On 28/09/2020 10:48, Chris Holmes wrote:
Hi All,

I recently bought and installed a Manrose timer board for one of
their inline fans (so it runs on after the lights are turned off). I
installed it this weekend (actually driving a similar fan from
another manufacturer).

It's working fine, but I found it a little curious...€¦.

It's a tiny PCB with quite small tracks. It only has about 10-12
components, from memory, a small transistor at the input end together
with a pot to adjust the delay, a big resistor, a handful of tiny
things most of which are probably resistors, but one or two could be
diodes or something else a chip, and another little transistor at the
output end. The permenant live is just a track that goes straight to
the output, and the neutral goes most of the way there and then gets
switched to the output.

Thing is, in my limited experience, transistors and chips required a
power supply of some sort to convert mains to 5V and or 12V DC. But
I couldn't see anything on the board that I recognised as being
capable of doing this. Are there now 240V AC chips? Have there
always been and I've just not come across them before?

Chances are that as a circuit that doesn't have to be exposed to people
they use a capacitive divider and a diode to generate the small amount
of DC power that the timer circuit needs to operate and that the thing
doing the switching is a power thyristor or triac.

Those have been available at mains voltages almost forever.

--
Regards,
Martin Brown