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View attachment 74820
As you can see.I built a circuit like above.I replaced 3.3Vdc instead of White LED(cant find them in my simulation software).The current for each LED suppose to get 11mA.but in practical board it is showing 4mA.Need to know what went wrong ?
There’s nothing wrong with the transistor. At 1mA in base, the collector current of the transistor rapidly increases to a value limited only by the external circuit.
The transistors is driven into saturation. ;-)
The DC current gain in your circuit is only 11.9. That's your Ic / Ib. From the **broken link removed**, with Collector current of 10mA, you should have a minimum currrent gain of 80. Your circuit doesn't seem to have that. If this was an actual constructed circuit, it would seem there is something wrong with your transistor. If this is just through similation, then maybe the parameters are set wrong in the similator for your 2n4401.
That being said, if you want to increase your collector current, then reduce your base resistor value to increase your base current. That will result in increased collector current. One other thing I just thought of is put a jumper across the collector and emitter. See what current that gives you. That would simulate a saturated transistor.
The DC current gain in your circuit is only 11.9. That's your Ic / Ib. From the **broken link removed**, with Collector current of 10mA, you should have a minimum currrent gain of 80. Your circuit doesn't seem to have that. If this was an actual constructed circuit, it would seem there is something wrong with your transistor. If this is just through similation, then maybe the parameters are set wrong in the similator for your 2n4401.
That being said, if you want to increase your collector current, then reduce your base resistor value to increase your base current. That will result in increased collector current. One other thing I just thought of is put a jumper across the collector and emitter. See what current that gives you. That would simulate a saturated transistor.
Those numbers don't match what's shown in the picture - what's simulated & what's measured?voltage across each led is 3.07v.
voltage at base = -2.15v
voltage at collector is = 1.84v
current to each LED is 4.77mA :O :O ....
Those numbers don't match what's shown in the picture - what's simulated & what's measured?
Circuit looks okay. But if you put multimeter in series with the LED's, it will have a small DC voltage over it (perhaps a few tenths of a volt). Due to very non-linear behavior of LEDs + transistor, and the small voltage over R3, this might reduce the measured LED current significantly. Therefore: don't put current meter in series... measure voltage over R3, calculate current through it using known R3 value. Since in series, that same current is flowing through each LED & collector of Q1. Then measure voltages over each LED & voltage between collector & emitter of Q1.
A 10:1 ratio for collector & base current (and only 10 mA to pull), should be more than enough to drive an ordinary transistor into saturation. So: first make absolutely sure that you haven't got collector & emitter of Q1 swapped. And replace Q1 if you suspect it may have been damaged.
If you use a wire for Q1 and LED voltage is 3.07V, then you'd get (12 - 3*3.07V) / 231 Ω = 12 mA, so R3 seems decent value. So the strategy would be to basically reduce R1 value until you measure ~2.31V across R3. Current is then 2.31V / 231 Ω = 10 mA. You should then be left with about 0.48V from collector to emitter of Q1, but reading will depend on exact LED voltage @ 10 mA. With Q1 in saturation, you might have to increase R3 a little to get 10mA LED current.