Hi,
I did my best using the search and google to find an answer to my problem, but unfortunately, I didn't succeed. If I might have missed something, I am sorry! I am no electronics specialist and would be happy to get some advice.
I am a biochemist and intend to selectively cleave a photocleavable bond at 365 nm (UVA) in a biological context, which is why I want to limit the radiation dose to a minimum. Exposure might require mixing of the solution, which is why I want to be able to regulate the brightness of the light source and don't want to apply a single highly intense pulse.
I bought a 10W high power LED that emits light at 365 nm (If = 900 mA, Vf=9-11V) and a CC source (LED driver) that provides constant 900 mA (input: 100-240V AC, output: 6-10V DC).
My aim is to switch the LED and regulate its brightness via PWM on a raspberry pi.
I noticed that the following thread deals with something similar, but without PWM and some links and attachments are not working anymore:
https://www.electronicspoint.com/fo...g-high-power-leds-with-a-raspberry-pi.272994/
For testing, I build the circuit with a blue low power LED, an NPN transistor, 5V power supply from the RaspberryPi and controlled the LED brightness via a GPIO PWM signal on the base of the transistor:
This works perfectly fine!
Now I would like to replace the low power LED with the high power LED. For testing and safety reasons I purchased an equivalent 10W (3x3 matrix COB) LED that emits white light (If = 900 mA, Vf=9-11V).
I ordered a Darlington BD681G NPN transistor and originally intended to build the following circuit:
Now, I am wondering what the CC source will do when I don't allow it to output any current ...
As far as I understood, the circuit at the end of chapter 3 (https://www.electronicspoint.com/forums/resources/got-a-question-about-driving-leds.5/)
should contain a solution for switching the LED on and off, but it is not suitable for fast switching... (?)
I am pretty much stuck and don't know how to go on without testing it and risking to blow up the Pi, the PS, the transistor, or the LED ...
How would you do this?
Another question: Would it be better to use an optocoupler to isolate the Raspberry Pi's circuit from the CC source? However, I have read that optocouplers can't operate at high frequencies such as 100Hz.
Thank you!
I did my best using the search and google to find an answer to my problem, but unfortunately, I didn't succeed. If I might have missed something, I am sorry! I am no electronics specialist and would be happy to get some advice.
I am a biochemist and intend to selectively cleave a photocleavable bond at 365 nm (UVA) in a biological context, which is why I want to limit the radiation dose to a minimum. Exposure might require mixing of the solution, which is why I want to be able to regulate the brightness of the light source and don't want to apply a single highly intense pulse.
I bought a 10W high power LED that emits light at 365 nm (If = 900 mA, Vf=9-11V) and a CC source (LED driver) that provides constant 900 mA (input: 100-240V AC, output: 6-10V DC).
My aim is to switch the LED and regulate its brightness via PWM on a raspberry pi.
I noticed that the following thread deals with something similar, but without PWM and some links and attachments are not working anymore:
https://www.electronicspoint.com/fo...g-high-power-leds-with-a-raspberry-pi.272994/
For testing, I build the circuit with a blue low power LED, an NPN transistor, 5V power supply from the RaspberryPi and controlled the LED brightness via a GPIO PWM signal on the base of the transistor:

This works perfectly fine!
Now I would like to replace the low power LED with the high power LED. For testing and safety reasons I purchased an equivalent 10W (3x3 matrix COB) LED that emits white light (If = 900 mA, Vf=9-11V).
I ordered a Darlington BD681G NPN transistor and originally intended to build the following circuit:

Now, I am wondering what the CC source will do when I don't allow it to output any current ...
As far as I understood, the circuit at the end of chapter 3 (https://www.electronicspoint.com/forums/resources/got-a-question-about-driving-leds.5/)
should contain a solution for switching the LED on and off, but it is not suitable for fast switching... (?)
I am pretty much stuck and don't know how to go on without testing it and risking to blow up the Pi, the PS, the transistor, or the LED ...
How would you do this?
Another question: Would it be better to use an optocoupler to isolate the Raspberry Pi's circuit from the CC source? However, I have read that optocouplers can't operate at high frequencies such as 100Hz.
Thank you!