JP2001275357A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize input voltage to a control circuit by improving the efficiency of the control circuit for activating a switching power supply. SOLUTION: In the switching power supply, a primary winding 11 of an output transformer is connected with a first rectifying/smoothing circuit A consisting of a rectifier 2 and a smoothing capacitor 3, a switching element 8 and a control circuit 6 for controlling such a switching element 8, the switching element 8 is connected to an auxiliary winding 13 of the output transformer, and the auxiliary winding 13 is connected with a second rectifying/ smoothing circuit B, consisting of a rectifying diode 9 and a smoothing capacitor 10. An input voltage to the control circuit 6 is divided with a resistor 4a and a constant voltage diode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to improving the efficiency of a control circuit for starting a switching power supply.

[0002]

2. Description of the Related Art Conventionally, as a switching power supply provided with a control circuit for controlling a switching element, for example, there has been one shown in FIG. In this switching power supply,
A rectifier 2 is connected to both ends of the AC power supply 1, and a smoothing capacitor 3 is connected to the output side of the rectifier to form a first rectifying / smoothing circuit A. A control circuit 6 for controlling the switching element 8 is connected between the piezoresistors 4a and 4b, the first rectifying / smoothing circuit A is connected in series with the primary winding 11 and the switching element 8, and the auxiliary winding of the transformer is connected. 13. The auxiliary winding 1
3 is connected to a second rectifying / smoothing circuit B composed of a rectifying diode 9 and a smoothing capacitor 10, and is connected to a voltage dividing resistor 4b. Further, the cathode of the rectifier diode 9 and one end of the smoothing capacitor 10 are connected to the control circuit 6. With the above circuit configuration, the DC voltage obtained by rectification and smoothing is divided by the voltage dividing resistors 4a and 4b, input to the control circuit, and starts the switching power supply. After startup, the control circuit is driven by the auxiliary winding 13 of the output transformer 7, and the switching power supply continues to operate. In the above switching power supply, in order to promote power saving (low power consumption) of the power supply, the current i flowing through the voltage dividing resistor 4b is increased.
Therefore, it is necessary to increase the resistance values of these voltage dividing resistors in order to reduce the number ₂ and the loss. However, in the circuit of FIG. 2, the resistance value is given by the combined resistance of the voltage dividing resistors 4a and 4b and the impedance of the control circuit, and is large enough to supply the voltage and current necessary for starting the control circuit. Could not be obtained.

[0003]

Because of the above-mentioned problems, there has been a demand for a circuit configuration capable of obtaining a voltage and a current necessary for starting the control circuit while suppressing the current flowing through the voltage dividing resistor. .

[0004]

The present invention SUMMARY OF] is intended to solve the above problems, the minute instead of the resistors 4b by using a constant voltage diode suppresses the current i ₂ flowing at the time of startup, and the constant voltage diode Is maintained at a constant value equal to or higher than the starting voltage of the control circuit and equal to or lower than the allowable voltage to improve the efficiency of the control circuit. That is, a first rectifier / smoothing circuit A including a rectifier 2 and a smoothing capacitor 3 is connected to a primary winding 11 of an output transformer, and a switching element 8
And the control circuit 6 for controlling the switching element 8, and the switching element 8 is connected to the auxiliary winding 13 of the output transformer, and the auxiliary winding 13 is connected to the rectifier diode 9 and the smoothing capacitor 10. A switching power supply comprising a second rectifying / smoothing circuit B, wherein an input voltage to the control circuit 6 is divided by a resistor 4a and a constant voltage diode.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG.
FIG. 4 shows an input voltage dividing circuit of FIG.
4 to increase the resistance value of the voltage dividing resistor 4a
Is the current i flowing through the voltage dividing resistor 4a.₀Need to be smaller
is there. i₀Is the current i flowing through the control circuit ₁And the resistor 4b
Flowing current i₂Of the current i₁Is control times
It cannot be reduced because it is determined by the road
No. Therefore, i₂Must be reduced, but i₂
Is reduced by the voltage dividing resistors 4a and 4b.
The input voltage of the control circuit is higher than the starting voltage of the control circuit.
And it must be set below the allowable voltage.
You. Therefore, instead of the voltage dividing resistor 4b of FIG.
When the arm 5 is connected, the circuit diagram according to the embodiment of FIG.
And the current i flowing around the control circuit 6₀, I ₁,
i₂Is as shown in FIG. Here, the constant voltage diode
Mode 5 gives i₂≒ 0, so that i₀= I₁
+ I₂≒ i₁Becomes Therefore, the current flows to the voltage dividing resistor 4a.
Current i₀Is higher than when the voltage dividing resistor 4b of FIG. 1 is connected.
And the resistance value is larger than
Significantly reduce the power consumption generated by the voltage divider
be able to. When the input voltage to the control circuit 6 is
a and the constant voltage diode 5
To a constant value that is higher than the starting voltage of the control circuit and lower than the allowable voltage.
Can be maintained.

