JPH0619318Y2 - Switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field The present invention is used for a DC / DC converter or the like.
The present invention relates to a switching power supply that obtains a switching output from a DC power supply by applying a pulse to a switching element.

(b) Conventional technology and its drawbacks A switching power supply is a circuit that obtains a switching output from a DC power supply by turning a switching element on and off by applying a pulse. A DC / DC converter can be configured by rectifying and smoothing the side output. Such a switching power supply generates a pulse in order to protect the switching element or load element when the switching element or the load side from this overheats or an abnormality such as overcurrent or overvoltage occurs due to overload, etc. There was a circuit that worked the pulse limit of the circuit and forcibly stopped the pulse.

As such a protection circuit, there is a conventional one using a thyristor. This is because the pulse generation circuit is provided with a pulse limiter terminal that can stop the pulse by forcing a pulse limit by setting the terminal voltage to a low potential, and this pulse limiter terminal is grounded via a thyristor. A detection circuit is provided on the load side, and when an abnormality such as an overcurrent is detected, a trigger signal is applied to this thyristor to make it conductive so that the pulse limit works.

The thyristor which has once become conductive in such a protection circuit can be restored to the cutoff state again by opening the main switch of the pulse generation circuit. However, actually, the DC power supply of the pulse generation circuit is supplied from the AC power supply through the rectifier and the smoothing capacitor, and the operation switch used as the main switch is generally arranged on the AC side in terms of capacity. Therefore, even if this operation switch is opened, the holding current continues to flow in the thyristor until the smoothing capacitor is completely discharged. Therefore, conventionally, in order to restart the switching power supply, after opening the operation switch, there is an inconvenience that it is necessary to wait for a long time until the thyristor is cut off.

(c) Purpose of the invention This invention has been made in view of such circumstances, and a restart circuit can be easily and easily restarted by connecting a reset circuit between the output terminals of the thyristor to quickly restore the thyristor. An object of the present invention is to provide a switching power supply that can be quickly operated.

(d) Configuration and effect of the invention This invention supplies a DC power supply from an AC power supply through an operation switch, a rectifier and a smoothing capacitor to a pulse generation circuit that applies a pulse to a switching element, and
This pulse generation circuit is provided with a pulse limiter terminal that can activate the pulse limit and forcibly stop the pulse by setting the terminal voltage to a low potential, and the detection circuit has a switching element and overheat on the load side, When an abnormality such as overcurrent or overvoltage is detected, a trigger signal is applied to the thyristor to make it conductive, and the pulse limiter terminal is grounded to activate the pulse limit and protect the switching element. An emitter is connected between the anode and the cathode of the thyristor, a base is connected to the DC power supply via a resistor, and a short-circuit transistor that short-circuits the anode and the cathode of the thyristor when turned on; Control transistor connected between base and emitter And a rectifying / smoothing circuit for inputting an AC voltage from between the operation switch and the rectifier, rectifying and smoothing the AC voltage, and supplying the rectifying / smoothing to the control transistor. When you cut off
When the control transistor is turned off and the short-circuit transistor is turned on, the output terminals of the thyristor are short-circuited to restore the cutoff state.

The schematic operation of the switching power supply of the present invention will be described first with reference to the block diagram of FIG. When the operation switch is turned on, the AC power is converted into DC through the rectifier and the smoothing capacitor and supplied to the pulse generating circuit. Then, when a pulse is generated from the pulse generation circuit, the switching element repeatedly turns on and off to generate a switching output. Further, when the operation switch is turned on in this way, the reset circuit inputs the AC voltage and is cut off. And
Initially, the thyristor was also shut down.

Next, if the switching element or the load side from it overheats or an abnormality such as overcurrent or overvoltage occurs due to overload, etc., the detection circuit detects it and applies a trigger signal to the thyristor to make it conductive. . Then, the pulse limiter terminal is grounded and has a low potential, so that the pulse limit works. Therefore, the pulse generation circuit is forced to stop the pulse and the switching element is turned off.
Since the switching output also stops, this switching element and the load side can be protected.

In order to restart the switching power supply in which the switching output has stopped in this way, it is only necessary to eliminate abnormalities such as overload, then momentarily open the operation switch and turn it on again. That is, even if the operation switch is opened, the holding current continues to flow in the thyristor until the end of this discharge because the capacity of the smoothing capacitor is sufficiently large in the related art. However, in this invention, when the operation switch is opened, the reset circuit, which has been interrupted along with this, becomes conductive. That is, when the operation switch is opened, the output voltage of the rectifying / smoothing circuit falls below a certain voltage, the control transistor is turned off, and the short-circuit transistor is turned on. Then, the output terminals of the thyristor are short-circuited, the holding current stops flowing, and the circuit is restored to the cutoff state. Then, when the operation switch is turned on again, the reset circuit is turned off again and the activation is started.

As explained above, the switching power supply of this invention is
Even if the switching output is stopped due to an abnormality on the load side, the operation switch can be instantly restarted by simply opening and reclosing the operation switch, so that the troublesome operation can be eliminated.

