Are you a clock collector? Got a lot of clocks on your wall? Tired of buying AA cells? Disturbed by the amount of leaked Duracell you have to clean? Here is a solution for you, make a simple circuit that will power multiple clocks just fine.
1. IC – LM317 with Heat sink and thermal compound.
2. Capacitor – 0.1μF, 10μF, 100μF and 1000μF, one each.
3. Resistor - 39Ω and 220Ω, one each.
4. Diode – 2 1N4001.
5. 12V power supply or 12V Center tapped transformer along with two 4007 diodes.
How does it work?
If we recall the voltage output equation for LM317 and put the values in there we will get -
Output Voltage = 1.25 * (1+ 39/220) V = 1.47V
Which is very close to the 1.5V of a standard AA cell.
To increase the output voltage slightly a 47Ω resistor can be used instead of the 39Ω one and to decrease it a 33Ω can be used.
1. Do keep in mind this circuit won’t work without a input power, so use an uninterruptible power source if you plan to run clocks.
2. Two 4001 diodes are used as bleeder diode that keep the circuit protected. D1 and D2 protect against charge stored in C3 and C2 respectively.
3. 0.1μF ceramic capacitor is used to reduce noise, which is very important here as noise can interfere with clock circuitry.
4. If the power supply output stage already has capacitor, the 1000μF one can be removed.
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