[0006]

1 is a basic circuit diagram according to an embodiment of the present invention, and FIG. 2 is a basic circuit diagram according to a conventional example. 3 and 4
3 is a diagram showing an input voltage circuit to the control circuit of FIGS. 1 and 2, respectively. When the current i ₀ flowing through the resistor 4a at the time of startup is measured and compared between the embodiment of FIG. 3 and the conventional example of FIG. 4, the example (FIG. 3) is 0.7 mA and the conventional example (FIG. 4) is 1.0 mA. In the embodiment in which the voltage resistance 4b is replaced by a constant voltage diode, the current value is reduced by 30% as compared with the conventional example, and the loss generated in the voltage dividing resistance 4b is also reduced by 30%.
Also, the current required by the control circuit after startup is 0.1 to
1.0A, but this is all
Supplied from 3. Actually, the auxiliary winding voltage after startup is 16 to 18 V, and the voltage applied to the constant voltage diode is 2
0 to 22 V (control circuit allowable voltage is 30 V). At this time, the current i ₂ = 0 flowing through the constant voltage diode after the start-up
Becomes

[0007]

As described above, the switching power supply according to the present invention has a circuit configuration in which the input voltage to the control circuit is divided by the resistor and the constant voltage diode, so that the current flowing through the voltage dividing resistor is significantly reduced. Power consumption generated by the voltage dividing resistor can be significantly reduced, which is effective in reducing the power consumption of the power supply device. Further, the input voltage to the control circuit can be maintained at a constant value equal to or higher than the starting voltage and equal to or lower than the allowable voltage by the constant voltage diode.

[Brief description of the drawings]

FIG. 1 is a basic circuit diagram according to an embodiment of the present invention.

FIG. 2 is a basic circuit diagram according to a conventional example.

FIG. 3 is a diagram illustrating a voltage dividing circuit of an input voltage to the control circuit of FIG. 1;

FIG. 4 is a diagram illustrating a voltage dividing circuit of an input voltage to the control circuit of FIG. 2;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 AC power supply 2 Rectifier 3, 10, 14 Smoothing capacitor 4a, 4b Voltage dividing resistor 5 Constant voltage diode 6 Control circuit 7 Output transformer 8 Switching element 9 Rectifying diode 11 Primary winding 12 Secondary winding 13 Auxiliary winding A 1st rectifying / smoothing circuit B 2nd rectifying / smoothing circuit

Claims (1)

[Claims] A first rectifier / smoothing circuit including a rectifier and a smoothing capacitor, a switching element, and a control circuit for controlling the switching element, which are connected to a primary winding of the output transformer; A switching element connected to the auxiliary winding of the output transformer, and a second rectifying / smoothing circuit including a rectifier diode and a smoothing capacitor connected to the auxiliary winding. And a constant voltage diode.