The operation switch may be of any type regardless of the symbols shown in FIG. 1, and if the contacts for opening and closing the circuit between the AC power supply and the rectifier and the operation unit for operating the contacts are mechanical only. Instead, it may be electrically connected.
Further, although the smoothing capacitor is shown as an electrolytic capacitor in the drawing symbol, it goes without saying that another type of capacitor may be used as long as a sufficient capacity can be obtained. Further, although the SCR is shown as the thyristor, any other thyristor may be used as long as it switches from the cutoff state to the conductive state by the trigger signal and returns to the cutoff state again when the holding current becomes lower than the holding current. Further, the resistance R interposed between the pulse limiter terminal and the rectifier is a protective resistance when the thyristor or the reset circuit is conducted, but it is not always necessary depending on the type of the pulse limiter terminal.

(e) Embodiment FIG. 2 is a circuit diagram of a switching power supply which is an embodiment of the present invention.

First, the configuration and operation of the switching power supply will be described.

This switching power supply uses pulse generation IC1, FET
2, power supply circuit at startup 3, power supply circuit at operation 4, detection circuit 5
And SCR6. The pulse generation IC 1 (pulse generation circuit) is an IC that is supplied with a voltage from the power supply circuit 3 at startup or the power supply circuit 4 at operation and emits a pulse to the gate G of the FET 2. Further, the pulse generation IC 1 is provided with a pulse limiter terminal 7 capable of exerting a pulse limit and forcibly stopping the pulse by setting the terminal voltage to a low potential. In addition, I to use
When C is designed to operate the pulse limit by setting the terminal voltage to a high potential, the pulse limiter terminal 7 may be constructed by drawing this terminal out through the inverter. FET2 (switching element)
Is a switching element that conducts between the drain D and the source S when a pulse is generated from the pulse generating IC 1. When the drain D and the source S conduct, a direct current flows through the primary winding of the transformer 8. Has been done. Therefore, the pulse from the pulse generation IC1 causes F
When ET2 is repeatedly turned on and off, a switching output is generated in the circuit of FET2 and transformer 8. This transformer 8 can obtain electric power of an arbitrary voltage which is insulated from the power supply side in the secondary winding by applying the switching output to the primary winding, and by rectifying / smoothing the DC / DC power. It can be operated as a converter. The start-up power supply circuit 3 is a voltage stabilizing circuit including a power transistor Tr that stabilizes a DC voltage via a resistor R with a Zener diode Z and uses it as an input voltage, and adds a Zener voltage from a DC voltage of 130 V to a base B and an emitter. E
Then, a constant voltage of 12 V is obtained from and is supplied to the pulse generating IC1. The power supply circuit 4 at the time of operation is 1 from the tertiary winding of the transformer 8.
It is a circuit that obtains an AC voltage of 3.5V, rectifies it with a diode D, smoothes it with electrolytic capacitors C, C, and supplies it to the pulse generation IC 1. It can supply an operating voltage only when a switching output is generated. it can. When the operating power supply circuit 4 supplies the operating voltage, the operating voltage has a higher potential than the starting voltage.
Since the switching circuit 9 composed of the diode D connected between and is cut off, the power supply circuit 3 at startup does not supply the startup voltage to the pulse generating IC 1. The detection circuit 5 is a circuit that generates a trigger pulse when an overcurrent of the switching output is detected, and includes a current transformer CT and a Zener diode Z. The current transformer CT is provided in the output circuit of the FET 2 and generates a voltage according to the magnitude of the switching output current. The Zener diode Z is connected so as to send a trigger signal to the gate G of the SCR 6 when the detected voltage of the current transformer CT exceeds the Zener voltage. This SCR 6 (thyristor) connects the anode A between the base B of the power transistor Tr of the power supply circuit 3 at startup and the Zener diode Z, grounds the cathode K, and sends a trigger pulse from the Zener diode Z to the gate G. It becomes conductive by being charged. The pulse limiter terminal 7 of the pulse generation IC 1 is connected to the anode A of this SCR 6. Therefore, when the SCR 6 becomes conductive, the terminal voltage becomes the ground potential and the pulse limit works.

The startup power supply circuit 3 and the DC power supply for switching output are supplied from the AC power supply 10 via the operation switch 11, the rectifier 12, and the smoothing capacitor C13. The operation switch 11 is used as a main switch of this switching power supply. The rectifier 12 is a full-wave rectifier using a diode. The smoothing capacitor C13 smoothes the pulsating current output from the rectifier 12 together with the resistor R connected in parallel.

Next, the operation of this switching power supply will be described.

