Simplest Full Bridge Inverter Circuit

Among the different existing inverter topologies, the full bridge or the H-bridge inverter topology is considered to be the most efficient and effective. Configuring a full bridge topology could involve too many criticality, however with the advent of full bridge driver ICs these have now become one of the simplest inverters one can build.

What's a Full-Bridge Topology

A full bridge inverter also called an H-bridge inverter, is the most efficient inverter topology which work two wire transformers for delivering the required push-pull oscillating current into the primary. This avoids the use of a 3-wire center tapped transformer which are not very efficient due to their twice the amount of primary winding than a 2-wire transformer

This feature allows the use of smaller transformers and get more power outputs at the same time.Today due to the easy availability of full bridge driver ICs things have become utterly simple and making a full bridge inverter circuit at home has become a kids play.

Here I have explained a full bridge inverter circuit using the full bridge driver IC IRS2453(1)D from International Rectifiers.

The mentioned chip is an outstanding full bridge driver IC as it single handedly takes care of  all the major criticality involved with H-bridge topologies through its advanced in-built circuitry.

The assembler simply needs to connect a few handful of components externally for achieving a full fledged, working H-bridge inverter.

The simplicity of the design is evident from the diagram shown below:

Circuit Operation

NOTE: Please join the SD pin of the IC with the ground line, if it is not used for the shut down operation.

Pin14 and pin10 are the high side floating supply voltage pinouts of the IC. The 1uF capacitors effectively keep these crucial pinouts a shade higher than the drain voltages of the corresponding mosfets ensuring that the mosfet source potential stays lower than the gate potential for the required conduction of the mosfets.

The gate resistors suppress drain/source surge possibility by preventing sudden conduction of the mosfets.

The diodes across the gate resistors are introduced for quick discharging of the internal gate/drain capacitors during their non-conduction periods for ensuring optimal response from the devices.

The IC IRS2453(1)D is also featured with an in-built oscillator, meaning no external oscillator stage would be required with this chip.

Just a couple of external passive components take care of the frequency for driving the inverter.

Rt and Ct can be calculated for getting the intending 50Hz or 60 Hz frequency outputs over the mosfets.

Important Calculations

Frequency Calculation for IRS2453 Oscillator

The IRS2453 chip uses external components R_t and C_t to set the PWM frequency.

Formula:

f = 1 / (1.453 × R_t × C_t)

• Where:
• f = Switching frequency (Hz)
• Rt = Timing resistor (ohms)
• Ct = Timing capacitor (farads)

Example Calculation:

Let us Assume R_t = 33 kΩ = 33 × 10³ Ω, Ct = 1 µF = 1 × 10⁻⁶ F:

f = 1 / (1.453 × (33 × 10³) × (1 × 10⁻⁶))

f = 1 / (1.453 × 33 × 10⁻³)

f ≈ 20.9 kHz

Thus the switching frequency is approximately 20.9 kHz. So you can adjust R_t and C_t to modify the frequency as needed.

Gate Resistors

The 33ohm resistors at the MOSFET gates limit the inrush current during switching and dampen oscillations.

Power Dissipation in Gate Resistors:

P_gate = Q_g × V_gate × f

• Where:
• Q_g = Gate charge of the MOSFET (63 nC for IRF540)
• V_gate = Gate drive voltage (10V)
• f = Switching frequency (20.9 kHz)

Substituting values:

P_gate = 63 × 10⁻⁹ × 10 × 20.9 × 10³

P_gate ≈ 0.013 W

Each gate resistor dissipates approximately 13 mW, which is negligible.

Power MOSFET Ratings (IRF540)

Drain-Source Voltage (V_DS):

The MOSFETs must withstand the full rectified supply voltage. For a 15V input, V_DS(max) must be higher than 15V. The IRF540 has a V_DS(max) of 100V, which is adequate.

Current Handling (I_D):

Each MOSFET handles half the load current:

I_D = I_load / 2

Ensure I_D(max) (33A for IRF540) exceeds this value.

