This is increasing output voltage 78xx using 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 Diodes. They have High efficiency and suitable for general use.

While the electric current is flowing a diode in forward-bias. It will have a voltage drop across that is very accurate, about 0.65V 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. When the output may have feedback voltage come back from a load. The D1 is connecting in the reverse bias, it will absorb current spike to protects this circuit.

Two capacitors C1, C3, we add them 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.

Keep reading: ‘12v to 6v step down circuit’ »

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

• 7805 Adjustable voltage regulator circuit
• Dual adjustable power supply circuit diagram

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