series voltage regulator circuit diagram f

series voltage regulator circuit diagram

In the whole “voltage regulator design series”, the series voltage regulator is the best & the most efficient voltage regulator as compared to all we designed before.

And before we move forward to design this regulator, choose the valuse of Vin(input voltage), Vo(output voltage) & I(supplied current) you require.

How to design series voltage regulator?

There are 6 basic steps to design a series regulator, they are:

1. Selection of series pass transistor Q1.

2. Selection of zener diode (reference element).

3. Selection of transistor Q2.

4. Selecion of series voltage resistor R(D).

5. Selection of sampling resistors R1 & R2.

6.  Selection of current limiting resistor R3.

Let's begin

1.selection of series pass transistor Q1.

selection of transistor Q1

We always choose transistors by checking their power dissipation handling limit.

So, we willl calculate V(CE1) & I(C1 max), then we wll calculate P(D1).

And, after calculating power dissipation, we will check the data sheets of transistors, in order to choose the transistor havin power dissipation more than or equal to calculated value.

choosing transistors having higher power dissipation handling factor than required is a good practice.

It also helps us to design the circuits which perform well in worst case scenarios like excess heat dissipation, flow of larger current than expected.

2.Selection of zener diode (reference element).

selection of zener diode

The next most important element is reference regulator zener diode.

So, we just have to calculate Vz in order to seelct the right zener diode.

& while calculating assume that 50% of the V(B1) gets divided between Q2 & Vz.

Then, As i suggested you in the previous post check the data sheet & select the best suitable zener.

3. Selection of transistor Q2.

3seelction of transistor Q2

As we all know that in transistor emitter current is approx. equal to collector current.

Here also we will calculate the power dissipation of the transistor Q2.

So, as we will get P(D2 max), we will check data sheets and choose the transistor having power dissipation higher or equal to calculated value.

It keeps the transistor from damaging due to excesss heat dissipation.

4. Selecion of series voltage resistor R(D).

Here R(D) is the most important element of the circuit, because it provides extra current to the zener diode to work efficiently.

seelction of series voltage resistor

From the equation above, you cakl easily calculate the resistor required for this branch of resistor.

But, here we also have to calculate its power dissipation in order to get better power handling capacity circuit.

5. Selection of sampling resistors R1 & R2.

division of I(L)

As, you can read from above, we will asssume only 10% of I(L) passing through sampling elements branch.

It’s because, when we calculated I(B2) just for estimation.

from the realtion of base current and collector current, we got the value of base current in uA.

So, 10% is more than enough for the assumption

calculation of values of R! & R2

As oyu can observe from above image R1 & R2 both gets 10% of load current.

6. Selection of current limiting resistor R3.

selection of R3

R3 is the last but most important element in the circuit to choose.

Because, R3 is the only resistor that provides current to the base terminal of Q1 & to the zener diode as well.

So, current through R3 consists of two current values. 1.Base current (max) & 2. zener current (min)

But, here most important step is to calculate the current dissipation of R3.

Because, R3 gets connected directly to the source current, so there are higher chances of heat dissipation throught it.  

Special thanks.....

This post could have been only possible with the help of my professor who taught me this.

If this post is not enought for your thirst of knowledge, 

click this link to get some more info,


The simulator in which I design these circuits, don’t have the feature of keeping values unknown or not keeping them at all.

So, the values I gave them are not zero, they’re unknown.

We have to either calculate it or have to assume them as per our requirement of design.


Here, we learned how to design a series volatge regulator in 6 basic steps.

Just by following these simple steps you can design an very efficient regulator for your own use.

If you have any queries related to this post or topic, feel free to ask in comment box down below.

This is the most efficient regulator from the “zener regulator series” .

BUT, if you have any better & efficient regulator designs, let us know about it. 

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