J
Jan Panteltje
Guest
On a sunny day (Wed, 14 Jan 2009 16:05:55 GMT) it happened Jan Panteltje
<pNaonStpealmtje@yahoo.com> wrote in <gkl2h7$js5$1@news.datemas.de>:
The trip value is set by R10.
It pre-biases Q1, so it opens earlier, at a lower volatge across the MOSFET.
Had to increase C2 to 220pF to avoid oscillations in the trip region.
Forgot the link:
ftp://panteltje.com/pub/MOSFET_low_dropout_regulator_with_short_circuit_protection2.gif
<pNaonStpealmtje@yahoo.com> wrote in <gkl2h7$js5$1@news.datemas.de>:
Here is the same one with >25A trip.On a sunny day (Mon, 12 Jan 2009 13:42:24 -0800 (PST)) it happened
"miso@sushi.com" <miso@sushi.com> wrote in
04e34b99-fd66-44c4-8bd6-c17bb8773598@p2g2000prf.googlegroups.com>:
In a discrete design, in theory you could use depletion mosfets.
http://www.aldinc.com/pdf/ALD114804.pdf
mm
Here is a simple example for a MOSFET low dropout regulation I just composed:
ftp://panteltje.com/pub/MOSFET_low_dropout_regulator_with_short_circuit_protection.gif
Output is over R7, so the regulator is in the *minus* lead.
Q1 is for start up, to hold current limit inactive for about 1.5 ms (C1 + R8).
The current is then measured by using the voltage drop over the MOSFET.
If it exceeds .75 V then Q1 starts conducting, and the MOSFET is switched off,
resulting in the voltage over it to become much higher, and Q2 conducting more,
output goes then to zero permanently.
It will, depending on the type of MOSFET, easily do 45A..... before it either evaporates
(too big a value for C1, too long current sense inhibit), or melts (huge heatsink needed).
You can limit much lower, I use a LM324 in my other project to sense the voltage over the MOSFET,
but did not find a spice model for the LM324 for LTspice, so maybe later.
C2 is needed to keep if from going bad if entering current limit.
You can leave Q1, Q2, and associated components out, and use a fast fuse I guess....
Good thing is that it seems stable with about any MOSFET I select.
Ripple rejection is about 10x for small signals..
The trip value is set by R10.
It pre-biases Q1, so it opens earlier, at a lower volatge across the MOSFET.
Had to increase C2 to 220pF to avoid oscillations in the trip region.
Forgot the link:
ftp://panteltje.com/pub/MOSFET_low_dropout_regulator_with_short_circuit_protection2.gif