Simple IC SG3525 Inverter Circuit using IRFZ44 MOSFETs

Using an special chip called the SG3525 and special transistors called MOSFETs this article explains how to build a converter that can transform car battery power from 12V DC to 220V AC to function outdoors.

It uses a new method called pulse width modulation (PWM) to produce the AC current.

Either normal appliances or a system that uses renewable energy sources like solar panels are powered by this converter.

WARNING: Building circuits with high voltage can be dangerous.

This should only be tried under the supervision of an adult.

What is a IC SG3525 Inverter Circuit using IRFZ44 MOSFETs:

The IC SG3525 is a PWM controller commonly used in inverter circuits to control the switching of power transistors such as MOSFETs or IGBTs.

The IRFZ44 IC are generally used in power MOSFET for inverter applications.

Below are the working and construction steps for simple SG3525 inverter circuit using IRFZ44 MOSFETs.

Understanding the SG3525 IC:

The SG3525 IC serves as a pulse width modulation PWM control integrated circuit commonly applied in switching power supplies and inverters.

Its versatile functionality extends to applications like motor control, lighting and lasting power supplies UPS.

The IC SG3525 regulates output voltage and frequency by adjusting the duty cycle of the PWM signal offering protection features such as over current and thermal shutdown.

Internal Blocks of SG3525:

To provide exact control over power delivery the IC SG3525 includes multiple internal blocks:

An accurate internal voltage source that supplies the error amplifier with a reference voltage.

The error signal generated by a differential amplifier is proportional to the difference between the reference and output voltages.

The clock signal that calculates the switching frequency of PWM waveforms is generated by an internal timer.

Logic that generates the PWM waveform by implementing the PWM control algorithm using the clock and error signals.

SG3525 Features and Functionality:

The IC SG3525 provides features like soft start under voltage lockout and over current protection making it suitable for demanding applications.

Adjusting elements allows control over output voltage, current or power by offering a cost effective solution for various power control needs.

Pin Configuration and Functionality:

Understanding the pin configuration is crucial for successful working:

Pins 1 and 2: Inputs to the onboard error amplifier influencing duty cycle based on voltage differentials.

Frequency of PWM: Dependent on timing capacitance CT timing resistance RT and dead time resistance RD.

Oscillator Frequency: 100 Hz to 400 kHz is measured by RT, CT and RD.

Pins 11 and 14: Drive signal outputs having a 100 mA continuous current rating and a 500 mA peak rating.

Pin 10: Shutdown pin that when low activates PWM and when high starts an immediate PWM latch.

Choosing a Power Transformer and MOSFET:

To get the 300W PWM output use the IRFZ44 MOSFET which has a maximum power rating of 300W.

Choose a power transformer that can handle 10 amps and has a 9-0-9V configuration.

It is advised to use a 12V 5A power source.

Circuit Working:

Parts List:

Section on Power Supply:

A 12V DC power source from a battery powers the SG3525 IC at the start of the circuit.

This power supply needs to fall within the datasheets recommended range.

SG3525 IC Working:

Pins 1 and 2 are connected to the onboard error amplifier.

The error amplifier compares the reference voltage from the internal voltage source with the output voltage generating an error signal.

The timing resistor RT and timing capacitor CT measure the PWM frequency.

The oscillator generates a clock signal setting the switching frequency of the PWM waveform.

The control circuit creates a PWM waveform with a controlled duty cycle using the error and clock signals..

Here the MOSFET IRFZ44 is one of the low side connected MOSFETs that are driven by the totem pole circuit in the SG3525.

Pin 10 is the shutdown pin when low PWM is generated and when high PWM latch is immediately set.

PWM Output:

• Pins 11 and 14 are the outputs which provide the drive signals.
• They are connected to the gate of the MOSFET IRFZ44.
• The MOSFET acts as a power switch turning on and off rapidly according to the PWM signal allowing the conversion of DC to AC.

Filter Section:

• The PWM output is then passed through a filter section which normally includes an inductor and capacitors.
• This section smoothens the PWM waveform producing a more sinusoidal AC output.

Transformer of Power:

The power transformer which has a 9-0-9V configuration increases the voltage for the AC output.

Results:

The final output which are used to power AC devices is a 220V 300W PWM AC waveform.

Formulas:

Below mentioned formula calculates the oscillator frequency (f) of the SG3525 pulse width modulation PWM controller IC.

Frequency (f) = 1 / (0.693 * (RT * CT + RD * CT))

RT: 2kΩ to 150kΩ

CT: 1nF to 0.2µF

RD measures the dead time.

here,

• The SG3525s internal wiring maintains a constant 0.693 which helps calculate the oscillator frequency.
• The external resistor known as an RT (timing resistor) is connected between pin 6 of the SG3525 and ground.
• The oscillation frequency is calculated by adding the CT and RT values.
• An external capacitor known as a timing capacitor (CT) is connected between ground and pin 5 of the IC SG3525.
• The output signal frequency generated by the IC SG3525 is indicated by the symbol f.
• The IC SG3525s RD (Dead Time Resistor) is an additional resistor connected to pins 5 and 7 which are the discharge pins.

In a push pull design RD adds a tiny delay between switching OFF one switching element and switching ON the other even though it is not directly engaged in frequency calculation.

Dead time is the term for this delay which aids in preventing shoot through current which can harm the circuit parts.

How to Build:

Below are the steps for building a Simple IC SG3525 Inverter Circuit using IRFZ44 MOSFETs :

• To learn about the pin configuration and functioning see the SG3525 datasheet.
• Consider the SG3525 PWM inverter use when designing the circuit configuration.
• Connect a 12V DC power source to the SG3525 integrated circuit.
• Ensure the power supply falls within the specified range.
• To keep the SG3525 ICs supply voltage VCC stable and add a voltage regulator.
• Connect the SG3525 ICs pins 1 and 2 to the circuit for the error amplifier.
• Connect the timing resistor RT and timing capacitor CT to calculate the PWM frequency.
• Use an external resistor RD to set the dead time.
• Connect the soft start capacitor between pin 8 and ground.
• Use the internal Totem Pole Circuit to drive low side connected MOSFETs.
• Connect MOSFET IRFZ44 to the SG3525 output for power switching.
• Connect pins 11 and 14 of the SG3525 to the gate of the MOSFET.
• Use a filter circuit using an inductor and capacitors to smooth the PWM output.
• Connect the IRFZ44 MOSFET for the 220V AC output.
• For information on correct pin connections check the datasheet.
• Make use of a power transformer that has a current rating of 10 Amperes and a 9-0-9V setup.
• Follow circuit layout carefully and put the circuit parts together on a PCB.
• To avoid short circuits make sure that components have sufficient distance from each other and should be well protected.
• For efficient heat dissipation connect the heat sink to the MOSFET.

Testing:

• Check that the inverter is operating properly once it is ON.
• A waveform and frequency of the output voltage is measured with an oscilloscope.
• Be sure the inverter can manage loads of up to 300W without facing any problems or overheating.

Conclusion:

One can effectively design a Simple IC SG3525 Inverter Circuit using IRFZ44 MOSFETs by following to these details and by using the given formulas.

For best results ensure that elements and component selection are carefully considered.

References:

Design of a single-phase power inverter with voltage controller using IC SG3525

Datasheet SG3525A