Step Voltage Power Supply from Fixed Voltage Regulator.

Design Challenge:

Design and development of  Regulated Four Step Voltage Power Supply from Fixed Voltage Regulator(7805 Voltage Regulator IC.).

Theory:

1.The 230V to 12V Step Down Transformer's primary is initially linked to the AC mains supply, while the     secondary is connected to a bridge rectifier. 

2.The bridge rectifier's output is filtered using a capacitor before being sent to the 7805 Voltage Regulator IC.

3.Between INPUT and COMM (GND of 7805), a 0.22F capacitor is connected, and between OUTPUT and COMM, a 0.1F capacitor is attached.

4.Now we'll get to the fun part. Between the COM and the OUT lies a 470 ohm resistor. To switch  between output resistors, a rotary switch is utilized, with the following resistors attached to it: 100, 220,330, and 470.

Circuit:

5.This is a basic project that implements a Variable Voltage Power Supply from a Fixed Voltage Regulator. The operating idea of this project is extremely straightforward.

6.Connect two resistors R1 and R2 as indicated in the diagram below: one between the output and the GND Pin, and the other between the GND Pin and the power supply's GND.

7.The current flowing through R2 is a mix of the current running via R1 and the 7805 standby current. We can calculate the value of this resistor based on the output voltage requirement, and then the output voltage can be computed as follows.

V_OUT = V_REG + R₂ * (V_REG/R₁ + I_S) 

where 

V_REG = 5V (at 7805)

I_S = stand by current of 7805 (=~2.5mA).

Using a 7805 Regulator and a 12V Supply, you can achieve anything between 5 and 12V.

The outputs obtained with a 7805 Voltage Regulator IC are shown in the following photos.

Envision that the resistor which is joined between the com terminal and the yield terminal of controller has a worth of 470ω. This infers that the worth of current is 10.6 mA (as V =5V besides V=IR).

Among the turning switch and ground there is some measure of backup current of 2.5 mA approx. Henceforth around 13.1 mA of generally current is accessible.

Presently accept that from the circuit we need 5V to 12V. With the controller yield we straightforwardly got 5V least. While on the off chance that there is a need of 12V, among com and yield 5V is accessible and for the rest 7V we need to choose the proper worth of the resistor.

 Here R =?

V = 7V

I =13.1mA

Hence V =I*R

R = 543ohm

 Subsequently, we need to join resistor of 543 Ω with 470 Ω so to get the needed yield for example 12V. While it is hard for us to get such a worth of the resistor on the lookout so we can utilize the close by worth of the resistor for example 560 Ω.

 Presently assuming we wish to have another voltage from 5V to 12V, we need to join another worth of the resistor.

Assume we need 6V, then, at that point,

V =6V

I = 10.6mA

R = 6V/10.6mA

R = 566 Ω

Yet, the resistor R1 is now on 470ω which is as of now associated in the circuit, subsequently for 6V worth of the resistor will be 100 Ω roughly (566-470=96).

 In similar way for various voltages distinctive worth of opposition will determined. Regardless of the various upsides of resistors accessible, a variable resistor can be utilized in the circuit to get various upsides of voltage.

Pcb layout: