JP3400442B2 - Switching power supply - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC power supply stopping means and a DC power supply starting means of a switching power supply for supplying DC power to electronic equipment. 2. Description of the Related Art Conventionally, as shown in FIG. 7, a connection between a commercial power supply 1 and a switching power supply 35 is opened and closed by an external operation switch 11 to control supply and stop of a DC power supply to an electronic device 8. The circuit was known. However, since the high voltage of the commercial power supply 1 is applied to the external operation switch 11 used in the above-mentioned prior art, a large and expensive switch has to be used. Further, when the external operation switch 11 is opened during the operation of the electronic device 8 and the DC power supply to the electronic device 8 is suddenly stopped, the electronic device 8 may be broken down in some cases. [0004] It is an object of the present invention to control the supply and stop of DC power from a switching power supply to an electronic device by a small and inexpensive external operation switch, and to turn off the external operation switch during operation of the electronic device to control the electronic device. An object of the present invention is to provide a switching power supply in which an electronic device does not break down even when the supply of DC power to the device is stopped. [0005] A switching power supply according to the present invention is a switching power supply for supplying DC power to electronic equipment using a commercial power supply as an input source. The switching power supply includes an external operation switch provided on a secondary side of a transformer. A detection circuit that is provided on the secondary side of the transformer and detects the state of the switch and outputs a first signal; and a detection circuit that is provided on the secondary side of the transformer and detects the state of the external operation switch. A detection circuit with a delay circuit that outputs a second signal after a delay time, and a control that is provided on a primary side of the transformer and controls an operation of the DC power supply by a second signal from the detection circuit with the delay circuit And a first signal from the detection circuit can be used to control the operation of the electronic device. In a preferred embodiment, the delay time can be set arbitrarily. With the above configuration, a signal is sent to the electronic device at the same time as the external operation switch for controlling the DC power supply of the switching power supply is turned off, and the operation of the electronic device is stopped. Since the DC power supply can be stopped, failure of the electronic device can be prevented. Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing a reference example on which the present invention is based. 1 is a commercial power supply, a diode bridge 2
The capacitor 3 is connected to a rectifier circuit, and a DC voltage is generated across the capacitor 3. Reference numeral 4 denotes a transformer. In the figure, the symbol “・” indicates the polarity of the winding of the transformer 4. A switching transistor 5 uses a field effect transistor. The a1 side of the primary winding 4a is connected to the anode of the capacitor 3, the a2 side of the primary winding 4a is connected to the drain of the switching transistor 5, and the source of the transistor 5 is connected to the cathode of the capacitor 3. Transistor 5
Performs a switching operation that repeats conduction and non-conduction, an AC voltage is applied to the primary winding 4a and an AC voltage is generated in the secondary winding 4c. The anode of the diode 6 is connected to the C2 side of the winding 4c, and the capacitor 7 is connected to the C1 side of the winding 4c.
Of the capacitor 7 is connected to the diode 6
Connected to the negative electrode. The AC voltage generated in the winding 4c is rectified by the diode 6 and the capacitor 7, and a DC voltage is generated across the capacitor 7. The electronic device 8 is connected to both ends of the capacitor 7 and receives supply of DC power. The drive circuit 9 is connected to both ends of the capacitor 3, the gate of the switching transistor 5, and the b1 side of the winding 4b.
A driving voltage VG is supplied between the gate and the source of the transistor 5 to perform a switching operation of the transistor. The detection circuit 10 includes a secondary winding 4d that supplies power to the detection circuit 10.
When the switch 11 is connected to the external operation switch 11 and detects the OFF state of the switch 11, it outputs a signal 12. When the control circuit 13 receives the signal 12 from the detection circuit 10,
The drive voltage VG of the switching transistor 5 is suppressed. When the external operation switch 11 is ON, the signal 12
Is not output, and the control circuit 13 does not operate. When the external operation switch 11 is turned off, a signal 12 is output from the detection circuit 10 and the control circuit 13 operates to perform switching.
The drive voltage VG of the transistor 5 decreases, and the transistor 5 cannot perform a sufficient switching operation. As a result, the DC voltage generated at both ends of the capacitor 7 decreases, and the DC power supply to the electronic device 8 stops. In this state, at the same time, the AC voltage generated in the winding 4d also decreases.
