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Old 28th April 2012, 02:40 PM   #1081
AndrewT is offline AndrewT  Scotland
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Bill,
I disagree with Salas.
Vdrop across the CCS resistor does decrease slightly as the CCS resistor is lowered in value. But it should ONLY drop by the increase in Vgs of the CCS FET.

Your massively dropping resistor voltage indicates you have strangled your shunt regulator.
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Old 28th April 2012, 02:50 PM   #1082
Salas is offline Salas  Greece
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With 9610 in BIB given the low current of the 3 LEDS CCS giving conservative Vf, VR1 can easily hover around 1V if pushing the current setting. Not weird.
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Old 28th April 2012, 02:51 PM   #1083
AndrewT is offline AndrewT  Scotland
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Ask him what the resistor Vdrop and FET Vgs and in/out Vdrop are with the different resistor values fitted?
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Old 28th April 2012, 02:54 PM   #1084
Salas is offline Salas  Greece
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When he will give data of AC input voltage and his current setting derived from his R1 value we will know if its due to normal reasons or strangled. Two possible scenarios, usually the 1st.
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Old 28th April 2012, 02:56 PM   #1085
AndrewT is offline AndrewT  Scotland
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Quote:
As I lower the CCS resistor value to increase the current, I notice that the voltage across the CCS resistor drops to a lower value as expected. I currently have 1.1 volts
tells me he has strangled the shunt regulator.
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Old 28th April 2012, 02:57 PM   #1086
Salas is offline Salas  Greece
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Don't bet on it before data. It might be or it might not.
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Old 28th April 2012, 05:37 PM   #1087
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Thanks for the answers. I did a few measurements:

V across CCS resistor = 1.20
CCS resistor = 4.2 ohms
CCS current = 284mA
Vgs of CCS Tr = 4.55
Voltage across 3 green LED's = 5.75
Current through 3 green LED's = 2.7mA (27mV across R108 which is 10 ohms)
DC Input Voltage after all R/C filtering = 22.3 V
DC Output Voltage = 14.8 V

I think that all is fine. I am using the regulator for the active crossover to my Orion speakers. I need the modify the crossover to add a notch filter and want to increase to current of the regulator while I have the crossover disassembled. I have plenty of heatsink capacity and transformer reserve current. While I work on the crossover it will be easy to modify the regulator. So the question is do I go the easy route and lower the CCS resistor value (add another resistor in parallel) or should I be more radical and add an additional LED to my string of 3.
Then I would reset the resistor value of the CCS resistor to around 7.5 ohms assuming a voltage drop of 3.1V across the CCS resistor yielding 410mA. If the input voltage drops below 22V I can easily change the input R/C filter to adjust that.
I guess that my real question is am I compromising the regulators performance by having just over 1V across the CCS resistor.
Thanks guys for the advice.
Bill
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Old 28th April 2012, 05:43 PM   #1088
AndrewT is offline AndrewT  Scotland
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How do the numbers come out when you had the higher value CCS resistor?
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Old 28th April 2012, 06:04 PM   #1089
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I added a series resistor to bring my CCS resistor value up to 8.6 ohms.
The Vgs drops to 4.35V. The LED's have the same 5.75V. The CCS R (now 8.6ohms) has a 1.4V drop.
The input voltage has gone up a volt and 160mA of the CCS is not enough current to supply the load.
I'm out of time for today but plan to do the crossover mods tomorrow.
Thanks,
Bill
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Old 28th April 2012, 07:06 PM   #1090
Salas is offline Salas  Greece
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Quote:
Originally Posted by Billc View Post
I guess that my real question is am I compromising the regulators performance by having just over 1V across the CCS resistor.
Thanks guys for the advice.
Bill
No, you don't compromise it as long there is enough Vin-Vo. You just save on Rset dissipation.
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