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schematic

simulate this circuit – Schematic created using CircuitLab

Hello!

I'm currently stuck trying to answer this question. The question asks for me to find the resistance of R2 for R1 to be at 4V when the PNP transistor has a beta of 250. My current train of thought was to substitute 4V as the voltage of R1 and solve for current which gave me 80mA, then use Ic = β/Ib to calculate Ib which was 0.32mA. I also worked the emitter current, Ie to be approximately 79mA.

This is where I got stuck, I now know the current of R2 but I don't know the voltage or the resistance so I can't work out either of these values. Is there something I'm not considering here? Am I going about this the wrong way? I'm really confused. Any help would be appreciated!

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    \$\begingroup\$ Was the VBE given to you? If not, are you told the saturation current for the BJT? \$\endgroup\$ – jonk Apr 24 '18 at 23:22
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The voltage across R2 is going to be 6- Vbe if your transistor is working in linear region, where Vbe=~ 0.6v is the PN junction voltage to be overcome in order to make the transistor work.

So the voltage across R2 is VR2 = 6-0.6= 5.4V

With this value you can apply the formula R2 = VR2/Ib and you´ll find the resistor value.

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  • \$\begingroup\$ If a given answer was helpful, you should give it an upvote accordingly :) \$\endgroup\$ – po.pe Apr 25 '18 at 6:17

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