The power for outputting 2 continues to be supplied to the detection circuit 10. FIG. 2 is a diagram showing a specific circuit example of the detection circuit 10 and the control circuit 13 in FIG. The control circuit 13 shown in FIG. 1 includes the diode 14, the capacitor 15, the light receiving transistor 161, the transistors 17, 18 and the resistor of the photocoupler 16 shown in FIG. When the switching transistor 5 performs a switching operation, an AC voltage is generated in the winding 4b. The b1 side of the winding 4b is connected to the anode of the diode 14, the b2 side of the winding 4b is connected to the cathode of the capacitor 15, and the anode of the capacitor 15 is connected to the cathode of the diode 14. The AC voltage generated in the winding 4b is rectified by the diode 14 and the capacitor 15, and a DC voltage is generated across the capacitor 15. The anode of the capacitor 15 is connected to the emitter of the transistor 17, and the collector of the transistor 17 is connected to the base of the transistor 18 through a resistor. The collector of the transistor 18 is connected to the gate of the switching transistor 5, and the emitter of the transistor 18 is connected to the source of the switching transistor 5. The collector of the light receiving transistor 161 of the photocoupler 16 is connected to the base of the transistor 17 through a resistor, and the emitter of the light receiving transistor 161 is connected to the emitter of the transistor 18. The detection circuit 10 in FIG. 1 includes the diode 19, the capacitor 20, the light emitting diode 162 of the photocoupler 16 and the resistor in FIG. When the switching transistor 5 performs a switching operation, the winding 4d
, An AC voltage is generated. The d1 side of the winding 4d is connected to the anode of the diode 19, the d2 side of the winding 4d is connected to the cathode of the capacitor 20, and the anode of the capacitor 20 is connected to the cathode of the diode 19. The AC voltage generated in the winding 4d is rectified by the diode 19 and the capacitor 20, and a DC voltage is generated across the capacitor 20. The cathode of the capacitor 20 is connected to one end of the external operation switch 11, and the other end of the switch 11 is connected to the cathode of the light emitting diode 162 of the photocoupler 16.
The anode of 62 is connected to the anode of capacitor 20 through a resistor. When the external operation switch 11 is closed (OFF state), a DC voltage generated in the capacitor 20 causes a current to flow through the resistor to the light emitting diode 162 of the photocoupler 16 and output a signal 12. Photo coupler 1
6, the light receiving transistor 161 includes a light emitting diode 162.
Is turned on by the signal 12 from the switch. Then, the DC voltage generated in the capacitor 15 causes the transistor 17
Flows through the light receiving transistor 161 and the resistor, and the transistor 17 is turned on. When the transistor 17 is energized and a base current flows to the transistor 18 and the transistor 18 is energized, the driving voltage VG supplied from the driving circuit 9 to the switching transistor 5 decreases, so that the transistor 5 performs a sufficient switching operation. You cannot do it. As a result, the capacitor 7
The DC voltage generated at both ends of the power supply decreases, and the supply of DC power to the electronic device 8 stops. In this state, the winding 4d
The DC voltage generated across the capacitor 20 also decreases, but the current sufficient to output the signal 12 continues to flow through the light emitting diode 162. When the switch 11 is open (ON state), the current flowing through the light emitting diode 162 of the photocoupler 16 is cut off, and the signal 12 is not output, so that the light receiving transistor 161 of the photocoupler 16 is turned off, and at the same time, the transistors 17, 18 Also become non-energized. As a result, the drive voltage VG of the switching transistor 5 is normally supplied from the control circuit 9, so that the transistor 5 performs a normal switching operation and DC power is supplied to the electronic device 8. FIG. 3 shows the windings 4d and 4c in FIG.
FIG. 14 is a diagram showing another reference example in which is shared. The detection circuit 10 in FIG. 1 includes the diode 21 and the capacitor 2 in FIG.
