# Integrating zener diode into my circuit

Discussion in 'The Projects Forum' started by Fobio Design, May 18, 2016.

1. ### Fobio Design Thread Starter New Member

May 11, 2016
17
0
Hello-

Hope you are all having a wonderful day so far.

I am looking to use a zener diode in my circuit (5.1V & 5W). My supply voltage is a 9V 600mAH battery.

My question is what type of resistor and NPN transistor I would need to use in my circuit before the zener diode?

Thank you!

2. ### ScottWang Moderator

Aug 23, 2012
4,858
768
Is this a homework or personal study?
Your circuit (5.1V & 5W), so I = W/E = 5W/5.1V = 0.98A
If the above is true then the current of your 9V 600mAH battery will be not enough for the circuit.

Are you trying to make a 5V/5W power supply from 9V battery (or any 9V power supply) using the npn R+zener diode+n bjt?

What is your circuit (R+zener diode+bjt, no matter will it work or not)?

3. ### Fobio Design Thread Starter New Member

May 11, 2016
17
0
Thanks for your reply. It is for a personal project. I am trying to implement a voltage regulator into my circuit. I have attached a picture of what I want the circuit to look like. I am just confused on what resistor and transistor I would need to use with the battery supply voltage I have to create 5V and 6W.

File size:
10.5 KB
Views:
13
4. ### crutschow Expert

Mar 14, 2008
13,056
3,245
You won't get anywhere near 6W from a 9V battery, at least not for very long.

5. ### Veracohr Well-Known Member

Jan 3, 2011
552
76
I assumed 5W is just the rating of the zener the OP has, not the target capacity of the supply.

You'd probably be better off using an IC regulator like 7805.

6. ### ScottWang Moderator

Aug 23, 2012
4,858
768
I thought the circuit would be like that, because that is the basic circuit.

The Vout = Vz + Vbe
Ic = Ib*10
Iout = 6W/5V = 1.2A
Ie = Iout
= Ic+Ib
= Ib*10+Ib
= Ib*11

Ib = Ie - Ic
= 1.2A/11
= 0.109 A
= 109 mA

If you using the zener diode + bjt circuit, when the load does not draw the current then the zener will be drawing too much current.

If you using two stages as 2sc1384 + mje3055 + 6.8V zener diode and then the Vout will be as
Vout = 6.8V-0.7V-0.8V = 5.3V

Another choice is using LM2576-5V_12V, 3A

Whatever which one you choose, the most important thing is the input current should be as
Ii = 1.2 A*(1+20%) = 1.44 A is better.

Fobio Design likes this.
7. ### Fobio Design Thread Starter New Member

May 11, 2016
17
0
Sorry for all the confusion. I have attached a new file of the setup I want. I am using a 5.1V 5W zener, I am just confused on what type of resistor and transistor I should be using.

File size:
45.6 KB
Views:
5
8. ### ScottWang Moderator

Aug 23, 2012
4,858
768
Iout = 5W/5V = 1A
Ib = 1A/11 = 90.9 mA
Vout = Vz -0.8V = 5.6V = 4.8V
I_R1 = Ib + Izd = 90.9 mA + 10 mA = 100.9 mA
V_R1 = 9V - 5.6V = 3.4V
R1 = 3.4 V/100.9 mA = 33.7 Ω = 33 Ω

As IN4734, it has Imax = 162 mA, and we will use it less then I = 162 mA(1/3) = 54 mA, and the Ib as 90.1 mA, so it has risk that you don't know when the zener will be burned, because too hot.