Hello everyone,
I need inverse of the attached circuit...means when I switch on led become off as soon as switch off led become on. LED should be on drain side as attached circuit shows. pls help me.
I need inverse of the attached circuit...means when I switch on led become off as soon as switch off led become on. LED should be on drain side as attached circuit shows. pls help me.
Translation:
I need inverse of the attached circuit
when I turn switch on , led turns OFF.
when I turn switch off, led turns ON.
Pretty obvious you need to replace the P-channel mosfet with an N-CHANNEL one and move the led.
Add another PNP transistor before the NPN, so when you drive the base low it pulls up the gate
Note that using a P-type MOSFET on the high side is making life harder for yourself. If you use an N-type mosfet on the low side of the load (source to Gnd, drain to - side of LED) and use a logic level MOSFET, you could get the behavior you have now without the transistor, and get the inverted behavior with just one transistor instead of two... (oh, and N-channel MOSFETs have better performance at a given price point than P-channel ones - easier to manufacture)
What limits the LED current when it is on?
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Good question I missed that one (-5 points)
...and circuit seems to use different grounds!
Ciao, Ale.
ilguargua:
...and circuit seems to use different grounds!Ciao, Ale.
Doesn't look like it to me - there are two ground connections drawn, but both connect to an identical ground symbol, indicating connection to a shared ground rail.
Yeah, most circuit diagrams don't draw lines between grounds, just terminate in the same symbol. Took me awhile to figure that one out. >:(
Yes, could be, maybe it's only bad drawn, I known that same symbol means same potential, but in this case a straight line could be better, at least for me.
Ciao, Ale.
DrAzzy:
Add another PNP transistor before the NPN, so when you drive the base low it pulls up the gate
Could you explain how do i connect those transistors?
thanks for all of you
I changed the circuit and add a 10k resistor at collector side of transistor. circuit is working good.
szacpp:
I changed the circuit and add a 10k resistor at collector side of transistor. circuit is working good.
Why all that just to control an LED?
Why all that just to control an LED?
We never got any specs on the led but I would guess it is either very large or is a strip which draws a lot more than the usual 20 mA.
raschemmel:
We never got any specs on the led but I would guess it is either very large or is a strip which draws a lot more than the usual 20 mA.
Only the Shadow knows.
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Why all that just to control an LED?
Because it is a class assignment he has been asked to do to prove he understands circuits. Which I will leave you to guess if he does.
Because it is a class assignment he has been asked to do to prove he understands circuits. Which I will leave you to guess if he does.
Well if that's true and all he did was follow our advice what does that prove ?
It proves that education today is sadly lagging behind the reality of a students life and cheating is rife.