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.
