How change 7805 Voltage using Diodes

This is increasing an output voltage 78xx using a diode. The 78xx series are very cheap, popular. Although It is a fixed voltage regulator, we can change the output voltage level with many how.

A diode is a normal component in many stores, such as 1N4148 Diode. They have High efficiency and suitable for general uses.

Diodes Increase voltage 7805 regulator
Circuit diagram of increasing output voltage 78xx using the diode

While the electric current is flowing a diode in forward-bias. It has a voltage across that is very accurate, about 0.65V in each diode.

In the circuit above…

We add a diode Both diodes D2, D3 – 1N4148 in series, at between a common leg of IC1 and Ground. The output voltage will rise to about 0.65V + 0.65V = 1.3V every diode.

Suppose…

We use an LM7809 having the output voltage of 9V. Thus, the output of this circuit is 1.3V + 9V = 10.3 V.

Then, if we add another diode into 3 diodes. The voltage drop across on them of 1.3V + 0.65V = 1.95V.


So the output is 9V + 1.95 = 10.95V

We add a diode D1 to protect the regulator damaged of the output. It may have a feedback voltage come back from a load. The D1 is connecting in the reverse bias, it will absorb current spike to protects this circuit.

Next, we add 2 capacitors C1, C3 to filter out the transient noise. Which it can be induced into the supply by stray magnetic fields.

In addition, adding a capacitor-C2 drop across both diodes to improve a stability regulation. It will reduce noise at the output.

Convert 12V to 6V step-down voltage »

Note Another way to increase voltage up
Also, we can use a resistor or potentiometer to adjust the voltage output.
So it is easy and cheap.

 

Or We use an op-amp to control a stable voltage regulator.
Variable regulated Power supply, 5V-13V using CA3140

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