JPH0716303B2 - Switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a switching power supply device, and more particularly to a power supply device capable of securing an auxiliary power supply for a control circuit even when a load is short-circuited.

(B) Summary of the Invention The present invention relates to a constant voltage control circuit provided on the output side for the purpose of constant voltage control and monitoring of the output voltage in a switching power supply device that outputs a positive voltage and a negative voltage, respectively. As an auxiliary power supply, by obtaining from the secondary winding of the switching transformer in which a voltage of the polarity opposite to the voltage generated by the output voltage detection winding of the switching transformer is generated, overcurrent limiting and The auxiliary power supply voltage of the constant voltage control circuit can be secured even when the load is short-circuited when the undervoltage detection function is provided.

(C) Prior Art FIG. 2 shows a configuration diagram of a conventional switching power supply device. Power supplied from an AC power supply 1 is rectified by a rectifier 2 and then smoothed by a capacitor 3 to switch a FET or the like. It is supplied to the primary winding 51 of the switching transformer 5 connected in series with the element 4. The electromagnetic energy stored in the switching transformer 5 during the ON period of the switching element 4 is smoothed by the capacitors 64 and 164 through the diodes 61 and 161 on the secondary side 6 during the OFF period of the switching element 4, and the load 7 , 17. It should be noted that FIG. 2 shows a case in which each of the circuits to which a positive voltage and a negative voltage are applied is one circuit, and each circuit is provided in an arbitrary number, but in this case, the load 7 has a positive voltage. As for the voltage, a negative voltage is applied to the load 17. Further, in order to control the supply voltage to the load 7 at a constant level, the constant voltage control circuit 8 controls the gate output pulse of the pulse width control circuit 9 according to the change of the load voltage E ₀ to turn on / off the switching element 4. An automatic control circuit is provided to control the percentage of the period.
The excitation energy absorption circuit 10 including the resistor 101, the diode 102 and the capacitor 103 is for absorbing the excitation energy of the transformer 5 when the switching element 4 is off.

(D) Problems to be Solved by the Invention Generally, although not shown in the constant voltage control circuit 8,
Each function such as overcurrent limitation, undervoltage detection, and overvoltage detection is provided. For this reason, the pulse voltage generated in the secondary winding 52 of the transformer during the period when the switching element 4 is off is applied to the diode 261 and the capacitor 264. Is used as an auxiliary power source for the constant voltage control circuit 8 after being rectified and smoothed.

In this type of circuit configuration, when the load 7 reaches a short-circuit state, the load voltage E ₀ drops to 0 volt, and the voltage generated in the winding 52 during the period when the switching element 4 is off is the forward voltage of the diode 61. Down to a value commensurate with the directional voltage drop. Therefore, the auxiliary power supply voltage to the constant voltage control circuit 8 also drops to near 0 volt, and there is a problem that the function of the constant voltage control circuit 8 is completely lost.

The present invention has been made for the purpose of eliminating such problems.

(E) Means for Solving the Problems In the present invention, a positive voltage and a negative voltage are each set as 1 as an output voltage.
Circuit A constant voltage that detects the positive or negative output voltage of the switching transformer in the switching power supply device and controls the switching element via the pulse width control circuit according to the change in the detected voltage. Provide a control circuit. Then, the auxiliary voltage of the control circuit is configured to be obtained via the diode from the winding that obtains the other positive or negative voltage of the secondary winding of the switching transformer.

(F) Action Since the voltage of the winding, which has a voltage of the opposite polarity to that of the winding on the output voltage detection side, is rectified by the diode and supplied to the constant voltage control circuit as an auxiliary power supply voltage, it is related to the state of the load. No voltage is obtained.

(G) Embodiment An embodiment of the present invention will be described in detail below with reference to FIG. 1. The difference from FIG. 2 is that the auxiliary power source of the constant voltage control circuit 8 is the tertiary winding 152 of the switching transformer 5. That is, the voltage is generated according to the polarity of the voltage. Ie diode
The anode of 261 is connected to the polarity side of the winding 152 in the figure.

The operation of the present invention configured as described above will be described.

The power from the AC power supply 1 rectified by the rectifier 2 is
When the switching element 4 is turned on, it flows through the route of the primary winding 51 of the transformer 5, the switching element 4, and the rectifier 2 and is accumulated in the winding 51 as electromagnetic energy.

Next, when the switching element 4 is turned off by the control command of the pulse width control circuit 9, the electromagnetic energy accumulated in the winding 51 is transferred to the windings 52 and 152, and a positive voltage is applied to the load 7. The negative voltage is applied to the load 17, respectively. The constant voltage control circuit 8 detects the terminal voltage E ₀ of the load 7 and outputs a signal corresponding to this detected voltage to the pulse width control circuit 9
The pulse width control circuit 9 controls the conduction ratio of the switching element 4.

On the other hand, since a positive voltage is generated on the polarity side (cathode side of the diode 161) of the tertiary winding 152 of the transformer 5, this voltage is rectified by the diode 261 and the capacitor 2
After being smoothed by 64, it is supplied as an auxiliary power source for the constant voltage control circuit 8. Therefore, even if a short-circuit accident occurs in the load, the number of turns N ₅₁ of the primary winding 51 of the switching transformer 5 and the winding 152 are irrelevant to the diode 261 regardless of the load state.
A pulse voltage having a peak value determined by the ratio of the number of turns N ₁₅₂ and the voltage of the capacitor 3 is supplied. That is, the peak value does not change depending on the load condition, and only the pulse width changes depending on the load condition. Therefore, when the load is short-circuited, the pulse width narrows but does not reach 0 volt. Therefore, the auxiliary power supply of the constant voltage control circuit 8 can be secured even when the load is short-circuited.

(H) Effects of the Invention As described above, according to the present invention, the auxiliary power supply voltage of the constant voltage control circuit provided for the purpose of output voltage control, monitoring, or the like is set to a voltage having a polarity opposite to that of the voltage generated in the output voltage detection side winding. Since it is obtained from the winding on the side where the voltage is generated, it is possible to secure the auxiliary power supply for the constant voltage control circuit even if a load short circuit accident occurs, and to reliably detect the short circuit. .

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention, and FIG. 2 is a circuit configuration diagram of a conventional switching power supply device. 1 is an AC power supply, 2 is a rectifier, 3,63, 103, 164 and 264 are capacitors, 4 is a switching element, 5 is a switching transformer, 7 and 17 are loads, 8 is a constant voltage control circuit, 9 is a pulse width control circuit, and 61, 102, 161, 261 are diodes.

Claims (1)

[Claims] 1. A switching element is connected in series with a primary winding of a switching transformer, and a plurality of windings are provided on the secondary side of the switching transformer, and at least positive and negative voltages are individually obtained from the respective windings. In the one that is supplied to the load, the voltage induced in one of the plurality of secondary windings that obtains either positive or negative voltage is detected, and the detected voltage is changed. A constant voltage control circuit for controlling the switching element via a pulse width control circuit is provided, and the auxiliary power supply voltage used in the constant voltage control circuit is set to the positive or negative one of the secondary windings. A switching power supply device characterized in that it is configured so as to be obtained from a winding for obtaining the voltage.