Nigel Goodwin said:
With Ron’s latest update, the base-emitter current is controlled by a 1.3k resistor and the 3.3V power supply. That gives an Ibe of 2mA (I think.) With an hFE somewhere around 50-75 (according to the sheet,) that should give an Ice somewhere around 125mA.
Going back to what you were saying about needing limiting, I thought that the 2mA current was what provided that limiting. Are you saying that I need something else to limit current? That there’s a problem if the voltage from the battery is dropped occurs across the transistor?
Sorry about the slow reply, I've been to bed :lol:
The base current doesn't provide any collector current 'limiting' at all, and transistors exhibit 'thermal runaway' as I mentioned previously. This is because the transistor is temperature sensitive, the more current it passes the hotter it gets (which is what you were looking for), BUT the hotter it gets the more current it passes (which is what you don't want). This will continue, passing more and more current, and getting hotter and hotter, until the device fails (which could occur in a very short space of time) - it's essential to have some kind of current limiting in the circuit, a simple resistor will do this, and become the heating element itself.