Joule Thief

[Dave45]

So yesterday I decided to give the little circuit some extra juice, since it didnt want to self run 
I applied 12v and it blew the transistor into a couple of pieces and fried the large led,,,,,then it hit me I had to reverse the large diodes to get them to light with the low voltage circuit, this means the bemf wasnt charging the cap, the led's were in blocking mode.
Im going to get more led's from the shack and give it another go.
Persist to Persevere.

dave

[Dave45]

I can see the logic behind the npn setup
but the pnp setup ?

[Dave45]

In the pnp setup why does the bemf run through the diode at all.

[MarkE]

I can see the logic behind the npn setup
but the pnp setup ?

They work exactly the same way: In each positive convention current flows clockwise around the loop formed by the power source, the transistor and the coil when the transistor conducts, and counter clockwise through the loop formed by the transformer secondary and the LED when the transistor turns off.  Positive conention current flows from top to bottom through the transformer secondary in all four cases.  When the transistor turns-off, the coil voltage changes in the direction that resists change in current:  NPN low side switch, the coil voltage increases above the power supply positive terminal voltage.  In the  PNP high side switch case:  The coil voltage decreases below the power supply negative terminal voltage. 

Note that the orientation of the LED is always up.  The LED is always oriented so that it is reverse biased when the associated transistor is on, and the LED always connects to the opposite power supply terminal as the transistor.

[MarkE]

There is only One God and thats with a capital G.
The rest were created and yes I hope and pray He gives us the answer.
dave

Missing 'o'.