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Old 17th May 2013, 03:58 PM   #2241
Salas is online now Salas  Greece
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How much voltage you got across the 1 Ohm? How much voltage input to the reg?
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Old 17th May 2013, 04:07 PM   #2242
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0.793V at 1 Ohm, 8.45AC input, output at 5.5V 600mA. Output drop when current higher than 600mA.

edit, max output current should be 800mA, not 600mA

Last edited by bigpandahk; 17th May 2013 at 04:14 PM.
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Old 17th May 2013, 04:19 PM   #2243
AndrewT is online now AndrewT  Scotland
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I think the CCS is getting starved.
The shunt then compensates by reducing the shunt current to try to keep the output voltage up.

You must get adequate voltage drop across the CCS to get proper CCS operation.
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Old 17th May 2013, 04:54 PM   #2244
Salas is online now Salas  Greece
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The sinking must be good for the CCS MOSFET at those currents also. Maybe an IRF9530 in place of the IRF9610 if the situation is too hot for given sinking at 1-1.2A setting. Looks like starving and TC shifting now. Circa 0.75R looks more appropriate to use now either as a single R101 or by piggyback of a 3.3R on the 1R. Check for possible ducking of input voltage while at work also. You can measure the rectified DC there:
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Old 17th May 2013, 05:03 PM   #2245
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Thanks Andrew and Salas.

Sink is big enough and it is not even warm.
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Old 17th May 2013, 05:10 PM   #2246
Salas is online now Salas  Greece
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But the CCS MOSFET conducts heat well to the sink? Is it too hot itself?
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Old 18th May 2013, 12:13 AM   #2247
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drawing 800mA for 10 minutes, the MOSFET temperature stable at 41 deg C.
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Old 18th May 2013, 01:07 AM   #2248
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Parallel a 3.3ohm to the 1 ohm but result is the the same. O/P drop when current exceed 800mA. Input voltage remain at 8.7Vdc till 900mA
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Old 18th May 2013, 01:28 AM   #2249
Salas is online now Salas  Greece
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It was at 600mA to start dropping before though. 8.7VDCin-5.5VDCout=3.2VDCdrop over the CCS. How many CCS Leds you use and what is the voltage from lowest one to ground?
And how much is going to be your max real load demand?
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Old 18th May 2013, 01:43 AM   #2250
Salas is online now Salas  Greece
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See this graph attached. Its the 9610's ID/VSD curves. If you want it pass ~1A it will need ~4.7VSD to maintain it. You got to add the R101 setting resistor's drop to that up to VinDC. If your Vin-Vout does not give you that margin it will start dropping from a lower draw. That is what Andrew wrote about too.
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