Easily Understand Inverter Welding Machine with Block Diagram

Hey, in this article we are going to learn how an inverter welding machine works. It is also known as an SMPS Welding machine. We will understand the working principle of this welding machine with a block diagram so it will be very easy to understand quickly. The Inverter ARC welding machine is more efficient and lightweight than a transformer-type electrical welding machine. It is built with solid-state power electronic devices such as MOSFETs or IGBTs. Its operating principle depends upon the high-speed switching power inversion process that is why the term inverter welding machine or SMPS Welding Machine came.

SMPS enabled Inverter Welding Machine Block Diagram

Here, you can see the block diagram of Inverter ARC Welding Machine that will help you to understand its working principle very quickly.

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Main Internal Parts

The main important internal parts are,

1. Main High Voltage Rectifier
2. Relay Bypass and Resistor
3. Filter Capacitor
4. Controlled Inverter
5. Step Down Transformer
6. Low Voltage Rectifier
7. Control Circuit or Processing Unit
8. Power Supply
9. Sensing Circuit
10. Manual Input and Indication

Internal Connection Description

First of all the input power supply is connected to a circuit breaker such as an MCB. 

The output from the Circuit Breaker is connected to a bridge rectifier Circuit. If the machine takes a single-phase power supply then a single-phase bridge rectifier circuit is used. If the machine takes three phase power supply then it used a three-phase bridge rectifier circuit. The rectifier circuit is built using PN Junction Diodes.

The output from the rectifier is connected to the high voltage and high capacitance rated filter capacitors. Generally, two or more than two capacitors are connected in parallel.

From the rectifier, two terminals are brought and connected to the capacitors which are positive and negative. The negative terminal is directly connected to the Capacitor but the positive terminal goes through an NTC Resistor and relays NO contact. The series NTC Resistor is used to limit the high inrush current at the start of capacitor charging. And the relay contact is used to bypass the NTC resistor when high current flow is required.

After, the filter capacitor the High Voltage DC power(generally 310V DC) is connected to the controlled inverter circuit and an SMPS power supply Unit.

A current transformer is connected before the inverter circuit that can measure the input current flow and send a signal to the driver module.

The SMPS provides low voltage DC supply to different units of the Welding Machine such as Cooling Fans, Inverter Control IC, Driver or controller circuit, Display Unit, etc. The relay that is used to bypass the NTC resistor also takes the power supply(generally 24-25V DC) from the SMPS unit.

The output of the control inverter circuit is connected to a step-down transformer. This inverter circuit is also connected to a pulse generation or duty cycle control driver circuit or IC chip.

The output from the step-down transformer is connected to a low-voltage rectifier circuit and the output of this rectifier circuit is used for welding or ARC generation.

The driver module is also connected to the machine output through a shunt resistor so it can measure how much current flowing at the output during welding.

The controlling devices such as the current setting(basically a potentiometer) are also connected to the driver module or Inverter control IC.

Other output or indication devices such as over-current LED, Overheat LED, and Current showing display are connected to the driver module.

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Working Principle

First of all, the high Voltage AC supply is entered into the machine and converted into high Voltage DC by the bridge rectifier and then filtered by the filter capacitors.

Now the high voltage pure DC power is applied to the inverter circuit. And the inverter circuit converts that high-voltage DC into high voltage high-frequency AC. 

This high-voltage high-frequency AC steps down into low-voltage high-frequency AC by the step-down transformer. As the voltage decreased so it is capable to carry high current.

Now this low voltage high-frequency AC supply is converted into low-voltage DC by the low-voltage rectifier circuit. And this low-voltage high current DC supply is used for Welding.

As we know that the IC measures the output current by measuring the voltage across the shunt resistor. So, when we set the current by rotating the potentiometer meter knob a specific Voltage is applied to the inverter control IC. The control IC compares two voltages(one from the potentiometer and another from the output shunt resistor) and generates a pulse signal(with a specific duty cycle) to control the inverter circuit. When the inverter circuit is controlled by the IC or driver circuit the output current also be controlled.

Basically, we applied different voltages to the control IC using the potentiometer to get different output currents. For example, when 1V is applied to the IC the output current will be 100A, when 2V is applied current will be 150A, when 3V is applied current will be 200A, etc.

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