SG3524N(PWM INVERTER IC)

Sg3524N is a regulated pulse width modulator (PWM) power control circuitry with low stand-by current. PWM is a good sine wave approximation. Nearly all types of equipment will run on this signal. The IC incorporates all the functions required in the construction of a regulated power supply, inverter, or switching regulator on a single chip. They can be used as a control element for high power-output application.
The Sg3524 is designed for switching regulators of either polarity,transformer-coupled d.c to d.c converter, transformerless voltage doublers and polarity converter applications employing fixed frequency, pulse-width-modulation (PWM) techniques. The complementary output allows either single ended or push –pull application. Each device includes an on-chip regulator, error amplifier, programmable oscillator, pulse-steering flip-flop, two uncommitted transistors, a high –gain comparator and current limiting and shut down circuitry. The Sg3524 has operating temperatures between 00C to 700C.
This IC Sg3524 can operate at a maximum voltage of 40V, the collector output current is 100mA and reference output current 50mA with lead temperature of 2600C.

OPERATION OF SG3524N
The SG3524 is a fixed frequency pulse width modulation voltage regulator control circuit. The regulator operates at a fixed frequency that is programmed by one timing resistor RT and one timing capacitor CT. RT establishes a linear control of the output pulse duration(width) by the error amplifier. The SG3524 contains an on board 5V regulator that serves as a reference, as well as supplying the SG3524 internal regulator control circuitry by a resistor ladder network to provide a reference within the common-mode range of the error amplifier or external reference can be used.

A second resistor divider network senses the output and the error signal is amplified. This voltage is then compared to the linear voltage ramp at CT .. The resulting modulated pulse out of the high-gain comparator is then steered to the appropriate output transistor Q1 and Q2 by pulse –steering flip-flop, which is synchronously toggled by the oscillator output.
The frequency of oscillation is mathematically given, thus.
Fo =1.30/RT*CT
Where
RT is in kilo Ohms
CT is in micro Farad
F0 is the frequency in Hz

For the purpose of this project, CT and RT were carefully selected and calculated for a frequency of 50Hz.

THE OUTPUT CIRCUITRY
The Sg3524 contains 2 identical NPN transistors, the collector and emitters of which are uncommitted. Each transistor has anti-saturation circuitry that limits the current through the transistor to a maximum of 100mA for fast response.
There are wide varieties of output configurations possible when considering the application of Sg3524 as a voltage regulator control circuit. They can be segregated into 3 basic categories;
capacitor diode –coupled voltage multipliers
Inductor- capacitor-implemented single ended circuit.
Transformer-coupled.

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INVERTERS AND OSCILLATORS

INVERTER:
An inverter is an electronics device that converts battery DC to an AC signal it is the same thing as an oscillator. The AC signal can be of various waveforms; sinusoidal, rectangular, square, saw tooth, etc. The type of waveform that we use in our industrial and domestic homes is a sinusoidal wave; this is the best waveform that can run our appliance with out any problem of over heat.

Most model produce a modified square wave. This waveform allow home owners to run 98% of the typical loads in a house such as fluorescent lights, TVs, stereos, vacuums and power tools. The few limitations include some type of electronic controls like dimmer, switches, sensitive electronics like laser printers and photocopiers, and some small rechargeable devices. Occasionally some of these products will not work, or even fail, with modified square wave power. Some appliances like microwave may be noisier and stereo equipment and TVs may have a slight hum or buzz with this type of inverter power.

Inverters that produces pure sine wave to mimic convectional grid power eliminates background noise so that all appliance, including electronics, work without problem. They are particularly suited for sensitive electronics found in some computers and higher quality sound equipment.

INVERTER FOR HOMES…
In large remote residences, particularly those using auxiliary generators, inverters can reduce the cost of power generator by up to 90%. Most inverters include a stand-by battery charger, so that when the generator is on, the batteries are automatically recharged. Once the generator is turned off, the inverter system powers the same AC circuits. Not only do you have quiet power available 24 hours a day, but in most cases the fuel savings alone can pay for the complete cost of the inverter system in less than a year!

WHY DO I NEED AN INVERTER?
Inverter converts DC battery power to standard AC power. They allow you to run regular 120V, 220VAC appliances; including TVs, computers, microwaves and power tools. With an inverter your AC loads are run off your batteries and they can be used any time of day and night - without a generator – and definitely during a utility power failure.

When designing an inverter the power rating of the load is taken into consideration at maximum capacity. Choose a size that can power the appliance you plan to use. Typical sizes installed in our home systems are 1000W to 2500W. Larger inverters from 4KW to 11KW are used in large power systems and industrial applications. Inverters are rated according to the continuous power that they can produce; however, they are also designed to deliver large amounts of current for short period of time – a feature called surge capacity

DESIGN OF AN INVERTER
When designing an inverter, the first thing that comes to mind is an oscillator circuit. An oscillator is an electronic device that converts battery DC to an AC signal. The AC signal produce are non sinusoidal – they are AC signals that shows a great deviation from sine/cosine waveform; square wave, rectangular wave, saw tooth wave, trapezoid wave, quasi sine wave, etc (are all complex waves). However, sine wave can be generated by using special kind of oscillators such as Wien Bridge, Hartley oscillator, RC oscillator, and other Radio frequency oscillators. This kind of wave is not very easy to generate.

The use of relaxation oscillators can produce square wave, quasi sine wave etc. Examples of these are the Multivibrators; Astable, Monostable, and the Bistable (flip- flop).

It is note worthy that it is the oscillator that produces the waveform signal for the inverter. So, the choice of oscillator matters.