I'm also trying to build a circuit to dim my 12V led strip.

Thread Starter

Phong Phan Thanh

Joined Jul 15, 2016
Gee, I don't know what program you used to draw the schematic, but the 555_Virtual timer pins are mislabled.
1 - GND
2 - Trigger
3 - Out
4 - Reset
5 - Control
6 - Threshold
7 - Discharge
8 - Vcc

The way you show it connected in the schematic, I'd be genuinely surprised if it did anything besides output smoke... :eek:

See the attached; it's a variation on a circuit Bill Marsden posted months back. C2 on the CTL pin (5) is optional, but it can help stabilize the frequency in a noisy environment.

R1 controls the ratio of on/off time. R2 limits maximum charge/discharge current through the diodes in case R1 is turned all the way to one or the other stops.
C3 is to help with the transients created when the 555's output toggles states. You can use your 470uF cap; the value really isn't critical.

This version uses an N-channel power MOSFET (IRF510) instead of a transistor to switch the load current. You could use a transistor if you wish, but as of yet you haven't told us what transistor you're using. R3 limits the current flowing into/out of the MOSFET's gate to prevent high frequency oscillations. R4 turns the MOSFET off in case the 555 timer is removed from the circuit or is damaged.

Even though this thread was started years ago but sir, your answers is extremely helpful!
I'm also trying to build a circuit to dim my 12V led strip and I'll follow the circuit and instructions you provided.

I have some following questions:
1. Can I replace R2 with a 100 Ohms resistor and replace R1 with a 100k? (As I don't have those required resistors at the moment)
2. R3 is for limiting the current, then it should be different if I use another N channel mosfet? I'm planning to use a TIP222 mosfet or maybe a TIP122 transistor.

Thank you!

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Dimming LED Strip with 555timer