Grazie mille (thks a lot).
Questo test serve anche per tutti i BJT, vero? (this test is ok for all BJT, ok?)
A presto, (see you soon)
When you say "short" are you refering that DVM set for 2K are reading some value, right?
Yes. It's not formally correct method (Andrew might kill me), but good for dummies
Short = 0.000
I checked right now an IRFP140 (working): the lowest value 170 ohms, most measures give over 2K thus no indication on DMM.
P.S. your Italian is better than my English!
Grazie di nuovo massimo, adesso tutto chiaro e a posto. (thks again, now all clear & ok)
Mine Italian is better than mine English too.
Have a look at this page, on how to test the bipolars and the mosfet.
MOSFET testing
Testing semiconductors with analog and digital multimeters
A simple test is usually enough to show problems.
Do you know what is the Vf of your LEDs? R1 should be roughly equal to (3 x Vf) / desired_current. So for testing, if your LEDs have Vf = 1.8V or even Vf = 2.1V, and we're aiming for something around 20mA, then you can use R1 = 300R.
For 1.8V LED
I = 3 * 1.8 / 300 = 18 mA
For 2.1V LED
I = 3 * 2.1 / 300 = 21 mA
The 300R resistor can be 1/2W or whatever you have around.
You will know it works well if you measure the voltage across R1 and divide it by 300 and if the result is close to about 20. Of course you should see the LEDs on.
Try to implement just the CCS portion with a 300R for R1.
MOSFET testing
Testing semiconductors with analog and digital multimeters
A simple test is usually enough to show problems.
Do you know what is the Vf of your LEDs? R1 should be roughly equal to (3 x Vf) / desired_current. So for testing, if your LEDs have Vf = 1.8V or even Vf = 2.1V, and we're aiming for something around 20mA, then you can use R1 = 300R.
For 1.8V LED
I = 3 * 1.8 / 300 = 18 mA
For 2.1V LED
I = 3 * 2.1 / 300 = 21 mA
The 300R resistor can be 1/2W or whatever you have around.
You will know it works well if you measure the voltage across R1 and divide it by 300 and if the result is close to about 20. Of course you should see the LEDs on.
Try to implement just the CCS portion with a 300R for R1.
Many thks for links to test devices, I printed to follow instructions
I have a Caddock MP820 301 ohms & another Caddock MP820 4K75 both 2.25W, could I use them?
Oh yes, it's totally for you
You think I took the time to type in all that for nothing?
Oh yes, it's totally for you
Sorry Iko, so if I understand well is possible that LEDs don't shine or shine very low, but the reg. still not works?
Yes. More importantly though, you should measure between 5 and 6 volts across the LEDs.
My advice is to implement the exact schematic (using bc546) that I showed above, and if you measures very close to the values indicated on the schematic, then you have the CCS, a current limiter, working well. Only then move to the next section, the shunt part, without fear. Because no matter what happens in the shunt portion, your current limiter will not allow anything to happen in case of a short circuit in the shunt.
My advice is to implement the exact schematic (using bc546) that I showed above, and if you measures very close to the values indicated on the schematic, then you have the CCS, a current limiter, working well. Only then move to the next section, the shunt part, without fear. Because no matter what happens in the shunt portion, your current limiter will not allow anything to happen in case of a short circuit in the shunt.
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