MOSFET for capacitor multiplier

[Mercury99]

I plan to use the attached circuit from Menno van der veen's article on AudioXpress in the power supply of a single ended EL84 amp. The voltage after the rectifiers will be 320V. The current is around 100 mA max.

I found this MOSFET IPAN70R450P7S from Mouser. The datasheet link is here https://www.infineon.com/dgdl/Infin...N.pdf?fileId=5546d4625f2e26bc015f499adf55405f.

What are the specific requirements for the MOSFET in this circuit? Is there any concerns on using IPAN70R450P7S? Since this part has built-in protection diodes, do I still need Z3? What will be the voltage drop across the circuit?

 

[v4lve lover]

L2 series is better, in therms of power handling.


Requirements are 1: very old mosfet with a big die, or 2: Linear FBSOA optimized mosfet.


Modern switching mosfets just wont survive.

 

[piano3]

Why won't switching mosfet survive? For instance, STP11NK40Z.

I would definitely use a gate-source zener and a small series current limiting resistor.

 

[v4lve lover]

IXAN0068 is the IXYS application note that explains this better, IXY's L2 optimized parts are much better at surviving DC operations as found in a cap follower.

 

[zdenoeddie]

If you want really multiplier, you have to use bipolar.

 

[ArcticBrew]

Thanks for the comment zdenoeddie. It made me do some research.

Rod Elliot provides a good explanation of the pros and cons for bipolar vs mosfet capacitance multipliers.

Capacitance Multiplier Power Supply Filter

I have been using a mosfet ripple filter and regulator for an SE Amp prototype that operates at 500 volts and 100ma per tube. I am quite pleased with the result. However, after reading this article I will mock up a bipolar version and compare them.

Steve

 

[Mercury99]

zdenoeddie, I am not chasing a real multiplier. I just want something that works.

If bipolar is better, why majority tube amps use MOSFET? I have yet seen one uses bipolar. Cost should not be an issue for DIY people.

 

[zdenoeddie]

A capacitance multiplier doesn't have to use bipolar transistors, but they will usually be the easiest option. The ready availability of good complements (NPN and PNP), low prices and ease of use mean that most people will use this option. However, a MOSFET version may be attractive in some cases, but initial testing (by simulation) indicates that transient performance is very poor - much worse than a circuit using otherwise identical values for passive parts but with bipolar transistors.

This is the reason.
I tested it on my headamp - MOSFet vs bipolar, and yes, there is huge difference.

 

[6A3sUMMER]

Capacitor Multipliers are often mis-understood.

A capacitor multiplier causes the output to have lower capacitive reactance.
May be used as a sort of voltage regulator.

Just remember this, there is no charge stored in the output of a capacitance multiplier.
The charge is in the cap that feeds the capacitor multiplier.

If you need lots of current, you have to provide that current to the input capacitor first, and the input cap has to have enough capacitance to keep outputting current when there is no current coming from the rectifiers (quite a few degrees of each alternation).

If the first cap runs out of charge, no capacitance multiplier in the world will do any good.

 

[Osuka]

A BJT drops 0.55~0.60V, while the MOSFET will drop at least its Vgs which can be a few volt to many volts depending on the device selected. On high voltage rails, a few or dozen volts loss might not be problem for the fed circuit, but the dissipated power (dVxI) will be much higher when using a MOSFET.

 

[Mercury99]

zdenoeddie and others,

Would you mind to share any suggested replacement bipolars for TIP36 and BD139 that can stand 320V and 100 mA?

If you have a preferred schematic for bipolars, could you share that too?

 

[Mark Johnson]

TIP36 ---> MJE5731AG qty=1 price USD 1.36 at DigiKey

BD139 ---> ZTX458 qty=1 price USD 0.65 at DigiKey

BUT... please add two reverse VBE protection diodes, and also please add a non-infinite collector load resistor for the NPN. 3.3K would be a nice choice in my opinion.



_

 

[timgrindell]

Hi Mark,
How about a ST901 HV darlington?
tim

 

[Mark Johnson]

Tim, please use whichever components you like! It's YOUR opinion that matters, after all it's YOUR audio equipment put at-risk when you connect up a home built capacitance multiplier.

 

[Osuka]

Watch this very useful tutorial, all to the end, and you'll know all there is to know about it:
EEVBlog #1116 - How to Remove Power Supply Ripple - YouTube

 

[timgrindell]

Oh Mark,
do you have to be like that?
t

 

[longspeak]

I've used a IXTH30N60L2 for ~500V B+ capx

 

[timgrindell]

For the record; I have used a ST901 in a cap multiplier 2 or 3 years ago in the PS of a 3 watt "spud" amp with an UCL113.
Seems to have worked very well.
t

 

[EUVL]

The FDP12N60NZ is used in Jan Didden's T-Reg as pass device.
I can't see why it should not also fit the purpose here.
T-reg HV regulator | Linear Audio NL


Patrick

 

[Mercury99]

TIP36 ---> MJE5731AG qty=1 price USD 1.36 at DigiKey

BD139 ---> ZTX458 qty=1 price USD 0.65 at DigiKey

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I put together a LTspice simulation based on Mark's suggestion. Mark, please make sure the schematic below is accurate.

Attached are the startup behavior and filtering result. Very nice!