Author Topic: Mosfet reverse polarity, voltage drop down  (Read 618 times)

antonis

Re: Mosfet reverse polarity, voltage drop down
« Reply #20 on: April 26, 2020, 12:56:38 PM »
Ok to form an high pass filter, i have to put R2 after C3.

You're a bit confused about H/L pass filter items configuration.. :icon_wink:
(you may remove R2 wherever you wish but, as long as C3 remains a shunt cap you can't form a HPF..!!)

P.S.
High-pass filtering in power supply is a strictly forbidden action..!!
(I let you guess the reason for it..) :icon_wink:
hint: Power supply is (idealy) DC..
What is (or should be) DC frequency..??

P.S.
For current consuming circuits it should be a good idea to "split" positive supply rail (more than one V+) and place an individual LPF before each one...
(to keep low shunt cap value..)
I don't understand this last suggestion.

It's just current sharing suggestion.. :icon_wink:

e.g. feeding 4 CE BJT amps of total current comsumption of 40 mA say, (each one of 10mA), result into a voltage drop of 1.88V across a 47R resistor (the series one of a LPF..)
By splitting the above configuration to 4 individual LPFs, you lower each circuit voltage drop to less than 500mV while keeping series resistor value the same..
By keeping resistor value the same, you also keep cap value the same - the last action is what actually counts, from space & money point of view.. :icon_wink: 
« Last Edit: April 26, 2020, 01:33:10 PM by antonis »
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

baloubass

Re: Mosfet reverse polarity, voltage drop down
« Reply #21 on: April 26, 2020, 02:15:42 PM »
You're a bit confused about H/L pass filter items configuration.. :icon_wink:
(you may remove R2 wherever you wish but, as long as C3 remains a shunt cap you can't form a HPF..!!)
P.S.
High-pass filtering in power supply is a strictly forbidden action..!!
(I let you guess the reason for it..) :icon_wink:
hint: Power supply is (idealy) DC..
What is (or should be) DC frequency..??
Ok i understand to form a HPF i have to put the cap before the resistor and then the resistor go to ground not the cap.
And ok for the HPF in a dc power supply.

Does this schematic look good for you:



antonis

Re: Mosfet reverse polarity, voltage drop down
« Reply #22 on: April 26, 2020, 02:35:27 PM »
Hmmm..

For across 4R7 resistor voltage drop, it should be OK..
(about 270mV taking into account 57mA V+ current draw - 9.42-8.05/24)

From LPF cut-off frequency point of view, 51 Hz are marginally OK..
If you're OK with -9db attenuation at 102Hz (-3db cut-off plus -6db for octave up)  it's also OK with me..
(just take into account that 100Hz is the rectified mains supply in Europe..)
470μF for C1 & C2 should lower cut-off frequency to about 36Hz with no space/cost burden..
« Last Edit: April 26, 2020, 02:57:35 PM by antonis »
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

baloubass

Re: Mosfet reverse polarity, voltage drop down
« Reply #23 on: April 26, 2020, 04:15:40 PM »
Hmmm..

For across 4R7 resistor voltage drop, it should be OK..
(about 270mV taking into account 57mA V+ current draw - 9.42-8.05/24)

From LPF cut-off frequency point of view, 51 Hz are marginally OK..
If you're OK with -9db attenuation at 102Hz (-3db cut-off plus -6db for octave up)  it's also OK with me..
(just take into account that 100Hz is the rectified mains supply in Europe..)
470μF for C1 & C2 should lower cut-off frequency to about 36Hz with no space/cost burden..
Ok thank you so much for your answer, you was really helpfull about the understanding what i do.
i think i will go with 470uf due to the space in the box. If i want a lower frequency cut-off increase the uF value but the space will be a problem, maybe with cms.

baloubass

Re: Mosfet reverse polarity, voltage drop down
« Reply #24 on: May 04, 2020, 12:18:56 PM »
Hello, i have finalized the project and and now the pcb with for a 3pdt board with, mosfet polarity, dc filtering, centralized jack and dc connection  fitted for 125b.
4x470uf and 4.7r for 18Hz Fc(2 on top and 2 on bottom).
Does it have difference between ENIG or standard finish? I've seen something about enig have a bad re-workability etc. For no smt board what's the avantage of enig finish?





« Last Edit: May 04, 2020, 12:40:47 PM by baloubass »

antonis

Re: Mosfet reverse polarity, voltage drop down
« Reply #25 on: May 04, 2020, 01:25:06 PM »
Continuing P.M.  :icon_wink:

A project is a project, despite popularity interest..
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

baloubass

Re: Mosfet reverse polarity, voltage drop down
« Reply #26 on: May 04, 2020, 01:34:14 PM »
Continuing P.M.  :icon_wink:

A project is a project, despite popularity interest..

I'm ok with you but i'm not looking for popularity etc.I don't know if poeple really read or find something with this kind of project. But you are right because, in the future if someone do a search about "polarity etc..." maybe it will be find an answer here, like me when i had make my search.
😉