JPS63209467A - Switching power source - Google Patents

Abstract

PURPOSE:To prevent an electric shock accident surely by discharging a smoothing capacitor in a power loss and an output loss of auxiliary winding. CONSTITUTION:In a switching power source, an AC power source 11 is rectified by a rectifier circuit 12 and a switching element 15 is ON-OFF controlled by switching control circuits 18-20 via a smoothing capacitor 13. Then, power is supplied from an output winding of switching transformer 14 to a load 17 via a rectifying and smoothing circuit 16. In this case, there are provided a discharging circuit and a transistor power circuit. Then, rectifying diodes 30-40 are connected with a connecting line to the rectifier circuit 12 to detect 32 a supply voltage. Said detection output and an output of the auxiliary winding 14A of said transformer 14 are inputted to a switch circuit 34, a transistor 35 is ON-OFF controlled, and a transistor power circuit 36 is connected in series with an initial charging resistance 21. Thus, the smoothing capacitor 13 can be discharged quickly when any abnormality occurs at the time of stop ping of an apparatus.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a switching power supply that obtains control power from an auxiliary winding of a switching transformer, and more particularly to a discharge circuit for a smoothing capacitor in a DC power supply circuit.

B0 Summary of the Invention The present invention operates in the event of a momentary power outage by discharging the smoothing capacitor when the power is lost and the output of the auxiliary winding is lost in a switching power supply that obtains control power from the auxiliary winding of a switching transformer! To enable quick discharge of a smoothing capacitor when stopping a device, etc., while enabling connection, and to eliminate the need for a dedicated discharge resistor.

C1 Conventional technology 71S2 Figure shows a circuit diagram of a conventional switching power supply.
AC voltage and power supplied from an AC power source 11 such as a commercial power source is rectified by a rectifier circuit 12 and smoothed by a smoothing capacitor 13 . A switching circuit to which DC power is supplied from this DC power supply circuit has a series circuit of a switching transformer 14 and a switching element 15 which is a power FET, and the switching element 15 is controlled by a switching control circuit.
AC power is obtained in the output winding of the switching transformer 14 by switching, and this AC output is passed through the rectifying and smoothing circuit 1.
6 converts it into DC power and supplies it to the load 17. The switching control circuit controls the load 17's ゛it! , pressure Eo
is detected by the voltage detection circuit 18, and the pulse width control circuit 19, which receives this signal as input, obtains an output with a pulse width corresponding to the comparison between the signal and the output setting voltage, and outputs the pulse width to the switching element 1.
5 is turned on and off. The switching transformer 14 is provided with an auxiliary winding &l1t14A in addition to the output a line, and the AC output from the auxiliary winding 14A is passed through a diode 20 to obtain a control power source for the pulse width control circuit 19. The auxiliary winding 14A and the diode 20 together with the initial charging resistor 21 and the capacitor 22 constitute a control power source, and when the switching element 15 (7) is not switching, control power is obtained from the resistor 21 side, and during the switching operation Control power is obtained from the auxiliary winding 14A side of the switching transformer 14.

That is, the pulse width control circuit 19 operates with power supply voltage characteristics as shown in FIG. 3, and does not generate drive pulses for the switching element 15 until the voltage Vc of the control power supply exceeds the set voltage VC2. Moreover, the equal-side internal resistance R becomes a minute current input ICI.

Then, the pulse width control circuit 19 changes the voltage VC to the voltage VC2.
When the current input voltage exceeds 0, the operation starts and a driving pulse for the switching element 15 is generated, and at this time, the large current input IC
The equal-sided internal resistance R becomes 2.

Further, the pulse width control circuit 19 has a hysteresis characteristic that stops operating when the voltage falls below VCI, thereby stabilizing the control power supply voltage.

