Transistor datasheet help ?

[curry87]

I have some questions about this datasheet and this transistor mentioned ?

**broken link removed**


Where is the maximum base-emitter current ?


Where is the current required to fully turn on the transistor ?


When it says vcb,vce,vbe how are those measurements taken with a multimeter (ie where to place the probes) ?


What formular is used for total power consumed in a transistor ?


How do you recalculate the current Ic when a change of Ib has occured ?


If Rb = 0.2 x RL x hfe(dc) then how is Rb calculated with a led + limiting resistor to the collector ?

 

[BrownOut]

Max collector current is 350mA, max base current will be about 1/10 of that or 35mA

A transistor isn't actually "fully turned on" Rather, it is operational in different regions, and that depends somewhat on the circuit.

The positive probe goes on the first connection, and negative on the second. So for example, for vcb, the positive on "c" and negative on "b"

P = Ic x Vce

Ic = β x ib = α x ie

Rb should be =~ IC/10 when using to light an LED.

 

[BrownOut]

PS:

Q: If Rb = 0.2 x RL x hfe(dc) then how is Rb calculated with a led + limiting resistor to the collector ?

A: Rb should be =~ IC/10 when using to light an LED.

Not very effecient. I would probably drive the LED with a current, using the transistor's active region, constant current capabilities. Connect the LED directly to the collector. Choose an emmiter resistor by this:

1) Determine base "On" voltage. Subtract .7V for vbe drop
2) Choose emmiter resistor as (Vbase(on) - .7V)/I(LED)
3) Make sure VCC - VLED < Vbase. Use resistive voltage divider as necessary.
4) Might need pulldown resistor on base connection for complete turnoff
5) Make sure ILED x ((VCC-VLED) - VE) < PMAX (.1W) VE is calculated in step 1.

 

[curry87]

What range should pull down resistors be in to avoid interfering with the circuit to much?

Whats the difference between having resistor +led to collector and emitter to ground VS led to collector resistor across emitter to ground ?

Should the base emitter current be at least 1/10 of collector current to fully saturate the transistor to avoid damage to the transistor ?

 

[BrownOut]

What range should pull down resistors be in to avoid interfering with the circuit to much?

Depends on how your driving the base. Use resistive divider equations and consider the resistance of your driving circuit to insure the "on" voltage is sufficiently high, and the "off" voltage is sufficiently low.

Whats the difference between having resistor +led to collector and emitter to ground VS led to collector resistor across emitter to ground ?

The second case is more efficient. In the first case, you need IC/10 amps to flow in your base circuit. Not all that bad, but could be better.

Should the base emitter current be at least 1/10 of collector current to fully saturate the transistor to avoid damage to the transistor ?

If you're gonna use a LED+resistor in the collector, 1/10 factor makes sure the transistor is fully saturated.