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Without some bistabil element(e.g.thyristor or flip-flop) You can build only current limiter not a fuse. Have You seen my small circuit (fuse.pdf)? It conduct up to 2A, when overloaded fired the thyristor and remain in this state. After resetting conduct again. Try out and apply serial with each outputs.
Yes i've seen it and you are right. First i thought it is not important to cut off the current if we can prevent it to increase over 2A. But when i saw transistor is burning with good smoke and smell, i decided that cutting off is a must.
Sebi, are you sure your circuit works?
The current-sensor transistor should be a PNP, with the emitter on the left and the base on the right.
In this way when the base goes 0.7V under the emitter, the collector source corrent to the resistors. With a NPN, the current pass from the base to the collector through the PN junction, and this is not correct.
Also you are using the other transistors as a darlington emitter follower, in other words a configuration that put the last emitter at 1.4V under the first base. It is ok if you want a power supply, but in this case the transistors have to be used as a switch and for this application it is used a PNP transistor (or a P channel Mosfet).
Polyswitch and similar are fine, but they are slow and you loss a few volts (they have to heat for breaking the circuit).
Seyyah, think about a circuit that switch off the power and try to restart every few seconds.
Pay attention the limiter is able to charge the capacitors of the circuit you are powering, otherwise it will not start.
for over current i use an scr and a zener too set a threshold
using a .22R resistor in series with v+ and the scr gets clamped too gnd the zener sets and threshold on a pot this gives a good protection
and blows a fuse if the scr fires
punny attampts at current limit are not worth the equipment
the best is a scr crowbar
the fuse can be replace by a semiconductor driven resetable fuse
or use an r2r ladder and comparitor too get steped current
using then 1ma and 1000 ma scaled pots also gives a voltage offset this can be used to give a current display 4 digit
a good psu is a 5 amp 0 - 30v 0 - 5000ma digital psu from rs
it allows for many adjustments
and has also some nice features
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