Values needed for Emitter Follower Voltage Regulator

Status
Not open for further replies.
J

joemmonster

Newbie level 3
Joined
Nov 10, 2012
Messages
3
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,306
Hi, im a newbie here and i am currently making a circuit for our school fair project. the only problem is i want to decrease the voltage of my battery from 9 volts to 5 volts without changing the current... then i searched through the internet and found out that the simplest way and efficient is to use an emitter follower voltage reducer/regulator like this:

http://hades.mech.northwestern.edu/...ransistors#Emitter_Follower_Voltage_Regulator

but i dont know what are the values needed for the resistor and zener diode, and type of transistor should i use.
if ever, i want the circuit to produce about 350 mA current, 5 volts...

thanks..
 

Your transistor has 9V in and 5 V out at .35 of a amp. so power in it is 4 X .35 = 1.4 Watts. So select a 2 watt transistor and put it on a heat sink if required. The next thing to do is to work out the voltage required on the base, for a single transistor = 5.8 V for a darlington transistor = 6.6 V, this is the zener diode voltage. The base current = 350 mA/gain of transistor, 100 for single, 3000 for darlington. So the current flowing down the resistor = this figure + 1mA extra for the zener diode to remain working., So the resistor will drop 9 - (the zener voltage) at a current (see above), so divide one by the other ( R = V/I) to get R. Or else buy a 5V stabilizer IC, LM317/7805 ? or similar.
Frank
 

thanks, they said that a 5v regulator will do better.. and now, i decided to go with it..
 

Is not darlington pairs stability lesser than that of LM7805 I am curious that is it
 

jeffrey samuel said:
Is not darlington pairs stability lesser than that of LM7805 I am curious that is it
Click to expand...

Yes. Voltage drop in transistor(s) will change with change in current, and thus power dissipation. So, a dedicated regulator chip such as LM7805 is better.
 
Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…