having an operation mode in which the output is substantially turned off. Further, in terms of configuration, the main component is a current resonance type switching regulator using a converter transformer.

[0002]

2. Description of the Related Art A typical conventional example of a switching power supply device with a standby output is shown in FIG. In this conventional example, a commercial output AC power supply E0 is connected to a main output current resonant switching regulator 100 via a relay switch SW1, and a standby output power supply circuit 200 independent of the switching regulator 100 is connected to the AC power supply E0. Are connected in parallel.

The conventional current resonance type switching regulator 100 is a circuit D for rectifying and smoothing an AC power supply E0.
1, C0, a converter transformer T1 having, for example, three secondary windings, a switching circuit Q1, Q2, C1 for coupling the DC output E1 of the rectifying and smoothing circuits D1, C0 and the primary winding of the transformer T1. And the main output Mout1, Mout by rectifying and smoothing the output of each secondary winding of the transformer T1.
2, main output circuits 101, 102, 1 for obtaining Mout3
03 and the switching circuits Q1, Q2 and C1 at appropriate frequencies to intermittently supply the outputs of the rectifying and smoothing circuits D1 and C0 to the primary winding of the converter transformer T1 to operate as a current resonance type switching regulator. And a frequency control circuit 110. The frequency control circuit 110 feedback-controls the switching frequency so that the output voltage on the secondary side of the transformer T1 is stabilized at the reference value.

The independent standby power supply circuit 200 directly transforms the AC output of the AC power supply E0 by the transformer T2,
Rectifying and smoothing circuit D20 ・ C20 for the secondary side output of transformer T2
Is converted into a standby output SBout of 5 volts, for example. The drive transistor Q20 and the relay coil R20 of the relay switch SW1 are connected to the standby output SBout.

A main output ON / OFF signal generated by another system such as a control system in a television, which is a load of the power supply device, is applied to the base of the transistor Q20, and the relay switch SW1 is turned on by this signal.・ Off controlled. When the relay switch SW1 is turned off, the AC input of the switching regulator 100 is cut off, so that the main outputs Mout1, Mout2, Mout3 are naturally turned off.

Another typical example of a conventional switching power supply device with a standby output is shown in FIG.
Here, there is no standby power supply circuit independent of the switching regulator 100 as in the example of FIG. 6, and instead, a tertiary winding for standby output is added to the converter transformer T1 in the switching regulator 100, and the tertiary winding A standby output circuit 120 is provided for rectifying and smoothing the output of the above to obtain a standby output SBout. A standby output SBout is supplied as the power supply of the frequency control circuit 110.

The main outputs Mout1, Mout2, Mou
In order to turn off t3, each main output circuit 101, 1
On the output lines of 02 and 103, output switches SW1, SW2 and SW3 composed of power transistors are interposed, and a transistor Q11 for simultaneously turning on / off these switches SW1, SW2 and SW3 is provided.
The main output ON / OFF signal given from another system is applied to the base of this transistor Q11, and the output switch SW
ON / OFF control of 1, SW2 and SW3. When the output switches SW1, SW2, SW3 are turned off, the main outputs Mout1, Mout2, Mout3 for the load are turned off. However, the switching regulator 100 itself continuously operates to generate the standby output SBout.

[0008]

In the conventional switching power supply device with a standby output shown in FIG. 6, the low frequency transformer T2 for the standby power supply circuit 200 is expensive and large and heavy. Output M
There is a problem that the relay switch SW1 for turning on / off out1, Mout2, and Mout3 and its drive transistor are expensive.

Even in the conventional switching power supply device with a standby output shown in FIG. 7, main outputs Mout1 and Mout are provided.
There is a problem that the output switches (power transistors) SW1, SW2, SW3 and the driving transistor Q11 thereof provided on the output lines of the main output circuits 101, 102, 103 for turning on and off 2, Mout3 are expensive. It was As the number of main output systems increases, the number of output switches must be increased, which is very expensive.

The present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to provide a standby output having an operation mode in which a large main output is practically turned off while making use of a minute standby output. The present switching power supply device is configured to be as inexpensive as possible, mainly as a current resonance type switching regulator using a converter transformer.

