I'm curious if any of these or other similar boards are still in the wild? Thanks.
MOSFET B+ reducer
Moderators: pompeiisneaks, Colossal
Re: MOSFET B+ reducer
Just plug it in, man.
-
- Posts: 4576
- Joined: Fri Jan 24, 2014 3:01 pm
- Location: 1/3rd the way out one of the arms of the Milkyway.
Re: MOSFET B+ reducer
Sounds like it’s time for implementation of a Peltier device!
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
- dorrisant
- Posts: 2628
- Joined: Tue Sep 21, 2010 1:27 pm
- Location: Somewhere between a river and a cornfield
- Contact:
Re: MOSFET B+ reducer
I have more of these boards if needed.
"Education is what you're left with after you have forgotten what you have learned" - Enzo
Re: MOSFET B+ reducer
Sorry I'm replying to an old thread, but one could place several MOSFETs in parallel to lessen the power dissipation of each, correct? Like using pass-transistors with a linear regulator?
I know that MOSFETs of the same type won't be perfectly matched, but I've seen them used in parallel in power amplifiers without the different rds values causing balancing issues.
Seems that it could save spending big on a large power MOSFETs.
I know that MOSFETs of the same type won't be perfectly matched, but I've seen them used in parallel in power amplifiers without the different rds values causing balancing issues.
Seems that it could save spending big on a large power MOSFETs.
Re: MOSFET B+ reducer
Hello, I built the Aiken circuit using an IRFPE50 instead of the STW20NK50Z. I used the resistor values with a 36V zener.
https://www.vishay.com/docs/91248/91248.pdf
I ran it up to a low voltage just to test it and it has no effect on the B+ . This is in a repurposed Marshall JCM800 Lead, modern combo and I want to drop the B+ down by about 10-15% . I used new new parts.
It’s so simple but its acting like it is fully on and conducting. Any test ideas? Thoughts?
In the picture, the zener was clipped to the terminal strip. There is a jumper between the lugs.
***PROBLEM SOLVED. I WAS USING THE WRONG CENTRE TAP. SEEMS TO BE PERFORMING PROPERLY NOW UNDER LOW V. TESTING***
https://www.vishay.com/docs/91248/91248.pdf
I ran it up to a low voltage just to test it and it has no effect on the B+ . This is in a repurposed Marshall JCM800 Lead, modern combo and I want to drop the B+ down by about 10-15% . I used new new parts.
It’s so simple but its acting like it is fully on and conducting. Any test ideas? Thoughts?
In the picture, the zener was clipped to the terminal strip. There is a jumper between the lugs.
***PROBLEM SOLVED. I WAS USING THE WRONG CENTRE TAP. SEEMS TO BE PERFORMING PROPERLY NOW UNDER LOW V. TESTING***
You do not have the required permissions to view the files attached to this post.
Re: MOSFET B+ reducer
I know this is an old thread, but I'm trying to figure out how to connect the pre filter cap in this instance, since my particular zener seems to be behaving oddly and having current spikes as the power tubes heat up.R.G. wrote: ↑Thu Feb 12, 2015 5:15 am The better way to do that is to have a pre-filter cap, which has a + terminal to the rectifiers and to the actual first grounded filter cap.
The negative side of this first pre-filter cap goes to the rectifier negatives, and the amplified zener goes between that point and the actual circuit ground on the first filter cap. This lets the zener setup handle the average current, not the rectifier pulses and helps keep it cooler.
You do not have the required permissions to view the files attached to this post.
Re: MOSFET B+ reducer
You basically got it right except for the components around the MOSFET.
You do not have the required permissions to view the files attached to this post.
Re: MOSFET B+ reducer
Another question, if I were to connect two of these in series, each with half of the zener voltage of the original zener amplifier, this would share the power dissipation between both, no? An amp that I"m building right now keeps destroying my irfp460's using the chassis as a heatsink. I don't want to stick a tiny fan in there or make room for a large heatsink, so it would be nice if I could share the load between two devices.
Re: MOSFET B+ reducer
Something like this?
You do not have the required permissions to view the files attached to this post.
- pompeiisneaks
- Site Admin
- Posts: 4222
- Joined: Sat Jan 14, 2017 4:36 pm
- Location: Washington State, USA
- Contact:
Re: MOSFET B+ reducer
Spot on. This circuit doesn't need series MOSFET. It would be unlikely to need paralleled ones, but if it did, you'd have to worry about paralleling them, not stacking them.
The voltage rating of the MOSFETs just have to be "big enough". In the ground to CT position, this is never more than the peak of the AC voltage from CT to one side of the AC winding. That only happens if you want to turn the MOSFET off for some reason. In a setup to just subtract voltage from the B+, the voltage won't ever get over maybe double the volts you're trying to subtract. 200V or so is likely to be overkill. An IRF820 or its bigger brother the 840 is probably fine.
- maint_tech
- Posts: 28
- Joined: Tue Feb 20, 2018 2:58 am
Re: MOSFET B+ reducer
It would seem that putting them in series would reduce the power dissipation per device.
With two, each would drop half the volts and would each have the same current thru them so half the power, no?
With two, each would drop half the volts and would each have the same current thru them so half the power, no?
- pompeiisneaks
- Site Admin
- Posts: 4222
- Joined: Sat Jan 14, 2017 4:36 pm
- Location: Washington State, USA
- Contact:
Re: MOSFET B+ reducer
This article explains it I think pretty well:maint_tech wrote: ↑Fri Jan 20, 2023 5:08 pm It would seem that putting them in series would reduce the power dissipation per device.
With two, each would drop half the volts and would each have the same current thru them so half the power, no?
https://resources.altium.com/p/should-y ... ets-series
~Phil
tUber Nerd!
Re: MOSFET B+ reducer
Yes, it would. So would paralleling two of them, as it's the same voltage and half the current. Parallel MOSFETs are far easier to bias than a series string, IMHO. Just apply the same bias voltage to both.maint_tech wrote: ↑Fri Jan 20, 2023 5:08 pm It would seem that putting them in series would reduce the power dissipation per device.
With two, each would drop half the volts and would each have the same current thru them so half the power, no?
Re: MOSFET B+ reducer
My reason for having them in series is based off of merlin blencowes book on power supply design, specifically the section on the zener cascode.R.G. wrote: ↑Fri Jan 20, 2023 11:11 pmYes, it would. So would paralleling two of them, as it's the same voltage and half the current. Parallel MOSFETs are far easier to bias than a series string, IMHO. Just apply the same bias voltage to both.maint_tech wrote: ↑Fri Jan 20, 2023 5:08 pm It would seem that putting them in series would reduce the power dissipation per device.
With two, each would drop half the volts and would each have the same current thru them so half the power, no?
Heres a picture of it. Not sure if this design has a strict advantage over the parallel method, but the biasing seems straightforward. However, in this instance, would RS be the winding resistance of the transformer?
You do not have the required permissions to view the files attached to this post.