How to bias a transistor into cutoff

In summary, the speaker wants to bias a transistor into cutoff and has a schematic with a collector cutoff current of 100nA. They performed DC analysis and used equations to set the input and output voltage. They are unsure if their equation will hold at cutoff and are considering increasing resistance values to ensure the transistor is in cutoff. The circuit is used for RF applications.
  • #1
zak8000
74
0
hi
i would like to bias a transistor into cutoff. i have the schematic shown below and for the transistor i am using it has a collector cutoff current at 100nA. so my approach was frist to perform Dc analysis:

Vth=5*(R10/(R10+R4)) Rth=(R4*R10)/(R10+R4)

so my input equation is:
Vth=Rth*Ib+0.9+Ie*R12
and output equation is:
5=Vce+Ie*R12

i would ussually say Ie=Ib+Ic=(B+1)Ib but i don't think this equation holds at cutoff so should i assume Ic>100nA like 105nA so the amplifier will be in the active region(so i can use Ic=B*Ib) and then increase resistance values so Ic<100nA and the transistor will be in cutoff please help!
 
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  • #2
zak8000 said:
hi
i would like to bias a transistor into cutoff. i have the schematic shown below and for the transistor i am using it has a collector cutoff current at 100nA. so my approach was frist to perform Dc analysis:

Vth=5*(R10/(R10+R4)) Rth=(R4*R10)/(R10+R4)

so my input equation is:
Vth=Rth*Ib+0.9+Ie*R12
and output equation is:
5=Vce+Ie*R12

i would ussually say Ie=Ib+Ic=(B+1)Ib but i don't think this equation holds at cutoff so should i assume Ic>100nA like 105nA so the amplifier will be in the active region(so i can use Ic=B*Ib) and then increase resistance values so Ic<100nA and the transistor will be in cutoff please help!

Looks like the schematic did not post. Can you try again? What is the application for the circuit?
 
  • #3
ops i taught i attached it. anway i figured it out, it is used for RF applications
 

1. How do I bias a transistor into cutoff?

To bias a transistor into cutoff, you need to apply a negative voltage to the base and a positive voltage to the collector. This will cause the transistor to conduct little to no current, effectively cutting it off.

2. What is the purpose of biasing a transistor into cutoff?

Biasing a transistor into cutoff is typically done to turn the transistor off and prevent it from conducting any current. This is useful in certain circuit designs where the transistor needs to be completely turned off.

3. What happens if a transistor is biased into cutoff?

If a transistor is biased into cutoff, it will not allow any current to flow through it. This means that the transistor will not be able to amplify any signals or perform its intended function.

4. How do I know if a transistor is biased into cutoff?

You can check if a transistor is biased into cutoff by measuring the voltage at the collector and base terminals. If the voltage at the collector is significantly higher than the voltage at the base, then the transistor is likely biased into cutoff.

5. Can a transistor be biased into cutoff using only one voltage source?

No, a transistor cannot be biased into cutoff using only one voltage source. To bias a transistor into cutoff, you need to apply a negative voltage to the base and a positive voltage to the collector, which requires at least two voltage sources.

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