I previously have excellent help from here, I'll be grateful for further advice. My quesion in one line: how do I specify the transistors /FETs for PWM LED dimming with a 100 count of LED on a mains adapted power?
My daughter was gifted a set of decorative lights. Ordinarily she keeps them in a very trendy glass jar. This is mains powered through an adapter, with a normal manual switch on them
She has seen lights can be made dimmable, and would like to ceiling mount them. She has asked me about this, I think this might be a possibility. Boundaries of the project are as follows.
The lights are supplied from a power adapter which I believe, gives direct current at about 24 V with a power rating of 3.6 W.
I have explored the cabling and it appears that the LEDs are set up in eight banks of 12 LEDs. I think there are 8 banks in series, each bank of 12 LEDs in parallel. Each LED has 3 or 4 cables going in and one to bypass, in a 12-LED repeating pattern. The negative of one bank becomes the positive of the next. That is a total of 12 * 8 = 96 LEDs, so 3.6w / 96 = 0.075w per LED.
24V across 8 banks gives about 3v each. P = I * V, gives 0.075W / 3V = 0.025 amps per LED.
In my mind, you brighten/fade LEDs with PWM. Can you do it on multiple banks of them at a time? She wants to dim the lot at once. So doing this to the 24v supply would need more than your normal transistor. I am in the dark here. How do you spec transistors/FETs/MOSFETs/? The Transistor (?Darlington pair?) would take power from the power adaptor and signal from Arduino/equivalent.
Where do I start with the Transistors?
My daughter was gifted a set of decorative lights. Ordinarily she keeps them in a very trendy glass jar. This is mains powered through an adapter, with a normal manual switch on them
She has seen lights can be made dimmable, and would like to ceiling mount them. She has asked me about this, I think this might be a possibility. Boundaries of the project are as follows.
The lights are supplied from a power adapter which I believe, gives direct current at about 24 V with a power rating of 3.6 W.
I have explored the cabling and it appears that the LEDs are set up in eight banks of 12 LEDs. I think there are 8 banks in series, each bank of 12 LEDs in parallel. Each LED has 3 or 4 cables going in and one to bypass, in a 12-LED repeating pattern. The negative of one bank becomes the positive of the next. That is a total of 12 * 8 = 96 LEDs, so 3.6w / 96 = 0.075w per LED.
24V across 8 banks gives about 3v each. P = I * V, gives 0.075W / 3V = 0.025 amps per LED.
In my mind, you brighten/fade LEDs with PWM. Can you do it on multiple banks of them at a time? She wants to dim the lot at once. So doing this to the 24v supply would need more than your normal transistor. I am in the dark here. How do you spec transistors/FETs/MOSFETs/? The Transistor (?Darlington pair?) would take power from the power adaptor and signal from Arduino/equivalent.
Where do I start with the Transistors?
