JPH079393Y2 - Light emitting diode lighting control circuit for electrical equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial field of application) The present invention is a so-called transformerless type which supplies power to a control circuit using a DC low voltage as a power source and controls lighting of a light emitting diode. The present invention relates to a lighting control circuit for a light emitting diode of an electric device.

(Prior Art) For example, in an electric device such as a fan, its operation control is performed by a control circuit including a microcomputer,
Along with this, there is provided a configuration in which the control circuit controls the lighting of the light emitting diode in order to display the operating state. In this case, a DC power supply of, for example, about 5V is required as a power supply for lighting the control circuit and the light emitting diode, but conventionally, for the reason of cost, a step-down transformer is not used and the configuration is as shown in FIG. Was there. In the figure, 1 is a commercial power supply, 2 is a DC constant voltage circuit, which is composed of a general series regulator in which a NPN transistor is provided in series and a constant voltage diode is provided in the base circuit of the transistor. A rectifying element 3 and a voltage sharing resistor 4 are connected in series between the DC constant voltage circuit 2 and the commercial power source 1 so that half-wave DC is applied to the input side of the DC constant voltage circuit 2. From the output side of the DC constant voltage circuit 2, DC power is supplied to the control circuit 5 including a microcomputer and the two light emitting diodes 6 and 7 whose lighting is controlled by the control circuit 5. Has become.

(Problems to be Solved by the Invention) However, the above configuration has a drawback that the power loss in the voltage sharing resistor is relatively large.

Therefore, an object of the present invention is to provide a light emitting diode lighting circuit of an electric device that can reduce power loss.

[Structure of the Invention] (Means for Solving the Problems) A light emitting diode lighting control circuit of an electric device according to the present invention comprises a rectifying element between a commercial power source and a direct current constant voltage circuit.
A voltage sharing resistor and a series circuit of a first light emitting diode are provided, and a series circuit of a second voltage sharing resistor and a second light emitting diode is provided in parallel with the series circuit of the first voltage sharing resistor and the first light emitting diode. Is provided, a switching transistor is provided in parallel with the second light emitting diode, and a control circuit for controlling ON / OFF of the switching transistor when DC power is supplied from the DC constant voltage circuit is provided.

(Function) When the switching transistor is turned on, a current flows through the transistor and the second voltage sharing resistor, and when turned off, a current flows through the second light emitting diode and the second voltage sharing resistor, thereby causing the second light emitting diode. Is lit, a constant current flows through the second voltage sharing resistor regardless of whether the transistor is on or off, and the sharing voltage is always constant. On the other hand, when the electric device is in operation, a current always flows through the first light emitting diode and the first voltage sharing resistor, and the first light emitting diode lights up. Further, in the conventional configuration, the current flowing through the voltage sharing resistor 4 is the sum of the current flowing into the control circuit 5 from the output side of the DC constant voltage circuit 2 and the current flowing into each of the light emitting diodes 6 and 7 in the DC constant voltage circuit 2. However, in the present invention, since the first and second light emitting diodes are located on the input side of the DC constant voltage circuit, the first and second voltage sharing resistors are The flowing current becomes equal to a value obtained by converting the current flowing only from the output side of the DC constant voltage circuit to the control circuit into the input side of the DC constant voltage circuit. As described above, the current flowing through the second voltage sharing resistor is substantially constant regardless of whether the switching transistor is on or off. Therefore, the current flowing through the first light emitting diode and the first voltage sharing resistor is also substantially constant. Therefore, the light emission luminance of the first light emitting diode does not change due to the blinking of the second light emitting diode.

(Embodiment) An embodiment in which the present invention is applied to a fan will be described below with reference to FIG.

10 is a commercial power supply, 11 is a DC constant voltage circuit, which is, for example, NP
It is composed of a general series regulator in which an N-type transistor is provided in series and a constant voltage diode is provided in the base circuit of the transistor. Reference numeral 12 denotes a control circuit including a microcomputer, for example, which receives supply of DC power from the output side of the DC constant voltage circuit 11 and controls ON / OFF of the blower motor 14 based on a signal from the operation key 13.

Now, between the commercial power supply 10 and the DC constant voltage circuit 11, there are a power switch 15, a rectifying element 16, a first voltage sharing resistor 17, and a first voltage sharing resistor 17.
The light emitting diodes 18 are connected in series, and the DC constant voltage circuit 11
A half-wave direct current is stepped down / applied to the input side by the first voltage sharing resistor 17. The series circuit of the second voltage sharing resistor 19 and the second light emitting diode 20 is connected in parallel to the series circuit of the first voltage sharing resistor 17 and the first light emitting diode 18. The first and second light emitting diodes 18 and 20 have the same standard, and therefore the first and second voltage sharing resistors 17 and 19 have the same resistance value.
Further, a collector of an NPN type switching transistor 21 is connected to the anode of the second light emitting diode 20 and an emitter is connected to the cathode thereof, so that the switching transistor 21 is connected in parallel to the second light emitting diode 20. Has become. A bias resistor 22 is connected between the base and emitter of the switching transistor 21, and the base is an output terminal of the control circuit 12 via a resistor 23.
Connected to O ₁ .

