Jim, Thanks, and see notes in flow. --- On Sat, 10/15/11, Jim Shorney <[email protected]> wrote:
> From: Jim Shorney <[email protected]> > Subject: Re: [Drakelist] PS-7 (12 volt) power supply questions > To: "[email protected]" <[email protected]> > Date: Saturday, October 15, 2011, 2:53 PM > On Sat, 15 Oct 2011 11:18:48 -0700 > (PDT), Ron wrote: > > >1) Based on pg 126 of the book "A Family Affair - The R > L Drake Story", I see that I should set the current limit > trip for ~31 Amp. Does anyone disagree with this > figure? > > That matches GW4ALG's notes: http://www.alg.myzen.co.uk/radio/tr7/mods.htm#16 > I should have mentioned that pg 126 is quoting Steve Rawling, GW4ALG. I was kind of looking for "second source" just to be sure. > >2) Can anyone explain to me how the 2N4402 > bias/conduction works for over current shutdown of the > LM1723? > > I haven't studied it that much, but here's how it looks > like it will work. The > current sense part of the 723 senses the voltage across the > emitter ballast of > one of the pass transistors. When this goes too high, the > internal transistor > at pins 3 to 13 goes low impedance, which starves the > output circuit of the 723 > for bias and decreases the output voltage. Pin 4 will > always be at a lower > voltage than pin 3, since it is farther down on the voltage > divider, so when > pin 4 falls below the reference voltage on pin 6 far > enough, the 4402 (PNP) > fires and kills power to the 723 through the 2N3566. > > I haven't worked it out completely with real world > voltages, so I'm guessing a > little. I could be missing something somewhere. > Just reading what you say and briefly looking back at the PS7 schematic this seems to make the circuit make sense. Thanks. > > 73 > > -Jim > > > -- > Ham Radio NU0C > Lincoln, Nebraska, U.S.S.A. > TR7/RV7/R7A/L7, TR6/RV6, T4XC/R4C/L4B, NCL2000, SB104A, > R390A, GT550A/RV550A, HyGain 3750, IBM PS/2 - all vintage, > all the time! > > "Give a man a URL, and he will learn for an hour; teach him > to Google, and he will learn for a lifetime." > > HyGain 3750 User's Group - http://groups.yahoo.com/group/HyGain_3750/ > http://incolor.inetnebr.com/jshorney > http://www.nebraskaghosts.org > > > > _______________________________________________ > Drakelist mailing list > [email protected] > http://mailman.zerobeat.net/mailman/listinfo/drakelist > _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist
