555 timer & parallel LEDs

[des.xav]

Hello to everyone,

I use a 555 to flash around 50 leds in parallel. The leds are made in a plastic strap, like a belt, and I want to flash 50% on/off.
The 555 is limited at 200mA and every leds use near 20mA....so I need around 1A (minimum!).
I was looking to use a TIP31 at the output (pin3) of the 555 to drive that high current.
Is it possible, or leds in parallele cannot flash?
Thank you,

Xavier

 

[kabiru]

Hi, you can use TIP31 but look into the datasheet of the transistor and calculate the Rb to protect your ic from getting damage.

 

[IanP]

Connecting several LEDs in parallel is not a good idea ..
Instead consider combination of series/parallel connections (+resistors) .. see attached example ..

Rgds,
IanP
:|

 

[des.xav]

ok I think a resistance of 220 or 330 ohms will be ok (Rb) to protect the transistor.

The strip of leds I have is in parallel so I dont have the choice to keep it like that.
So the thing is, at the end, I need to drive around 1 Amp to light those leds.
Each led already have a resistor of 330 ohms integrated in the strip.

I build my circuit and see what happened. Thank you!

X

 

[GrandAlf]

It is much better that you have a resistor in series with each led, this will prevent current hogging. You just need a transistor or mosfet with sufficient current carrying capability. If you dont mind it clicking, you could use a small relay, 555 will drive or sink 200ma, plenty enough. Dont forget to use a diode or vdr across the coil though, cathode to plus.