Hi All,

I have put together a basic LED flasher using a 555 and 4017 chips. It works just fine powering 4 yellow LEDs (alternating 3 pulses each). These are rated 20mA each.

I wanted to make it brighter and purchased 3 watt LEDs that are rated 700mA each.

My question is this...

What is the best way to power the larger 3w LEDS? Is it possible to increase the output of the 4017?

I borrowed an LED Driver (Velleman vm143/3w) and simply replaced the small 20mA LED with the driver and connected it to the 3w LED... as Im sure you guessed... this did not work. The LED is very dim.

Any suggestions?
SHould I scrap the original schematic and start from scratch? Can I use the same design (555 and 4017) but power 3w LEDs?

Im very new to this and enjoying learning and reading about it. Any pointers would be great!


Thanks again

 

We don't see a photo nor a schematic. So we don't know if the supply voltage is high enough for the 4017 to turn on Mosfets that drive the LEDs.

Do you expect us to guess at the colour and current needed by your LEDs?
A 2V red LED uses 3W/2= 1.5A.
A 5V blue LED uses 3W/5= 0.6A.

 

Hello Ericb,
One thing we're pretty consistent about is requesting to see a schematic diagram of your circuit before wanting to offer opinions on the problem.

Schematics are the 'language' of electronics; in this case, a schematic image is a huge time-saver for all concerned; it also eliminates most of the guesswork.

If we have to simply make guesses, it will take much longer until you get a reply that you can actually use to fix the problem you are experiencing.

 

Sorry for the lack of detail on this.

Here is the circuit as it currently stands (and works with standard 20mA LEDs)

The 3w LEDs I am wanting to utilize are 3w (2 green and 2 white)
They are star type (off brand) from local electrical depot. They stated that they are 700mA.

Please let me know your thoughts.

Thanks in advance

 

White LEDs are about 3.5V. Green LEDs are much less if they are old or are the same if they are new. The datasheet will say but off-brand LEDs do not have a datasheet (maybe defective sweepings off the floor at the manufacturer).

The supply voltage is 9V and the transistors have a small loss when turned on so the current in the 4700 ohm current-limiting resistors and LEDs is only (9V - 3.5V)/4700 = 1.2mA which is extremely dim. Most small LEDs are bright with 20mA or 25mA.

The current in the LEDs with the 470 ohm current-limiting resistors is (9V - 3.5V)/470 = only 11.7mA which is not bright.

To have 700mA then you need power Mosfets and a current-limiting resistor that is (9V - 3.5V)/0.7A = 7.9 ohms but we are guessing about the LED voltage. Maybe your 9V supply is a tiny battery that cannot supply enough current so it won't work anyway.

 

Thanks for the reply.

I agree with you. I am guessing/taking the stores word for it with regard to the LED voltages. I am currently researching MOSFETS and how they work. Again... I am very new to this and am learning.

As for the battery, the store employee simply attached a 9v alk battery to the LED and they illuminated extremely bright. Granted there is more to this than just a couple LEDs and a battery, so if upgrading to a more appropriate battery is required, I will grab one.

Any guidance with which MOSFET would be appropriate and why?

Thanks again!

 

Any guidance with which MOSFET would be appropriate and why?

For your configuration, any logic level gate, enhancement mode, N-Channel MOSFET that can handle your voltage and current levels will work.

You don't mention the technology you are using (surface mount or thru-hole), so you can do the searching.

 

This is an automotive circuit, though not a very good one. It is also used for RC cars. Your wattage strongly suggests automotive.

Automotive circuits are not allowed on this site. I have helped people at ElectroTech (another forum similar to this one), including designing a PCB.

If this is for automotive please PM me, and discontinue this project on AAC. If it is not for automotive carry on. The PCB layout could be useful for either, but due to a conflict of interest I will not discuss this project on AAC. I can point you to it elsewhere.

 

If you want to stick with a 9V supply, use one of those battery holders for 8 AAs. That should supply enough power.