Simple IC SG3525 Inverter Circuit using IRFZ44 MOSFETs

This article describes how to construct a converter that uses a special chip called the SG3525 and special transistors called MOSFETs to convert vehicle battery power from 12V DC to 220V AC for using at homes.

It generates the AC current using an innovative method known as pulse width modulation (PWM)

This converter includes into a system that uses renewable energy sources such as solar panels or it can be used to power standard appliances.

WARNING: Creating high voltage circuits can be risky.

This should be experimented only under adult supervision.

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 boasts features like soft start under voltage lockout and over current protection making it suitable for demanding applications.

Adjusting parameters allows control over output voltage, current or power by offering a cost effective solution for diverse 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: Measured by RT, CT and RD within a range of 100Hz to 400kHz.

Pins 11 and 14: Outputs for drive signals with a continuous current rating of 100mA and peak rating of 500mA.

Pin 10: Shutdown pin enabling PWM when low and triggering immediate PWM latch when high.

Power Transformer and MOSFET Selection:

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

Select a power transformer with a 9-0-9V setup that can manage 10 amps.

12V 5A power supply should be used.

Circuit Working:

Parts List:

Power Supply Section:

• The circuit begins with a 12V DC power supply from a battery feeding into the SG3525 IC.
• This power supply should be within the recommended range mentioned in the datasheet.

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.

Power Transformer:

• The voltage for the AC output is increased by the power transformer which has a setup of 9-0-9V

Output:

• A 220V 300W PWM AC waveform is the final output which can be used to power AC devices.

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,

• f is an indication of the output signal frequency produced by the IC SG3525.
• 0.693 is constant with the SG3525s internal circuitry which makes figuring out the oscillator frequency easier.
• RT (Timing Resistor) is the external resistor wired between the SG3525s pin 6 and ground the oscillation frequency is calculated by the combination of CT and RT values.
• CT (Timing Capacitor) is an external capacitor connected between pin 5 of the IC SG3525 and ground.
• RD (Dead Time Resistor) is extra resistor is linked to pin 7 which is the discharge pin and pin 5 of the IC SG3525.

In a push pull design RD adds a tiny delay between turning off one switching element and turning 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:

You can effectively design a basic PWM inverter with the SG3525 IC by according to these specifications and using the given formulas.

For best results make sure that parameters and component selection are carefully considered.

References

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

Datasheet SG3525A