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This is my first time doing anything at a component level. I am trying to follow this circuit build, but breadboarding instead of soldering for now: https://www.youtube.com/watch?v=Xyi6eaRnn9c

I am using the following components:

  • TI NE555P timer
  • NTE 2N2222A NPN transistor
  • Capacitor is 1000 μF
  • Resistor at 18b to 27+ is 100 Ω
  • Resistor at 17c to 17h is 1 kΩ
  • Resistor at 13b to 15b is 10 kΩ

I am able to get the circuit to work as expected using a single, typical LED light. However, the end goal is to power/fade a 3 W LED automotive brake light (I am trying to build a blinking light for a marching band prop; it needs to be bright enough to see during daylight). You can see the circuit as wired here: https://i.sstatic.net/K8LmR.jpg

When I power the 3 W brake light directly using 9 V, it is very bright. As soon as I connect it to the circuit, nothing happens.

I also tried with an 11 V, 4000 mAh drone battery. Again, the normal LED worked, but not the brake light LED.

Any suggestions for changes to the circuit? How can I get enough current to the 3 W LED?

Something brought to my attention is that the 3 W brake light bulb is drawing 0.22 A at 12 V while the 555 timer has a max output less than that. It seems like that is my bottleneck, but like I said, this is my first attempt at building any circuit and I am unsure what adjustments to make. I did find this resource, but I don't know what to do with it: http://www.555-timer-circuits.com/increasing-output-current.html

Any help would be appreciated!

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    \$\begingroup\$ Hi! Indeed you cannot drive a powerful LED with the 555 directly. But your 2N2222 transistor should take care of that. People will appreciate if you add a schematic diagram of your circuit rather than just a photograph of the breadboard. It will greatly improve your odds of receiving helpful answers. \$\endgroup\$
    – polwel
    Commented Aug 30, 2022 at 20:11
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    \$\begingroup\$ For schematics there is an integrated editor you can use. \$\endgroup\$
    – polwel
    Commented Aug 30, 2022 at 20:13
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    \$\begingroup\$ 3 W Could be 1 or more LEDs with resistors, Which is it? share a link to LED or photo \$\endgroup\$ Commented Aug 30, 2022 at 23:57
  • \$\begingroup\$ @polwel- I will look into learning how to use CircuitLab and keep that in mind for the future! \$\endgroup\$ Commented Aug 31, 2022 at 21:07
  • \$\begingroup\$ @tony-stewart-ee75 In regards to the 3w LED, it is this auto brake light bulb- link \$\endgroup\$ Commented Aug 31, 2022 at 21:08

2 Answers 2

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The circuit is using a BJT as an emitter-follower fed from the electrolytic capacitor voltage. The timing resistor is 10K. With a 220mA load you'll need a current gain of minimum 1000 (preferably more) or the BJT base will load the capacitor excessively and the oscillator will stop. A BC547 does not have that much gain, and if it did it would likely overheat and fail.

One option is to add a TIP31 power transistor as so:

schematic

simulate this circuit – Schematic created using CircuitLab

You might also be able to replace both with a logic-level MOSFET such as IRLZ44 connected as a source follower.

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  • \$\begingroup\$ Thanks for posting this! I have a collection of new transistors on the way and will give this a try this weekend! \$\endgroup\$ Commented Aug 31, 2022 at 21:03
  • \$\begingroup\$ First.. I tried to draw the circuit... I hope I got it correct- imgur.com/a/ypsngcj \$\endgroup\$ Commented Sep 2, 2022 at 20:06
  • \$\begingroup\$ Second.. I added the TIP31. It runs with the normal LED, but still not running with the 3w LED (.22A @ 12V). Adding the TIP31 also is not fading out as expected... 30s video- imgur.com/a/8wyc9mL \$\endgroup\$ Commented Sep 2, 2022 at 20:09
  • \$\begingroup\$ Are you sure you got the TIP31 pinout correct? It's B-C-E from the front. \$\endgroup\$ Commented Sep 2, 2022 at 20:13
  • \$\begingroup\$ Yes I have the emitter of the 2n2222a going to the base of the TIP31. The collector is connected to the positive of the battery. The emitter is going to the positive of the 3w LED. This is my first thing I've ever tried... so I'm certainly open to the idea I have something wired wrong. I did tear everything down and rebuilt it \$\endgroup\$ Commented Sep 2, 2022 at 21:28
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I was unable to get this working properly... so I moved on to an arduino nano approach.

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