Automatic Voltage Stabilizer - Syed Tahmid Mahbub

PIC16F873(A) based automatic voltage stabilizer

Syed Tahmid Mahbub

AUTOMATIC VOLTAGE STABILIZER (AC – AC) USING THE PIC16F873A SYED TAHMID MAHBUB www.tahmidmc.blogspot.com

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PIC16F873(A) based automatic voltage stabilizer

Syed Tahmid Mahbub

INTRODUCTION My first semester at Cornell University ended late December (2013). I went back home to Dhaka, Bangladesh for my winter break. During this period of time (late December to mid January), there was a lot of political turmoil in the country due to which I could not leave the house a lot to spend time with friends and family. So I ended up spending a lot of time in the house with electronics  – specifically  – specifically on two things: making some small projects with the PIC32MX250F128B (Microchip PIC32 series), and, making an automatic voltage stabilizer circuit.

I’ll talk about the automatic voltage stabilizer here. First I’ll give a short introduction as to the motivation behind me working on it before I go on to talk about the operating mechanism of the voltage stabilizer and then the circuit diagram and source file.

At the end of the article, you’ you’ll find the links to download all the files. Also do check out the Youtube videos where I demonstrate the t he voltage stabilizer and its operating mechanism.

MOTIVATION My dad knows a man named Kamruzzaman who worked under my dad (in electronics) for a very short amount of time, doing stuff like soldering boards, etc. A few days after I went back to Dhaka, Kamruzzaman called my dad and mentioned that he wanted to talk to my dad about something. We invited him home, where he showed us a nice Chinese-made automatic voltage stabilizer circuit he was trying to “replicate” albeit unsuccessfully. At the same time, he mentioned about his financial hardship and asked for our help with designing the automatic voltage stabilizer so that he could have some good financial support from this product.

In Bangladesh, the automatic voltage stabilizer (AC-AC) is a ubiquitous little piece of hardware that is used to somewhat compensate for the varying line voltages (which while being advertised as 220V, can on a given day vary between 170V and 240V in Dhaka and can vary over a larger range in other parts of the country, due to t he unreliable electrical grid).

This was a good learning opportunity, a great opportunity to gain some experience and most importantly, a great way to help someone in need through doing something I truly love.

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PIC16F873(A) based automatic voltage stabilizer

Syed Tahmid Mahbub

And I got to it. I spent about somewhere between a day and a half, and two days thinking about how best to go about designing this voltage stabilizer circuit, while maximizing performance and minimizing build hassle. Then I built the test prototype on verroboard and tested it out. Kamruzzaman and I tested the entire product through a long eight-hour testing process where I kept on refining and improving the circuit until I achieved what I wanted  –   –  a blend of the right amount of performance and a minimal amount of build effort/hassle. After that, I designed the PCB for the board; it was a long night designing the PCB – PCB  – fuelled  fuelled by coffee (=P), I started at around 12 AM and finished at around 9.30AM after which Kamruzzaman got the PCB made (that very day) and we performed the final testing of the product that night. The circuit worked as expected and the project was complete.

SPECIFICATIONS Now, let’s go on to talk about the technical part of the project. project . For this automatic voltage stabilizer, the parameters were decided initially: 

Output voltage must lie between 200V and 240V for all input voltages above 150V and upto 260V.

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Input voltage range must be 150V to 260V, preferably wider.

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Output frequency and waveform should be unchanged from the input frequency and waveform.

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The voltage stabilizer must be inexpensive.

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There should be no variable resistors in the final finished product. This was something recommended by Kamruzzaman, as he said that sometimes, some of the variable resistors he uses tend to drift in resistance slightly and this causes the circuit to become less reliable over time. Although this seemed quite challenging (due to resistor tolerances in the voltage sense section, tolerances in the diode forward voltages in the AC-DC rectification section, etc), I quite liked the idea.

Based on the above initial design decisions, the final parameters/specifications are as follows: 

Input voltage:

125V/135V (I’ll explain this later) to 270V

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Output voltage:

>=200V and