[0011]

A switching power supply device according to the present invention comprises a rectifying / smoothing circuit for rectifying and smoothing an AC power supply,
A converter transformer having a secondary winding that is relatively coarsely coupled to the primary winding and a tertiary winding that is relatively dense, and the main output by rectifying and smoothing the output of the secondary winding. A main output circuit for obtaining, a standby output circuit for rectifying and smoothing the output of the tertiary winding to obtain a standby output, and an output of the rectifying and smoothing circuit are coupled to the primary winding of the converter transformer. A switching circuit and a control circuit that constitutes a current resonance type switching regulator by driving the switching circuit at an appropriate frequency to intermittently supply the output of the rectifying / smoothing circuit to the primary winding of the converter transformer. Further, the control circuit switches the drive frequency of the switching circuit to a predetermined value in response to a main output OFF command from another system, thereby maintaining the standby output at a specified voltage or more and maintaining the main output at a specified voltage. The following includes control means for greatly reducing.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. A circuit configuration of a switching power supply device according to a first embodiment of the present invention is shown in FIG. In FIG. 1, a commercial AC power source E0 is full-wave rectified by a rectifier circuit D1, smoothed by a capacitor C0, and converted into a DC E1. This direct current E1 is intermittently supplied to the primary winding N1 of the converter transformer T1 via a switching circuit including transistors Q1 and Q2 and a capacitor C1.
The frequency control circuit 10 which is a control circuit complementarily turns on and off the transistors Q1 and Q2 at a sufficiently high appropriate frequency to realize an operation as a current resonance type switching regulator.

The converter transformer T1 has a primary winding N1.
Three secondary windings N2 with relatively coarse coupling to
It has A, N2B, N2C and a tertiary winding N3 which is relatively tightly coupled to the primary winding N1. Each secondary winding N
2A, N2B, N2C are connected to main output circuits 21, 22, 23 for rectifying and smoothing the outputs to obtain main outputs Mout1, Mout2, Mout3. The output of the tertiary winding N3 is rectified and smoothed, and the standby output SB
A standby output circuit 31 for obtaining out is connected.
The standby output circuit 31 is composed of a diode D2 and a capacitor C2.

The frequency control circuit (control circuit) 10 operates by using the output SBout of the standby output circuit 31 as a power source, and feedback-controls the switching frequency so that the voltage of the main output Mout1 is stabilized at the reference value.
Further, the frequency control circuit 10 switches the drive frequency of the transistors Q1 and Q2 to a predetermined value in response to a main output OFF command from another system, thereby making the standby output SBout obtained from the tertiary winding N3 equal to or higher than a specified voltage. 2 each while keeping
Main output Mou obtained from the next winding N2A, N2B, N2C
It includes a control means for substantially turning off the main output by greatly reducing t1, Mout2, and Mout3 below a specified voltage.

Transistor Q by frequency control circuit 10
1, Q2 switching frequency and each secondary winding N2A,
Main outputs Mout1, Mout2 obtained from N2B and N2C
The relationship between the voltage of Mout3 and the voltage of the standby output SBout obtained from the tertiary winding N3 is shown in the graph of FIG.

In FIG. 2, main outputs Mout1, Mout
In the steady operation mode in which 2 and Mout3 are turned on, the switching frequency is the predetermined value F1, and at this time, it operates as a highly efficient current resonance type switching regulator.
At this time, the main output voltage and the standby output voltage are each set to 100%.

When the main output OFF command signal is supplied to the frequency control circuit 10, the frequency control circuit 10 switches the switching frequency to a predetermined value F2 higher than F1. Then, as shown in the graph of FIG. 2, the standby output voltage drops to about 75% of the specified value, and the main output voltage drops to about 25% of the specified value. The standby output voltage reduced to about 75% of the specified value is within the rated range, and the load circuit can be driven. However, since the main output voltage drops significantly to about 25% of the specified value, it completely falls outside the rated range, the load circuit is cut off, and no current flows. That is, the main outputs Mout1, Mout are substantially
2, Mout3 is off.

When the switching frequency is switched to F2 in this way, the main outputs Mout1, Mout2 and Mout are output.
Standby output SBout even though 3 is practically turned off
Maintains the rated voltage for the following reasons. That is, as described above, the main outputs Mout1, Mout
2, secondary windings N2A, N2B, N to obtain Mout3
2C has a relatively coarse coupling with the primary winding N1, whereas it has a tertiary winding N3 for obtaining the standby output SBout.
Is because the coupling with the primary winding N1 is relatively dense.

The structure of the converter transformer T1 according to the present invention is illustrated in FIGS. 3 and 4. FIG.
In the examples of (a) and (b), the primary winding N1 is uniformly wound on one section of the two-section type bobbin B, and the secondary winding N2 is uniformly wound on the other section. Also,
A tertiary winding N3 is wound around the uppermost layer of the primary winding N1. The tertiary winding N3 may be wound around the lowermost layer of the primary winding N1. In the example of FIGS. 4 (a) and 4 (b), a three-section type bobbin B is used, and a tertiary winding N3 is wound around a small section at the left end, a primary winding N1 is wound around a central section, and a section at the right end. A secondary winding N2 is wound around. By adopting such a structure, a "converter transformer having a secondary winding whose coupling to the primary winding is relatively coarse and a tertiary winding which is relatively dense" can be easily realized. .

