Nigel, There are 2 SCRs in the PS-7. One is the 40 Amp over voltage crowbar which you speak of. The other is a 2N5060 which ultimately drops the power off of the LM1723 and "turns off" the pass transistors when an over current "event" gets to a "knee" in its downward spiral. I believe that the idea is to prevent continual heating and eventual destruction of all the electronic components within the PS-7.
I have seen other LM1723 circuit "oscillate" in an over current situation. Goes from 13 V to 0 V and back again. Current of course follow the voltage. The Drake just go int a "locked down" kind of powered off state. 73, Ron WD8SBB --- On Sat, 10/15/11, Nigel A. Gunn, W8IFF/G8IFF <[email protected]> wrote: > From: Nigel A. Gunn, W8IFF/G8IFF <[email protected]> > Subject: Re: [Drakelist] Drakelist Digest, Vol 40, Issue 25 > To: [email protected] > Cc: [email protected] > Date: Saturday, October 15, 2011, 6:53 PM > It doesn't. > The SCR is for OVERVOLTAGE protection. > > > > > On 15/10/11 23:11, [email protected] > wrote: > > 2) Can anyone explain to me how the 2N4402 > bias/conduction works for over current shutdown of the > LM1723? > > > > I've been looking at the the LM1723 "circuit" and the > PS7 schematic. I cannot see how over current will > cause the 2N4402 to change states in order to fire the SCR. > > > > TNX es 73, > > > _______________________________________________ > Drakelist mailing list > [email protected] > http://mailman.zerobeat.net/mailman/listinfo/drakelist > _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist
