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?

1/. Yes there are. But probably you only have one on the board. To
switch the mains.
2/. As far as the rest of the circuit is concerned the easiest way to
drop voltage if the current draw is constant is via a mains rated
capacitor. Then rectify and smooth the output enough.
3/ a more expensive way is to have a high frequency mains transistor
chop the mains and feed that through a tiny transformer, but it sounds
like that is more complex than your circuit's designer wanted to pay for..

I got it for about £10 by the way (on special offer, reduced by
50-ish %), so a nice cheap simple way to add a timer to something
that doesn't require much wattage.

Digital crap is so cheap that it probably uses some sort of timer, and
doesn't therefore need any greatly smoothed power supply.

--
The lifetime of any political organisation is about three years before
its been subverted by the people it tried to warn you about.

Anon.