[sdiy] 12VDC to 12VAC converter solution...
seb at burnit.co.uk
Thu Sep 6 16:55:23 CEST 2007
Thanks everyone for your help with this, I've now got a good solution
Went for the MOSFET H-bridge in the end (L6203) which gives a 12VAC RMS
square wave output.
The motor (a shower fan) seems to be quite happy running on a square
wave: it doesn't seem particularly noisy (no more than one would expect
for a fairly powerful domestic shower fan) and the motor's not getting hot.
I'm glad I didn't go for the audio power amp solution as even the very
efficient L6203 is getting quite hot driving this fan (it needs a decent
heatsink to be comfortable to touch).
Note that there's no reason I'm using a 556 as opposed to a 555 other
than the fact that I blew up my only 7555 and had to switch to using an
NE556. In fact the 7555 blew up immediately on connecting the fan so I
guess the delicate CMOS architecture didn't like all those nasty voltage
spikes from the motor on the power rails! The 556 seems quite happy ..
had it running continuously for about 30 minutes now.
Now I just have to add the humidity sensing circuitry .. should be quite
easy as I already have 50Hz AC to run through the resistive humidity
sensor, and the ENABLE input of the L6203 can be used to switch the fan
on and off. So just the addition of a couple of opamps should do it ..
1 to rectify and 1 to compare the current through the sensor .
More information about the Synth-diy