JP2000014151A - Auxiliary power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize reduction in size and cost through elimination of a transformer or the like by connecting a first diode and a second diode of reverse polarity, in parallel with a series circuit of first and second capacitors and then outputting a voltage across the second capacitor. SOLUTION: When a AC voltage is impressed to the terminals 1 and 2 and the terminal 1 becomes positive and the terminal 2 becomes negative, a current flows through a path formed of a first capacitor C1, first diode D1, second capacitor C2 and third capacitor C3. A charging voltage of the second capacitor C2 is impressed with the reverse polarity with respect to the first diode D1. The first and third capacitors C1, C3 are repeatedly charged and discharged via the first and second diodes D1, D2, corresponding to the AC voltage applied to the terminals 1, 2. The second capacitor C2 is charged by the voltage rectified by the diode D1. A terminal voltage of the second capacitor C2 is obtained by dividing the AC voltage, depending on the capacitance ratio of the second capacitor C2, first and third capacitors C1, C3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an auxiliary power supply circuit for supplying power from a commercial AC power supply or the like to a relatively low voltage and low current load. In various electronic devices that supply power from a commercial power supply such as AC 100 V or 200 V, DC 1
An auxiliary power supply circuit is provided to supply power to an electronic circuit requiring a very small current of about 1 mA at a low voltage of about 0 V. There is a demand for such an auxiliary power supply circuit to be smaller and more economical.

[0002]

2. Description of the Related Art FIG. 3 is an explanatory diagram of a conventional auxiliary power supply circuit. Reference numeral 10 denotes an auxiliary power supply circuit; An AC voltage is applied from the AC power supply 14 to the main circuit 13 and the auxiliary power supply circuit 10, and the main circuit 13 supplies operating power in the main circuit 13 by a transformer, a rectifier circuit, or the like (not shown). Also, a low voltage and a small current such as a gate voltage of a field effect transistor, not shown, in the main circuit 13 are omitted from the auxiliary power supply circuit 10. That is, the AC voltage from the AC power supply 14 is
The DC voltage rectified and smoothed by the rectifying and smoothing circuit 12 is supplied to the main circuit 13.

FIG. 4 shows a conventional auxiliary power supply circuit in which a main circuit is a switching power supply circuit. In the figure, 20 is a main circuit, 21 is a rectifier circuit, 22 is a switching circuit, 23 is a transformer, 24 and 25 are diodes, 2
6 is a choke coil, 27 is a capacitor, 30 is an auxiliary power circuit, 31 is a rectifier circuit, 32 is a switching circuit,
Reference numeral 3 denotes a transformer, 34 denotes a rectifier circuit, and 35 denotes a capacitor.

The main circuit 20 rectifies an AC voltage by a rectifier circuit 21, switches a rectified output voltage by a switching circuit 22, and supplies the rectified output voltage to a primary winding of a transformer 23.
The induced voltage of the secondary winding of the transformer 23 is
The DC voltage is output after being rectified by the chokes 4 and 25 and smoothed by the choke coil 26 and the capacitor 27.

The auxiliary power supply circuit 30 has a configuration similar to that of the main circuit 20, rectifies an AC voltage by a rectifier circuit 31, switches a voltage supplied to a primary winding of a transformer 33 by a switching circuit 32, The induced voltage of the secondary winding of the transformer 33 is rectified by the rectifier circuit 34, smoothed by the capacitor 35, and supplied to the main circuit 20, for example, the switching circuit 22.

[0006]

A conventional auxiliary power supply circuit has a configuration including a transformer 11 and a rectifying / smoothing circuit 12, for example, as shown in FIG. 10V, 1
Even an auxiliary power supply circuit that supplies DC power of about mA or less has a problem that it is not easy to reduce the size because the configuration includes the transformer 11.

[0007] As shown in FIG.
2 and the transformer 33, the auxiliary power supply circuit 30 differs from the main circuit 20 only in voltage and current.
Since they have the same configuration, it is difficult to reduce the size and cost. It is also conceivable to divide the AC voltage by a resistor and rectify the divided output to supply a low voltage and minute power to an auxiliary circuit or the like. However, power loss occurs due to the resistance and the AC voltage side and the DC voltage side There is a problem that cannot be separated. It is an object of the present invention to reduce the size and economy by omitting a transformer and the like.

[0008]

An auxiliary power supply circuit according to the present invention comprises: (1) a first capacitor C1, a first diode D1, and a second capacitor with respect to AC voltage power terminals 1 and 2; C2 and a third capacitor C3 are connected in series, and a second diode D2 having a polarity opposite to that of the first diode D1 is connected in parallel with a series circuit of the first diode D1 and the second capacitor C2. Connected to the second capacitor C
2 to output a voltage between both ends. Therefore,
Since it is composed of the capacitor and the diode, the size can be reduced, and the number of parts is small, so that economy can be achieved.

(2) Voltage stabilizing means for stabilizing the voltage across the second capacitor C2 can be provided. As the voltage stabilizing means, a Zener diode, a series regulator, or the like can be applied.