FIG. 5 shows a switching power supply device according to a second embodiment of the present invention. This is a self-oscillation type current resonance type switching regulator.
The quadrature transformer T3 is used to drive the switching transistors Q1 and Q2 that couple the direct current E1 obtained by rectifying and smoothing 0 and the primary winding N1 of the converter transformer T1. This orthogonal transformer T3 and its peripheral circuits correspond to the frequency control circuit 10 in the embodiment of FIG. That is, the control current flows through the control winding Nc of the orthogonal transformer T3 by the standby output SBout from the standby output circuit 31 connected to the tertiary winding N3 of the converter transformer T1. Further, the voltage of the main output Mout from the main output circuit 20 connected to the secondary winding N2 of the converter transformer T1 is monitored by the shunt regulator 11, and the control winding Nc is adjusted so as to stabilize the main output voltage to a specified value. Feedback control is performed to adjust the current flowing in the.

Further, a main output ON / OFF signal from another system is applied to the base of the transistor Q3. The current flowing through the control winding Nc is largely switched in two stages according to this command signal, and the switching frequency of the transistors Q1 and Q2 is set to a predetermined low value F1 in the steady operation mode in which the main output is turned on, and the main output is substantially In the standby operation mode in which the switching frequency is turned off, the switching frequency is switched to a predetermined high value F2. As a result, as described with reference to FIG. 2, the standby output voltage drops to about 75% of the specified value, and the main output voltage drops to about 25% of the specified value.

[0022]

As described in detail above, according to the present invention, a converter transformer having a secondary winding whose coupling to the primary winding is relatively coarse and a tertiary winding which is relatively dense. A current resonance type switching regulator is configured by using a secondary winding to obtain a main output from a secondary winding and a standby output from a tertiary winding. Switching is performed in response to a main output OFF command from another system. By switching the drive frequency of the regulator to a predetermined value, while maintaining the standby output obtained from the tertiary winding above the specified voltage,
Since the main output obtained from the secondary winding is greatly reduced to a specified voltage or less and the main output is substantially turned off, a larger input current or a larger input current than the conventional switching power supply device with standby output is used. This eliminates the need for a high-priced power switch element for turning on / off the main output current, which can be expected to have a large cost reduction effect, and contributes to downsizing of the device.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a switching power supply device with a standby output (first embodiment).

FIG. 2 is a graph showing characteristics of output voltage with respect to switching frequency (first embodiment).

3A is a perspective view of a converter transformer, FIG.
Is a sectional view thereof (first embodiment).

FIG. 4A is a perspective view of a converter transformer, and FIG.
Is a sectional view thereof (first embodiment).

FIG. 5 is a circuit diagram of a switching power supply device with a standby output (second embodiment).

FIG. 6 is a circuit diagram of a switching power supply device with a standby output (conventional example).

FIG. 7 is a circuit diagram of a switching power supply device with a standby output (another conventional example).

[Explanation of symbols]

E0 ... AC power supply, D1, C0 ... Rectifying and smoothing circuit, Q1, Q
2, C1 ... Switching circuit, T1 ... Converter transformer, N1 ... Primary winding, N2A, N2B, N2C ... Secondary winding, N3 ... Tertiary winding 21, 22, 23 ... Main output circuit, 10 ... Frequency Control circuit (control circuit), 31 ... Standby output circuit.

Claims (1)

[Claims] 1. A converter transformer having a rectifying / smoothing circuit for rectifying and smoothing an AC power source, a secondary winding having a relatively coarse coupling to a primary winding, and a relatively dense tertiary winding. A main output circuit for rectifying and smoothing the output of the secondary winding to obtain a main output; a standby output circuit for rectifying and smoothing the output of the tertiary winding to obtain a standby output; Output of the circuit and one of the converter transformers
A current resonance type switching regulator is constituted by a switching circuit which couples the secondary winding, and by driving this switching circuit at an appropriate frequency to intermittently supply the output of the rectifying and smoothing circuit to the primary winding of the converter transformer. A control circuit is provided, and the control circuit switches the drive frequency of the switching circuit to a predetermined value in response to a main output OFF command from another system, thereby maintaining the standby output at a prescribed voltage or higher and the main output. A switching power supply device comprising control means for greatly reducing the output to a specified voltage or less.