Controlling high power LED with transistor and Arduino

Other Hardware General Electronics
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Hello,
I'm doing a small project and I'm stuck. I want to control brightness of 90v 185mA LED strip with my Arduino Uno. I used bd941 transistor in series with LED strip and I'm sending signal form arduino PWM digital pin to 100om resistor and then to transistor base.(in datasheets for transistor hfe is 40) I was able to fully light up and down my LED but when i tried to modulate signal and lower the brightness of led it was at first barely visible change(brightness is lower but it is barely visible change) and at certain point led diodes start to blink fast and then transistor starts to warm up. I'm using arduino pin at fullest arduinoWrite(pin, 255) and when i want to turn down brightness so I lower number 255 by 25. So after maybe 6 times lowering when number is 100 led strip starts to blink. I could stop at 5 but i didn't accomplish to lower brightness.
I hope someone can help me with this, I'm new at electronics and I'm really bad at reading datasheets for transistors, I'm not even sure that I'm using right one.

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I am sure you are not.
What we need is a schematic of how you are wiring things up, your words do not make sense.
Also your led strips are very unusual is that voltage AC or DC? Can you post a link to where you got it from.

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1600×1211 41.2 KB

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I forgot to draw resistor between Arduino and transistor

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Thanks for that, have you got that link I asked for?
The problem with a transistor for that application is that it drops too much voltage and so it will heat up. The transistor is designed to be used with a heat sink, have you got one?
It is also likely that the Arduino simply can’t supply enough current to drive he transistor into saturation.

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I don't have led specification because they are part of ceilings lights. This transistor works for turing leds on and off but when I try to dimm lights their brightness lower just a little every time I lower analogWrite and at 100 maybe they start blinking

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We need to know the current the LEDs draw in order to see if the transistor is being driven correctly. Have you a current meter can you measure it?
Do you know how to measure current with a meter?

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Hi,
Welcome to the forum.

Please read the post at the start of any forum , entitled "How to use this Forum".
OR
https://forum.arduino.cc/index.php?topic=712198.0
Then look down to "code problems" about how to post your code.
It will be formatted in a scrolling window that makes it easier to read.

If you are using ceiling lights is the supply you are using meant for the LEDs?
If so then it is probably a SMPS and the 195V is PWM already.

Can you post an image of the powersupply please?

Thanks.. Tom... :grinning: :+1: :coffee: :australia:

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I guess you need to get the spec. There might be internal electronics that do not harmonize with you switching...

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You cannot dim these LED strips, do not try! :astonished:

The driver module is a constant-current supply and almost certainly has a capacitor across the output. Attempting to switch the output will lead to driving the LEDs with excess current and substantially hastening their failure.

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