JPS63290163A - Switching power source circuit - Google Patents

Abstract

PURPOSE:To improve efficiency and to reduce noise, by carrying out pulse width control of a switching power source only in respective secondary circuits. CONSTITUTION:A power source 1 is connected in series with the primary winding 4a, of a transformer 4 and a switching element 3, then the switching element 3 is ON/OFF controlled through alternating pulses fed from an oscillation circuit 2. A load 8 is connected through a rectifier circuit comprising a switching element 5 and a bypass diode Db and a smoothing circuit comprising a coil L and a capacitor C to the secondary winding 4b of the transformer 4. Here, a control winding 4c is connected in series with the winding 4b of the transformer 4 with one end thereof being connected through a bias resistor R with the gate of the switching element 5. Furthermore, pulses are fed from a pulse width control circuit 10 for controlling ON pulse width corresponding to the output voltage from the smoothing circuit are fed to the gate of the switching element. Consequently, output current can be controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a switching power supply circuit, and particularly to a switching power supply circuit suitable for multiple outputs.

[Conventional technology]

In the conventional multi-output switching power supply circuit, as shown in the circuit diagram of FIG. After connecting a rectifier circuit consisting of bypass diodes D1 and D2 and a smoothing circuit consisting of a coil L1 and a capacitor C1, a pulse width control circuit is installed so that the voltage of one output (output of load 8-2) becomes a predetermined value. 13 controls the switching element 3 on the primary side on and off, and after smoothing the other output, the pulse width control circuit 12 controls the switching element 15 on and off, and the subsequent diode D3,
It controls a smoothing circuit consisting of a coil L3 and a capacitor C3.

[Problem that the invention seeks to solve]

The conventional multi-output switching circuit described above is 1
Since a method is adopted in which the on/off signal whose pulse width is controlled only by the output voltage is fed back to the primary side, if the voltage of the secondary winding connected to this increases due to load fluctuations on this 1st output side, , performs feedback control to shorten the on period of the primary side switching element. As a result, the load voltage on the feedback side can be maintained at a predetermined value, but if the voltage of the other secondary windings drops too much, the load voltage connected thereto cannot be maintained at a predetermined value. In order to avoid such an uncontrollable state, in conventional switching power supply circuits, the ratio of other output voltages to the control output voltage is limited to less than 1 (or less than a fraction depending on the design of the transformer). There are drawbacks.

[Means for solving problems]

The circuit of the present invention includes a transformer having one primary winding and at least one set of secondary windings each consisting of an output winding and a control winding, and a switching element connected in series to the primary winding. , an oscillator that generates an on/off control signal for the switching element, and a commutating diode connected in series between the source and drain of an FET (field effect transistor) between both ends of each of the output windings to determine the gate voltage of the FET. a rectifier circuit having a configuration in which the control winding provides output voltage from the control winding, with both ends of the diode being output terminals, a smoothing circuit continuously connected to the output terminal of each of the rectifier circuits, and a smoothing circuit that responds to the output voltage of each of the smoothing circuits. and a control circuit that controls the timing of applying the gate voltage to the FET.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of the present invention. A power supply 1 is an input DC power supply, and includes a winding 4a on the primary side of a transformer 4 and a switching element 3 (between the source and drain of an N-channel field effect transistor (FET)).
Connected in series. The switching element 3 is turned on and off by an alternating pulse given from the oscillation circuit 2 (to the gate of the FET). Winding 4 for secondary output of transformer 4
0 winding to which a load 8 is connected to b through a rectifier circuit consisting of a switching element 5 (between the source and drain of the FET) and a bypass diode Db, and a smoothing circuit consisting of a coil and a capacitor C. One end of the control winding 4C provided in series with the control winding 4b is connected to the control terminal (gate of the FET) of the switching element 5 via a bias resistor R. Furthermore, the output pulse of the pulse width control circuit 10, which controls the on-pulse width according to the output voltage of the smoothing circuit, is applied to the control terminal of the switching element.

