Light dimmer help

116

02:11:57

Hi everybody, i'm a hobbiest. I took one of the exemples given(left up) and redid it (left down) and got different results this is my first question.  I did a third one (right side) removing the pnp bipolar transistor and foumd that the dimmer still works. Why do I have to use this pnp since same results. Thanks

published 12 years ago

thebugger

12 years ago

Check your lamps again.adjust the power to sync them and then it should work perfectly :)

pip

12 years ago

You have a 30mw lamp top left and 12 watt lamp bottom left hence the results. You don't need the pnp transistor for this circuit it's providing no purpose at all. Don't know why the original included it unless there was other parts on ac maybe or a dc clamp possibly you should post comment on the publishers site and seek there explanation i suspect if it wasn't part of something more elaborate it was just someone playing.

Secuture

12 years ago

U forgot to set bulb rated power in bulb parameters. It's set to 30mw by default. And bulb in example is set to12w Next question answer is this two transistors connection are called shiklai pair and you will crete such pair to enchance transistor ampliffication ratio simply reducing required base curent to achievethe same gain ( but beware cuz this raise required voltage we need to put in base emiter junction in exchange especially when a darlington connection ) when u set properly bulb power ratio it will be seen better in both circuits.

abdo

12 years ago

Thank you all for you reply. Have a great day

UncleRick

12 years ago

You are correct that without the 2nd transistor, the circuit still works. However you sacrifice the gain that the second transistor provided and increased the power demand on the potentiometer.

YuHan

12 years ago

if your load need bigger current but your driving voltage is small then you need a couple of bipolars

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