High Power LED Driver Circuits controlled by relay - Page 1
Forum section: electronics / beginners

author: themoog
author_rank: Newbie
timestamp: April 06, 2016, 11:25:09 am
content: Im not sure if its because i'm on nights or i'm a pleb but I want to control this circuit with a relay dry contact not a MCU.... what am i not getting todayhttp://www.instructables.com/id/Circuits-for-using-High-Power-LED-s/step8/a-little-micro-makes-all-the-difference/Thanks chaps....feeling odd today

author: bookaboo
author_rank: Frequent Contributor
timestamp: April 06, 2016, 12:05:06 pm
content: You want to switch LEDs on/off using the relay or you want to PWM them? relays will be to slow for PWM.

author: themoog
author_rank: Newbie
timestamp: April 06, 2016, 12:20:09 pm
content: Hi Bookaboo, yes sorry i was a bit vague there!Well i was hoping for the option...So I might want to use a Mcu to PWM...... or in a very basic case I just want to turn a high brightness led on with a dry relay closure.....set brightness...Depends if I fit a MCU in the light or not....Thanks so much for your help

author: danadak
author_rank: Super Contributor
timestamp: April 06, 2016, 12:31:57 pm
content: Relays switch very slowly, unsuitable for most PWM applications. Thats reasonMOSFETs are used. You can use relay for simple on off switching. Note thereare specialized relays that switch fairly fast, but no low cost, still PWM applicationnot suitable.When you switch a power MOSFET you are looking into a large C load, so eitheryou run PWM at low rates, frequency, or you use a MOSFET gate driver circuit/IC.Regards, Dana.

author: themoog
author_rank: Newbie
timestamp: April 06, 2016, 12:40:46 pm
content: No i understand the difference between the relay and a mcu PWM signal... I want to ensure im driving the LED at constant current thats my main concern

author: themoog
author_rank: Newbie
timestamp: April 06, 2016, 12:53:39 pm
content: More detailIve 3d printed some tally lights for Panasonic ptz heads. I'll send you a photo once version 2 is off the printer.I want to use high brightness rgb LEDs. Now I want to make a little general purpose PCB where you can either use a pwm from a mcu to drive each channel (3 mosfets for each channel) or don't use the micro and just control from a relay 'dry'Here's a nice constant current driver for pwmhttp://cdn.instructables.com/FV0/2PEY/J4VEWIFNTO8/FV02PEYJ4VEWIFNTO8.MEDIUM.jpg

author: Kilrah
author_rank: Unknown
timestamp: April 06, 2016, 01:01:15 pm
content: Just wire the relay to shunt Z1, which is what the micro would do in such an open collector scenario. Relay closed = LEDs off.

author: themoog
author_rank: Newbie
timestamp: April 06, 2016, 01:24:27 pm
content: simples of course! How though could I invert the relay? Normal closed = on?

author: senso
author_rank: Frequent Contributor
timestamp: April 06, 2016, 02:04:47 pm
content: You can use the Normally open or the normally closed relay pins so that it behaves like you want.

author: highvoltpower
author_rank: Newbie
timestamp: April 07, 2016, 07:41:37 am
content: Designing and types of relay circuit is vast, but in many electrical projects uses MOSFET as their main switching device, that’s why use are using these. We are only use relay for simply on/off switch. Ya justrelay closed and LED off.

author: danadak
author_rank: Super Contributor
timestamp: April 07, 2016, 10:41:30 am
content: Note in your circuit if you used an open drain output on UP you could usethat as switch to ground for the MOSFET base, providing R1's current (whenbottom end grounded) did not exceed ratings of output, typically 20 mA orso.Not Z1's high valued tolerance must meet the limitation most pins have onUP that pin not exceed Vdd + .3V, otherwise you will be supplying currentinto the pin, hence change Vdd rail of UP inside part. Cause is parasitic pro-tection diode inherent in all CMOS I/O structures that will turn on. So dothe DC error analysis on Vdd and Z1's tolerance to make sure you do notinject any current into pin. Use .3V as the CMOS parasitic diode turn on V.https://www.fairchildsemi.com/application-notes/AN/AN-339.pdfRegards, Dana.