JP6935137B2 - Switching power supply - Google Patents

Description

The present invention relates to a switching power supply device having a latch function of stopping a switching IC and holding the stopped state for a certain period of time when an abnormality occurs on the secondary side.

A switching power supply device that rectifies AC power supplied from an external commercial power source to generate DC power of a predetermined voltage includes a capacitor that rectifies the AC power from the outside and then smoothes it. On the other hand, a safety device is provided on the secondary side to stop oscillation by the switching IC provided on the primary side and prevent DC power from being generated on the secondary side when an abnormality such as a short circuit occurs on the secondary side. (See, for example, Patent Document 1). Then, in order to hold the transmission stop state of the switching IC for a certain period of time, a second capacitor different from the smoothing capacitor is provided (see, for example, Patent Document 2).

JP-A-2007-116890 (Fig. 1) Japanese Unexamined Patent Publication No. 2015-126656 (Fig. 2)

When the above abnormality occurs, the power supply from the external commercial power supply is stopped first, then the cause of the failure is eliminated, and after the cause of the failure is eliminated, the power supply from the external commercial power supply is restarted. Let me. When the oscillation stop signal for the switching IC disappears while the power supply from the external commercial power supply is stopped in this way, the switching IC operates again due to the electric charge stored in the capacitor for smoothing. There is a problem that electric power is generated on the next side.

Therefore, when the power supply from the external commercial power supply is stopped, a latch circuit is provided to maintain the oscillation stop state of the switching IC until the charge of the smoothing capacitor is discharged. However, even if the cause of the failure is eliminated and the power supply from the external commercial power supply is restarted, the charge of the second capacitor provided in the latch circuit is discharged and the oscillation stop state is released. Causes a problem that the switching power supply cannot be operated again.

Therefore, in view of the above problems, it is an object of the present invention to provide a switching power supply device capable of shortening the oscillation stop state of the switching IC as much as possible.

In order to solve the above problems, the switching power supply device according to the present invention includes a rectifying unit that rectifies AC power from an external commercial power supply and a first capacitor that smoothes the power rectified by this rectifying unit. A switching IC that oscillates based on the smoothed DC power supplied through the first capacitor and supplies it to the primary side coil of the transformer, and a secondary connected to the secondary side of the transformer. When an abnormality occurs in the side circuit, an oscillation stop signal is generated to stop the oscillation of the switching IC on the primary side, and after the power supply from the external power supply is stopped, this oscillation stop signal is held for a certain period of time. In a switching power supply device having a latch circuit unit provided with a second capacitor, the latch circuit stops the oscillation of the switching IC and the power supply from the commercial power supply is cut off. When the amount of charge of the capacitor falls below the minimum amount of charge required for the operation of the switching IC, the second capacitor is discharged and a forced discharge circuit unit is provided to release the oscillation stop state. do.

When the amount of charge of the first capacitor is less than the minimum amount of charge required for the operation of the switching IC, it is not necessary to stop the oscillation of the switching IC, so that the oscillation stopped state can be maintained. The second capacitor was forcibly discharged to release the oscillation stop state.

When the charge amount of the second capacitor is less than the minimum charge amount, it is not always necessary to discharge the first capacitor, but the forced discharge circuit unit uses the second capacitor. At the time of discharging, the first capacitor may be discharged at the same time.

As is clear from the above description, in the present invention, when the power supply from the external commercial power supply is stopped due to the occurrence of an abnormality, and then the power supply from the external commercial power supply is restarted after the abnormality is resolved. It is possible to provide a switching power supply device that can operate quickly.

A circuit diagram showing the configuration of an embodiment of the present invention.

This figure shows the circuit on the primary side of the switching power supply device according to the present invention. Reference numeral 1 denotes an external commercial power source, and 100 volts of AC power is supplied from the commercial power source 1. The AC power becomes DC power smoothed by the first capacitor 21 after being rectified by the diode bridge 2. By turning the FET 22 on and off, the DC power is intermittently passed through the primary coil 31 of the transformer transformer 3.
The FET 22 is configured to be switched on and off by the switching IC 4.

