Had another go today.
Geek Pulse DAC draws 392ma on switch-on, 700ma + 3 secs, peaks at 930ma at + 9 secs, drops to 911ma at +11 secs and settles at 925ma after 2 minutes. Stable with SMPS 12V supply and also with basic LM317 12V supply.
Salas reg gives steady voltage with dummy loads of 619ma, 830ma, 1.004A and even 1.206A. Max temp of IRF9610 tab = 85°C and IRF9530 tab = 53°C. Ambient case temp = 35°C, so they're hot, but within spec.
Salas reg measurements with dummy load of 829ma;
Vout = 12.73
Vin = 20.6V
R101 = 0R33. 420Mv (5% resistor not measured)
R108 = 104.5mv
IRF9610 VGS = 5.942V
IRF9530 VGS = 3.7V
D106 + 105 drop = 3.59V
D102 > D104 drop = 6.35V
Q103 VDG = 0.6V
Q104 VCE = 9.1V
Q105 VDG = 3.668V
Salas connected to Pulse DAC drawing 925ma. (2 wire connection)
Vout = 7.46V
Vin = 20.6V
R101 = 0R33. 425Mv
R108 = 107mv
IRF9610 VGS = 5.9V
IRF9530 VGS = 3.82V
D106 + 105 drop = 3.39V
D102 > D104 drop = 6.34V
Q103 VDG = 0.536V
Q104 VCE = 3.69V
Q105 VDG = 3.8V
So everything seems to be working fine in isolation, it's just that the Salas and the Pulse won't play nice together! Hmmmm.
Geek Pulse DAC draws 392ma on switch-on, 700ma + 3 secs, peaks at 930ma at + 9 secs, drops to 911ma at +11 secs and settles at 925ma after 2 minutes. Stable with SMPS 12V supply and also with basic LM317 12V supply.
Salas reg gives steady voltage with dummy loads of 619ma, 830ma, 1.004A and even 1.206A. Max temp of IRF9610 tab = 85°C and IRF9530 tab = 53°C. Ambient case temp = 35°C, so they're hot, but within spec.
Salas reg measurements with dummy load of 829ma;
Vout = 12.73
Vin = 20.6V
R101 = 0R33. 420Mv (5% resistor not measured)
R108 = 104.5mv
IRF9610 VGS = 5.942V
IRF9530 VGS = 3.7V
D106 + 105 drop = 3.59V
D102 > D104 drop = 6.35V
Q103 VDG = 0.6V
Q104 VCE = 9.1V
Q105 VDG = 3.668V
Salas connected to Pulse DAC drawing 925ma. (2 wire connection)
Vout = 7.46V
Vin = 20.6V
R101 = 0R33. 425Mv
R108 = 107mv
IRF9610 VGS = 5.9V
IRF9530 VGS = 3.82V
D106 + 105 drop = 3.39V
D102 > D104 drop = 6.34V
Q103 VDG = 0.536V
Q104 VCE = 3.69V
Q105 VDG = 3.8V
So everything seems to be working fine in isolation, it's just that the Salas and the Pulse won't play nice together! Hmmmm.
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85C on the case's tab its not good because there is RthetaJC 6.4 and 9.6W on the 9610 MOSFET for 20V in 12V out = 8V across at 1.2A. That means 6.4x9.6=61C junction to case extra, so 85+61=146C for a 150C max rated part at the chip level. Lets not even talk about longevity. Try drop to 17V DC in with some power resistor dropper at the secondary and use 0.39R R101 if you have no way to sink it better. Or use a 9530. Slower but RthJC 1.7
As for the persisting Vout drop if you don't have an oscilloscope to see if it is some oscillation with elements on the client board since this is a high bandwidth reg let me know what you use for output termination on the reg as I can't see that section fully on the photos. I.e. is it film cap + small R or electrolytic and no R? I think its a gray film cap?
As for the persisting Vout drop if you don't have an oscilloscope to see if it is some oscillation with elements on the client board since this is a high bandwidth reg let me know what you use for output termination on the reg as I can't see that section fully on the photos. I.e. is it film cap + small R or electrolytic and no R? I think its a gray film cap?
Heatsink's pretty big, around 1.7 °C/W and the 9610's torqued to 0.4NM, so I'm stuck with that.
I'm using 15v secondaries but with our local mains at around 247v the tx puts out nearer 17v. I'll drop the AC in and get some different values for R101. I was aiming for 1100ma originally but now I've confirmed the DAC's draw at 925ma, I'll drop it to 1 amp. I'll see how that goes with the 9610 and if the temp's still high (and I can get the 12V into the DAC!!) I'll swap it out for the 9530.
Output's via 15uf film cap (KEMET R60DN51505030J) + 1R0. I'll dig the scope out as soon as I get chance and see what's happening.
Thanks for your help here. I appreciate your patience.
I'm using 15v secondaries but with our local mains at around 247v the tx puts out nearer 17v. I'll drop the AC in and get some different values for R101. I was aiming for 1100ma originally but now I've confirmed the DAC's draw at 925ma, I'll drop it to 1 amp. I'll see how that goes with the 9610 and if the temp's still high (and I can get the 12V into the DAC!!) I'll swap it out for the 9530.
