JPS63277472A - Switching power source - Google Patents

Abstract

PURPOSE:To eliminate trouble due to overcurrent, by a method wherein the flux reset voltage of a magnetic amplifier is controlled so as to be on the side of limiting the overcurrent when a load current has exceeded a given value. CONSTITUTION:A switching power source is constituted of a switching transformer 13, a switching element 14, a saturatable reactor 17, a rectifying and smoothing circuit 18 and the like to supply electric power to a load 19. The saturatable reactor 17 constitutes a self feedback type magnetic amplifier together with an automatic voltage control circuit 20. In this case, a circuit 27, which increases a flux reset voltage to be impressed on the saturatable reactor 17 when the current of the load 19 has exceeded a given value, is provided. The circuit 27 is provided with a current detecting resistor 28 in a power source return line, connecting between the output winding of said transformer 13 and one terminal of the load 19 while a voltage at the resistor 28 is impressed on a transistor 29. According to this method, a flux reset voltage is impressed on the saturatable reactor 17 under a heavy load such as the short- circuit of the load 19 or the like to restrict the saturation thereof whereby an output voltage and an output current may be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a switching power supply using a magnetic amplifier as an output voltage control means.

B0 Summary of the Invention The present invention provides a circuit for increasing the magnetic flux reset voltage of the magnetic amplifier due to an abnormal load current in a switching power supply in which a magnetic amplifier is provided between a switching transformer and a load, and the load voltage is controlled by the magnetic flux reset amount of the magnetic amplifier. By providing this, it is possible to limit overcurrent in the event of a load short circuit.

C0 Prior Art FIG. 2 shows a circuit diagram of a conventional switching power supply. DC power supplied from a power supply 11 is smoothed by a smoothing capacitor 12 and is applied to the primary side of a switching transformer 13. The switching transformer 13 is switched by a switching element 14 of a power FET, magnetic energy is regenerated by a flywheel diode 15, and high-frequency pulse power is obtained in an output winding by switching with a duty ratio of 50% by a drive circuit 16. The output winding of the switching transformer 13 is connected to a series circuit of a rectifier f-slip circuit 18 and a load 19 via a saturation reactor 17. The automatic voltage control circuit 20 detects the load voltage Eo using resistors 21 and 22, obtains a control voltage for the shunt regulator 23 according to this heavy pressure EO, and controls the transistor 24 according to this control voltage.
A constant current output determined by the resistor 25 is obtained, and this current is fed back as the magnetic flux reset voltage of the saturable reactor 17 through the diode 26 to adjust the time until the iron core of the saturable reactor 17 is saturated, that is, the amount of magnetic flux reset Automatically adjusts load voltage through control.

FIG. 3 is a waveform diagram for theoretically explaining the voltage control operation in the above-mentioned self-feedback magnetic amplifier. A reset voltage of voltage e 20R is supplied from the automatic voltage control circuit 20 to the output voltage waveform 813 of the switching transformer 13 during its negative period.

In the +ir saturation reactor 17, the magnetic flux in the iron core has an area AR
In the case where the saturable reactor 17 has an area A equal to the area AR during the positive period of the voltage e13,
After the magnetic flux in the iron core is set by S, it is saturated and the Tagata voltage eo is obtained. This voltage eo is rectified and smoothed by a rectification and smoothing circuit 18 to become a load voltage EO.

D0 Problems to be Solved by the Invention In conventional circuits, the voltage e178 applied to the saturable reactor 17 during the negative period of the switching transformer 13 changes with fluctuations in the load 19 to perform automatic voltage control. When a short-circuit accident occurs in the saturable reactor 19, the voltage Eo becomes zero, the transistor 24 is turned off, and the voltage applied to the saturable reactor 17 also becomes zero. That is, when the load voltage falls below a certain value, the reset voltage is no longer applied to the 0.times. saturation reactor 17, making it impossible to control the voltage, and there is a risk of overcurrent failure due to load short circuit.

Means and operation for solving the E0 problem The present invention has been made in view of the above problem, and includes a switching transformer and a switching element for driving the switching transformer in parallel with the DC power supply, and connecting the output winding of the switching transformer and the load. A switching power supply including a magnetic amplifier installed between the load voltage and the load voltage, further comprising a circuit that controls the magnetic flux reset voltage of the magnetic amplifier to the overcurrent limit side when the load current exceeds a certain value, and For heavy loads such as short circuits, the reset voltage of the magnetic amplifier is increased from the load current to delay the saturation of the magnetic amplifier and limit the current.

F. Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention. This figure differs from FIG. 2 in that a circuit 27 is provided to increase the magnetic flux reset voltage applied to the saturable reactor 17 when the current of the load 19 exceeds a certain value. This circuit 27 includes a current detection resistor 28 in the power supply return line connecting between the output winding of the switching transformer 13 and one end of the load 19, and converts the voltage drop across the current detection resistor 28 into a base-emitter voltage. A transistor 29 is provided, and a series circuit of a resistor 30 and a diode 31 is connected to the collector of the transistor 29.

In this configuration, automatic voltage control is normally performed by the automatic voltage control circuit 20 as in the conventional case. In this control state, if a heavy load such as a short circuit occurs on the load 19 and the voltage drop corresponding to the load current generated in the current detection resistor 28 exceeds the voltage between the base and emitter of the transistor 29, the A magnetic flux reset voltage is applied to the saturable reactor 17 using the current. This reset voltage is applied only to the negative period of the output winding of the switching transformer 13 due to the connection polarity of the diode 31, and the voltage level is approximately determined by the resistance value of the resistor 30.

Therefore, by appropriately setting the resistance value of the current detection resistor 28, when the load current exceeds a certain value corresponding to the resistance value, the magnetic flux reset voltage of the saturable reactor 17 will rise, and the saturable reactor It is possible to obtain an overcurrent limiting operation that suppresses the saturation of 17, lowers the output voltage, and lowers the output current.

In addition, in the embodiment, when the load current exceeds a certain value, the current limit is determined by the resistance value of the resistor 30. By operating within the range or switching the plurality of resistors 30, it is possible to realize a current limiting circuit according to the weight or weight of the load. Further, the design of the circuit 27 is changed as appropriate, such as detecting the load current using a Hall element.

Further, in the embodiment, the case where the magnetic amplifier is a single waveform is shown, but it is of course applicable to other circuit systems such as a full waveform.

G0 Effects of the Invention As described above, the present invention provides a switching power supply that uses a magnetic amplifier as a voltage control means, when the load current exceeds a certain value (the magnetic flux reset voltage of the magnetic S amplifier is controlled to the overcurrent limit side). This has the effect of eliminating overcurrent failures due to load short circuits, etc.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, ft52 is a conventional circuit diagram, and Fig. 3 is a waveform diagram for theoretically explaining the operation of a switching power supply using a magnetic amplifier as voltage control means. It is. 13... Switching transformer, 17... Saturable reactor, 18... Rectifying and smoothing circuit, 19... Load,
20... automatic voltage control circuit, 27... circuit, 28...
...Resistor for current detection, 29...Transistor.

Claims (1)

[Claims] In a switching power supply, a switching transformer and a switching element to drive it are installed in parallel with a DC power supply, and a magnetic amplifier is installed between the output winding of the switching transformer and the load to control the load voltage.The load current is a constant value. 1. A switching power supply characterized by comprising a circuit that controls a magnetic flux reset voltage of the magnetic amplifier to the overcurrent limit side when the voltage exceeds the overcurrent.