microwat flasher

Microwatt L.E.D. Flasher -

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The Circuit of Fig.3 is a complementary relaxation oscillator that has been utilised to form a Iow power l.e.d. flasher. The heart of the Circuit is the 5-1V 0-5W Zener diodę D2, the absence of which reduoes the oper-ating efficiency of the Circuit. Current ff om the anodę of the Zener diodę provides base bias for transistor TR2.

In order to reduce the current reąuirement of TR2 to a minimum, a high gain Ytpn transistor (BC549C) has been selected. The resistor R1 is the energy saver which acts in conjunction with capacitor Cl, a reservoir for the whole Circuit. Transistor TRI (BC559) is apnp type that provides current for the flash.

To get a flash of fairly good intensity Cl has to be kept fully charged and the action is obtained by keeping the time constant of Rl/ Cl smaller than the time constant of the timing Circuit around TR2, which consists of com-ponents R3 to R5 and C2. The capacitors should ideally be Iow leakage tantalum types.

Using component values as per the Circuit diagram, the flash ratę obtained was approximately 40 per minutę with fairly good intensity using a 9V battery. The actual current consumption at the precise time of flash is we 11 be Iow 04mA. The Circuit is tolerant of voltages ranging from 6V to 12V though a freąuency variation is noticeable when supply voltage varies.

Unlike many other flasher circuits, this one has a very short flash dura-tion. The instantaneous release of energy from the lOO^F capacitor (Cl) has to be fully utilised to illuminate the l.e.d., and a 3mm elear red l.e.d. was chosen as a satisfactory compromise.

Fig.3. Circuit diagram for a Mjerowatt L.E.D. Flasher.

Experimenters might find various other applications due to the very economical power consumption, e .g. by replacing R1 with a 2k2 resistor and addition of a smali piezo buzzer in place of the l.e.d. or in parał lei with it, thus converting it into a Iow current bleeper.

K.N.S. Ncdr, Selongor; Molaysut