Electronics > Beginners
Darlington pairs resistors.
sureshot:
Thank you for the replys. I will use them, as well as the diode, I have some 6 Amp axial diodes. Just one more question, I'm thinking these resistors, especially the lower values need to be a couple of watts to dissipate the heat ? Like 0.5 watt resistors is just not enough power handling.
sureshot:
Guess i measure the voltage across these junctions with a multimeter, then do the maths and select a value power rating.
Anyway thanks again for all the help with this. :)
exe:
In my opinion these resistors shouldn't dissipate much because it's a waste of power, reduces efficiency and make cooling more complicated. I'd limit dissipation to 100-200mW. But again, it's a design decision. Less value -- more power dissipation, but better performance. I'm designing a linear PSU now and I assembled a prototype where I change value and observe performance.
Simulators can be useful to some extend, but models not always accurate. So, better make a real device and measure it.
sureshot:
Oh ok thanks for getting back to me. So looks like 0.25 to 0.5 watts is more than enough for resistors power rating. Thanks again.
Kleinstein:
The voltage for the resistors is small (about 0.8 V maximum, as there is the base emitter junction in parallel). So even with 10 Ohms resistor this would be some 80 mA max and thus 64 mW. So nothing to really worry about.
With a relatively small resistor at the output stage one may have to check the power dissipation for the smaller transistor, as that extra current needs to be driven by the small one.
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