2. It is composed of the light emitting diode 162 of the photocoupler 16 and a resistor. When the switching transistor 5 performs a switching operation, an AC voltage is generated in the winding 4c. The cathode of the diode 21 is connected to the C2 side of the winding 4c, the anode of the capacitor 22 is connected to the C1 side of the winding 4c, and the cathode of the capacitor 22 is connected to the anode of the diode 21. The AC voltage generated in the winding 4c is rectified by the diode 21 and the capacitor 22,
A DC voltage is generated at both ends. The cathode of the capacitor 22 is connected to one end of the switch 11, the other end of the switch 11 is connected to the cathode of the light emitting diode 162 of the photocoupler 16, and the anode of the light emitting diode 162 is connected to the anode of the capacitor 22 through a resistor. When the switch 11 is closed, a current flows through the resistor to the light emitting diode 162 of the photocoupler 16 due to the DC voltage generated at both ends of the capacitor 22 to output the signal 12. Switch 1
When 1 is opened, the current flowing through the light emitting diode 162 of the photocoupler 16 is cut off, and the signal 12 is not output. FIG. 4 is a circuit diagram showing one embodiment of the present invention.
The detection circuit 10 in FIG. 1 is replaced with a detection circuit 23 and a detection circuit 25 with a delay circuit, and an operation stop circuit 34 is added to the electronic device 8. The detection circuit 23 outputs the signal 24 immediately after the external operation switch 11 is turned off, and the operation stop circuit 34 stops the operation of the electronic device 8 immediately after inputting the signal 24. When the external operation switch 11 is turned off, the detection circuit 25 with a delay circuit outputs the signal 12 after an arbitrarily set delay time. When the external operation switch 11 is in the ON state, the signals 12 and 24 are not output, and the DC power is supplied to the electronic device 8. When the external operation switch 11 is turned off,
The signal 24 is immediately output, and the operation stop circuit 34 to which the signal 24 is input stops the operation of the electronic device. After the delay time, the signal 12 is output and the DC power supply to the electronic device 8 is stopped. FIG. 5 shows the external operation switch 1 shown in FIG.
FIG. 1 is a diagram showing specific circuit examples of 1, a detection circuit 23, and a detection circuit 25 with a delay circuit. FIG. 6 is a timing chart showing the operation of the main part of FIG. The external operation switch 11 in FIG. 4 includes a switch 11a and a switch 11b in FIG. 5. When the external operation switch 11 is operated, the switches 11a and 11b open and close simultaneously in conjunction with each other. The detection circuit 23 in FIG. 4 includes the Zener diode 26 in FIG. 5 and a resistor. Zener diode 2
The cathode of No. 6 is connected to the anode of the capacitor C7 through a resistor, and the anode of the Zener diode 26 is connected to the cathode of the capacitor C7. The cathode of the Zener diode 26 is connected to one end of the switch 11a and the operation stop circuit 34, and the other end of the switch 11a is connected to the anode of the Zener diode 26. Switch 11a closed (ON state)
In this case, the signal 24 is not generated because both ends of the Zener diode 26 are short-circuited. When the switch 11 a is opened (OFF state) while a DC voltage is being generated in the capacitor 7, the Zener voltage of the Zener diode 26 is output as a signal 24 and input to the operation stop circuit 34. 4 includes a winding 4d, a diode 27, a capacitor 28, a transistor 29, a Zener diode 30, a capacitor 31, and a photocoupler 16 in FIG.
162 and a resistor. When the switching transistor 5 performs a switching operation, an AC voltage is generated in the winding 4d. The anode of the diode 27 is connected to the d1 side of the winding 4d.
The negative side of the capacitor 28 is connected to the
Is connected to the cathode of the diode 27. Winding 4d
The AC voltage generated in the diode 27 and the capacitor 28
And a DC voltage is generated across the capacitor 28. The anode of the light emitting diode 162 of the photocoupler 16 is connected to the anode of the capacitor 28 through a resistor,
The cathode of the light emitting diode 162 is connected to the collector of the transistor 29. The base of transistor 29 is connected to the anode of capacitor 31, and the emitter of transistor 29 is connected to the cathode of capacitor 28. The anode of the Zener diode 30 is connected to the cathode of the capacitor 28,
The cathode of Zener diode 30 is connected to the anode of capacitor 28 through a resistor. The cathode of the capacitor 31 is connected to the anode of the Zener diode 30, and the capacitor 3
One anode is connected to the cathode of the Zener diode 30 through a resistor 32. One end of the switch 11b is connected to the anode of the capacitor 31 through the resistor 33,
The other end of b is connected to the cathode of the capacitor 31. Resistance 3
If the value of 3 is sufficiently smaller than the resistance 32, the voltage applied between the base and the emitter of the transistor 29 is sufficiently small when the switch 11b is closed (ON state).