Reverse Gate Diodes

The 1N4148 diodes ensures instant gate capacitance discharge for the MOSFETs, which ensures efficient switching response from the MOSFETs.

Reverse Recovery Time:

The recovery time for 1N4148 is 4ns, suitable for high-frequency switching.

Power Dissipation:

P_diode = V_f × I_load

Where V_f = Forward voltage of the diode (0.7V for 1N4148).

Load Power

The load determines the current through the MOSFETs and resistors.

Load Current (I_load):

I_load = P_load / V_supply

For P_load = 50 W and V_supply = 15V:

I_load = 50 / 15 = 3.33 A

Power Dissipation in MOSFETs:

P_MOSFET = I_D² × R_DS(on)

For IRF540, R_DS(on) = 0.044 Ω:

P_MOSFET = (3.33 / 2)² × 0.044 = 0.122 W per MOSFET.

Capacitor Selection

Input Capacitor (100 µF/25V):

Filters the rectified AC and smooths the supply voltage. The ripple current rating should exceed the load current (I_load).

Bootstrap Capacitors (1 µF/25V):

These provide gate drive voltage for the high-side MOSFETs. Ensure the value can handle the gate charge (Q_g) of the MOSFETs.

High Voltage Feature

Another interesting feature of this IC is its ability to handle very high voltages upto 600V making it perfectly applicable for transformeless inverters or compact ferrite inverter circuits.

As can be seen in the given diagram, if an externally accessible 330V DC is applied across the "+/- AC rectified lines", the configuration instantly becomes a transformerless inverter wherein any intended load can be connected directly across the points marked as "load".

Alternatively if an ordinary step-down transformer is used, the primary winding can be connected across the points marked as "load". In this case the "+AC rectified line" can be joined with pin#1 of the IC and terminated commonly to the battery (+) of the inverter.

If a battery higher than 15V is used, the "+AC rectified line" should be connected directly with the battery positive while pin#1 should be applied with a stepped down regulated 12V from the battery source using IC 7812.

Although the below shown design looks too easy to construct, the layout requires some strict guidelines to be followed, you may refer to the post for ensuring correct protection measures for proposed simple full bridge inverter circuit.

Simple H-Bridge or Full Bridge Inverter using two Half-Bridge IC IR2110

Parts List

The diagram above shows how to implement an effective full bridge square wave inverter design using a couple of half bridge ICs IR2110.

The ICs are full fledged half bridge drivers equipped with the required bootstrapping capacitor network for driving the high side mosfets, and a dead-time feature to ensure 100% safety for the mosfet conduction.

The ICs work by alternately switching the Q1/Q2 and Q3/Q4 mosfets in tandem, such that at any occasion when Q1 is ON, Q2 and Q3 are completely switched OF and vice versa.

The IC is able to create the above precise switching in response to the timed signals at their HIN and LIN inputs.

These four inputs needs to be triggered to ensure that at any instant HIN1 and LIN2 are switched ON simultaneously while HIN2 and LIN1 are switched OFF, and vice versa. This is done at twice the rate of the inverter output frequency. Meaning if the inverter output is required to be 50Hz, the HIN/LIN inputs should be oscillated at 100Hz rate and so on.

Oscillator Circuit

This is an oscillator circuit which is optimized for triggering the HIN/LIN inputs of the above explained full-bridge inverter circuit.

A single 4049 IC is used for generating the required frequency and also for isolating the alternating input feeds for the inverter ICs.

C1 and R1 determine the frequency required for  oscillating the half bridge devices and could be calculated using the following formula:

f = 1 /1.2RC

Alternatively, the values could be achieved through some trial and error.

Discrete Full Bridge Inverter using Transistor

So far we have studied a full bridge inverter topologies using specialized ICs, however the same could be built using discrete parts such transistors and capacitors, and without depending on ICs.

A simple diagram can be seen below: