Can somebody explain the operation of this circuit, please?

Hi Guys,

This is the schematic of a Pye charger I recently received that's designed to charge 8.4V NiCad's.

What I want to know is; Do I get any indication when charging is complete? Is the bulb meant to extinguish?

If someone could explain how the circuit operates, I would be grateful.

Cheers,

Damian

The bulb will extinguish when the current through the battery falls below ~2mA (that's 0.6V / 330 ohms)

Thanks for the reply.

Please can you explain how the circuit works, and also the purpose of the Zener Diode?

Damo666 said:

)Please can you explain how the circuit works, and also the purpose of the Zener Diode?

Click to expand...

The transformer converts the 240VAC to 27VAC. D1 rectifies this to 38VDC and C1 smooths the waveform somewhat. R3 and D2 regulate the voltage to 20V. R4 and R6 limit the current to the battery. The battery current passes through R5 and if the current is >~2mA, through TR1 Base-Emitter, which turns LP1 on brightly. If the current is <~2mA, TR1 will be pretty much off and LP1 will be dimmer (but possibly still glowing).

Thanks a lot for the explanation, you covered it nicely for me.