Circuit diagram for Pulse Width Modulation controller for Dew Heaters ?

[Inmykombi]

Hi,
Does anyone have a schematic diagram for a reliable Pulse width modulation controller for dew heaters ?
Power handling capacity would be 16 watts max.
I would love to see one if anyone has one, or has designed one.

Cheers.

Geoff.

[citivolus]

There is one here: http://www.iceinspace.com.au/index.php?id=63,285,0,0,1,0 (http://www.iceinspace.com.au/forum/../index.php?id=63,285,0,0,1,0)

I suspect something simpler could be designed utilizing a PIC, a pot, a MOSFET, and a capacitor to cut switching transients & EM noise.

Eric

[Omaroo]

Geoff - here's the one I made - using a single TIP120 Darlington transistor and a 555 timer:

http://www.backyard-astro.com/equipment/accessories/dewheater/dewheater.html

Works wonderfully.

Here's my finished product and a couple of images of that website. All I needed to buy was a good old etching kit from Jaycar and away I went. Mine drives the primary heater, one for the secondary (if there is one), the finder scope as well as the eyepiece - all off the one parallel heater circuit.

[Inmykombi]

Thanks for the replies everyone.

I will look at them in detail tonight and get stuck into the project ASAP.

Geoff.

[AndrewJ]

Here's a simple one made using an LM324 and a MOSFET

Andrew

[erick]

Handy! Don't lose this thread - how can we keep these ideas from getting buried?