connecting to a 555

I am new to electronics. I have built a 555 timer circuit to run an LED cluster but the output of the timer circuit is not enough to run the LED's so I am looking for an indirect way of connecting them. I have heard this can be done with a transistor, but am unsure how this works is there some material to look at for this?

Here is a circuit. Take a look at the output section:




http://forum.allaboutcircuits.com/showthread.php?t=13426

Hello,

Have a look at this post made by Bill_Marsden:
http://forum.allaboutcircuits.com/showpost.php?p=117646&postcount=11

It is part of this thread that might interest you:
LEDs, 555s, Flashers, and Light Chasers

Bertus

Is there a big difference between a MOSFET and a NPN transistor as they have been both mentioned as a solution to my project enquiry

The biggest difference in your circuit is that a MOSFET requires almost no current on its gate pin to turn on, whereas the BJT (normal transistor) needs a base pin current up to about 10% of the current it is controlling. So if your bank of LEDs needs 5A, the base current of a BJT would need to be designed for 0.5A. That's more than the 555 can handle, so you'd need another transistor to help (a darlington configuration). So for switching big currents at low speed, think MOSFET.

At very high frequency (>1? MHz), the capacitance of the MOSFET gate becomes an issue - you have to rapidly charge and discharge the gate capacitance and this can become a challenge relative to using a BJT. Also, a BJT can easily be configured to give a proportional or linear response to the base current. A MOSFET is far better at being either on or off, not in between.

I have been looking to buy an npn for this circuit and am a bit confused by the spec.
some of these I think i understand but have put them all in just in case

"Maximum Collector Base Voltage 30 V" is this the maximum voltage for the base and collector, or the maximum basic voltage for the collector?

"Maximum Collector Cut-off Current 0.0001mA" - is the minimum current for the collector to work?

"Maximum Collector Emitter Saturation Voltage 1.5 V" - is this the minimum voltage for the collector and emitter to work?

"Maximum Collector Emitter Voltage 30 V" - it does not work over 30 volts through Collector and Emitter

Maximum Continuous Collector Current 0.5 A - must not run a over 0.5 A through the collector

"Maximum Emitter Base Voltage 10 V" - maximum voltage through the emitter and base, or maximum base voltage through the emitter, or maximum basic voltage for the emitter?

depending on how many leds in your cluster-if you want to increase the number within reason you can also use this op stage using a fet