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General Category => Digital discussion => Topic started by: emueyes on May 26, 2012, 10:42:28 AM

Title: Two 555s and a FET to make robust dimming circuit
Post by: emueyes on May 26, 2012, 10:42:28 AM

Hi all

It looks like this topic has been addressed here before, but I couldn't find a solution for my requirement. I'd like to drive an LED bulb with a PWM circuit that allows full 100% on for the LEDs. The bulb in this vase is a car foglamp replacement with 120 surface mount LEDs.  It requires 12V and draws 200mA (and is very bright - I want to use it as an indoor table lamp, but it really needs dimming, and I'd like to control that).

I've seen such a circuit, I believe it uses two 555s to give a fixed frequency and variable duty cycle, so avoiding the frequency drift problem a single 555 astable has.

I guess getting the oscillator circuit wouldn't be too hard, but I don't know how to drive the FET properly with my somewhat patchy knowledge. If anyone has such a circuit it'd be a great help.

Rob

Title: Re: Two 555s and a FET to make robust dimming circuit
Post by: kam on May 27, 2012, 00:04:36 AM
hello,
a transistor solution:
http://www.pcbheaven.com/circuitpages/LED_PWM_Dimmer/

a mosfet solution:
http://www.pcbheaven.com/circuitpages/High_Frequency_PWM_Fan_Controller/
(second circuit)