Before starting, the SCR 6 is cut off and the FET 2 is also in the OFF state. Then, when the operation switch 11 is turned on and a DC voltage is applied to the power supply circuit 3 at startup, the pulse generation IC
The starting voltage is supplied to 1 and a pulse is generated. Then F
ET2 repeatedly turns on and off to generate a switching output, and the supply of electric power to the secondary side of the transformer 8 is started. At this time, a voltage is also generated in the tertiary winding of the transformer 8, and is fed back by the operating power supply circuit 4 to start supplying the operating voltage to the pulse generating IC 1. When the supply of the operating voltage from the operating power supply circuit 4 is started, the startup power supply circuit 3 is disconnected by the switching circuit 9. Such switching of the power supplies is performed because the power generation circuit 3 at startup drives the pulse generation IC 1 as it is after startup, and a large current flows through the power transistor Tr of the power circuit 3 at startup for a long time, resulting in overheating. This is because there is a risk.

Next, when the switching output becomes an overcurrent, the detection voltage of the current transformer CT of the detection circuit 5 becomes equal to or higher than the Zener voltage, a trigger pulse is sent to the gate G through the Zener diode Z, and the SCR 6 becomes conductive. Then, the pulse limiter terminal 7 of the pulse generation IC 1 is at a low potential, so that the pulse limit is activated and the pulse is forcibly interrupted and F
ET2 is turned off. Therefore, the switching output is stopped and an accident due to overcurrent can be prevented. Further, since the SCR 6 is turned on, the Zener diode Z in the power supply circuit 3 at startup is grounded at both ends thereof, so that the power transistor Tr is cut off. For this reason, the power supply circuit 3 at the time of starting also stops the supply of the starting voltage, and no current flows unnecessarily in the power transistor Tr. Since the switching output is not generated in this way, the operating power supply circuit 4 also stops supplying the operating voltage to the pulse generating IC 1.

This embodiment comprises a reset circuit 14 for restoring the conducting SCR 6 in such a switching power supply. The reset circuit 14 obtains an AC voltage from the AC power supply 10 through the operation switch 11 to the two-stage transistors Tr and Tr 'that perform switching operation, rectifies the AC voltage with the diodes D and D', and the resistors R and R'and This is a circuit that is smoothed by a capacitor C and receives a DC voltage. The second stage transistor Tr 'of the reset circuit 14 is connected in parallel between the output terminals of the SCR 6 by connecting the collector C to the anode A of the SCR 6 and grounding the emitter E. While the operation switch 11 is turned on, the transistor Tr is turned on and the transistor Tr 'is turned off, so that the operation of the SCR 6 is not affected. However, when the operation switch 11 is opened, the transistor Tr is turned off and the transistor Tr 'is turned on. Therefore, when the SCR 6 is in the conductive state, the output terminals of the SCR 6 are short-circuited, so that the holding current from the smoothing capacitor C13 is bypassed and the cutoff state is restored. After that, if the operation switch 11 is turned on again, the second-stage transistor Tr 'of the reset circuit 14 is turned off with the SCR 6 restored.
F and restart can be performed. Since the capacitor C of the reset circuit 14 is set to have a capacity sufficiently smaller than that of the smoothing capacitor C13, the transistor Tr is turned off almost immediately when the operation switch 11 is opened.
Can be made.

As described above, in this embodiment, when the detection circuit 5 detects an abnormality and the SCR 6 is conducted and the pulse limit is activated, the cause of the abnormality such as overload is removed, and then the operation switch 1 is removed.
The SCR 6 can be instantly restored and restarted by simply opening and closing 1. For this reason, the operator can restart by a simple operation of opening and closing the main switch of the switching power supply, so that the troublesome operation is eliminated.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a switching power supply of this invention, and FIG. 2 is a circuit diagram of a switching power supply which is an embodiment of this invention. 1 ... Pulse generation IC (pulse generation circuit), 2 ... FET (switching element), 5 ... Detection circuit, 6 ... SCR (thyristor), 7 ... Pulse limiter terminal, 10 ... AC power supply, 11 ... ... Operation switch, 12 ... Rectifier, 13 ... Smoothing capacitor, 14 ... Reset circuit.

Claims (1)

[Scope of utility model registration request] 1. A pulse generator circuit for applying a pulse to a switching element is supplied with a DC power source from an AC power source through an operation switch, a rectifier and a smoothing capacitor, and
This pulse generation circuit is provided with a pulse limiter terminal that can activate the pulse limit and forcibly stop the pulse by setting the terminal voltage to a low potential, and the detection circuit has a switching element and overheat on the load side, When an abnormality such as overcurrent or overvoltage is detected, a trigger signal is applied to the thyristor to make it conductive, and the pulse limiter terminal is grounded to activate the pulse limit and protect the switching element. An emitter is connected between the anode and the cathode of the thyristor, a base is connected to the DC power supply through a resistor, and a short circuit transistor that short-circuits the anode and the cathode of the thyristor when turned on; Control transistor connected between base and emitter And a rectifying / smoothing circuit for inputting an AC voltage from between the operation switch and the rectifier, rectifying and smoothing the AC voltage, and supplying the rectifying / smoothing to the control transistor. When you cut off
A switching power supply, wherein the control transistor is turned off and the short-circuiting transistor is turned on to short-circuit the output terminals of the thyristor to restore the cutoff state.