PWM LED strip dimmer trouble

[Johny05]

Hello, i am new to making electronic circuits... I made a 12v pwm led strip dimmer using 555 timer and when i turn it on the led strip only lights up like 40% of its brightness so i am asking for some help.

 

[rjenkinsgb]

Most likely, the LED lamp has some internal capacitors that are holding it on for some time after external power is removed.

Try lowering the PWM frequency? eg. make C2 rather larger; 0.22 or 0.47uF?

 

[Nigel Goodwin]

Or the FET isn't been switched properly?, there seems little in the way of a driving circuit and it may be working more as a linear device than a switching one?. A scope would be useful, for checking what's coming out the chip, and what's on the drain of the FET.

 

[sagor1]

10k ohm to gate of MOSFET is quite large, try 1k ohm.

 

[Johny05]

so i tried the 1k ohm and its little brighter but still very much the same. And i am using a LED strip.

 

[eTech]

so i tried the 1k ohm and its little brighter but still very much the same. And i am using a LED strip.

Remove R3, you don't need it.

Increase C2 as stated in post #2 to lower frequency

 

[rjenkinsgb]

Remove R3, you don't need it.

I'd suggest not going below about 33 Ohms, as a power MOSFET may have very large gate capacitance & cause current spikes without some level of limiting.

 

[eTech]

I'd suggest not going below about 33 Ohms, as a power MOSFET may have very large gate capacitance & cause current spikes without some level of limiting.

I didn't think that was a concern since the 555 output stage is totem pole and capable of 200mA.