Output's via 15uf film cap (KEMET R60DN51505030J) + 1R0. I'll dig the scope out as soon as I get chance and see what's happening.
Thanks for your help here. I appreciate your patience.
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Thanks Andrew. Understand the logic of what you're saying, but I logged the DAC current drawn from the smps supply for over an hour and didn't get above 925ma. That was under the same conditions that I'd had the DAC when fed by the Salas reg.
I've just re-measured current draw when the Salas reg was connected to the DAC. It peaked at 545.7ma and settled around 543ma. I only got 6V out this time so even V out is inconsistent? I'm convinced I'm giving the DAC as much juice as it needs.
As per Salas's advice, I'm going to change the output to electrolytic with a jumper and take it from there. Before that I'll check with the 'scope for any anomalies.
OK, now I've got a 47uf Blackgate at C104 and a jumper at R107, same result. Around 6.5V out. 'scope pics show a 71hz, 3v wave riding on the dc.
This is looking like a no-goer, unless it's worth increasing the value of C104? It's a shame really because the output into the dummy loads between 0.6-1.2A is rock steady, however it looks like the DAC may be causing the problem.
This is looking like a no-goer, unless it's worth increasing the value of C104? It's a shame really because the output into the dummy loads between 0.6-1.2A is rock steady, however it looks like the DAC may be causing the problem.
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To be fair I didn't check max current when I logged the current draw, I just took readings every second, so I'll check that first. I could have been unlucky not picking up a high reading.
I was a little perplexed by the 71hz!
The 9530 was going to be my next plan as I thought the 9610 might be running too hot, as you intimated. I'll up the current after the above.
Back to it!
I was a little perplexed by the 71hz!
The 9530 was going to be my next plan as I thought the 9610 might be running too hot, as you intimated. I'll up the current after the above.
Back to it!
Checked DAC max current draw and it's 988ma within first few seconds. Definitely settles out around 925ma.
Swapped the 9610 for the 9530 and got just over 12 volts. Perfect! BUT, noticed the temp of Q101 shooting up, so switched off. Switched on again whilst checking voltage across R101 (0R33) and got over 1.1V. Ooops, >3.3A! Q106 died before I could switch off.
So, I had a look at the transfer characteristics of the 9530 and I'm reckoning I should have changed R101 from 0R33 to ≥1R8.
No spare 9530's left so I'll get some ordered. May be worth getting some IRFP9240's to try in view of the heat issues.
I'm away until mid-week, so I'll order some parts, take a break and maybe find some inspiration!
Swapped the 9610 for the 9530 and got just over 12 volts. Perfect! BUT, noticed the temp of Q101 shooting up, so switched off. Switched on again whilst checking voltage across R101 (0R33) and got over 1.1V. Ooops, >3.3A! Q106 died before I could switch off.
So, I had a look at the transfer characteristics of the 9530 and I'm reckoning I should have changed R101 from 0R33 to ≥1R8.
No spare 9530's left so I'll get some ordered. May be worth getting some IRFP9240's to try in view of the heat issues.
I'm away until mid-week, so I'll order some parts, take a break and maybe find some inspiration!
Eventful, but you confirmed. Congrats. That is why I was worried about the internal temperature of the 9610 right from the start. It was thermally unstable already. Now only to find time and set it right regarding a sturdier MOSFET's Vgs and RthC for proper Rset in given sinking. As you already said. 
Update.
Replaced both 9530's to be on the safe side. I'm now using 2 white LED's which drop a total of 5.48V. Changed R101 to 1R0, paralleled with a 10R0 trimmer. Voltage after the bridge has been dropped from 20.6V to 17.8V. (1R8 in series with the secondaries.) Heat of Q101 9530 tab is now OK at around 34°C.
With 1.25A through R101, the 12V output is stable into a 10R0 dummy load. With total current increased to 2A the output remains stable.
With 1.25A into the DAC, output voltage won't go higher than 8.2V. So, increased total current to 2A, but the output voltage now maxes out around 4.7V and the voltage reference LED's dim? Same result with 4 and 2 wire output.
I'm out of ideas now, so I'm just going to accept that this won't work with the Pulse DAC and use the reg for something else.
Replaced both 9530's to be on the safe side. I'm now using 2 white LED's which drop a total of 5.48V. Changed R101 to 1R0, paralleled with a 10R0 trimmer. Voltage after the bridge has been dropped from 20.6V to 17.8V. (1R8 in series with the secondaries.) Heat of Q101 9530 tab is now OK at around 34°C.
With 1.25A through R101, the 12V output is stable into a 10R0 dummy load. With total current increased to 2A the output remains stable.
With 1.25A into the DAC, output voltage won't go higher than 8.2V. So, increased total current to 2A, but the output voltage now maxes out around 4.7V and the voltage reference LED's dim? Same result with 4 and 2 wire output.
I'm out of ideas now, so I'm just going to accept that this won't work with the Pulse DAC and use the reg for something else.
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Its the oscillation that makes for the erratic behavior. Something at the rails of the load is at odds with the specific wide bandwidth regulator. Maybe some decoupling scheme fights it. The ESR can make a difference restoring stability. Try 1R in series with the output capacitor. Remove the R107 jumper and try with the R there.