# 7805 voltage regulator circuit | Fixed & adjustable output

Here is a 7805 Adjustable voltage regulator circuit. I recommend many projects that use IC-7805 or 78xx types.

Today, it will modify from the old circuit, IC-78xx series has many numbers.

We can choose the desired voltage. such as “12V” should use IC-7812, but sometimes we don’t have this number for any reason.

But we have too many IC-7805 numbers since it is applied often in digital circuits.

And with the reason above, so it is cheaper than others and easy to look for in a store.

Therefore, I think to apply the IC-7805 to adjust various voltage level, such as 7.5V, 8.4V, and 10V, etc.

As application and low budget.

If you are beginer. You should read!
7805 power supply datasheet
5V 1A power supply project
12V to 5V DC converter

Finally, it is this adjustable dc voltage regulator that can supply output of 5V to 22V at 1A

## 7805 Variable Voltage Regulator

With a habit of playing the circuit and set up suspected in various circuits.
In this case, too:

Firstly, Assemble components as the circuit in Figure 1, a negative lead.

Then, use a digital multimeter measure voltage at various point.

Appear voltage at the output and negative pin are about 16.6V And also measure current. Release the pin negative and measure voltage at various point

Then, I take 1K-resistor joint between negative-ground pin as Figure 2.

And next measure at the output of 9.5V.

Next measure across R1 has a voltage of 4.5V.

After that measure the output-negative lead of IC1 same 5-volts that a steady voltage at all time. Put R1 across negative and ground

It means that we begin to see the way.

Thus, replace R1 with a 5K-potentiometer.

And then rotate it, can measure the output of 9.5 volts, cause voltage output during 5V to 14.8V.  Show that IF put the resistor drop across between the negative and ground lead.

It can change output voltage and measure voltage the output lead compare with negative lead of IC1 of 5V at all time.

## A formula of 7805 variable Regulator

I always like to calculate the various devices. For ease of use.

When see in Figure 2 will see that the current flow through R1-1K will cause a voltage drop across it around 4.5-volts.

Following the sequence, we came to the current flowing through it together.

The simplest and most obvious way is measured by an ammeter.

R1 = VR1/IR1

VR1 = 4.5V , IR1 = 4.6mA

Results : R1 = 4.5V / 4.6mA = 0.98K omhs

The value was close to R1. But we still inconclusive.

I replaced R1 with the potentiometer again. Then adjust voltage since 6V,7.5V,8V,9V,10V and 12V etc.

I found that all the voltage value have one current value flow the potentiometer same together is 4.6mA at all time.

Then we try to calculate the resistance again, We want to supply voltages up to 12V, we would have thought from the formula :

By: VR1 = Vout – Vic

Set to: Vout = 12V, Vic = 5V

Instead value :VR1 = 12V – 5V = 7V

Then replacement in (1) the formula :

R1 = 7V / 4.6mA = 1.5mA

Thus can find the resistance 1.5K replace on R1, the output appears voltage of 11.9V nearly well.
Conclusion is my the formula is R1 = (Vout – Vic) / IR1.

## Real 7805 adjustable voltage regulator circuit

Next, we see a real use for me. It can adjust the supply voltage 5V to 22V and under 1A. Which is enough for normal use of us. As Figure 3 as the full circuit in the application.

The concept for the device in the circuit

This 7805 variable voltage regulator circuit is nothing special, Similar circuit ago.

So it is recommended only priority is device-specific:

1. T1 is a transformer to provide to the entire circuit, From the conditions of the circuit, we should select the transformer and 1A is sufficient.

And can use more than this, such as 2A. But it will be larger and more expensive.

Section voltage ratings required to calculate it.

Determined from (Vout/1.4) +3 V, in when Vout = 22V.

Try to replace the value (22V/1.4) +3 V = 18.7V. I chose 18V Size, may be used transformers 9V CT 9V (don’t use CT) or Use an 18V CT 18V (use only, 18V and CT lead, but 18V lead the rest not used).

The origin of the …

-1.4 is a constant number. from voltage between DC and AC is the relationship between the VDC = 1.4 x VAC.

-3V is the voltage value lost in the IC.

C5 is capacitor act as voltage filter. I calculated about 1,515 uF, but this value without sell. Thus use 2,200 uF 35V instead.

R1 is a resistor to reduce current to LED1. I calculated about 3.12 K and chose value 3.3k.

C7 is the capacitor act as noise filter from between of the variable resistor-VR1. I select the value of 0.01uF 100V.

D6 is Diode acts as Prevent reverse flow of electricity to the power circuit, may cause damaged circuit, as mentioned above. In this circuit, I chose the diode type 1N4007 diode.

## Build 7805 adjustable voltage regulator

First-order for the device to complete first. Details are as follows:

IC1: LM7805, 5V DC fixed voltage regulator or equivalent
D1-D6: 1N4007, 1000V 1A Diodes
LED1: LED as you need
C1-C4,C6,C7,C8: 0.01uF 50V, Mylar or Ceramic capacitors
C5: 2,200uF 35V, Electrolytic capacitor
C8: 100uF 35V, Electrolytic capacitor
R1: 3.3K 0.25W +5%
VR1: 5K Single Potentiometer type B
F1: 0.5A Fuse
F2: 1 A Fuse
T1: Transformer, 18V 1A
Etc.

Look at 7805 pinout

Further, makes the PCB layout as Figure 4 or use the universal PCB board.

Because of a few components and easy to builds.

Then place components layout as Figure 5 and wiring to the parts successfully.

Check error to make good again, before applying the circuit.

What I want to warn, to be careful about polarity electrolytic capacitor and diodes.

Should connect the voltage measurement lead.

Before the input voltage is fed, and rotate potentiometer-VR1 lowest. Before will have a voltage of 5 volts.

## Many 7805 Circuits How to change 7805 voltage using Diodes Design 12V 5A Power supply using 7805 7805 Constant current charger 6V power supply circuit diagram The step down 12 volts to 6 volts DC converter using 7805 and diodes Variable Regulated Power supply using 7805 and op-amp 12V to 5V converter step down Connect 7805 in parallel and increase current up to 3A

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MR OHM 1970

This is a Handy Dandy Little Circuit!! I May Build This One day..Many Thanks From MR.OHM!!

MR OHM 1970

Many Years Ago I Designed A Voltage Divider In a LM317.I Designed It with A 6 position 1 Pole Rotary Switch Which Offered Me 6 assorted Voltages..Too Bad I Threw the Diagram away..Oh Well!!!Anyway Your design is AWESOME!!!

leonidas

Your circuit is a disaster. It will have huge output voltage variation from part to part due to spread of current into the adj pin. You need two resistors. The correct circuit is all over the web and in many datasheets. My 50 cents

asd

wow .. very nice and handy circuit

ElecCircuit.com

Hi Mr ohm 1970,