Estimating Vc of transistor (darlington)

[TsAmE]

Homework Statement

Estimate the collector voltage VC when vin is +1, +2 and +3V. (assume IC/IB = 1000)

Homework Equations

IC/IB = 1000

The Attempt at a Solution

I know that a transistor becomes saturated when VCE and RCE are reduced to 0 and when the maximum IB flows, but in this instance, how can you tell if the darlington is partly-on or fully on (for the +2 and 3V)?

 

[berkeman]

Homework Statement

Estimate the collector voltage VC when vin is +1, +2 and +3V. (assume IC/IB = 1000)

Homework Equations

IC/IB = 1000

The Attempt at a Solution

I know that a transistor becomes saturated when VCE and RCE are reduced to 0 and when the maximum IB flows, but in this instance, how can you tell if the darlington is partly-on or fully on (for the +2 and 3V)?

That's not a Darlington connection. But the gain you quote (1000) would fit with a Darlington connection.

Is the figure misdrawn? It's important to show the full (2 x NPN) Darlington configuration if you want to get the voltage drops correct.

 

[TsAmE]

Sorry I ment for an NPN transistor, there was a similar question with a darlington I did that's why I wrote darlington by mistake.

 

[vk6kro]

With one base-emitter junction, assume 0.6 volts across it before current will flow.

So, work out the voltage across the 200 K resistor for the various input voltages (ie subtract 0.6 volts from each input).

Then work out the current in the 200 K. This is the base current.

Then multiply this by 1000 to get the collector current.

Then work out the voltage across the collector resistor when that current flows in it. If this is more than the supply voltage, the transistor is saturated and this current can't really flow.

Subtract this from the supply voltage to get the voltage across the transistor.

 

[TsAmE]

Oh I see, thanks a lot :)