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From DC TIG inverter to AC and pulse TIG inverter - idea

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berger.h

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I have a welding inverter for TIG, in essence it is a switched current source DC 5-160A.

An AC inverter is required for aluminum welding, or the polarity of the electrodes must be changed.
Expensive inverters also allow pulse welding with adjustable pulse length and frequency, etc.
I don't want to spend $ 2,000 on an inverter that can do it all

My idea

Add a full H bridge to the output of the DC inverter. With 8pcs 80V 300A MOSFETS 1.2m Ohm it is possible to build a bridge with a resistance of 1.2mOhm.
8x IPT012N08N5 15$
4x driver for exmaple TC4452VOA 5$
2x Digital isolator for HS MOSFET any as SI8620BB 3$
2X DV/DV for HS MOSFET 5$
1z STM32F334 5$
Sum 35$ + ALU PCB

DC TIG+
DC TIG-
DC Pulse 0-500 Hz frequency control, etc.
AC frequency control etc.


Am I missing something?
 

If you wish to experiment, here's how a single clock can control a full H-bridge. The lefthand half-bridge drives the righthand half-bridge.

It's successful if you can manage to turn the mosfets fully On and fully Off. (This simulator appears to partially turn mosfets on.)

If your welder produces pulsed DC then that can serve as the control signal.

Or, consider installing a divide-by-2 somewhere so that pulses travel through the left and then the right half-bridge, alternately back and forth.

one clock drives full H-bridge load gets AC sqr wave.png
 

My idea in matter
1IPT012N08N5 input capacitance 13nF, 2pcs paralel 26nF
TC4452 is 12A High Speed MOSFET Driver on high side full isolated DC/DC and Digital Isolator SI8620BB.
In my opinion, a simple and suitable solution for piece production with 12A excitation MOSFET. The pair of MOSFETs can theoretically withstand 600A, limiting the resistance of the PCB, probably ALPCB

Controls
STM32F334 is MCU with High-resolution timer 217ps for digital power conversion and they can directly control the full H bridge
MCU is on buttom and drive bridge, measure U on bridge and current on bridge voltage drop at Q5.



PCB.jpg
 

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  • Schematic Prints.pdf
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I wonder if your DC TIG limits its output voltage to safe values for the MOSFET bridge?
 

Good question .
We have a fairly precise inverter
On 20A is output voltage 21V
On 80A is output voltage 22V
Voltage without load does not exceed 50V.
At a given switching speed, it is 80V in the entire SOA current range
Infineon offers similar transistors for 100V, but RdsOn 2mOhm

The question is HF ignition? 7
At the output of the inverter (behind the bridge) there is a coil/transformer on which the HF and HV voltage of about 6 kV is infected, which ignites the arc.
I admit, I haven't researched how it works yet, but the diodes at the inverter output don't mind.
 

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