JPH035610B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-output power supply device, and more particularly to a compact and economical overcurrent protection circuit that allows easy overcurrent setting of each output circuit. Figure 1 shows this type of conventional circuit. In the figure, EDC is a DC power supply, T1 is an output transformer, N1 is an input (primary) winding, N2, N3
is an output (secondary) winding, Q1 is a switching element (hereinafter referred to as a transistor), D1 is a rectifier diode, D2 is a flywheel diode, L1 and C1 are a choke coil and a capacitor that form a smoothing circuit; D1 to capacitor C1 are connected to the output winding N2, respectively.
connected to the side to form an output circuit I. D3, D
4, L2 and C2 are the rectifier diode, flywheel diode, choke coil and capacitor that form the output circuit as above, OSC is the basic oscillator, AMP is the output voltage detection amplifier CT1 and
CT2 is a current transformer for detecting the load current of each output circuit, and FC is a control circuit. First, transistor Q1 performs a switching operation via the control circuit FC at the frequency determined by the oscillator OSC. The converted AC output is supplied to the output transformer T1. As a result, each output winding N
In the output circuits 2 and N3, predetermined DC outputs are respectively supplied to loads (not shown) through rectifiers and smoothing circuits. Output voltage detection amplifier
AMP detects the output voltage of one output circuit (an example of an output circuit is shown in the embodiment), and sends the detection signal to the control circuit FC, whereby the phase of the transistor Q1 is controlled, and the output of each output circuit is controlled. The voltage is maintained at a predetermined value.

In addition, current transformers CT1 and CT2 each detect and amplify the load current of the output circuit, and send this signal to the control circuit FC.
By adding , each output circuit is operated drooping at the overcurrent set point. (In this circuit example, the output voltage and overcurrent control is performed by controlling the transistor Q1 depending on the output voltage or overcurrent state of one output circuit, and simultaneously performing the output control and current droop operation of all output circuits.) In such a conventional circuit, Since the current transformer for detecting the load current is installed independently for each output circuit, the overcurrent protection circuit not only becomes large and expensive, but also causes disturbances (hunting) when each output circuit is in drooping operation. There are some drawbacks. Therefore, in order to prevent the above-mentioned disturbance, a response delay is provided in each overcurrent detection circuit, and as a result, the average value is detected. Alternatively, as shown by the dotted line in FIG.
A method is used to control the current by detecting the current in the next winding, but in the former, input/output fluctuations cause a "discrepancy" in the overcurrent setting value of each output circuit, and in the latter, the overcurrent setting value is set in advance for each output circuit. If there is a large difference in the output capacitances, there is a problem that the rectifier diode, load, switching element, etc. of the small-capacity output circuit may be destroyed.

In view of these drawbacks, the present invention provides a power supply device that detects overcurrents in multiple output circuits with a single current transformer, thereby providing a stable overcurrent protection function regardless of the capacity of each output circuit. The present invention will be explained in detail below using the drawings.

FIG. 2 is a circuit diagram of an embodiment of the present invention, in which the same reference numerals as in FIG. 1 indicate equivalent parts.

The present invention provides one current transformer CT for output current detection, and the current transformer CT has a common iron core wound with a number of current detection windings (secondary windings) S1 and S2 corresponding to each output circuit. In this way, the load current of each corresponding output circuit is detected, and the number of turns of each detection winding is set so that the ampere-turns with each output circuit current are approximately equal, and each detection winding is connected in parallel. It is characterized by the following. That is, according to the present invention, for example, the output capacity of the output circuit is 10W (10V1A),
When the output capacity of the output circuit is 100W (10V10A), if the number of turns of current detection winding S1 is set to 10 turns and the number of turns of S2 is set to 1 turn, the apparent load sharing will be The circuit + ampere turns of the circuit = ampere turns of the common detection winding. With this setting, the sum of the load currents in the output circuit will be
At 11A (ampere), current transformer CT is 20A
(200W) equivalent current detection signal can be obtained. Therefore, if the overcurrent protection circuit is set to perform drooping operation via the control circuit FC when a detection signal equivalent to 20A or more is obtained, the load current of the output circuit will be overloaded with respect to a current change of the same ratio. Can provide current protection. This means that, for example, when the load current of the output circuit changes from 1A to 1.1A, or from 10A to 11A, each of them will go into drooping operation. For example, assuming a light load or no-load operation state of the output circuit, in the conventional circuit (in the case of detecting the primary current of the output transformer T1 in Figure 1), the output circuit greatly exceeds the drooping point. However, according to the present invention, even in the above-mentioned operating state, the output circuit will be damaged. is capable of drooping operation with slight changes in load current.

Therefore, as described above, setting the ampere turns between each current winding to be equal is effective for protecting a small capacity output circuit. Further, according to the present invention, since only one current transformer is required, the cost is low, and the overcurrent protection circuit can be made smaller and lighter.

In the conventional circuit (Figure 1), the current detection signal was obtained independently for each output circuit, so mutual interference (disturbance) of the signals in the overcurrent protection circuit was likely to occur, and furthermore, it was difficult to add more output circuits. However, according to the present invention, since each detection winding is wound around a common core, there is no disturbance between signals, and furthermore, it is easy to add an output circuit, and each circuit and configuration can be simplified.

There is an advantage that the overcurrent setting (dripping setting) of each output circuit can be set arbitrarily by selecting the number of turns of each current detection winding.

In the above embodiments, an example was explained in which each current detection winding was made with equal ampere turns (1:1). It is obvious that the same implementation can be achieved even if the relationship is set to approximately equal ampere turns, and it is also obvious that the output circuit can be further added. As is clear from the above description, the present invention has great practical effects because it can provide a compact and economical power supply device with a stable overcurrent protection function regardless of the output capacity of each output circuit. .

[Brief explanation of the drawing]

FIG. 1 is a conventional circuit diagram, and FIG. 2 is a circuit diagram of an embodiment of the present invention. In the figure, T1 is an output transformer, N1 is an input (primary) winding, N2 and N3 are output (secondary) windings, Q1 is a switching element (transistor), D1 and D3 are rectifying diodes, D2,
D4 is a flywheel diode, L1, L2 and C1, C2 are output smoothing coils and capacitors, OSC is a basic oscillation circuit, AMP is an output voltage detection amplifier, FC is a control circuit, CT, CT1, CT2,
CT3 is a current transformer for output (negative circuit) current detection, S1,
S2 is a current detection (secondary) winding.

Claims (1)

[Claims] 1. An output transformer having an input winding and a plurality of output windings has a switching element on the input winding side, an output circuit consisting of a diode, a smoothing circuit, etc. on the output winding side, and an output (load) ) In a multi-output power supply device equipped with an overcurrent protection circuit that detects current and controls the switching element, a current transformer for output current detection is provided, and the current transformer is connected to the output circuit on a common iron core. A multi-output power supply device characterized in that a current detection winding is formed by winding corresponding windings such that the product of each number of windings and each corresponding output current is the same or a constant ratio.