JP4415559B2 - Switching power supply - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a switching power supply, and more particularly to a switching power supply that supplies a predetermined DC voltage and DC current to an electronic device or the like.
[0002]
[Prior art]
An AC adapter output current and output voltage control method widely known as a representative example of a switching power supply having an RCC circuit is shown in FIG. 4 in which an AC input voltage supplied from a power supply 101 is converted into a rectifier 102 and a smoothing unit. 103 is converted into a DC power source, and the DC power source is converted into a pulse by switching of the main transistor 105 and supplied to the switching transformer 104 to output to the output side circuit unit. The output voltage 113 and the output current 114 are output to the output voltage. The detection circuit unit 109 and the output current detection circuit unit 110 detect the detection result, and the subtransistor 112 is controlled through the output transmission circuit unit 111, thereby controlling the switching of the main transistor 105 and the output voltage 113 of the AC adapter. And output control of the output current 114 That.
[0003]
In an AC adapter which is an AC-DC converter having such an RCC circuit configuration, generally, a regulator device having functions of a voltage detection circuit unit 109 and an output current detection circuit unit 110, and an output transmission circuit The secondary output voltage 113 and the output current 114 are controlled using a photocoupler having the function of the unit 111.
[0004]
Further, according to the configuration of the switching power supply device of FIG. 5, constant voltage control of the output voltage V2 on the secondary side can be performed only on the primary side of the transformer 2, so that the secondary side regulator device and 2 It is not necessary to use a photocoupler for feedback from the secondary side to the primary side, and cost reduction can be realized (see, for example, Patent Document 1).
[0005]
[Patent Document 1]
Japanese Patent Laid-Open No. 5-304778 (first page)
[0006]
[Problems to be solved by the invention]
In the switching control method for performing feedback from the secondary side to the primary side, the regulator circuit having the functions of the output voltage detection circuit 109 and the output current detection circuit 110 and the photocoupler having the function of the output transmission circuit 111 are RCC circuits. The above components account for a large portion of the material cost of the switching power supply product because they are important components that constitute the circuit and are not inexpensive components.
[0007]
In the conventional switching control method shown in FIG. 5, the control circuit 8a uses the output voltage V4 generated by the back electromotive voltage of the bias winding 2c wound in the same phase as the primary winding 2a. In general, the back electromotive voltage generated in the winding of the switching transformer contains a lot of ringing components, so it is easy to further improve the output accuracy on the secondary side while keeping the output voltage V4 substantially constant. Rather, many additional parts are required, and there are too many issues for commercialization.
[0008]
The present invention solves the above-described problems, and does not use a regulator circuit having the functions of the voltage detection circuit 109 and the output current detection circuit 110 and a photocoupler having the function of the output transmission circuit unit 111. To provide a switching power supply capable of controlling an output voltage and output current with high accuracy at low cost by adding a secondary control winding and adding a simple control circuit on the primary side. With the goal.
[0009]
[Means for Solving the Problems]
The present invention provides a switching transformer in which a control winding for controlling a secondary output is provided on the primary side in a circuit configuration of the RCC system, and a rectification in which an anode is connected to one end side of the control winding. A diode, a smoothing capacitor connected between the cathode side of the rectifier diode and the ground line, a Zener diode having a cathode connected to the cathode side of the rectifier diode, and a current from the Zener diode are amplified, and the switching transistor By providing a secondary side control transistor that supplies a base current of a sub-transistor that performs control, a base of the secondary side control transistor, and a phase correction capacitor connected between the ground lines, the secondary side Is supplied with a predetermined output voltage.
[0010]
Further, the secondary output voltage can be adjusted by changing the operating voltage of the Zener diode.
[0011]
Further, the secondary output current can be adjusted by changing the constant of the resistance connected between one end of the base winding provided in the switching transformer and the base of the sub-transistor.
[0012]
Further, a capacitor connected between the base of the sub-transistor and the ground line and adjusting the switching frequency is connected between the base of the sub-transistor and the voltage dividing resistor connected between the base winding of the switching transformer. By connecting, it is possible to reduce the fluctuation of the secondary side output with respect to the fluctuation of the input voltage.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
[0014]
FIG. 1 shows a block diagram of an RCC switching power supply which is a first embodiment of the present invention. In the present invention, in order to control the output voltage on the secondary side to be constant, the switching transformer 104 inscribes the control winding 104d wound in the same phase as the secondary winding 104c, and the generated voltage of the control winding 104d is rectified. In 119, it is converted into a DC voltage. When the voltage of the control winding 104d rises during the off period of the switching transistor 105, the control voltage adjusting Zener diode 120 connected to the rectifier diode 119 flows when the applied voltage exceeds the Zener voltage. A base current is supplied to the secondary control transistor 118. The input base current is amplified by the operation of the secondary side control transistor 118, moves charges between the collector and emitter of the control transistor 118, and supplies the base current of the sub-transistor 112. By such an operation, the ON period of the switching transistor 105 is shortened, the output voltage of the secondary winding 104c of the switching transformer 104 is lowered, and the secondary output voltage 113 can be controlled to be substantially constant.
[0015]
Further, the secondary output voltage can be easily adjusted by changing the operating voltage of the control voltage adjusting Zener diode 120 by making the number of turns of the control winding 104d sufficiently larger than the number of turns of the secondary winding. Is possible.
[0016]
