I'm making a simple non inverting amp using a LM741 amp op.
I'm shure about the theoric circuit and about the physical connections.
I need a gain of 5 and the circuit will work on 12 volts to light up a small led.
The input is 0-2 volts PWM @ 10 kHZ and I want the led to light up. This idea works, but the led lights up really dim. Tha't why I wanted to put an amp op and to rise the voltage to be able to light the led up.
The problem, however, is that as soon as I put the power on, with no signal, I get 10V at the output (pin 6).
I connected the +Vcc to +12V and the -vcc to ground.
I wonder if that has to do anything?
When I connect the signal, I see the PWM signal on top of the 10V and it tops out at 10V.
It's as if I had a 10V offset in my signal.
I looked up the input of the circuit on the scope and I have avour 200mv of noise.
I looked up the output and the 10V is a straight line with a bit of noise over it.
A bright LED will need about 10-20mA of current.. Can you 741 provide that? Check the datasheet. So You will have a 10V PWM signal.
Dont put 10V directly across the LED. You need to have a current limiting resistor in series with the LED. Your diagram did not show the hookup of your LED which, is important. Show us the WHOLE schematic please.
Your basic circuit looks ok. If it is not working, you have a wiring error.
Double check your wiring. And when you are convinced its connected properly, check it again.
Your opamp output might be railed (feeback pin not hooked up??) -check it.
Is your 0-2V input PWM smoothed? Whats the PWM frequency? If it is too high, the 741 at a gain of 5 might be having problems. - Check it.
Keep in mind the LED could be dim because it is on the threshold of destruction. Make sure you are current limiting 10-20mA. (I doubt the 741 can put out that much at 10V) - check it.
No, it doesn't really matter - it's more likely that you have left pin 3 disconnected - connect it to 0V, and your output should become closer to zero.
However, an opamp is rather overkill for driving an LED? - a single transistor and two resistors would be enough (and one of the resistors is the current limiting resistor for the LED).
No, it doesn't really matter - it's more likely that you have left pin 3 disconnected - connect it to 0V, and your output should become closer to zero.
However, an opamp is rather overkill for driving an LED? - a single transistor and two resistors would be enough (and one of the resistors is the current limiting resistor for the LED).
Check from my PIC tutorials, in particular the third graphic' "'Sinking' current from a lamp." - you just need to replace the lamp with your LED and series resistor.
In my Ultra-Bright Chaser projects, the LEDs were still very dim when the PWM brightness control was turned all the way down. The pulse was so narrow that I couldn't see it on my 'scope. Adding C7 at the base of the driver transistor fixed it.
Sorry for the JPG fuzzyness. I was still a pc noobie.