Understanding Transistor Data - base current?

Question

How do I find the minimum and maximum base current to turn on, and then saturate a transistor

Answer 1

I assume you are talking about a bipolar transistor, not field effect, under its normal operating conditions.

There isn't a minimum current or a specific 'turn on' point. Any amount of base current will result in a higher collector current, by a factor of the value of beta for that transistor at that operating point.

At some point, further increases in base current no longer increase the collector current. That's saturation. You can find this point by looking at the specifications for that transistor type, or by putting it in a circuit and measuring it.

Answer 2

some comments / tricks to function. definite, the backside modern-day might desire to be limited by using a resistor. in case you hook the battery up quickly around the backside emitter junction, you are going to be able to break the transistor. I did that once and smoked the little guy. I advise beginning with an consumer-friendly circuit to gentle a LED with a transistor change. Setup the LED + resistor + battery to artwork first w/o the transistor. Then use between the various examples on the internet to construct one. Cool challenge.

Answer 3

It will depend on the type of transistor. Roughly about 100th of the emitter output.

The information you require will be in the manufacturers technical data sheet.

Answer 4

Look at the HFEsat(min) (for max base current).

You set the collector current at saturation by picking a rail voltage VCC, a pullup resistor value, RPU. Your data sheet should give you a value for VCE(sat) at different collector currents.

IC(sat) = [VCC - VCE(sat)]/RPU.

IB(max) = IC(sat) / HFEsat(min)