1
\$\begingroup\$

I've been doing some circuit analysis questions as practice but came across one that seemed very odd:

Problem

As far as I can tell, this question is missing information and therefore unsolvable? I was able to find Iload since I had all the information needed there. However, I am unable to find RB simply because I'm missing V (voltage for the base). As there are two unknowns there, the problem cannot be solved. Am I correct in this judgement, or am I not seeing something?

Thanks.

\$\endgroup\$
4
  • \$\begingroup\$ You are given Vbe. \$\endgroup\$
    – JRE
    Commented Oct 16, 2018 at 6:19
  • 1
    \$\begingroup\$ It is possible that the problem allows you to choose both \$V\$ and \$R_\text{B}\$? (I think their value for \$V_\text{BE}\$ is really the value for \$V_{\text{BE}_\text{SAT}}\$. So you know the base voltage (relative to ground), by definition.) \$\beta_\text{SAT}\$ isn't specified. But you may be allowed a reasonable guess for that, as well. But who knows? \$\endgroup\$
    – jonk
    Commented Oct 16, 2018 at 6:19
  • \$\begingroup\$ i don't think there is enough information. and \$V_{BE} = 0.95\$ V seems awful high. \$\endgroup\$ Commented Oct 16, 2018 at 6:45
  • \$\begingroup\$ The voltage measurements indicate the Collector voltage is well below the Base voltage, thus the transistor is operating in Saturation. You know the Base voltage, so derive a formula that depends on the unknown Vin. \$\endgroup\$ Commented Oct 17, 2018 at 6:31

1 Answer 1

0
\$\begingroup\$

You can’t come up with a numerical answer, however you can come up with an expression for Rb using the unknown voltage V and the forced beta (often Ic/Ib = 10), since you can easily calculate the collector current.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.