Hi all,
I'm looking to build a opamp pwm to drive a 1w single Led.
Looking around this forum and other sources I've gone for a design which I've seen in a few places and then as luck would have it I found a circuit on here posted by Stgwookie for the exact opamp's I have (TL071).
Ok so I've built this up and attached a normal low power led with a small resister to the pwm output and everything works. I put in a bigger cap on the frequency side and have introduced flicker in the led to prove the frequency adjustment works. The duty cuycle adjustment also seems good with the led dimming and turning off as well as going to full brightness.
I get issues though when I try to hook up a high power led.
Using a transistor to power the led results in the led not turning off it goes dim but still has a sight glow to it. I've tried different transistors in different ways including a darlington setup, but always the same result. Now I've no experence with transistors so fumbling in the dark here!
What I want is to fully turn the led off (dimmer) and also to incorpora contant current for the Led. I have a few transistors but would like to hear recommendations on the best ones for the job.
Source is up to 12v and I plan later to create multiple sets of leds controlled from this circuit. At the moment I'm planning to provide just enough voltage from the pwm to to power the led minimising waste.
Led uses 700mA (peak 1000mA) and has between 3.2-3.8 voltage drop.
Any ideas please.
I'm looking to build a opamp pwm to drive a 1w single Led.
Looking around this forum and other sources I've gone for a design which I've seen in a few places and then as luck would have it I found a circuit on here posted by Stgwookie for the exact opamp's I have (TL071).
Ok so I've built this up and attached a normal low power led with a small resister to the pwm output and everything works. I put in a bigger cap on the frequency side and have introduced flicker in the led to prove the frequency adjustment works. The duty cuycle adjustment also seems good with the led dimming and turning off as well as going to full brightness.
I get issues though when I try to hook up a high power led.
Using a transistor to power the led results in the led not turning off it goes dim but still has a sight glow to it. I've tried different transistors in different ways including a darlington setup, but always the same result. Now I've no experence with transistors so fumbling in the dark here!
What I want is to fully turn the led off (dimmer) and also to incorpora contant current for the Led. I have a few transistors but would like to hear recommendations on the best ones for the job.
Source is up to 12v and I plan later to create multiple sets of leds controlled from this circuit. At the moment I'm planning to provide just enough voltage from the pwm to to power the led minimising waste.
Led uses 700mA (peak 1000mA) and has between 3.2-3.8 voltage drop.
Any ideas please.