JPH0640472Y2 - Switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a switching power supply having an overload protection function, and more particularly to improvement of an overload protection function of a switching power supply that drives a plurality of transformers at the same time. .

(Prior Art) Generally, in a multi-output switching power supply, when the current rating of each output is large, each DC / DC converter has an independent DC / DC converter and each converter is operated by PWM control.

(Problems to be solved by the invention) Therefore, there is a problem that a protection circuit against an overload is independently provided for each converter, and the circuit configuration becomes complicated.

When limiting the total output of all outputs, it is necessary to take the sum of the output of the current transformer of each converter and apply the control signal to the control terminal of the PWM circuit (PWM IC) of each converter at that output. is there. Therefore, the configuration is complicated.

The present invention has been made in view of such problems, and an object thereof is to provide a switching power supply capable of performing overload protection of each transformer and overload protection for all outputs with a simple configuration. To do.

(Means for Solving the Problem) The present invention which solves the above-mentioned problem is a pulse width modulation (PW
M) Detects the current flowing in the first pulse transformer in the switching power supply that simultaneously drives the first pulse transformer controlled by the control and the second pulse transformer controlled by the voltage on the secondary side by the PWM control circuit. In order to detect the current flowing through the first current transformer and the second pulse transformer connected in series with the first current transformer, the second current transformer connected in series with the first current transformer and the first pulse transformer are detected. In order to detect the total of the flowing current and the current flowing through the second pulse transformer, a third current transformer, a first current transformer, a second current transformer and a third current transformer connected in series to them are detected. It is characterized by including a diode OR that supplies the voltage generated on the secondary side to the control terminal of the PWM control circuit.

(Operation) In the switching power supply of the present invention, the current value of the first output is detected by the first current transformer, the current value of the second output is detected by the second current transformer, and the first output and the second output are detected. The total current value is detected by the third current transformer. Then, the detection results of the three sets of current transformers are input to the control terminal of the PWM control circuit via the diode OR, and the first output,
The second output and the current value of the sum of these are controlled by pulse width modulation so that the current value does not become an overcurrent.

Embodiment An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In the figure, 1 is a PWM control unit that detects an output voltage of a power supply and generates a switching pulse with a variable width (variable duty ratio) for driving a switching element so that a difference from a reference voltage is minimized. 3 is a drive transformer for transmitting a switching pulse from the PWM control unit 1 to a switching element which will be described later, and 4 and 5 are for alternately repeating switching by the switching pulse from the PWM control unit 1 to convert direct current into pulsed alternating current. It is a switching element.
The switching elements 4 and 5 are composed of transistors, power MOSFETs, etc., and are connected in parallel with the capacitor C. Reference numeral 6 is a first pulse transformer that transforms alternating current to generate the first output, 7 is a diode that rectifies the transformed alternating current, and 8 is a choke coil that smoothes the rectified pulsating current. 9 is a second pulse transformer that transforms alternating current to obtain the second output, 10 is a mag-amp that controls the second output to a constant voltage, 11 is a diode that rectifies the transformed alternating current, and 12 is a rectified pulsating current. It is a choke coil for smoothing. 13 is a first current transformer connected in series with the first pulse transformer 6, 14 is a diode for supplying the detection output of the first current transformer 13 to the control terminal OLP of the PWM control unit 1, and 15 is a second A second current transformer connected in series with the pulse transformer 9, 16 is a diode that supplies the detection output of the second current transformer 15 to the control terminal OLP of the PWM control unit 1, and 17 is the first pulse transformer 6 and the first pulse transformer 6. A third current transformer 18 connected in series to both of the two pulse transformers 9 is a diode for supplying the detection output of the third current transformer 17 to the control terminal OLP of the PWM controller 1.

The operation of the device of the present invention thus constructed is as follows.

The PWM control unit 1 detects the output voltage of the first output by the F / B terminal and switches 4 to minimize the difference from the set voltage.
Pulses of variable width are generated to control the open / close duty ratios of 5 and 5.

Since the pulse width controlled in this manner is for controlling the first output, a constant voltage cannot be obtained at the second output. Therefore, the mag-amplifier 10 functioning as a voltage control circuit is provided to obtain the second output controlled to a constant voltage. The second output cannot be taken out unless there is a pulse width of a certain value or more.

When the OLP terminal receives a constant voltage, the PWM control unit 1 operates so as to narrow the pulse width and reduce the voltage of the first output.

For example, when the current of the first output exceeds the specified value, the output voltage of the first current transformer 13 increases and the diode 14
After that, the voltage applied to the OLP terminal also becomes larger than a predetermined value. As a result, the PWM control unit 1 operates so as to narrow the output pulse width and reduce the voltage of the first output.

Similarly, when the current of the second output exceeds the regulation, the output voltage of the second current transformer 15 increases and the diode 16
After that, the voltage applied to the OLP terminal also becomes larger than a predetermined value. As a result, the PWM control unit 1 operates so as to narrow the output pulse width and reduce the voltage of the second output.

Then, when the sum of the currents of the first output and the second output (total output) exceeds the regulation, the output voltage of the third current transformer 17 increases, and the voltage applied to the OLP terminal via the diode 18 also reaches a predetermined value. Is greater than the value of. As a result, the PWM control unit 1 operates so as to narrow the output pulse width and reduce the voltages of the first and second outputs. Therefore, the overcurrent of the total output can be limited.

In the above embodiments, the case where two sets of outputs and the sum of these outputs are controlled by a single control circuit has been described, but it is also possible to control more outputs.

(Effect of the Invention) As described in detail above, in the present invention, the first output current value is detected by the first current transformer, and the second output current value is detected by the second current transformer. The current value of the sum of the 1st output and the 2nd output is detected by the 3rd current transformer, and the detection results of the 3 sets of current transformers are input to the control terminal of the PWM control circuit via the diode OR. The two outputs and the current value of the sum of these outputs are controlled by pulse width modulation so as not to become an overcurrent. As a result, with a simple configuration,
It is possible to realize a switching power supply that can perform overload protection for each transformer and overload protection for all outputs.

[Brief description of drawings]

FIG. 1 is a block diagram showing the construction of an embodiment of the present invention. 1 ... PWM control unit 2, 3 ... Drive transformer 4,5 ... Switching element 6 ... Pulse transformer, 7 ... Diode 8 ... Choke coil, 9 ... Pulse transformer 10 ... Mag amplifier, 11 ... Diode 12 ... Choke coil 13,15,17 … Current transformers 14,16,18… Diodes

Claims (1)

[Scope of utility model registration request] 1. A PWM control circuit (1) comprising a first pulse transformer (6) controlled by pulse width modulation (PWM) control and a second pulse transformer (9) voltage-controlled on the secondary side. In the switching power supply which is driven simultaneously by, the first current transformer (13) connected in series with the first pulse transformer (6) is detected in order to detect the current flowing through it.
And a second current transformer (15) connected in series with the second pulse transformer (9) to detect the current flowing therethrough.
And a third current transformer (1) connected in series with them in order to detect the sum of the current flowing through the first pulse transformer (6) and the current flowing through the second pulse transformer (9).
7) and the voltage generated on the secondary side of the first current transformer, the second current transformer, and the third current transformer, the PWM control circuit (1)
A switching power supply comprising: a diode OR (14, 16, 18) which is supplied to the control terminal of the.