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I have a 12V, 5m long LED strip and an adapter (12V 1A). I want to control the brightness of the LED strip with a potentiometer, I found a simple circuit that involves only a pot and IRFZ44N transistor.( datasheet here ) It was working great, but it wasn't very bright.

When i connected the LED strip only to the adapter it was very bright but as I soldered the circuit it wasn't very bright. Also I measured that the output voltage dropped from 12V to about 9.6V.

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  • \$\begingroup\$ you should use 12v 5A adapter. 14Watt/mt. \$\endgroup\$ Aug 23 '20 at 21:58
  • \$\begingroup\$ The motor driving 555 circuit in Mark's answer with LED where motor is & driving your MOSFET would work OK. No series resistors needed with strip as it is already internal. \$\endgroup\$
    – Russell McMahon
    Aug 24 '20 at 3:12
  • \$\begingroup\$ This does not answer the question - he is asking how to VARY the LED brightness. \$\endgroup\$
    – Russell McMahon
    Aug 24 '20 at 3:14
  • \$\begingroup\$ @Ahmet and Passerby are making the point that LED strips may require 5 Watts per meter (this varies but that's typical enough). SO you may need an ~= 60-70 Watt power supply. The fact it was very bright is surprising - maybe it is capable of substantial;ly more than rated current when overloaded. \$\endgroup\$
    – Russell McMahon
    Aug 24 '20 at 3:17
  • \$\begingroup\$ I noticed that C1 and C2 don't have specific "values" (can't find the exact word for this, sorry). One of them is 0.1 and the other is 0.01, but what pF, uF, mF...? @RussellMcMahon \$\endgroup\$
    – Tkalcec87
    Aug 24 '20 at 10:48
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the mosfet should do a reasonable job of dimming your LED strip using this circuit.

schematic

simulate this circuit – Schematic created using CircuitLab this is more efficient than the 555 PWM circuit but it does cause heat in the MOSFET instead of in the strip.

But the video seems have this circuit.

schematic

simulate this circuit

Which isn't going to work well.

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  • \$\begingroup\$ Op is using a mosfet and its not working. What are you trying to say? \$\endgroup\$
    – Passerby
    Aug 24 '20 at 6:41
  • \$\begingroup\$ the probably have the parts arranged wrong. \$\endgroup\$
    – Jasen
    Aug 24 '20 at 10:37
  • \$\begingroup\$ I built this circuit @Jasen youtube.com/watch?v=8e64L5RWYGM \$\endgroup\$
    – Tkalcec87
    Aug 24 '20 at 10:59
  • \$\begingroup\$ well that exlpains why it didn't work well. \$\endgroup\$
    – Jasen
    Aug 25 '20 at 6:46
  • \$\begingroup\$ So, in theory, if I solder the circuit in the first picture it should work better? \$\endgroup\$
    – Tkalcec87
    Aug 25 '20 at 10:08
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A circuit using a potentiometer and transistor attempts to regulate brightness by adding resistance in series with the LED strip. As you've noticed, it interferes with the maximum brightness. Also, as you dim the strip, you'll be wasting energy as heat in the transistor.

It's much more efficient to regulate brightness by turning the LED strip ON and OFF at a rapid, repetitive rate. To control brightness, you vary the percentage of time that the strip is ON versus the time it's OFF.

You can buy one ready-made (like this). But you'll learn more if you design your own. Here's an article with a simple design using a 555 timer and an NPN transistor. Have fun!

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  • \$\begingroup\$ Thank you, I actually would rather build my own circuit than buy a ready-made one. I'm gonna buy the components tommorow and then try to build it. I will let you know if I have any other problems. \$\endgroup\$
    – Tkalcec87
    Aug 23 '20 at 22:21
  • \$\begingroup\$ @tk you need a bigger power supply too. 1 amp isn't really enough for 5M of any color \$\endgroup\$
    – Passerby
    Aug 24 '20 at 0:01
  • \$\begingroup\$ It doesn't waste energy. it just warms the transistor instead of warming the resistors on the strip. \$\endgroup\$
    – Jasen
    Aug 24 '20 at 5:56

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