JPH07295500A - Power supply voltage stabilization circuit - Google Patents

Abstract

(57) [Abstract] [Purpose] When the light emitting diode (LED) is displayed in blinking, the fluctuation of the power supply voltage due to the blinking of the LED is prevented,
Prevents the effect on other circuits sharing the power supply. [Structure] A light emitting diode D2 having an anode connected to a power supply B1 of a required voltage, a collector connected to a cathode of the light emitting diode, an emitter grounded, and a square wave pulse S1 applied to the base to blink the light emitting diode And a second transistor TR2 having a collector applied with the required voltage from the power source B1, a grounded emitter, and a base to which the required voltage from the collector of the first transistor is applied. When the light emitting diode D2 is turned off, a required current is passed through the second transistor TR2 to prevent the voltage fluctuation of the power source B1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply voltage stabilizing circuit, and more particularly to a power supply voltage stabilizing circuit for preventing a voltage fluctuation that occurs when a light emitting diode (LED) is displayed in a blinking manner. .

[0002]

2. Description of the Related Art Conventionally, light emitting diodes (LEDs) have been widely used for various displays. FIG. 4 shows an example of a display circuit using a light emitting diode, which is simply turned on.
Alternatively, there are two light emitting diodes, that is, D1 (for example, power on / off display) that is turned off (off) and D2 (for example, special mode display) that blinks by a rectangular wave signal of a predetermined cycle. And, as shown in the figure, D2 has a transistor
TR1 is provided in series, a rectangular wave signal S1 of a predetermined cycle is applied to the base of TR1, and TR2 is turned on / off by the rectangular wave to blink D2. Here, when the power source of this circuit is B1, the B1 may be shared with another circuit, for example, a D / A converter (DAC) that converts a digital control signal from a microcomputer into an analog control signal. . In this case, the voltage of B1 fluctuates due to the fluctuation of the load current due to the blinking of the light emitting diode D2. When the shared circuit is the DAC as in the above example, the analog conversion output fluctuates due to the fluctuation of B1. FIG. 4 has such a drawback.

[0003]

DISCLOSURE OF THE INVENTION The present invention has been made to improve the above-mentioned drawbacks, and in the case of being used as a power source for a display circuit using a light emitting diode for blinking display, it is also used for other circuits. An object of the present invention is to provide a power supply voltage stabilizing circuit that prevents voltage fluctuation due to blinking of a light emitting diode.

[0004]

According to the present invention, a light emitting diode having an anode connected to a power supply of a required voltage, a collector connected to a cathode of the light emitting diode, an emitter grounded, and a base blinking the light emitting diode. And a first transistor to which a required voltage from the power source is applied to the collector, the emitter is grounded, and the required voltage from the collector of the first transistor is applied to the base. The present invention provides a power supply voltage stabilizing circuit which includes two transistors and prevents a voltage change of the power supply by causing a required current to flow through the second transistor when the light emitting diode is turned off.

[0005]

When the first transistor for blinking the light emitting diode is turned off by the blinking rectangular wave pulse to cut off the current of the light emitting diode, the second transistor is turned on and the current amount is supplied to the second transistor. Shed. As a result, the load current does not change and the fluctuation of the power supply voltage is prevented. Further, in the method in which a diode is provided instead of the second transistor, the diode is turned on / off by a blinking rectangular wave pulse. This ON / OFF has a timing opposite to the ON / OFF of the first transistor. Therefore, the load current seen from the power supply is constant.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A power supply voltage stabilizing circuit according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an essential part showing an embodiment of a power supply voltage stabilizing circuit according to the present invention, and FIGS. 2 and 3 are other embodiments. In FIG. 1, + B1 is a power source stabilized by the present invention, D1 and D2 are light emitting diodes (LEs).
D), TR1 is a first transistor for switching for blinking the light emitting diode D2, TR2 is a second transistor for stabilizing the power supply voltage, S1 is for turning on and off the first transistor, and a light emitting diode D2 is provided. Square pulse for blinking display, 1 is a microcomputer, etc. (not shown)
It is a DAC (D / A converter) for converting a digital control signal from the device into an analog control signal. 2 is the second of FIG.
Is a case where the transistor (TR2) in FIG. 3 is changed from NPN type to PNP type, and FIG. 3 shows TR2 in FIGS. 1 and 2 as diode D3.
Is replaced with. What is common to FIGS. 1 to 3 is that the power source B1 is shared by the display circuit including the light emitting diodes D1 and D2 and the other circuits (DAC1 in this embodiment). Also, the light emitting diode D1 of the display circuit
Is not a blinking operation but is lit or extinguished (for example, power on / off display), and the same D2 blinks with a rectangular wave pulse S2 (for example, special mode display). this
The load current fluctuates because D2 blinks, and the voltage of the power supply B1 fluctuates.

