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How to use pc817 and tip122 to control rectified mains LED array? Answered

I have 3sets of leds that conduct at 250v so I wanted to use my 100v TIP122 NPN(with TVS diodes to protect it from over voltage) and PC817 opto-isolator to PWM the LEDs which are common cathode, is there a way?
Thank you all for all the superb suggestoins!

Tags:ledpwm

9 Replies

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iceng (author)2017-06-24

Your PC817 opto-isolator is only able to handle 80V and TIP122 is only a 100V 5A Darlington NPN..

I never design a transistor switch without 150% Voltage safety.. LEDs may not turn on, but they do not start blocking at a magic value, especially a module..

If you know how to use a voltmeter put it in place of the Tip122 !

Included is a simple way to light anything from a uP..

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yagoa (author)iceng2017-06-25

I think your circuit would have a higher BOM, since the led conduct only within this 100v range, even 70v range worked ok, do you know any good 100v opto-isolator? The PWM would also be better with the transistor right?

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yagoa (author)yagoa2017-07-06

I dont really need a multimeter check since I will have a tvs or zener diode to protect the transistor and optocoupler

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yagoa (author)2017-06-26

LTV-358T seems to be a great optoisolator for this situation

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yagoa (author)2017-06-24

the opto-isolator is only 35v that is the issue

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yagoa (author)yagoa2017-06-24

It is rectified 220VAC, 310-320VDC

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steveastrouk (author)yagoa2017-06-25

Iceng's scheme with a triac is a good one, and easy to make.

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steveastrouk (author)2017-06-25

You don't have any suitable parts for the voltages you want to work with.

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Downunder35m (author)2017-06-23

No clue without proper info ;)

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