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diyAudio Chief Moderator

Join Date: Oct 2002
Location: Athens-Greece
Quote:
 Originally Posted by roger57 Salas, Still a bit curious as to why the math doesn't work out here: I measured the exact drop across the green LED's (2.07V each) Now the drop across the 4.7R is 2.51V (2.07 x4) = 8.28; 8.28-2.51 = 5.77V The curve indicates for Vgs at 5.7V with Ta=25C to be about 1A. (Clearly; more to the numbers that this calculation?) It's interesting to note the spreadsheet indicates a total current of 650mA output using a 4.7R resistor, for 5.3V and 450mA load. All circuit parts as recommended. Can you provide some insight? How to account for this difference? I can understand variations of perhaps 10% due to parts, but it seems a bit much in this case. Thanks.
If you could curve trace that individual MOSFET taking into account the VDS (equals vin-vout in this case) to test at, and the junction temperature Tj in your particular set up, it would surely show the deviation parameters that make sense.
Making the basic VRset/Rset verification first when assembly is over with a light load resistor, shows the truth without all the above.
Tj in particular can play a big part when targeting over 400mA for an IRF9610. Beyond batch deviations etc. See how it can vary for 0.6A between extreme temp cases at -6V VGS as an example.
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diyAudio Member

Join Date: Sep 2006
Location: Edmonton, Alberta
Quote:
 Originally Posted by Salas If you could curve trace that individual MOSFET taking into account the VDS (equals vin-vout in this case) to test at, and the junction temperature Tj in your particular set up, it would surely show the deviation parameters that make sense. Making the basic VRset/Rset verification first when assembly is over with a light load resistor, shows the truth without all the above. Tj in particular can play a big part when targeting over 400mA for an IRF9610. Beyond batch deviations etc. See how it can vary for 0.6A between extreme temp cases at -6V VGS as an example.
Thanks Salas; appreciate the insight.

diyAudio Member

Join Date: Oct 2008
Bummer, no go. LEDs don't light up still, and I measure 1.5v on the outputs. I do notice some voltage drop on the inputs, from 15 down to ~9 or so.

I'm just going to build another board, as I started this one a way back and only recently got back to it so maybe I messed something up along the way.

R101: 12ohm
R103: 2Kohm
R105: 1K trimmer

Quote:
 Originally Posted by yammy1688 I didn't realize the unpopulated LEDs needed to be jumpered. What resistor value should I select for the dummy load? I'm looking to simulate 90ma, am not quite making sense of the calculation. I end up with 1.3k, but that seems way too high compared others. I think 30something Ohm seems more appropriate? I'll try that tonight. Thanks!
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diyAudio Member

Join Date: Sep 2009
Location: Catalonia new Europe state
Quote:
 Originally Posted by yammy1688 Bummer, no go. LEDs don't light up still, and I measure 1.5v on the outputs. I do notice some voltage drop on the inputs, from 15 down to ~9 or so. I'm just going to build another board, as I started this one a way back and only recently got back to it so maybe I messed something up along the way. R101: 12ohm R103: 2Kohm R105: 1K trimmer
If you start a new reg first to complete the pcb populate & check only the CCS, if OK continue to complete the rest of the board.

 11th July 2013, 11:49 AM #2305 diyAudio Chief Moderator     Join Date: Oct 2002 Location: Athens-Greece It can only be a wrong orientation for an LED or a dead one. I would check that each one can light up in the PCB noted direction with a 9V battery or a capable DMM in diode mode.
 11th July 2013, 05:19 PM #2306 diyAudio Member   Join Date: Jul 2011 Location: Birmingham, UK Hi, hopefully someone can point me in the right direction. Ive built 3 salas shunts v1.1, one BJT based for buffalo dac which works perfectly. The other two IRF base shunts not working as desired: looking for circa 290ma for legato IV inc. 100ma shunt @ 12-15v. Transformer is 2x15v 30va. Measured dc after shunt rectifier as ~20.5v] Both IRF have same problem - With 75R dummy load; V can be set to 12-15v seems ok but with real load; legato 3.1 IV stage, no red leds lit, output V drop to near 2v. Across R201/301 (8r2 /3w) measures 2.5v. So. Measuring the negative shunt current out to dummy load (75r) I get 144ma at 13v (too low to power the legato and hence no leds and V drop?) and also this rises with increase in V to 169ma at 14.5v. Can anything be concluded from this? I have also tested with CCS separated, shorted current out is 312ma 2r load 310ma 8r2 load 302ma 75r load 133ma
 11th July 2013, 07:54 PM #2307 diyAudio Chief Moderator     Join Date: Oct 2002 Location: Athens-Greece 2.5V/8R2=305mA. That is their CCS. 312mA shorted measurement ties with that by only 2.3% experimental error. 20-30mA from that should go to the reg itself as a minimum. If legato IV draws about 290mA then the regs are almost choked. Use 5.6R 3W-5W. Set Vo so to have 7V DCVin-Vout minimum. It helps the CCS rigidity.
 11th July 2013, 08:38 PM #2308 diyAudio Member   Join Date: Jul 2011 Location: Birmingham, UK Thanks for the reply Salas. Apologies - to be clearer in description: my legato requires +190ma and -205ma (based on twisted pear placid BP HD measurements). So 290ma output would allow 85-100ma of healthy shunt. Ive tried with 12v 13v 14v etc for output, it seems to not make much difference, except for increasing current with V !? With the load over a certain amount - I guess somewhere nearer to 75r, the current drops off below functioning output. 12V out should allow decent V drop from 20.5vdc in? but from measuring, it shows the lowest current (75r load 133ma). Last edited by lucaslucas; 11th July 2013 at 08:41 PM.
 12th July 2013, 02:37 AM #2309 diyAudio Chief Moderator     Join Date: Oct 2002 Location: Athens-Greece That's weird then. What value are the gate stoppers? Can you confirm that?

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