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DFI 15th June 2004 06:24 PM

Need help on car SMPS
2 Attachment(s)
Can anyone plz help me by telling me if the attached schematic is going to work ? :scratch: Thanks.

Tensop 16th June 2004 04:10 AM


emre 16th June 2004 05:59 AM


It is not possible to tell if the SMPS is going to work or not by just checking the schematic, the PCB layout is quite critical too. So, I guess the only way to tell if this is going to work is to build the circuit and test it!

If you want to check the basic circuit (i.e. switching characteristics, loop stability) , I can recommend you to use Spice for circuit analysis( like LTspice, make a search on google).



DFI 16th June 2004 01:10 PM

Thanks emre for the tip.

DFI 16th June 2004 05:43 PM

One more question. Knowing that the MOSFETs are IRF 1405, how much power can I achieve from this power supply ??

Tensop 17th June 2004 11:29 AM

the limits wont be in the mosfets. more likely the toroidal transformer and/or (if used) output inductors

sss 17th June 2004 01:07 PM

:drool: :drool: :drool: :drool:

man u are crazy :) :) :) :)
u are using 10 pairs of irf1405 ??? those are rated at 169A each :) :) :)
3 pairs will be enough for 500W smps
u cant just add million paralelled transistors to get more power , u gotta use 2 or more transformers if u really want to make a 2000KW + amp , is this what u are trying to do ???:D

plus :
i didnt check all the schematic but u allready got a serious problem !!
this is not the right way to connect the base transistors to the power mosfets !!!
R10 to R18 should be connected to the emmiters of Q9 and Q10 and not to each other !!
and Q9, Q10 , Q31 , Q32 should have emmiter resistors .

i guess there are more things wrong with this schematic , u better look at other circuits to see how its done



SkinnyBoy 17th June 2004 01:50 PM

parts will cost more than buying an amp premade....

sss 17th June 2004 02:15 PM


Originally posted by SkinnyBoy
parts will cost more than buying an amp premade....
if u are doing it the wrong way.......

DFI 17th June 2004 02:18 PM

thanks sss for the reply. can you draw a little schematic on how to connect those resistors pls so I can understand better? I would appreciate your help.

Tensop, I am planning on using two toroids R 80/40/15 which you can find at

SkinnyBo, that is not the problem. Maybe where you live the assembled amplifiers are much cheaper, but here in Romania they are very expensive. For example, a 300W RMS amp is no less than $200, and the parts here cost me about $300 and I get to have a much more powerful amp than I can buy with those money.

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