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Old 9th August 2009, 07:56 PM   #2141
RCruz is offline RCruz  Switzerland
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I am strugling with heatsinks....

Would this one be suitable for the shunt ? H S MARSTON - 05DN-00500-A-200 - HEAT SINK, 4.5C/W http://pt.farnell.com/jsp/search/pro...jsp?sku=414189

Or two of those (one per mosfet) AAVID THERMALLOY - 6398BG - HEAT SINK, TO-220/218, 4.4C/W

http://pt.farnell.com/jsp/search/pro...sp?sku=1213473

Ricardo
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Old 9th August 2009, 08:58 PM   #2142
Salas is offline Salas  Greece
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I prefer the second one per Mosfet, and R1=10R.
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Old 9th August 2009, 09:12 PM   #2143
RCruz is offline RCruz  Switzerland
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Thank you...

I believe I will have to review the shunt pcb layout... because of the fins in the heatsinks.

Ricardo

PS
I have R1 = 14r 1w
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Old 9th August 2009, 09:17 PM   #2144
Salas is offline Salas  Greece
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If its a big problem, use the first option, with 14R is surely enough.
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Old 10th August 2009, 12:45 PM   #2145
RCruz is offline RCruz  Switzerland
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I did a new layout so I can fit the individual heatsinks....

I calculated a led string dropout of 6,39v, using 14r I have ICCS with load = 174 mA

Using R1 = 10, I get 259mA... is this viable ?

Ricardo
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Old 10th August 2009, 12:47 PM   #2146
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Default PCB

Hi Jaap,


I can not PM you, your e-mail button is disabled.
Please contact me regarding your PCB's for the SALAS RIAA.

Thanks in advance.

Best regards,


Audiofanatic
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Old 10th August 2009, 01:37 PM   #2147
Salas is offline Salas  Greece
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Quote:
Originally posted by RCruz
I did a new layout so I can fit the individual heatsinks....

I calculated a led string dropout of 6,39v, using 14r I have ICCS with load = 174 mA

Using R1 = 10, I get 259mA... is this viable ?

Ricardo
Depends on the Vgs of the exact part, but with such Leds I would surely use the 14R so not to overshoot 200mA.
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Old 11th August 2009, 12:06 AM   #2148
RCruz is offline RCruz  Switzerland
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The green leds I used presented an average of 2,1v drop.

I now found some smaller yellow leds with 1,9 drop. Using 3 leds I get 5.7v... if my calculator is correct, admiting Vgs 3.4v, i can use R1=10r and get away with 190mA ICSS (230-40)... am I right ?

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Old 11th August 2009, 02:40 AM   #2149
Salas is offline Salas  Greece
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Yes if Vgs will be like that. You just measure the drop across the resistor in the end, and if its non usefully excessive, you make it higher R. I prefer the yellows slightly for best noise also. Its that the greens are easier to predict for those they don't match them.
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Old 11th August 2009, 01:54 PM   #2150
RCruz is offline RCruz  Switzerland
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I will match the leds before use so I will know vdrop in advance.

Using your formulae: ICCS=(Vdrop-VGS)/R1 I can find R1.

After building the shunt I will measure R1 drop and using ohmlaw I will verify the current.

Looking very good already.

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