Transistor 29 is turned off. Transistor 2
When the power supply 9 is not energized, no current flows through the light emitting diode 162 of the photocoupler 16, so that the signal 12 is not output, and DC power is supplied to the electronic device 8. Switch 11
b (OFF state), the resistor 31
2, the charging current flows, and the voltage Vbe applied between the base and the emitter of the transistor 29 gradually increases. The Zener voltage of the Zener diode 30 is Vz (V), the resistance value of the resistor 32 is R (Ω), and the capacitance of the capacitor 31 is C
(F), the time after opening the switch 11b is t (second)
Then, Vbe (V) is expressed by the following equation. Vbe = Vz (1−exp (−t / (C × R))) When the voltage Vbe reaches the base-emitter saturation voltage Vs of the transistor 29, the transistor 29 is turned on and the photocoupler 16 emits light. The current flows through the diode 162 to output the signal 12, and the DC power supply to the electronic device 8 stops. The time T from when the switch 11b is opened to when the voltage Vbe reaches Vs is expressed by the following equation.
By changing the values of R and C, the value of T can be set arbitrarily. T = C × R × ln (Vz / (Vz−Vs)) When the external operation switch 11 is operated to close the switches 11 a and 11 b (ON state), a signal 12 is output.
And the signal 24 is not output, and the DC power is supplied to the electronic device 8. When the external operation switch 11 is operated to open the switches 11a and 11b (OFF state), the signal 24 is immediately output, and the operation stop circuit 34 which has received the signal 24 immediately stops the operation of the electronic device. After the arbitrarily set delay time T, the signal 12
Is output, and the DC power supply to the electronic device 8 is stopped.
Switch 11a, switch 11b, signal 24, signal 12
FIG. 6 shows the relationship between DC power supply and DC power supply. Although the field effect transistor is used as the switching transistor 5 in the above embodiment, the present invention can be similarly implemented by using a bipolar transistor. As described above, the switching power supply of the present invention can prevent failure of electronic equipment.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing a reference example of the present invention. FIG. 2 is a diagram showing a specific circuit example of FIG. 1; FIG. 3 is a diagram showing another specific circuit example of FIG. 1; FIG. 4 is a circuit diagram showing one embodiment of the present invention. FIG. 5 is a diagram showing a specific circuit example of FIG. 4; FIG. 6 is a timing chart showing the operation of the main part of FIG. FIG. 7 is a diagram showing a conventional example. [Description of Signs] 1 Commercial power supply 2 Diode bridge 3, 7, 15, 20, 28, 31 Capacitor 4 Transformer 4a, 4b, 4c, 4d Winding 5 Switching transistor 6, 14, 19, 21, 27 Diode 8 Electron Device 9 Drive circuit 10, 23 Detection circuit 11 External operation switch 11a, 11b Switch 12, 24 Signal 13 Control circuit 16 Photocoupler 17, 18, 29 Transistor 25 Detection circuit 26 with delay circuit 26, 30 Zener diode 32, 33 Resistance 34 Operation Stop circuit 35 Switching power supply

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 3/28

Claims (1)

(57) [Claim 1] In a switching power supply for supplying DC power to electronic equipment using a commercial power supply as an input source, an external operation switch provided on a secondary side of a transformer; A detection circuit that is provided on the secondary side and detects the state of the switch and outputs a first signal; and a detection circuit that is provided on the secondary side of the transformer and detects the state of the external operation switch and can be set arbitrarily. A detection circuit with a delay circuit that outputs a second signal after an appropriate delay time; and a detection circuit provided on the primary side of the transformer, wherein the operation of the DC power supply is controlled by a second signal from the detection circuit with the delay circuit. And a control circuit, wherein the first signal from the detection circuit can be used to control an operation of the electronic device.