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Old 8th November 2011, 09:10 AM   #4611
Tham is offline Tham  Malaysia
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Hi Salas,

Can Vo be adjusted to 24V using V1.2R Low curcuit on #3200?

Rgds
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Old 8th November 2011, 11:24 AM   #4612
Salas is offline Salas  Greece
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Are you talking the bjt cascode or the jfet cascode type ccs circuit?
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Old 8th November 2011, 11:30 AM   #4613
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Hi Salas,

The JFET circuit.
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Old 8th November 2011, 11:40 AM   #4614
Salas is offline Salas  Greece
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You can give it 30V absolute max raw DC input and 24V out. The stop is the top cascode Jfet that has 25V max. By the time the input Mosfet drops there is about Vin-5V potential for the top Jfet. If you watch that or you got a higher max device it can go higher, no problemo. If you can find BF245C which is 30V device you could be safer for input max due to mains and trafo uncertainties regarding max raw dc input and distance to output for solid regulation.
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Old 8th November 2011, 12:52 PM   #4615
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Hi Salas,

I will keep to the 22v max then. Will build another one using bjt cascode for higher Vout.

Thanks.
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Old 8th November 2011, 01:02 PM   #4616
Salas is offline Salas  Greece
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Remember, only the top one to change. It should be twice the Vgs spec of K170 at least and give higher free IDSS than the K170 under it so to best cascode.
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Old 8th November 2011, 02:29 PM   #4617
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Hi Salas,

Noted. I do not have any BC546 now. Can I substitute it with say BD139?
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Old 8th November 2011, 02:47 PM   #4618
Salas is offline Salas  Greece
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I don't know if it can bring problems due to much larger Cob (output capacitance). Try it until having a fast low noise high hfe TO-92 to restore.
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Old 8th November 2011, 06:38 PM   #4619
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Salas, what is the reason why you propose a 100R between output of the reg and an IC?

Why 100R?
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Old 8th November 2011, 07:05 PM   #4620
Salas is offline Salas  Greece
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It buffers the termination not to change the OLG shape and bandwidth due to a shunting local decoupler, and that RC with just 100R does not drop too much itself. Lower value it starts interfacing too much.
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