The operation of the above configuration will be described. When the power switch 15 is turned on, a half-wave DC is applied to the DC constant voltage circuit 11 by the first voltage sharing resistor 17 with a predetermined voltage sharing. As a result, a DC constant voltage is output from the output side of the DC constant voltage circuit 11 and applied to the control circuit 12. In this case, a part of the input current to the DC constant voltage circuit 11 flows through the first light emitting diode 18, so that the first light emitting diode 18 lights up to indicate that the fan is in an operating state. Where operation keys
When the operation speed of the blower motor 14 is changed to a high speed by operating the blower motor 13, the output terminal O ₁ of the control circuit 12 changes from high level to low level and the switching transistor 21 is turned off. Therefore, the second light emitting diode 20 A current starts to flow in the LED, which lights up to indicate, for example, that the operation is "strong wind". When the operation key 13 is operated again in this state to change the operating speed of the blower motor 14 to a low speed, the output terminal O ₁ of the control circuit 12 turns from low level to high level and the switching transistor 21 turns on. Thus, the second light emitting diode 20 is turned off. In this case, substantially the same current flows through the second voltage sharing resistor 19 regardless of whether the switching transistor 21 is on or off, so that the first and the second light-emitting diodes 20 are turned on regardless of the lighting state. The total sum of the currents flowing in the second voltage sharing resistors 17 and 19 does not change, and the same voltage is always shared between both ends of the resistors 17 and 19.

Now, assume that the current flowing into the control circuit 12 is I [A], and the corresponding input current of the DC constant voltage circuit 11 is I ′ [A]. Then, since both light emitting diodes 18 and 20 are connected to the input side of the DC constant voltage circuit 11, this input current I '[A] is shunted to both light emitting diodes 18 and 20, and in the case of this embodiment, 1st and 2nd voltage sharing resistor 1
Since 7 and 19 have the same resistance value, both LEDs 18 and 2
The value of the current flowing through the resistors 17 and 19 is equal to each other and is I '/ 2 [A]. Therefore, if the voltage shared by the voltage sharing resistors 17 and 19 is V [V], the total loss P ₁ at both resistors 17 and 19 is expressed by the following equation.

P ₁ = 2 × V × I ′ / 2 = VI ′ [W] (1) Here, the loss in the voltage sharing resistor 4 in the conventional circuit shown in FIG. 2 is calculated under the same condition as follows. Become. That is, the current flowing into the control circuit 5 is I [A], which is the same as that in this embodiment, and the current flowing into each light emitting diode 6, 7 is i [A]. Then, the current flowing out from the DC constant voltage circuit 2 becomes I + 2i [A] when both the light emitting diodes 6 and 7 are lit. If the current value obtained by converting the current on the output side into the current on the input side is I '+ 2i' [A], the shared voltage in the voltage sharing resistor 4 is V [V] as in the present embodiment. The loss P ₀ at the resistor 4 is expressed by the following equation.

P ₀ = V (I ′ + 2i ′) [W] (2) Here, since i is a positive value, it is clear that P ₁ <P _0. Power loss can be reduced by 2Vi ′ [W]. Moreover, while the light emitting diodes 18 and 20 are arranged on the input side of the DC constant voltage circuit 11 as described above, the switching transistor 21 is connected in parallel to the second light emitting diode 20 and the light emitting diode is turned on and off by the transistor 21. Since the lighting of 20 is controlled, the current flowing through the first light emitting diode 18 is always constant, and the current flowing into the DC constant voltage circuit 11 changes depending on whether the second light emitting diode 20 blinks. And accordingly the first light emitting diode
The emission brightness of 18 does not change.

In the above embodiment, the first and second light emitting diodes are used.
Although 18 and 20 have the same standard, the present invention is not limited to this, and different rated currents can be used, in which case each voltage sharing resistor 17, when each rated current flows. The resistance value may be selected so that 19 shares the same voltage. Further, the number of light emitting diodes is not limited to two, and three or more may be provided. In that case, the second light emitting diode 20, the switching transistor 21, and the resistor 1 are provided.
A set of circuits composed of 9,22,23 may be further connected in parallel to a series circuit of the first voltage sharing resistor 17 and the first light emitting diode 18. Besides, the present invention is not limited to being applied to a fan, but can be variously modified and implemented within a range not departing from the gist, such as being widely applicable to a light emitting diode lighting control circuit of other electric equipment.

[Effects of the Invention] As described above, according to the light emitting diode lighting control circuit of the electric device of the present invention, the power loss in the first and second voltage sharing resistors provided on the input side of the DC constant voltage circuit is reduced. This is an excellent effect that the light emission luminance of the first light emitting diode does not change due to the blinking of the second light emitting diode.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a view corresponding to FIG. 1 showing a conventional example. In the drawing, 10 is a commercial power supply, 11 is a DC constant voltage circuit, 12 is a control circuit, 16 is a rectifying element, 17 is a first voltage sharing resistor, 18 is a first light emitting diode, and 19 is a second voltage sharing resistor. , 20 is a second light emitting diode, and 21 is a switching transistor.

Claims (1)

[Scope of utility model registration request] 1. A series circuit of a rectifying element, a first voltage sharing resistor and a first light emitting diode is provided between a commercial power source and a DC constant voltage circuit, and the first voltage sharing resistor and the first light emitting diode are provided. A series circuit of a second voltage sharing resistor and a second light emitting diode is provided in parallel with the series circuit of, and a switching transistor is provided in parallel with the second light emitting diode, and DC power is supplied from the DC constant voltage circuit. A light emitting diode lighting control circuit for electric equipment, comprising a control circuit for controlling on / off of the switching transistor.