JP3060486U - Power circuit - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a power supply circuit which is cheaper and outputs a DC voltage lower than a given DC voltage. An input terminal to which a first DC voltage (5V) is to be supplied, a transistor having a first terminal connected to the input terminal, a common terminal having a common fixed potential, and a second terminal of the transistor. A first capacitor C1 connected therebetween, a semi-fixed resistor R connected between the first terminal and the second terminal of the transistor Tr, and a semi-fixed resistor R
And a zener diode D3 reversely connected between the intermediate tap and the common terminal, and a second DC voltage (3.3 V) lower than the first DC voltage (5 V) is supplied from between the third terminal and the common terminal of the transistor Tr. ).

Description

[Detailed description of the invention]

[0001]

[Technical field to which the invention belongs]

 The present invention relates to a power supply circuit which is supplied with a DC voltage and outputs a DC voltage lower than the supplied DC voltage.

[0002]

[Prior art]

 Recently, in electronic equipment, a semiconductor element with a working voltage of, for example, 5 V and a semiconductor element with 3.3 V are both used, and a DC power supply of 5 V converted from a commercial AC power supply in the electronic equipment is further replaced by a DC power supply of 3.3 V. Often converted to power. In this case, it is common to use a regulator made into an IC.

[0003]

[Problems to be solved by the invention]

 However, IC-based regulators are expensive, which has been a factor of increasing parts costs. A configuration that uses a three-terminal regulator in addition to the IC-based regulator is also conceivable, but the present invention considers another configuration. As a power supply circuit using a transistor as in the present invention, "Power supply circuit for non-contact switch" is disclosed in Japanese Utility Model Application Laid-Open No. 6-46346, and "Stabilization is disclosed in Japanese Utility Model Application Laid-Open No. 6-21336. A "power supply circuit" and a "DC power supply circuit" are disclosed in JP-A-7-44250. The present invention has been made in view of the above-described circumstances, and has as its object to provide a less expensive power supply circuit that outputs a DC voltage lower than a given DC voltage.

[0004]

[Means for Solving the Problems]

 The power supply circuit according to the first invention includes an input terminal to which a first DC voltage is to be applied, a transistor having a first terminal connected to the input terminal, a common terminal having a common fixed potential, and a second terminal of the transistor. A first capacitor connected between the terminals, a semi-fixed resistor connected between the first terminal and the second terminal, a middle tap of the semi-fixed resistor, and a Zener diode reversely connected between the common terminal and the common terminal; And a second DC voltage lower than the first DC voltage is obtained from between the third terminal of the transistor and the common terminal.

In this power supply circuit, a first DC voltage is applied to an input terminal, and a first terminal of a transistor is connected to the input terminal. A first capacitor is connected between a common terminal having a common fixed potential and a second terminal of the transistor, a semi-fixed resistor is connected between the first terminal and the second terminal of the transistor, and an intermediate tap of the semi-fixed resistor and the common tap are connected. A zener diode is reversely connected between the terminals. Then, a second DC voltage lower than the first DC voltage is obtained from between the third terminal and the common terminal of the transistor. This makes it possible to provide a cheaper power supply circuit that outputs a DC voltage lower than a given DC voltage.

[0006] The power supply circuit according to the second invention is characterized by further comprising one or more diodes sequentially connected between the input terminal and the first terminal.

In this power supply circuit, since one or more diodes are connected in series between the input terminal and the first terminal of the transistor, the DC voltage applied to the transistor is reduced by the voltage drop caused by the one or more diodes. And the heat generated from the transistor can be suppressed.

[0008] The power supply circuit according to the third invention is characterized by further comprising a second capacitor connected between the first terminal and the common terminal.

In this power supply circuit, since the second capacitor is connected between the first terminal and the common terminal of the transistor, the ripple current included in the given first DC voltage can be smoothed, and The second DC voltage can be output.

[0010] The power supply circuit according to the fourth invention is characterized by further comprising a third capacitor connected between the third terminal and the common terminal.

In this power supply circuit, the third capacitor is connected between the third terminal and the common terminal of the transistor, and the output voltage is smoothed and output, so that a stable second DC voltage can be output.

[0012]

[Embodiment of the invention]

 Hereinafter, the present invention will be described with reference to the drawings showing an embodiment thereof. FIG. 1 is a circuit diagram showing a configuration of an embodiment of a power supply circuit according to the present invention. In this power supply circuit, a DC voltage of 5 V is applied to an input terminal Tin. The DC voltage of 5 V is stepped down from a commercial AC power supply, and the AC voltage output from the secondary side of the transformer is rectified by a diode D4, smoothed by a smoothing circuit S, and applied to an input terminal Tin.