Next, the operation of the present invention will be described with reference to the drawings. In FIG. 1, the blinking of the light emitting diode D2 is a predetermined period T in which the first transistor TR1 is applied to its base.
It is performed by turning on and off by the rectangular wave pulse S1 of. Same TR
For 1, the collector voltage is low when it is on (D2 is lit) and high when it is off (D2 is off). The second transistor TR2 that uses this TR1 collector voltage as the base voltage is the same TR1.
Turns on when is off and turns on when is off. Therefore, if the resistor R1 is selected so that the collector current when the TR2 is on becomes the same as the current that flows in D2 during lighting, the load current seen from the power supply B1 will be constant regardless of whether D2 is on or off, and voltage fluctuations are prevented. To be done.

FIG. 2 is basically the same as FIG. 1, and TR2
1 is of the NPN type, while FIG. 2 is of the PN type.
A P-type transistor is used. Therefore, the blinking rectangular wave pulse S1 is transmitted through the resistor R3 as shown in the figure.
Applied to the base of TR2. Further, the constant of the base voltage of TR2 is set by the resistors R2 and R3 so that it is turned on when the rectangular wave pulse S1 is applied and is turned off otherwise.
This causes TR2 to turn off when TR1 is on and D2 is on, and is on when TR1 is off and D2 is off. As a result, the load current becomes constant as in the case of FIG.
Voltage fluctuation of B1 is prevented.

FIG. 3 shows the transistor (TR
This is an example of using a diode D3 instead of 2). A rectangular wave pulse S1 is applied to TR1 and also to the cathode of the diode D3. When there is the same rectangular wave pulse S1, the diode D3 becomes reverse biased and turns off.
Turns on when there is no S1. The on / off state of this diode D3 and the on / off state of TR1 are opposite to each other.
A current flows through D3 when it is off, and D3 is cut off when D2 is on. Therefore, the fluctuation of the load current seen from the power source B1 is reduced. However, in the case of FIG. 3, the voltage fluctuation is larger than that in FIG. 1 or 2. However, this method is also effective if the variation is acceptable. Further, in the case of FIG. 3, when the repetition frequency of the rectangular wave pulse S1 is high, the voltage fluctuation can be improved by providing the resistor R4 with a bypass capacitor.

[0010]

As described above, according to the present invention, when the power supply of the display circuit for blinking and displaying the light emitting diode (LED) is shared with the power supply of other circuits, the same blinking LED causes the same power supply. It is possible to prevent and stabilize the voltage fluctuation of the power supply. Therefore, even if the circuit related to the sharing is, for example, a DAC that converts a digital control signal into an analog control signal, it is possible to prevent an adverse effect such as affecting the control voltage conversion. It becomes possible without.

[Brief description of drawings]

FIG. 1 is a main part circuit diagram showing an embodiment of a power supply voltage stabilizing circuit according to the present invention.

FIG. 2 is a main part circuit diagram showing another embodiment of the power supply voltage stabilizing circuit according to the present invention.

FIG. 3 is a main part circuit diagram showing another embodiment of the power supply voltage stabilizing circuit according to the present invention.

FIG. 4 is a main part circuit diagram showing an example of a conventional display circuit.

[Explanation of symbols]

 ＋ B1 Power supply D1 Light emitting diode (LED) D2 Light emitting diode (LED) D3 Diode TR1 First transistor TR2 Second transistor S1 Square wave pulse 1 DAC (D / A converter)

Claims (4)

[Claims] 1. A light emitting diode having an anode connected to a power source of a required voltage, a collector connected to a cathode of the light emitting diode, an emitter grounded, and a base to which a rectangular wave pulse for blinking the light emitting diode is applied. First
And a second transistor to which a required voltage from the power source is applied to the collector, an emitter is grounded, and a required voltage from the collector of the first transistor is applied to the base. A power supply voltage stabilizing circuit, characterized in that when the light is turned off, a required current is passed through the second transistor to prevent voltage fluctuation of the power supply. 2. A light emitting diode having an anode connected to a power source of a required voltage, a collector connected to a cathode of the light emitting diode, an emitter grounded, and a base to which a rectangular wave pulse for blinking the light emitting diode is applied. First
And a second transistor that applies a required voltage from the power source to the emitter, grounds the collector, and applies a required bias voltage from the power source to the base and applies the rectangular wave pulse to the base, A power supply voltage stabilizing circuit, characterized in that when the light emitting diode is turned off, a required current is passed through the second transistor to prevent voltage fluctuation of the power supply. 3. A light emitting diode having an anode connected to a power supply of a required voltage, a collector connected to a cathode of the light emitting diode, an emitter grounded, and a base to which a rectangular wave pulse for blinking the light emitting diode is applied. First
And a diode in which the anode is connected to the power supply and the cathode is grounded via a series resistor having a required value, and the rectangular wave pulse is applied to a connection point between the cathode of the diode and the resistor to emit the light. A power supply voltage stabilizing circuit, wherein when the diode is turned off, a required current is passed through the diode to prevent voltage fluctuation of the power supply. 4. The power supply voltage stabilizing circuit according to claim 3, wherein a capacitor is provided in parallel with the series resistor.