Interesting circuit.

Looks like the BC327 could do with a B-E turn off resistor. When
the switch is open the base is floating. This could allow the
transistor to partially turn on or even oscillate, especially if noise is
present. This in turn means the circuit may try to activate the
MOSFETs, and as insufficient gate voltage is available they are
most likely operating in a linear mode outside of their safe operating
area. For example Vds = 6V, Ids = 30A, P=180W,- poof!

Maybe a 10k or 22k resistor? Might need to be higher to stop it
affecting the pot characteristics, but the lower the better. Make the
pot 1k and the capacitor 100nF to compensate.

Does the power switch need to be where it is? (Maybe it is part of
the pot). Better if it was independant of the timing circuit.

Looks like a 12V to 6V converter for a VW wiper motor.

To make it even safer, but add complexity, add a brownout circuit
that disables the MOSFETs when the power supply is below say 8
or 10V.

Brent Brown
Electronic Design Solutions
16 English Street
Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile/text: 025 334 069
eMail:  brent.brown@clear.net.nz

--
http://www.piclist.com hint: The list server can filter out subtopics
(like ads or off topics) for you. See http://www.piclist.com/#topics