In the smoothing circuit S, a positive electrode is connected to a cathode of the diode D4, and a negative electrode is connected to an electrolytic capacitor C4 connected to a common terminal to which a potential of the housing is applied, and one terminal is connected to a cathode of the diode D4. And a negative electrode connected to a common terminal of the reactor L. The other terminal of the reactor L is connected to the electrolytic capacitor C5. Output from the common connection point of the negative electrodes.

The input terminal Tin is connected to the anode of the diode D1, and the cathode of the diode D1 is connected to the anode of the diode D2. The cathode of the diode D2 is connected to the positive electrode of the electrolytic capacitor C2 (second capacitor), and the negative electrode of the electrolytic capacitor C2 is connected to the common terminal. A common connection point between the cathode of the diode D2 and the positive electrode of the electrolytic capacitor C2 is connected to the collector (first terminal) of the NPN transistor Tr, and the base (second terminal) of the transistor Tr 2 is connected to the electrolytic capacitor C1 (first capacitor). And the negative electrode of the electrolytic capacitor C1 is connected to a common terminal.

A semi-fixed resistor R is connected between the collector and the base of the transistor Tr, a semi-fixed terminal of the semi-fixed resistor R is connected to a cathode of a Zener diode D3, and an anode of the Zener diode D3 is connected to a common terminal. It is connected. The positive electrode of an electrolytic capacitor C3 (third capacitor) is connected to the emitter (third terminal) of the transistor Tr, the negative electrode of the electrolytic capacitor C3 is connected to the common terminal, and the emitter of the transistor Tr and the positive electrode of the electrolytic capacitor C3. Are connected to the output terminal Tout.

In the power supply circuit having such a configuration, the DC voltage of 5 V is reduced by the diodes D1 and D2, and the reduced DC voltage is smoothed by the electrolytic capacitor C2. The smoothed DC voltage is further adjusted to be constant by the semi-fixed resistor R and the Zener diode D3, and applied between the collector and the base of the transistor Tr. The semi-fixed resistor R and the Zener diode D3 have an output voltage from the output terminal Tout of 3. according to a load (not shown) connected to the output terminal Tout. It is adjusted to be kept at 3V.

The semi-fixed resistor R, the transistor Tr, and the electrolytic capacitor C1 constitute a ripple filter, and smoothes the input DC voltage and outputs it while holding it at 3.3V. The 3.3 V DC voltage output from the ripple filter is further stabilized (smoothed) by the electrolytic capacitor C3 and output from the output terminal Tout. The difference between the DC voltage input to the collector of the transistor Tr and the DC voltage of 3.3 V output from the emitter is set to about 1 V due to the voltage drop by the diodes D1 and D2. Is suppressed.

[0018]

[Effect of the invention]

 According to the power supply circuit according to the first invention, it is possible to provide a power supply circuit that outputs a DC voltage that is lower in cost and lower than a given DC voltage.

According to the power supply circuit of the second invention, the DC voltage applied to the transistor can be reduced by the voltage drop by one or a plurality of diodes, and the heat generation from the transistor can be suppressed. .

According to the power supply circuit according to the third invention, it is possible to smooth the ripple current included in the given first DC voltage and to output a stable second DC voltage.

According to the power supply circuit of the fourth invention, the third capacitor is connected between the third terminal and the common terminal of the transistor, and the output voltage is smoothed and output, so that the stable second DC voltage is output. You can do it.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of a power supply circuit according to the present invention.

[Explanation of symbols]

 C1 electrolytic capacitor (first capacitor) C2 electrolytic capacitor (second capacitor) C3 electrolytic capacitor (third capacitor) D1, D2 diode D3 Zener diode R semi-fixed resistor Tin input terminal Tout output terminal Tr NPN transistor (transistor)

Claims (4)

[Utility model registration claims] An input terminal to which a first DC voltage is to be applied, a transistor having a first terminal connected to the input terminal, a common terminal having a common fixed potential, and a second terminal connected to the transistor. A first capacitor, a semi-fixed resistor connected between the first terminal and the second terminal,
A middle tap of the semi-fixed resistor and a Zener diode reversely connected between the common terminal; and obtaining a second DC voltage lower than the first DC voltage from between the third terminal and the common terminal of the transistor. A power supply circuit characterized by what it does. 2. The semiconductor device according to claim 1, further comprising one or more diodes connected between the input terminal and the first terminal.
Power supply circuit as described. 3. The power supply circuit according to claim 1, further comprising a second capacitor connected between said first terminal and said common terminal. 4. The power supply circuit according to claim 1, further comprising a third capacitor connected between said third terminal and said common terminal.