Reference numeral 5 denotes a latch circuit. When an abnormality such as a short circuit occurs on the secondary side (not shown), an LED, which is also one of the components of a photocoupler (not shown), emits light, and a phototransistor 51 paired with the LED emits light. Turn on. Then, the transistor 6 is turned on, and the feedback terminal 41 of the switching IC 4 falls to the ground. Then, the switching IC 4 stops oscillating, and as a result, no electric power is generated on the secondary side.

When the abnormality on the secondary side is resolved, the LED goes out, and as a result, the phototransistor 51 returns to off, but even after the second capacitor 52 is provided in the latch circuit 5 and the phototransistor 51 returns to off. The ON state of the transistor 6 is continuously maintained.

When the above abnormality occurs, the supply of AC power from the commercial power supply 1 is first stopped, the cause of the abnormality is eliminated in that state, and the power supply from the commercial power supply 1 is restarted after the cause of the abnormality is eliminated. do.

In this way, while the power supply from the external commercial power source 1 is stopped, both the first capacitor 21 and the second capacitor 52 are gradually discharged, and the amount of charged charge gradually increases. It will decrease. When the charge of the second capacitor 52 becomes low and the oscillation stop state for the switching IC 4 is released while the amount of charge of the first capacitor 21 remains sufficiently, the power is not supplied from the outside. Even if there is, the switching IC 4 operates due to the electric charge remaining in the first capacitor 21. Therefore, the charge amount of the second capacitor 52 is designed to be sufficiently maintained until the charge amount of the first capacitor 21 is less than the minimum charge amount required for the operation of the switching IC 4.

However, even if the cause of the abnormality is resolved and the power supply from the commercial power supply 1 is restarted, the charge of the second capacitor 52 remains, and the oscillation stopped state for the switching IC 4 is maintained. The switching power supply cannot be restarted. Therefore, the forced discharge circuit unit 7 is provided.

Two transistors 71 and 72 for discharging the second capacitor 52 are connected in series to the forced discharge circuit unit 7. When the transistor 6 is on and the switching IC 4 is stopped oscillating, the transistor 71 is also on as well as the transistor 6. However, in that state, since the transistor 72 is in the off state, the second capacitor 52 is not discharged.

When the amount of charge of the first capacitor 21 is less than the minimum amount of charge required for the operation of the switching IC 4, the FET 73 is turned off, and therefore the transistor 72 is turned on. Then, both the transistor 71 and the transistor 72 are turned on, so that the second capacitor 52 is discharged. At this time, the large first capacitor 21 was also configured to be discharged.

In this way, when the power supply from the external commercial power supply 1 is restarted in the state where both the two capacitors 21 and 52 are forcibly discharged, the switching power supply device immediately resumes operation.

The present invention is not limited to the above-described embodiment, and various modifications may be made without departing from the gist of the present invention.

1 Commercial power supply 2 Diode bridge 3 Transformer transformer 4 Switching IC
5 Latch circuit 7 Forced discharge circuit 21 First capacitor 52 Second capacitor

Claims (2)

A rectifying unit that rectifies AC power from an external commercial power supply and a first capacitor that smoothes the power rectified by this rectifying unit are provided, and the smoothed power is supplied through the first capacitor. Switching between the switching IC that oscillates based on DC power and supplies it to the primary side coil of the transformer, and the switching on the primary side when an abnormality occurs in the secondary side circuit connected to the secondary side of this transformer. A switching power supply having a latch circuit unit provided with a second capacitor that generates an oscillation stop signal that stops the oscillation of the IC and holds the oscillation stop signal for a certain period of time after the power supply from the external power supply is stopped. In the device, the amount of charge of the first capacitor is the minimum required for the operation of the switching IC in a state where the latch circuit stops the oscillation of the switching IC and the power supply from the commercial power supply is cut off. A switching power supply device provided with a forced discharge circuit unit that discharges the second capacitor and releases the oscillation stop state when the amount of charge falls below the above. The switching power supply device according to claim 1, wherein the forced discharge circuit unit discharges the first capacitor at the same time as discharging the second capacitor.

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