Now, when the switching element 3 on the primary side turns on, the winding 4
When a voltage appears on b, the switching element 5 is turned on by the voltage on the winding 4c, and the output voltage is obtained from the rectifier circuit.
Next, when the switching element 3 is turned off, the winding 4C
The driving voltage disappears, the switching element 5 turns off, and the diode Db turns on to maintain the rectified current. When the output voltage increases and enters the control range of the pulse width control circuit 10, even if the switching element 3 is on, the gate voltage of the switching element 5 is cut off by the output on of the pulse width control circuit 10, and the switching Since element 5 is turned off and current is commutated to diode Db, the output voltage can be controlled in a steady state. Further, output current control can be performed by applying a current detection signal of the secondary circuit to the pulse width control circuit 10.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention, -
The switching element 5 is controlled during the P channel FE 12.
It differs from Fig. 1 in that it is driven by . The basic operation of this circuit is the same as that in FIG. 1, except that the operation of the pulse width control circuit 11 is always on and is an inverted operation that is turned off only when the control circuit is activated. This circuit has the advantage that the driving power of the pulse width control circuit 11 compared to that shown in FIG. 1 can be small, and that the on-speed of the switching element 5 can be increased by eliminating the bias resistor R shown in FIG.

FIG. 3 is a circuit diagram showing an example of application of the first embodiment to a multi-output power supply, in which n windings and circuits are provided on the secondary side of the transformer 6, and voltage control is performed independently at each output. As a result, a stable output voltage can be obtained regardless of the balance between the loads.

In the circuit shown in Fig. 3, the oscillation period of the DC converter is a single and fixed frequency set by the oscillation circuit 2.
Unlike the case of a multiple oscillation type, low frequency noise is not generated due to the beat of each output, and noise in the voice band is limited, making it suitable for a multi-output power supply for an exchanger. Also, compared to the second output shown in Fig. 4, which has two-stage switching of switching elements 3 and 15, the entire circuit is one-stage switching, so the power exchange loss is small, and furthermore, since switching element 5 is an FET, , the on-resistance can be reduced, so the normal diode D! The forward voltage effect can be reduced compared to the conventional method, and a low-loss DC converter can be realized.

〔Effect of the invention〕

As explained above, the present invention controls the on/off of the primary side of the transformer using a free-running oscillator, connects the FET switch to the output winding of the secondary side, and connects the control winding of the secondary side to the FE
By connecting between the drain and gate of the T-switch and configuring the output voltage control circuit to gate control the off timing of the FET switch, pulse width control of the switching power supply can be performed only with each secondary circuit. Therefore, a multi-output power supply circuit with an arbitrary number of outputs can be constructed simply by arranging a plurality of this circuits in parallel on the secondary side of the transformer. As a result, it is possible to realize a power supply with higher efficiency and lower noise than conventional multi-output power supplies, and because the control signal form is completed on the secondary side, coupling between the primary and secondary is small and high withstand voltage is achieved. This has an effect that can be easily realized by a power source.

[Brief explanation of drawings]

1 to 3 are circuit diagrams showing embodiments of the present invention, and FIG. 4 is a water circuit diagram showing the configuration of a conventional switching power supply circuit. 1... Input power supply, 2... Oscillation circuit, 3, 5.5-1
~5-n, 15... switching element, 4.6...
Transformer, 8, 8-1 to 8- n- load, 10 to 1
3.10-1 to 10-n...Pulse width control circuit, RH
RI~Rn, r...-resistance, L, L1-Ln--coil, C, C1-Cn-1 capacitor, D1-D3゜Db, D
b 1-Dbn---diode. $ I Closed grass 2 Concave grass 3 Figure grass 4 Figure

Claims (1)

[Claims] a transformer having one primary winding and at least one set of secondary windings each consisting of an output winding and a control winding;
A switching element connected in series to the next winding, an oscillator that generates an on/off control signal for the switching element, and a commutation diode between the source and drain of an FET (field effect transistor) between both ends of each of the output windings. a rectifier circuit having a configuration in which the FETs are connected in series and the gate voltage of the FET is applied from the control winding, and both ends of the diode are used as output ends; and a smoothing circuit continuously connected to the output ends of each of the rectifier circuits. A switching power supply circuit comprising: a control circuit that controls the timing of applying the gate voltage to the FET in response to the output voltage of each of the smoothing circuits.