[0010]

FIG. 1 is an explanatory view of a first embodiment of the present invention, wherein reference numerals 1 and 2 denote terminals for applying an AC voltage,
3, 4 are DC voltage output terminals, and C1 to C3 are first to third
, D1 and D2 are first and second diodes.

The first and third capacitors C1 to C3 and the first diode D1 are connected in series to the terminals 1 and 2, and both ends of the second capacitor C2 are connected to the output terminals 3 and 4. , The second diode D2 is connected in parallel with the series circuit of the first diode D1 and the second capacitor C2 with the opposite polarity to the first diode D1.

Therefore, when the AC voltage applied to the terminals 1 and 2 is such that the terminal 1 has a positive polarity and the terminal 2 has a negative polarity, the first capacitor C1, the first diode D1, and the second capacitor C2 A current flows through the path to the third capacitor C3. Then, when the terminal 1 has the negative polarity and the terminal 2 has the positive polarity, a current flows through the path of the third capacitor C3, the second diode D2, and the first capacitor C1. At that time,
The charging voltage of the second capacitor C2 is applied to the first diode D1 with the opposite polarity.

Therefore, the first and third capacitors C1, C
3 repeats charging / discharging in response to the AC voltage applied to the terminals 1 and 2 via the first and second diodes D1 and D2, while the second capacitor C2 includes the diode D1
Is charged with the rectified voltage.

The terminal voltage of the second capacitor C2 is derived from terminals 3 and 4 and supplied to an auxiliary circuit and the like. In this case, the terminal voltage of the second capacitor C2 has a value obtained by dividing the AC voltage by the capacitance ratio of the second capacitor C2 to the first and third capacitors C1 and C3.

In this case, terminals 1 and 2 for applying an AC voltage
Are connected directly to the first and third capacitors C1 and C3.
When the AC voltage is set to 100 V, the capacity of ordinary electronic equipment is limited so that a current of about 1 mA or more does not flow. Therefore, in the case of a 50 Hz 100V AC power supply, the combined capacitance of the first and third capacitors C1 and C3 is, for example, about 3 μF or less. Then, when a DC voltage of, for example, 15 V is output to the output terminals 3 and 4, the capacity of the second capacitor C2 is about 0.5 μF.

FIG. 2 is an explanatory view of a second embodiment of the present invention. The same reference numerals as those in FIG. 1 denote the same parts, and reference numeral 5 denotes a voltage stabilizing means, which is constituted by a zener diode ZD and a resistor R1. The case of is shown. When the DC voltage appearing at the output terminals 3 and 4 exceeds the Zener voltage of the Zener diode ZD, a current flows through the Zener diode ZD and the resistance R
1 causes a large voltage drop, and the output terminals 3 and 4
A DC voltage limited to the Zener voltage of Zener diode ZD is output.

In this case, since the current supplied to the minute capacitance load connected to the output terminals 3 and 4 is very small, the fluctuation of the DC voltage at the output terminals 3 and 4 is extremely small, but the influence of the fluctuation of the AC voltage is small. You will get In such a case, it can be stabilized by the Zener diode ZD. It is also possible to apply a series regulator. Since such a voltage stabilizing means 5 is for a minute current, it can be easily formed into an integrated circuit.

[0018]

As described above, according to the present invention, the first capacitor C1, the first diode D1, the second capacitor C2, and the third capacitor C3 are sequentially connected in series. The first diode D1 and the second capacitor C2
And a second diode D2 having a polarity opposite to that of the first diode D1 is connected in parallel to the series circuit, and both ends of a second capacitor C2 are connected to output terminals 3 and 4, respectively. Various low-voltage, low-power loads can be connected to 3 and 4.

Therefore, the AC voltage side and the DC low voltage side can be separated by the first and third capacitors C1 and C3, and the first and third capacitors C1 and C3 and the second capacitor C2 can be separated. A desired low voltage can be obtained in accordance with the capacitance ratio of. This eliminates the need for a transformer or the like as in the conventional example, so that there is an advantage that the size and cost can be reduced. Even when the voltage stabilizing means 5 is provided, since the voltage stabilization is performed for a minute current, a small-sized one is sufficient and the cost does not increase.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a second embodiment of the present invention.

FIG. 3 is an explanatory diagram of a conventional auxiliary power supply circuit.

FIG. 4 is an explanatory diagram of a conventional auxiliary power supply circuit.

[Explanation of symbols]

 1, 2 terminals 3, 4 output terminals C1 to C3 first to third capacitors D1, D2 first and second diodes

Claims (2)

[Claims] 1. A first capacitor, a first diode, a second capacitor, and a third capacitor are connected in series to a power supply terminal of an AC voltage, and the first diode and the third diode are connected in series. A second diode having a polarity opposite to that of the first diode is connected in parallel with a series circuit with the second capacitor, and a voltage between both ends of the second capacitor is output. Auxiliary power circuit. 2. The auxiliary power supply circuit according to claim 1, further comprising voltage stabilizing means for stabilizing a voltage between both ends of said second capacitor.