555 LED PWM PCB layout - Page 1
Forum section: electronics / projects

author: Grayfox
author_rank: Regular Contributor
timestamp: July 30, 2013, 11:17:40 am
content: I am trying to make a LED PWM circuit but i am having trouble getting this schematic designed on a single sided board I really want to avoid using 0-ohm links or wire bridges.

author: Tita
author_rank: Contributor
timestamp: July 30, 2013, 11:27:33 am
content: Google?I only look one minute on google and i found a pcb ! O0http://xtronic.org/circuit/fake-car-alarm-circuit-555-led-flash/

author: Rerouter
author_rank: Super Contributor
timestamp: July 30, 2013, 11:36:49 am
content: as i went to the effort i'll post it anyway,

author: Grayfox
author_rank: Regular Contributor
timestamp: July 30, 2013, 02:16:38 pm
content: Thanks for the help.I take it with the caps and resistors i will be using will get theseFrequency: 128.267 KHz Cycle Time: 7.796 uSDuty Cycle: 50.22 %Time High: 3.915 uS Time Low: 3.881 uS

author: Grayfox
author_rank: Regular Contributor
timestamp: August 01, 2013, 02:05:35 pm
content: I had to remake the pcb design due to my luck screwing me over yet againI added a SPDT relay since this will be a DRL controller and would like to know if there is any issues with it.During the day DRLs will work at full brightness, but at night the DRLs will work at 50% brightness.

author: JoeO
author_rank: Frequent Contributor
timestamp: August 01, 2013, 07:04:38 pm
content: No one knows since you haven't included a new schematic.

author: Dave
author_rank: Super Contributor
timestamp: August 01, 2013, 08:25:17 pm
content: (14V)^2 / 5 ohm = 39WYou really think that resistor is going to survive that?

author: JoeO
author_rank: Frequent Contributor
timestamp: August 01, 2013, 09:37:22 pm
content: I think you may be missing a diode across the coils.

author: EpicIntelGamer
author_rank: Regular Contributor
timestamp: August 02, 2013, 01:14:43 am
content: Not to hijack the thread but is there an adjustable PWM output 555 based circuit that doesn't require any weird value caps (pF and nF)?

author: Rerouter
author_rank: Super Contributor
timestamp: August 02, 2013, 02:16:09 am
content: a 555 timer relies on a time constant to work, if you want to use bigger caps, you lower the resistance, if the resistance gets too low, you buffer the 555 discharge pin, etc until you get a working solution, pF and nF are not weird in fact in most cases they are conveniently tiny and in more reliable constructions,

author: amyk
author_rank: Super Contributor
timestamp: August 02, 2013, 02:44:48 am
content: @Rerouter: Your name is most appropriate for this thread.

author: Grayfox
author_rank: Regular Contributor
timestamp: August 02, 2013, 03:41:43 am
content: Quote from: Dave on August 01, 2013, 08:25:17 pmIt is based on routers design.The resistors are for the cycle speed.

author: Rerouter
author_rank: Super Contributor
timestamp: August 02, 2013, 07:24:06 am
content: yes its understandable that they are for cycle speed, but why not swap to smaller capacitances so you can use higher value resistors... my design was a quickly tossed together thing, if the package size doesn't match, just upsize.

author: Grayfox
author_rank: Regular Contributor
timestamp: August 02, 2013, 08:52:05 am
content: What is the best frequency to use for LED?I heard that you can get squeaking below 20Khz

author: Rerouter
author_rank: Super Contributor
timestamp: August 02, 2013, 10:45:26 am
content: your driving an relay on your circuit... which has a max speed of probably 5Hz,as for an led, anything over 200Hz is not visible, and unless you have a multi layer ceramic or metal core inductor on the output your circuit should not make noise (you need a speaker either magnetic or electrostatic to make noise) the higher frequencies are just more ideal for low duty cycles, as you notice less and brightness is more linear at the bottom end,

author: Grayfox
author_rank: Regular Contributor
timestamp: August 02, 2013, 12:08:43 pm
content: The relay is just to switch from full brightness during the day to the nightmode where they will be dimmed.Going for the audi styled look where there DRLS become sidelights.With a 5nF cap and using a 100ohm and 120Kohm 1 watt resistors I found laying about.I should get this, if the calc i'm using is correct.or is R1 still too low?Frequency: 1.202 KHz Cycle Time: 831.947 usDuty Cycle: 50.02 %Time High: 416.146 us Time Low: 415.800 us

author: Rerouter
author_rank: Super Contributor
timestamp: August 02, 2013, 02:06:45 pm
content: comes to ~2W, so still a bit hot...

author: Grayfox
author_rank: Regular Contributor
timestamp: August 02, 2013, 02:21:52 pm
content: Could i use a picofarad cap?with a 1nF cap and a 400ohm R1 and a 480Kohm R2 i still get the same values which is 1/2w heat dissipation could even use 800ohm R1 and 1Mohm if i can use a 500pF cap.

author: TerminalJack505
author_rank: Super Contributor
timestamp: August 02, 2013, 06:10:25 pm
content: You might want to change your schematic. There are a couple of better ways to get a 50% duty cycle with a 555.One is shown inthis datasheeton page 12.Another way is to use a couple of diodes to change the charge/discharge paths.This circuitshows the basic concept.