Re: Wow! Thanks.
jeremybb said:
I will definetely let you know how it turns out. I am too much of a poser to understand the circuit but for the most part I can follow it enough to build it. A couple of quick questions though:
When you say I can change C5, my guess is that it is the draining of this cap through R8 that causes the reset. This suggests to me that I should increase C5 if the circuit is still catching the tail end of the power-on buzz.
I'm new to MOSFETs. Looking at the digikey product sheet for the one you have given it's not clear to me which lead will be which. It appears that two fo the four pins are tied together and this is the drain. Will the other leads be marked or is there a convention?
Are there any other constraints on the type of capacitor other than the voltage ratings? Is a typical electrolytic OK?
Thanks again, I'll be making my digikey order ASAP.
With power off, C5 starts out with zero volts across it. When you turn on power, the junction of C5 and R7 jumps to +12V. C5 slowly charges through R7, causing the reset node to eventually reach GND potential. This process holds the two flip-flops reset for several seconds. The reset switch will quickly discharge the cap, pulling reset back up to +12V. Yes, making C5 larger will hold the flip-flops reset for a longer period of time.
If you expect the power to be cycling rapidly (<1 minute ON or OFF), you should connect a 1N4001 diode across R7, anode to GND.
Here is the
package info. Source and drain are indicated on the
datasheet. On my schematic, the top terminal is the source, the bottom terminal is the drain, and, of course, the left terminal is the gate.
I think Digikey has a minimum order. Mouser has a lot of Zetex parts that should work, but they all seem to be surface mount (which may be OK with you). The last time I checked, Mouser didn't have a minimum order. If you want further help picking a MOSFET, let me know.