Voltage Doubler Circuit

Voltage doubler is the circuit where we get the twice of the input voltage, like if we supply 5v voltage, we will get 10 volt at the output. Generally transformers are there to step-up or step-down the voltage, but sometimes transformers are not feasible because of their size and cost. So here is the quick, easy and practical solution to double the voltage, using 555 timer IC.

Components

• 555 timer IC
• Diodes -2 (1N4007)
• Resistors- 10k, 33k
• Capaciotors- 22uf (2),  0.01uF (2)
• 3-12v Power supply source

Voltage Doubler Circuit Diagram & Explanation

We can divide the circuit into two parts, first part consist the 555 time IC in Astable mode, to generate the square wave and second part consist 2 diodes and 2 capacitors to double the output voltage.

We have configured 555 Timer IC in Astable multivibrator mode to generate the square wave of approx. 2KHz, this frequency is decided by the resistor R1, R2 and capacitor C1. Below is he formulae for the same:

F = 1.44 / (R1+2*R2) * C1

When the output at PIN 3 of 555 IC is low, Diode D1 get forward biased and capacitor C3 get charged through the D1. Capacitor C3 get charged up to the same voltage at the source, in our case 5v.

Now when output at PIN 3 goes high, D1 get reverse biased and blocks the discharging of the capacitor C3, and at the same time D2 is forward biased and allow the capacitor C4 to charge. Now the capacitor C4 charges with the combined voltage of Capacitor C3 and the input source voltage, means  5v of capacitor C3 and 5v of input supply, so it charges up to 10v (twice the voltage of input source). But in practical we get output voltage less than the twice of input voltage, like in our case we get approx. 8.76v instead of 10v.

There are also some disadvantages of this voltage doubler circuit:

1. However this circuit is very useful to generate higher voltage from a low power source, but this can only deliver up to 50mA current. So it should only be used for low current driven applications.
2. Also the output voltage may be unstable, so a voltage regulator (IC78XX) of proper rating can be used regulation and smooth output. But voltage regulator IC itself consume some current, and reduce the deliverable current (must not exceed 70mA).

Notes:

• Input voltage should be between 3-12 volt, higher voltage will destroy the 555 timer IC.
• The load at output should not draw more than 70mA current.
• Voltage wont double instantaneously but it will increase slowly and after some time, it will set to the twice of input voltage.
• The voltage rating of capacitor C4 should be at least twice the input voltage.
• The output voltage is not exactly the twice of input voltage, it will be less than Input voltage. Like we got 8.76v for 5v input supply and if you apply 12v, output voltage would be 18-20 volt.