The simplistic Salas low voltage shunt regulator - Page 462

Tham · 8th November 2011, 09:10 AM

Hi Salas,

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

Rgds

Salas · 8th November 2011, 11:24 AM

Are you talking the bjt cascode or the jfet cascode type ccs circuit?

Tham · 8th November 2011, 11:30 AM

Hi Salas,

The JFET circuit.

Salas · 8th November 2011, 11:40 AM

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.

Tham · 8th November 2011, 12:52 PM

Hi Salas,

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

Thanks.

Salas · 8th November 2011, 01:02 PM

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.

Tham · 8th November 2011, 02:29 PM

Hi Salas,

Noted. I do not have any BC546 now. Can I substitute it with say BD139?

Salas · 8th November 2011, 02:47 PM

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.

studiostevus · 8th November 2011, 06:38 PM

Salas, what is the reason why you propose a 100R between output of the reg and an IC?

Why 100R?

Salas · 8th November 2011, 07:05 PM

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.

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read


	Please consider donating to help us continue to serve you. Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving

8th November 2011, 09:10 AM	#4611
Tham diyAudio Member Join Date: Jun 2006	Hi Salas, Can Vo be adjusted to 24V using V1.2R Low curcuit on #3200? Rgds

8th November 2011, 11:24 AM	#4612
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	Are you talking the bjt cascode or the jfet cascode type ccs circuit?

8th November 2011, 11:30 AM	#4613
Tham diyAudio Member Join Date: Jun 2006	Hi Salas, The JFET circuit.

8th November 2011, 11:40 AM	#4614
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	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.

8th November 2011, 12:52 PM	#4615
Tham diyAudio Member Join Date: Jun 2006	Hi Salas, I will keep to the 22v max then. Will build another one using bjt cascode for higher Vout. Thanks.

8th November 2011, 01:02 PM	#4616
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	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.

8th November 2011, 02:29 PM	#4617
Tham diyAudio Member Join Date: Jun 2006	Hi Salas, Noted. I do not have any BC546 now. Can I substitute it with say BD139?

8th November 2011, 02:47 PM	#4618
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	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.

8th November 2011, 06:38 PM	#4619
studiostevus diyAudio Member Join Date: Oct 2009 Location: Brunei	Salas, what is the reason why you propose a 100R between output of the reg and an IC? Why 100R?

8th November 2011, 07:05 PM	#4620
Salas diyAudio Chief Moderator Join Date: Oct 2002 Location: Athens-Greece	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.