With such a control power supply circuit, when the device is started up or when the pulse width control circuit 19 is stopped operating due to no load or load short circuit, the capacitor 22 is charged with a small cardiac flow through the resistor 21, and the voltage is reaches voltage VC2 and starts operation. After this operation starts, operating power is obtained from a large current from the auxiliary winding 14A side. This reduces the current that passes through the resistor 21 until the switching operation starts, and reduces power loss and costs compared to the case where the control power is obtained from the high voltage smoothing capacitor 13 side through a dedicated control power supply circuit. Aim to reduce

D5 Problem to be solved by the invention In the conventional circuit, the AC power supply 11 is used to stop the operation of the device.
The disconnection between the main switch and the rectifier circuit 12 is effected by a main switch. Furthermore, when an abnormality such as a load short circuit occurs, the switching drive of the switching element 15 is stopped. When the switching operation is stopped from the operating state in this way, the charging energy of the smoothing capacitor 13 in the device is transferred to the resistor 21.
However, as mentioned above, the resistor 21 has a high resistance, and the internal resistance R of the pulse width control circuit 19 is large, so the discharge time constant becomes large, and the high voltage of the smoothing capacitor 13 is maintained for a long time. There was a risk of electric shock.

Regarding this point, 1. For example, the UL standard in the United States requires that a display be provided when the voltage of the smoothing capacitor 13 exceeds 50 volts or the stored energy of the smoothing capacitor 13 exceeds 20 units one second after the power is turned off. In order to prevent electric shock accidents, it is desired to reduce the discharge time constant.

In order to quickly discharge the smoothing capacitor 13 described above, a relatively resistive resistor 1 is connected in parallel to the smoothing capacitor 13.
It is conceivable to provide a discharge resistor with a small value of n, but if this discharge resistor is used, the resistor is required, and this results in increased power loss and heat generation when the device is in operation. In addition, when a momentary power outage occurs in the AC power supply 11 while the device is in operation,
The charge in the smoothing capacitor 13 is quickly discharged by the discharge resistor, and there is a problem in that the operation cannot be continued during a relatively long momentary power outage.

E9 Means and Action for Solving Problems The present invention has been made in view of the above problems, and includes a DC power supply circuit having a smoothing capacitor, and a switching transformer and its switching from the DC power of this DC core source circuit. a switching circuit that obtains control power from a control circuit and supplies it to a load; and a switching circuit that is initially charged from the DC power source through a resistor and, during operation, receives control power for the switching control circuit from a switching output of an auxiliary winding of the switching transformer. a transistor power supply circuit that generates the initial charging voltage through the resistor; A discharge circuit is provided that discharges the smoothing capacitor through the resistor and the transistor power supply circuit upon detection, and when both conditions of power loss and switching operation are satisfied, the smoothing capacitor is discharged by the transistor power supply circuit and the initial charging resistor. Discharge operation is prohibited during normal operation of the device and when power is lost due to momentary power outage, and early discharge is performed when the device is stopped or an abnormality occurs.

F. Embodiment FIG. 1 is a circuit diagram showing an embodiment of the present invention. The difference between this figure and FIG. 2 is that it is provided with an open market circuit and a transistor power supply circuit shown at 30 to 38. AC power supply 1
A voltage detection circuit 32 is provided which connects rectifier diodes 30 and 31 to the connection line of the AC power supply 11 to the fi current open circuit 12 to detect the voltage of the AC power supply 11. A switch circuit 34 which receives the detection output of this voltage detection circuit 32 and the output of the auxiliary @ line L4A of the switching transformer 14, which is taken in through a diode 33, turns on/off the transistor 35 by using the re-input as an OR signal. Make it a control signal. on the other hand,
A transistor power supply circuit 36 is connected in series to the initial charging resistor 21 . The output transistor 37 of the transistor power supply circuit 36 has a base voltage of the Zener diode 3.
8, has a resistor 21 at its collector, and supplies power from the emitter output terminal to the pulse width control circuit 19 side. The voltage of Zener diode 38 is made lower than the voltage of auxiliary winding 14A, and transistor 37 is turned off during normal operation. When the switch circuit 34 turns on the transistor 35, the output end of the transistor power supply circuit 36 is grounded, that is, the resistor 21 is connected in parallel to the smoothing capacitor 13 via the on-resistances of the transistors 36 and 34.

