GB2067368A - LED decorative light source power supply - Google Patents

Abstract

A LED decorative light comprises a DC-powered RC circuit (3) to which a plurality of parallel LEDs in two sets (4,4') are connected so that the LEDs flicker in accordance with the time constant of the circuit. LEDs of different colours may be mounted in a lamp cover. <IMAGE>

Description

SPECIFICATION LED decorative light The present invention relates to a LED decorative light. A resonant circuit output has a plurality of LEDs connected in parallel as its load. In the result these LEDs flicker at a set frequency and give a beautiful and decorative light.

This means that the following advantages can be obtained by a suitable embodiment of the invention: 1. Low voltage and low current can be used and little power consumed.

2. It need not be necessary to change the colours of a lamp cover surface since LED's of different colours can be employed.

3. It may be made compact so as to be applied to various environments such as outdoors, on a dining table or inside a car.

4. Safety.

5. Because the LED's are connected in parallel the formal functioning of other LEDs will not be unfavourably affected even if one LED is damaged.

The composition and action principles of the present invention are best described below in reference to the Figure, which is a circuit diagram of one embodiment.

This has a DC power source which may be a storage battery or a DC voltage source in any other form for making up the power loss of the oscillatory loop and LED's, a switch element which may be selected according to requirements and control the cut-in of the DC power source and a resonant circuit which consists of transistors Tr, and Tr2, capacitors C1 and C2, and resistors R1, R2 R3 and R4 and wherein C1, C2, R2 and Rg respectively determine a time constant so as to decide the flickering time period of the LED's (4). The transistors Tr, and Tr2 are used for power output, and R1 and R4 are the collector load resistors of Tr1 and Tr2.

The circuit also has LED's 4, 4' in parallel which may be respectively connected in series to R1 and R4, according to requirements so as to form the load of the resonant circuit 3. When switch 2 is closed, LEDs flicker at a frequency set by the time constant of C1, C2, R2 and R3. A transparent lamp cover may be used to cover the LEDs in line with requirements but so as to enhance the appearance of the LEDs.

Since the prohibited energy band of a LED is very wide, when a forward voltage is applied to the PN junction surface of LED (4) the carrier current energy level flowing into the LED (4) is raised to a state of instability. When the said level drops again, the excess energy is emitted in the form of light, and the light emitting efficiency of LED (4) is very high, over a range extending from the infrared into the visible, so various LEDs in different colours may be used.

When the transistor Tr1 conducts more current than the transistor Tr2, C2 discharges through F3 so that the base electrode of Tr2 forms a reserve bias to cut off the current and at the same time C1 is subject to the external voltage Vcc, and C1 charges so as to increase and saturate the forward bias of Tr1 base electrode.

Therefore Tr1 is in a state of saturation and Tr2 is in a state of cut-off current.

When the original charging voltage of C2 has discharged through F3 until it has gradually reached the reverse voltage of the Tr2 base electrode, the Tr2 base electrode then acquires a forward bias and Tr2 then conducts current.

When Tr2 conducts current, the terminal voltage drops, C1 discharges through R2 so that the Tr1 base electrode acquires a reverse bias and cuts off the current. At the same time, the terminal voltage of C2 is made equal to the external voltage Vcc, C2 then charges so as to increase and saturate the forward bias of Tr2 base electrode. Therefore, Tr1 is in a state of cut-off and Tr2 is in a state of saturation.

When C1 has discharged through R2 until the reverse bias of the Tr1 base electrode has reached zero and the tri base electrode become more forward biassed Tr1 will be in a state of saturation and Tr2 in a state of cut-off once again. Such an endless circulation leads to the LEDs connected in series to R1 and R4 respectively to flicker along with the cut-off of current through Tr1 and Tr2. The oscillatory frequency is given by: 1 0.69(R2C1 + R3C2) Period T = T1 + T2 = 0.69(R2C1 + R3C2) If R2 = R3 =R,C1 = C2 = C Then F - 1.38FC andT = 1.38FC Thus, it is best to have the added voltage between the collector and emitted equal to one half of the external voltage.

In the specific example of embodiment seen in the drawing, specifications are as follows: Reference Specification C1,C2 10-17 Rf R1,R4 15-270 R2, R3 5.6K-22K Tr1,Tr2 NPN

Claims (4)

1. A decorative light a DC-powered resonant circuit and a piurality of light-emitting diodes (LEDs) as the load of the resonant circuit.

2. The decorative light as ciaimed in Claim 1 wherein there are two sets of LEDs connected respectively to the outputs of two transistors of the resonant circuit.

3. The decorative light as claimed in Claim 1 or Claim 2 wherein the LEDs or sets of LEDs are covered with various shaped lamp covers.

4. The decorative light circuit substantially as herein described with reference to and as illustrated in the accompanying drawings.