I have a problem related with a transistor circuit. Please tell me whether my approach is correct or not.

enter image description here

I need to find the current through the 94.6ohms transistor.

My approach (Assuming PN voltage is 0.6V)

  1. Since the NPN transitor has 5.6V between the base and emitter, it will be biased. So, the voltage at the base of NPN will be 0.6V with respect to ground.
  2. So, current through 1K resistors will be (15V-0.2V)/2kohms = 7.4mA. (Vce = 0.2V)
  3. Since the voltage at the top of 1k emitter resistor is at 0.6V, , the PNP transistor now, will turn as, the voltage between the base and the emitter is greater than 0.6V (As 15V-0.6V > 0.6V)

  4. So,Current through the 94.6ohms is (15V-0.2V)/94.6Ohms = 156mA.

Is my calculation right?

  • \$\begingroup\$ The circuit is interesting because the PNP emitter is at the same voltage as the NPN base, idealistically speaking. (It is also the basis for a practical circuit, though this isn't a good example of one.) This would imply about 100 mA in the resistor you mentioned (99 mA would be closer.) \$\endgroup\$ – jonk Nov 2 '19 at 4:09
  • \$\begingroup\$ Could you explain your 100mA calculation ? \$\endgroup\$ – Newbie Nov 2 '19 at 4:10
  • \$\begingroup\$ And the voltage at the base of NPN is 0.6V and PNP is also 0.6V with respect to ground, right ? \$\endgroup\$ – Newbie Nov 2 '19 at 4:11
  • \$\begingroup\$ No. I see 5.6 V at the base of the NPN, relative to the wire at the bottom of the image, which is also what I'm assuming the 15 V supply rail is also relative to. \$\endgroup\$ – jonk Nov 2 '19 at 4:12
  • \$\begingroup\$ No. I don't think so. When the NPN has more than 0.6V drop, the transistor will turn ON, right. So , it will drop only the required Vbe , right? \$\endgroup\$ – Newbie Nov 2 '19 at 4:13

In your example circuit we have this situation:

Assuming \$V_{BE} = 0.6V\$ and \$I_C = I_E\$

enter image description here

Do you have any questions?

|improve this answer|||||
  • \$\begingroup\$ Thank you for your help \$\endgroup\$ – Newbie Nov 2 '19 at 12:28
  • \$\begingroup\$ Thank you for your help! \$\endgroup\$ – jonk Nov 2 '19 at 19:12

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