FIG. 2 shows a block diagram of an RCC switching power supply according to the second embodiment of the present invention. The difference between the embodiment of the switching power supply and the embodiment of FIG. 1 will be described mainly. The base current between one end of the base winding provided in the switching transformer 104 and the base of the sub-transistor 112 is described. An adjustment resistor 223 is connected. When the secondary output current 114 is gradually increased and the output current 114 reaches a certain value, the sub-transistor 112, the switching frequency adjusting capacitor 115, and the base current adjustment of the sub-transistor 112 are adjusted. The output current 114 is limited by the operation with the resistor 223.
[0017]
The value limiting the output current 114 can be easily adjusted by changing the constant of the base current adjusting resistor 223.
[0018]
FIG. 3 shows a block diagram of an RCC switching power supply which is a third embodiment of the present invention. In FIG. 2, the switching frequency adjusting capacitor 115 is connected between the base and the emitter of the sub-transistor 112, but as shown in FIG. 3, the switching frequency adjusting capacitor 315 is connected to the base of the sub-transistor 112 and the switching transformer 104. The voltage is connected between voltage dividing resistors 324 and 325 connected between the base windings 104b. Both the voltage of the base winding 104b of the switching transformer 104 and the voltage between the voltage dividing resistors increase as the AC input voltage increases, but conversely, the charge of the switching frequency adjusting capacitor 115 decreases and the input voltage increases. In some cases, the output characteristics fluctuate in a decreasing direction at a certain input voltage point. In the second embodiment shown in FIG. 2, the value that limits the output current 114 increases as the input voltage increases. However, when the circuit is configured as in the third embodiment shown in FIG. 3, for example, in a world wide input switching power supply with an input voltage range of 100 to 240 V, the output characteristic fluctuation in the entire rated input voltage range is It is possible to reduce.
[0019]
【The invention's effect】
As in the above embodiment, according to the present invention, in the RCC circuit configuration, a switching transformer having a control winding for controlling the secondary output on the primary side, and one end of the control winding. A rectifier diode having an anode connected to the side, a smoothing capacitor connected between the cathode side of the rectifier diode and a ground line, a Zener diode having a cathode connected to the cathode side of the rectifier diode, and a Zener diode from the Zener diode A secondary side control transistor that supplies a base current of a sub-transistor that amplifies the current and controls the main transistor, and a phase correction capacitor connected between the base of the secondary side control transistor and the ground line. Thus, the secondary output voltage can be controlled. Further, the secondary output voltage can be easily set by selecting the operating voltage of the Zener diode.
[0020]
Further, by adding a voltage dividing resistor between the base windings of the switching transformer and changing the connection of the switching frequency adjusting capacitor, it becomes possible to reduce the fluctuation of the secondary output current with respect to the fluctuation of the input voltage. .
[0021]
By these inventions, the output voltage is obtained by adding a simple control circuit on the primary side without using a regulator device having a function of secondary side output detection or a photocoupler having a function of an output transmission circuit, Since a switching power supply capable of controlling the output current can be configured, a significant cost reduction can be realized as compared with the conventional configuration.
[Brief description of the drawings]
FIG. 1 is a block diagram of an RCC switching power supply that is a first embodiment of the present invention. FIG. 2 is a block diagram of an RCC switching power supply that is a second embodiment of the present invention. Block diagram of RCC switching power supply as an example [FIG. 4] Block diagram of conventional RCC switching power supply [FIG. 5] Circuit diagram of conventional switching power supply [Explanation of symbols]
101 Power supply 102 Rectifying unit 103 Smoothing unit 104 Switching transformer 104a Primary winding 104b of switching transformer 104 Base winding 104c of switching transformer 104 Secondary winding 104d of switching transformer 104 Control winding 105 of switching transformer 104 Switching transistor 106 Output Rectifier diode 107 Output smoothing capacitor 108 Output current detection resistor 109 Output voltage detection circuit unit 110 Output current detection circuit unit 111 Output transmission circuit unit 112 Subtransistor 113 Output voltage 114 Output current 115 Switching frequency adjusting capacitor 116 Base current of switching transistor 105 Adjustment resistor 117 Driving capacitor 118 for switching transistor 105 Secondary side control transistor 119 Control winding Rectifier diode 120 Zener diode for control voltage adjustment 121 Phase correction capacitor 122 Smoothing capacitor 223 for control winding 104d Base current adjustment resistor 315 for sub-transistor 112 Switching frequency adjustment capacitor 324 Output characteristic adjustment voltage dividing resistor 325 Output characteristic Voltage divider resistor for adjustment

Claims (2)

In the circuit arrangement of the RCC system, the switching transformer that installed inside a control winding for controlling the secondary-side output to the primary side, a rectifier diode having an anode connected to one end of the control winding, wherein and connected to the smoothing capacitor between the cathode side and the ground line of the rectifier diode, the Zener diode having a cathode connected to the cathode side of the rectifier diode, the sub-transistors for controlling the main transistor to amplify the current from said Zener diode configuration of the secondary control transistor for supplying a base current, and a connection phase correction capacitor between the base and the ground lines of the secondary side control transistor, and outputs a predetermined secondary output voltage And one end side of a base winding provided in the switching transformer and the sub-trailer. Comprising a resistor connected between the base of the register, the switching power supply device and outputs a predetermined secondary output voltage and output current. In the circuit configuration of the RCC system, a capacitor connected between the base of the sub-transistor and the ground line and adjusting a switching frequency is connected to a capacitor connected between the base of the sub-transistor and the base winding of the switching transformer. 2. The switching power supply device according to claim 1 , wherein the switching power supply device is connected between the piezoresistors to reduce the fluctuation of the secondary output current with respect to the fluctuation of the input voltage.

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