In this configuration, when the device starts up, the pulse width control circuit 19 is initialized by the operation of the transistor power supply circuit 35, and during normal operation, the transistor of the power supply circuit 35 is turned off and power is supplied from the auxiliary winding 14A side. In the normal operating state, the voltage of the AC power supply 11 is detected by the voltage detection circuit 32 and the switching transformer 14
The switching operation of the auxiliary winding 14A is also detected, and both inputs of the switch circuit 34 are normal, the transistor 35 remains off, and the transistors 37 and 3
The smoothing capacitor 13 is not discharged through the capacitor 5. Therefore, in the normal operating state, the current flowing through the resistor 21 becomes zero, so there is no power loss in the resistor 21, and unnecessary discharge is also eliminated, increasing power efficiency.

Next, when a momentary power outage occurs in the AC power supply 11 during operation, the detection output of the voltage detection circuit 32 is lost, but the off state of the transistor 35 is maintained by the continued output of the auxiliary winding 14A of the switching transformer 14. . Therefore,
If the last instantaneous power outage of the AC power supply 11 is within the time period during which the accumulated energy of the smoothing capacitor 13 can continue operation, normal operation will be maintained.

Next, when the equipment stops operating or the operation stops due to a load short circuit, etc.
When the AC power supply 11 is disconnected, the transistor 35 is turned on, and the resistor 21 is connected in parallel to the smoothing capacitor 13 through the transistor 35 and the transistor 37 of the transistor power supply circuit 35 . As a result, the energy stored in the smoothing capacitor 13 is transferred to the resistor 21 and the transistor 3.
It is discharged through the on-resistances of 5 and 37. This discharge is performed by the low on-resistance of both transistors 35 and 37, and the internal resistance R of the pulse width control circuit 19 becomes high.
This occurs without any intervention, resulting in relatively fast discharge. Therefore, when the device is stopped, etc., the smoothing capacitor 13 is quickly discharged, and an electric shock accident due to the high voltage charged in the smoothing capacitor 13 is prevented. Moreover, the resistor 21 is
Since the time required for discharging the smoothing capacitor 13 is short and the current is normally zero during four rotations, the power capacity can be made small and short-time rated, and the resistance value is smaller than that of the conventional resistor 21. When this is done, the smoothing capacitor can be discharged quickly.

In the embodiment, a case is shown in which the AC power supply 11 is used as a power source, but this can be similarly configured even when power is supplied from a DC power source.

G9 Effects of the Invention As described above, the present invention provides a switching power supply that obtains control power for a switching control circuit from an initial charging resistor and a switching output of an auxiliary winding of a switching transformer, which generates the initial charging voltage via the resistor. Continuation of operation in the event of a momentary power outage is possible due to the provision of a transistor power supply circuit that connects the initial charging resistor in parallel to the smoothing capacitor via the transistor power supply circuit in the event of a loss of power or the output of the auxiliary winding. However, when the equipment is stopped, the smoothing capacitor is quickly discharged, which is effective in reliably preventing electric shock accidents. Furthermore, since the initial charging resistor is used as the discharging resistor, a dedicated discharging resistor is not required, and the number of components in the discharging circuit can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention, FIG. 2 is a conventional circuit diagram, and FIG. 3 is a power supply characteristic diagram of the pulse width control circuit 19. 13... Smoothing capacitor, 14... Switching transformer, 14A... Auxiliary winding, 18... Voltage detection circuit, 19... Pulse width control circuit, 32... Voltage detection circuit, 34... ...Switch circuit, 36...Transistor power supply circuit.

Claims (1)

[Claims] A DC power supply circuit having a smoothing capacitor, a switching circuit that obtains control power from the DC power of the DC power supply circuit using a switching transformer and its switching control circuit and supplies it to a load, and a switching circuit that is initially charged from the DC power supply via a resistor. A transistor power supply circuit that generates the initial charging voltage via the resistor in a switching power supply comprising: a control power supply circuit that obtains control power for the switching control circuit from a switching output of an auxiliary winding of the switching transformer during operation; and a switching device comprising: a discharge circuit that discharges the smoothing capacitor through the resistor and the transistor power supply circuit upon detection of loss of the power supply supplying power to the DC power supply circuit and loss of output of the auxiliary winding. power supply.