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Juma's Easy-Peasy Capacitance Multiplier
Juma's Easy-Peasy Capacitance Multiplier
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Old 13th October 2016, 06:53 PM   #21
Mooly is offline Mooly  United Kingdom
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Juma's Easy-Peasy Capacitance Multiplier
As Mark said really, a logic level low Rds device. This is the PSMN1R025YLD.

Looks good

Ripple at 1.7 amps steady state and pulsed 1.7 amp.

I've attached the spice file set up for the IRF240 which will run straight off in LT IV. The PSMN1R025YLD FET model might only be available in LT XVII
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Old 13th October 2016, 07:16 PM   #22
xrk971 is offline xrk971  United States
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Juma's Easy-Peasy Capacitance Multiplier
That PSMN1R025YLD looks like an awesome FET, however it has 25v limit which sort of limits it to 15v class A head amps or maybe preamps. A 25v typical class A supply might be too much. I like the 890 microOhm Rs_on, and continuous 100A!

This could be a very useful little FET to make a cap multiplier for my F5 head amp.

http://datasheet.octopart.com/PSMN1R...t-62336464.pdf

Is the input capacitance too large to use it as an audio OPS?

Last edited by xrk971; 13th October 2016 at 07:31 PM.
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Old 13th October 2016, 07:49 PM   #23
Mooly is offline Mooly  United Kingdom
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Juma's Easy-Peasy Capacitance Multiplier
The capacitance shouldn't be much of a problem at audio frequencies, and these things are meant to be used at high speeds in DC/DC convertors and so on.

Wouldn't like to say just how suitable it would be overall though but it could make for an interesting project. Maybe there are other higher voltage devices available in a similar series of parts.
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Old 13th October 2016, 08:00 PM   #24
xrk971 is offline xrk971  United States
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Juma's Easy-Peasy Capacitance Multiplier
For $1.70ea I might buy a few to play with, if not for cap multiplier, then maybe as OPS. The high capacitance will require a low impedance driver though.
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Old 13th October 2016, 08:16 PM   #25
Mooly is offline Mooly  United Kingdom
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Juma's Easy-Peasy Capacitance Multiplier
The driver has to be able to both charge and discharge the gate capacitance and so a few milliamps need to be available.
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Old 13th October 2016, 08:23 PM   #26
xrk971 is offline xrk971  United States
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Juma's Easy-Peasy Capacitance Multiplier
Quote:
Originally Posted by Mooly View Post
The driver has to be able to both charge and discharge the gate capacitance and so a few milliamps need to be available.
Perhaps something like this could be done for a small amp to drive headphones but replace the IRF610 with this unit (assuming there is a complementary p-channel)?

Another Juma creation:
Click the image to open in full size.
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Old 13th October 2016, 10:44 PM   #27
jkuetemann is offline jkuetemann  Canada
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Quote:
Originally Posted by xrk971 View Post
Thanks, Jason. I don't know enough to understand why it has so many transistors though - are there added benefits like lower dripeout voltage or better ripple control vs the Juma "Easy Peasy" circuit? I submit, the Juma circuit is dead simple, still.
You grabbed the schematic from post #1, not the final version in post #65. You won't like it though since it is more complicated yet again .

Lower 'drop-out' is possible with normal Vgs devices since they operate common source rather than as a follower. Two pole filtering reduces ripple a fair bit over the usual single pole.

Juma's arrangement is a pretty classic implementation.
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Old 14th October 2016, 07:47 AM   #28
Mooly is offline Mooly  United Kingdom
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Juma's Easy-Peasy Capacitance Multiplier
Quote:
Originally Posted by xrk971 View Post
Perhaps something like this could be done for a small amp to drive headphones but replace the IRF610 with this unit (assuming there is a complementary p-channel)?
I don't see why not although as always, it would be advisable to do some real measurements and weigh up the pros and cons compared to more traditional devices.
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Old 14th October 2016, 08:21 AM   #29
xrk971 is offline xrk971  United States
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Juma's Easy-Peasy Capacitance Multiplier
I just ran some sims in TINA and see that this cap multiplier can really save one some money with the cost of big caps. For example, if I simply removed my CRC consisting of a 33mF//0.12R//33mF and replaced it with a single 33mF and then couple that to the cap multiplier - it still works well with probably 100uV ripple with a 2amp steady load. So right there, one can eliminate qnty 4 x 33mF caps in a class A PSU. That's a significant savings in money and volume needed inside the case.
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Old 14th October 2016, 08:50 AM   #30
sgrossklass is offline sgrossklass  Germany
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Guess why people like cap multipliers in this application...

Just be careful not to optimize dropout voltage too much, or otherwise it might drop out of regulation given high input ripple. Less of a problem with MOSFETs, more so with BJTs.
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