Led dimmer with 555

298

04:45:03

Third attempt creating a led dimmer with 555. This actually worked earlier IRL before running in some problems and restarting many times. Going back to this one, and posting results from testing (IRL) ASAP!

Comments welcomed

Based on:
https://forum.allaboutcircuits.com/attachments/img_2251-png.132991/

published 6 years ago

zanini007

6 years ago

if you want to just dimmer a 20ma LED there's no need of a transistor or MOSFET, the out pin of the 555 have enough power for it

mxO_o

6 years ago

I will drive a 12v led strip (each color has its own circuit) with this

mxO_o

6 years ago

This for some reason doesn't work, and is still WIP (see picture for working version above)

BillyT

6 years ago

1. Time base needs to be set at a 1second rate to see what happens in real time. 2. The 1k drain resistor on the FET needs to be decreased to allow enough current through the led. 3. The gate resistor can be increased by a fair bit. 4. The circuit would be easier to understand if the layout was a bit better. For more information on FETS see 2ctiby posting http://everycircuit.com/circuit/5214638451195904 For a Cct with a few changes see http://everycircuit.com/circuit/5069722318274560

WTFCircuit

6 years ago

BillyT if you set the time base to 1s/s you wont be able to get it working because of subsampling

BillyT

6 years ago

WFTCircuit, this is true, but to see if the rest of the circuit works in the real world, you need the 1second rate, also I've added a capacitor to the circuit to extend the on time.

mxO_o

6 years ago

It is working now, but I don't know if its fast enough to seem dimmed?

BillyT

6 years ago

There is <15mA led current, reduce the 300 Ohm resistor to150 to get > 20mA. As the circuit won't work at the 1second time base rate, it might not work in real life. Check my circuit for one that actually works dimming

hurz

6 years ago

Billy, never do a sub-sampling simultions and expect clever results.

BillyT

6 years ago

@hurz I agree, but at the same time I make sure that the circuit appears to work in real time, then I have a bit of a look up and down the time base. If you are driving Leds for a visual effects I find that sampling at 5ms can be misleading as to what will happen in real time, also this circuit excepted, a person driving a Led at 30Hz or more and expecting to see a flasher in real time might also be very disappointed.

hurz

6 years ago

Its not a flasher, its a dimmer at least from headline.

BillyT

6 years ago

The original circuit was WIP

hurz

6 years ago

WIP?

BillyT

6 years ago

Work In Progress - not working yet.

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