i have checked in the data sheets where it explains roughly how to do this, but i dont understand it all and really need it explaining to me (sorry)
how can i get a 1A voltage regulator to work with higher currents... i know youve got to use a pnp transistor but i do not understand the rest of the circuit... could someone show me what circuit i will need to do this (please)
thanks alot
how can i get a 1A voltage regulator to work with higher currents... i know youve got to use a pnp transistor but i do not understand the rest of the circuit... could someone show me what circuit i will need to do this (please)
thanks alot
fezz said:thanks for that, i assume it is the same for a higher voltage circuit - but i still do not understand how R is defined - and why it is there
Hi
here is my calculation, maybe help
First choose max current thru 78xx (must be smaller then 1A to avoid excessive heating, and bigger then 0,1A for stable operation) I choose in my PS I(reg)=0,25A),
Then R =Vbe/Ireg=ca 0,7/ 0,25=2,8 E, ( power transistor will start conduct when Vbe reach ca 0,7V)
Power dissipation on R is Pr=0,7*0,25=0,13W, I use 1W resistors.
If calculated R have not standard value, take bigger one (smaller current thru 78xx), or smaller one (bigger current thru 78xx). In this case god values are 2E2, 2E7, 3E3.
regards
fezz said:ah, its clear now, thanks very much - i promise i wont ask anymore stupid questions for at least a week
LMAO@Fezz.......ask away!!!!!....thats why we all come here!~!!
Put a NPN...
Yes!!!
do i change the PNP transistor to an NPN transistor when using a negative regulator?
Yes!!!
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