Flashing a lot of LED's.

[audioguru]

Voodoo,
Please learn about PWM if you want by looking for Pulse-Width-Modulation in Google.
It is used for dimming lights and for DC motor speed controls.

 

[colin55]

Pulse Width Modulating incandescent lights and motors is entirely different pulsing LEDs. Lights and motors have a delay factor that averages the pulses. LEDs do not. They have instant response-time.
Look up multiplexing LEDs and see the results.

 

[voodoo5293]

By increasing the current 25% and turning a LED on for 25% of the time, produces the same brightness as a constant current but draws less than 50% of the current.

Hmm. Maybe I will look into doing some PWM flashing. But for my first project I think I will keep it simple.

 

[voodoo5293]

It is a stupid circuit because it has nothing to limit the current so the LEDs will blow up.
The transistors amplify the current:
1) The current from the 555 into the base of the 2N2222 transistor is limited by the 1k resistor to about 5mA.
2) With a 5mA base current then the emitter current of the 2N2222 transistor is about 600mA.
3) With a 600mA base current then the collector current of the 2N3055 transistor is about 8A.

Sorry. I should have explained it better. The LED array has resistors built into it. That circuit is just to power the LED array.

 

[colin55]

Using a Hex schmitt trigger IC is no more involved than using a 555. And you don't have the wasted 10mA taken by the 555.

 

[voodoo5293]

"With a 600mA base current then the collector current of the 2N3055 transistor is about 8A."

This is not true.

The current into the base of the 2N3055 is limited to the current taken by the load in the circuit under investigation.

Could you explain how the circuit is working then? It is really throwing me for a loop. Transistors in general just confuse the heck out of me.

 

[voodoo5293]

Voodoo,
Please learn about PWM if you want by looking for Pulse-Width-Modulation in Google.
It is used for dimming lights and for DC motor speed controls.

I read up on it a bit. I think I understand it a lot better now.

 

[audioguru]

"With a 600mA base current then the collector current of the 2N3055 transistor is about 8A."

This is not true.

The current into the base of the 2N3055 is limited to the current taken by the load in the circuit under investigation.

No.
The base current of the 2N3055 is the emitter current of the 2N2222.
Even if there is no load then the base-emitter of the 2N2222 is forward biased as a diode and it still provides base current to the 2N3055.

 

[voodoo5293]

Using a Hex schmitt trigger IC is no more involved than using a 555. And you don't have the wasted 10mA taken by the 555.

That may be. But I have a lot more to learn about PWM before I would feel comfortable building a circuit designed around it.