Flasher for 3 watt 3 volt LED COB - Page 1
Forum section: electronics / projects

author: geobee
author_rank: Contributor
timestamp: August 17, 2018, 12:39:14 am
content: Hi all, looking to build up some flashers for the 3 watt, 3 volt LED COB. Need it to be as basic as possible, just a blinking, or flash type would do well. Have to build them in quantity so simplicity would be the way to go. Any ideas would be great. Cheers.

author: james_s
author_rank: Super Contributor
timestamp: August 17, 2018, 12:44:03 am
content: The cheapest way to do this is probably using the cheapest AVR, PIC or other microcontroller you can get, there are some tiny 6 pin AVRs that cost only about 34 cents each in single quantity. If you want to avoid firmware then there's the ubiquitous 555, or you could build a transistor multivibrator or relaxation oscillator.As far as controlling the actual LED, many LED driver ICs have a logic level enable input, if you're not using a driver IC you could use a transistor as a switch. You haven't provided enough details for me to offer more specific advice than that.

author: GadgetBoy
author_rank: Regular Contributor
timestamp: August 17, 2018, 12:44:53 am
content: A very simple circuit would be to use a 555 in PWM configuration, use the output to drive a logic level MOSFET.Sent from my ONEPLUS A3000 using Tapatalk

author: geobee
author_rank: Contributor
timestamp: August 17, 2018, 01:53:14 am
content: Many thanks, yes, I thought a transistor could be the easiest option to do the switching. Not much more to tell you really, just has to be simple, cheap and few components. The flash rate can be quite fast, so a cap could be included to help with this. I did see a circuit years ago where they used a small flashing led to drive a BD139 or similar to then switch the main LED, but since then, these COB units have emerged and may require something different, but a transistor such as the one mention ed should cover it, I would think.

author: GadgetBoy
author_rank: Regular Contributor
timestamp: August 17, 2018, 04:11:55 am
content: Quote from: geobee on August 17, 2018, 01:53:14 amYou'll definitely want to use a MOSFET for switching power to the led. I'll whip up a schematic if you'd like. How fast do they need to flash?Sent from my ONEPLUS A3000 using Tapatalk

author: geobee
author_rank: Contributor
timestamp: August 17, 2018, 04:24:00 am
content: Many thanks for that, no need to be too fast as in a strobe like effect, just flashing at one second intervals would be fine, if that is to be controlled by a cap, I could experiment with different values.

author: james_s
author_rank: Super Contributor
timestamp: August 17, 2018, 06:58:14 am
content: If you want to play with a retro technique, you could use a unijunction transistor to generate the pulses.

author: Zero999
author_rank: Super Contributor
timestamp: August 17, 2018, 11:35:06 am
content: If the circuit runs off 3V, then the ordinary 555 won't do. Use the 7555 and you'll need a MOSFET capable of passing 1A, with a gate voltage of 3V and a low on voltage.Possible MOSFETs:https://www.mouser.com/ds/2/149/FDD6530A-1007256.pdfhttps://www.vishay.com/docs/91328/91328.pdfhttp://www.onsemi.com/pub/Collateral/FDN337N-D.PDF

author: geobee
author_rank: Contributor
timestamp: August 18, 2018, 06:50:43 am
content: Many thanks for the ideas, but all good, remembered the details of the VERY simple idea from years ago. A BD139, two 100 ohm resistors and a small flashing led, very easy, no board required and cheap. Cheers.

author: Ian.M
author_rank: Super Contributor
timestamp: August 18, 2018, 07:03:39 am
content: If you need a slow flash rate without a physically large timing capacitor, look at the CD4060 14-stage binary ripple counter with oscillator, (or 74HC4060 if you need a supply voltage below 5V). It will give a 50% duty cycle squarewave. You'll still need a MOSFET with Vgs_threshold < Vcc/2.

author: Zero999
author_rank: Super Contributor
timestamp: August 18, 2018, 01:43:46 pm
content: Quote from: geobee on August 18, 2018, 06:50:43 amCare to post it?At least, two transistors are required to do this properly. There's the reveres bias transistor oscillator, but it won't run off 3V and tends to ruin the transistor.http://www.learningaboutelectronics.com/Articles/Relaxation-oscillator-circuit-with-a-transistor.php