Calculating base voltage of an npn transistor

  • Thread starter jearls74
  • Start date
  • #1
jearls74
53
1
i have been trying to solve this problem for about 14 hours and have gotten nowhere, I am trying to figure out the voltage going into the base of an npn transistor, I am trying to build a circuit where i can take the current from the battery and build a circiut from 7npn transistors in a common emitter mode and a voltage regulator, up to 20 amps of steady current at output. i can't seem to figure out the the voltage going into the base of the first transistor. i know it needs to be atleast .7 volts to turn on the transistor. I've used ohms law several times and only end up with what i started with, how do you figure the voltage drop through the resistor? how many volts are dropped when 12 volts are passed through a 470 ohm resistor? the 470 ohm resistor is connected to the base. any explanations would be appreciated. thanks
 

Answers and Replies

  • #2
Averagesupernova
Science Advisor
Gold Member
4,199
1,040
You need to post a schematic.
 
  • #3
NoTime
Science Advisor
Homework Helper
1,585
0
how many volts are dropped when 12 volts are passed through a 470 ohm resistor?
Since you already gave the answer, it's 11.3v to good approximation, assuming grounded emitter.

A bipolar transistor is a current device not a voltage device.
Ic = Ib Hfe over the linear range.

Hope that helps some.
 

Suggested for: Calculating base voltage of an npn transistor

  • Last Post
Replies
9
Views
2K
Replies
16
Views
2K
Replies
41
Views
2K
  • Last Post
Replies
3
Views
1K
Replies
1
Views
368
Replies
60
Views
11K
Replies
10
Views
530
  • Last Post
Replies
21
Views
470
Replies
11
Views
1K
  • Last Post
2
Replies
48
Views
2K
Top