microwat flasher

Microwatt L.E.D. Flasher ■

MdkisfbEg

The Circuit of Fig3 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-IV 0-5W Zener diodę D2, the absence of which redu ces the oper-ating efficiency of the Circuit. Current from the anodę of the Zener diodę provides base bias for transistor TR2.

In order to reduoe 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 apytp 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 tantalu m types.

Using component values as per tte Circuit diagram, the flash ratę obtained was approximately 40 per minutę with fairly good intensity using a 9V battery. The actual current consumption at tte 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

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