MOSFET or Bipolar for shunt regulators?

GregH2 · 6th March 2011, 06:21 AM

Hi All,

I am trying to design a simple shunt regulator to supply a small class a JFET preamp. It will be required to supply a maximum of about 15mA. I was intending to use a design similar to the one shown here in figure 3:

Minimalist Discrete Hi-Fi Preamp

I am interested to know if a fet or bipolar transistor (as shown) is better to use for this application? Which one has a lower ouput impedance? I have heard that the fet will make a more stable supply as the current draw through the zener will be more consistent if used in this circuit, but I suspect the bipolar version will have a lower output impedance. What are your thoughts?

Your advice is appreciated.

Greg,

Elvee · 6th March 2011, 06:55 AM

It is true that the base current of a bipolar will vary according to the shunted current, but this variation can be made negligible by choosing a suitable B-E resistor.

On the other hand , a MOS has no gate current, but it does have a much lower transconductance, which means a poorer regulation, and variations in the zener current caused by the variations across the G-S resistor.

GregH2 · 6th March 2011, 11:13 AM

Ok thanks Elvee. I'll stick with the bipolar for this supply.

Greg.

davidsrsb · 6th March 2011, 11:24 AM

At low voltages, as I presume this project is, bipolar is best.
Somewhere in the 50 to 100V range mosfets become better as high voltage bipolars have low Hfe and SOA limitations

apexaudio · 6th March 2011, 07:42 PM

I suggest to use this shunt regulator with bipolars, schematic and pcb is here:
A-class Preamp PSU
Regards

6th March 2011, 06:21 AM	#1
GregH2 diyAudio Member Join Date: Oct 2009	MOSFET or Bipolar for shunt regulators? Hi All, I am trying to design a simple shunt regulator to supply a small class a JFET preamp. It will be required to supply a maximum of about 15mA. I was intending to use a design similar to the one shown here in figure 3: Minimalist Discrete Hi-Fi Preamp I am interested to know if a fet or bipolar transistor (as shown) is better to use for this application? Which one has a lower ouput impedance? I have heard that the fet will make a more stable supply as the current draw through the zener will be more consistent if used in this circuit, but I suspect the bipolar version will have a lower output impedance. What are your thoughts? Your advice is appreciated. Greg,

6th March 2011, 07:42 PM	#5
apexaudio diyAudio Member Join Date: Feb 2010 Location: Serbia	I suggest to use this shunt regulator with bipolars, schematic and pcb is here: A-class Preamp PSU Regards __________________ http://www.facebook.com/APEXaudio.MileSlakovic

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6th March 2011, 06:55 AM	#2
Elvee diyAudio Member Join Date: Sep 2006	It is true that the base current of a bipolar will vary according to the shunted current, but this variation can be made negligible by choosing a suitable B-E resistor. On the other hand , a MOS has no gate current, but it does have a much lower transconductance, which means a poorer regulation, and variations in the zener current caused by the variations across the G-S resistor.

6th March 2011, 11:13 AM	#3
GregH2 diyAudio Member Join Date: Oct 2009	Ok thanks Elvee. I'll stick with the bipolar for this supply. Greg.

6th March 2011, 11:24 AM	#4
davidsrsb diyAudio Member Join Date: Dec 2005 Location: Kuala Lumpur	At low voltages, as I presume this project is, bipolar is best. Somewhere in the 50 to 100V range mosfets become better as high voltage bipolars have low Hfe and SOA limitations