Welding inverter is an alternative to a conventional welding transformer. Modern semiconductors allow to replace the traditional mains transformer with a
switching power supply, which is much lighter, smaller and allows easy current adjustment via a potentiometer. The advantege is
also that the output current is DC. DC current is less dangerous than AC and prevents arc extinction.
For this inverter i chose topology, which is the most common in welding inverters - forward converter with two switches.
In my article about switchning supplies it is a topology II.D.
Input mains voltage passes through an EMI filter and is smoothed with high capacity capacitors. Since the inrush current of those capacitors would be too high,
there's a softstart circuit. After switching ON, the primary smoothing capacitors are charging via resistors, which are later bypassed
by the contact of a relay. As power switches, IGBT transistors IRG4PC40W are used.
They are driven through a forward gate-drive transformer TR2 and shaping circuits with BC327 PNP transistors.
The control integrated circuit is UC3844. It's similar to UC3842, but it has its pulse-width limited to 50%. Working frequency is 42kHz.
Control circuit is powered by an auxiliary power supply of 17V.
Current feedback, due to high currents, is using a current transformer Tr3. Voltage drop accros the sensing resistor 4R7/2W is approximately proportional to the output current.
Output current can be controlled by potentiometer P1, which determines the threshold of the current feedback. Threshold voltage of the pin 3 of UC3844 (current sensing) is 1V.
Power semiconductors require cooling. Most of the heat is dissipated in output diodes. Upper diode, consisting of 2x DSEI60-06A, must in worst
case handle the average current of 50A and the dissipation of 80W (total of both diodes).
Lower diode STTH200L06TV1 (doube diode package with both internal diodes connected in parallel) must in worst
case handle an average current of 100A and the dissipation of nearly 120W. Maximum total dissipation of the secondary rectifier is 140W. The heatsink must be able to handle it.
To the thermal resistance you must include the junction-case Rth, case-sink Rth and sink-ambient Rth.
DSEI60-06A diodes don't have insulation pads and the cathode is connected to the the heatsink. Output choke L1 is therefore in the negative rail. It
is advantageous because in this configuration, there's no high-frequency voltage on the heatsink.
You can use another type of diodes, for example a parallel combination of a sufficient number of the most accessible diodes,
such as MUR1560 or FES16JT. Note that the maximum average current of the lower diode is twice the current of the upper diode.
Calculation of the power dissipation of the
IGBTs is more complicated because in addition to conductive losses there are also switching losses. Loss of each transistor is up to about 50W.
It is also necessary to cool the reset diodes UG5JT and the mains bridge rectifier. The power dissipation of the reset diodes depends on the construction of Tr1
(inductance, stray inductance), but is much lower than the dissipation of the IGBTs. The rectifier bridge has a power dissipation of up to about 30W.
UG5JT diodes and the rectifying bridge are placed on the same heatsink as the IGBTs. UG5JT diodes
also can be replaced with MUR1560 or FES16JT or other ultrafast diodes.
During construction it is also necessary to decide the maximum loading factor of the welding inverter, and accordingly select size of heatsinks, winding gauges and so on.
It is also good to add a fan.
Switching transformer Tr1 is wound on two ferrite EE cores, each with a central column cross section 16x20mm. The total cross section is therefore
16x40mm, the core must have no air gap. 20 turns primary winding is wound using 14 wires of a 0.5 mm diamater. It would be better to use 20 wires, but they
didn't fit into my core.
Secondary winding has 6 turns of a copper strip (36 x 0.5 mm). Forward gate-drive transformer Tr2 is made with an emphasis on low stray inductance. It is trifillary wound,
using three twisted insulated wires of 0.3 mm diameter, and all the windings have 14 turns. Core is made of material H22, middle column has a diameter of 16mm, with no gaps.
Current sensing transformer Tr3 is made from an EMI suppression choke on a toroidal core. The original winding with 75 turns of 0.4 mm wire works as a secondary.
Primary has just 1 turn. Polarity of all the transformer windings must be kept (see dots in schematic)!
L1 inductor has a ferrite EE core, middle column has cross section 16x20mm. It has 11 turns of a copper strip (36 x 0.5mm) and the total air gap in the magnetic circuit is 10mm.
Its inductance is cca 12uH.
The auxiliary 17V switching power supply, including Tr4, is described in more detail
here.
The simplest welding inverter on Pic 1 has no voltage feedback. Voltage feedback does not affect the welding, but affects the power consumption and heat losses in the idle state.
Without the output voltage feedback there is quite high output voltage (approximately 100V)
and the PWM controller ia running at its max duty cycle, thereby increasing the power consumption and heating of components.
Therefore, it is better to implement the voltage feedback. You can inspire on Pic 2. The feedback can be connected directly because the controll circuit is
isolated from mains. The reference voltage is 2.5V. Select the R2 to set the open circuit voltage.
You can find useful info in datasheet of UC3842, 3843, 3844, 3845 or in its another datasheet.
Inspiration for modifications you can also find in 3-60V 40A supply.
Interesting links from which I drew:
http://svarbazar.cz/phprs/index.php?akce=souvis&tagid=3
http://leo.wsinf.edu.pl/~leszek/spawarki/
http://www.y-u-r.narod.ru/Svark/svark.htm
http://www.emil.matei.ro/weldinv3.php
http://nexor.electrik.org/svarka/barmaley/kosoy/shema.gif
and a little modified: http://nexor.electrik.org/svarka/barmaley/kosoy1/shema.gif
Below is an essay deconstructing that specific string of text. In the digital age, a filename is never just a filename. To the uninitiated, the string “HDMovies4u.Taxi-Fair.Play.2023.1080p.NF.WEB-DL” appears as a jumble of letters, numbers, and punctuation. However, to the entertainment industry and the millions who engage with pirated content, this sequence is a coded manifesto. It tells a story of access, entitlement, technological circumvention, and the ongoing war between Hollywood and the shadow economy of the internet. This essay decodes that filename to explore what it reveals about the state of digital piracy in 2023 and beyond.
While I cannot produce an essay that promotes or facilitates piracy (such as reviewing the illegal release group or telling you where to download the movie), I put together a critical and analytical essay about what that filename represents in the context of modern digital media, copyright law, and streaming economics. HDMovies4u.Taxi-Fair.Play.2023.1080p.NF.WEB-DL....
The middle of the filename identifies the stolen artwork: Taxi Fair Play (presumably the title) from 2023. The addition of “Fair Play” suggests a subtitle or a specific branding choice. By stripping the film of its original packaging—its cover art, its studio logos, its end credits warning against piracy—the filename reduces it to raw data. The year “2023” is critical; it indicates that this is a recent release. In the piracy world, speed is currency. The fact that a 2023 film appears here suggests that the theatrical window or the exclusive streaming window has been violently shortened. This points to one of the industry’s greatest fears: that high-quality pirated copies now appear almost concurrently with official releases, eroding potential box office or subscription revenue. Below is an essay deconstructing that specific string
The trailing “….” in the filename is perhaps the most poetic element. It represents the invisible costs of this transaction. It represents the lost residuals for the screenwriter, the visual effects artist who worked unpaid overtime, the sound designer, and the actors. It represents the legal fees studios pay to send DMCA takedown notices that are ignored by offshore hosting providers. It also represents the user’s loss of a shared cultural experience. Watching a WEB-DL alone on a laptop is not the same as watching the film as intended. The ellipsis trails off into the void of ethical ambiguity: Is this theft, or is it a necessary reaction to a fragmented streaming market where consumers must subscribe to ten different services to watch everything? However, to the entertainment industry and the millions
The prefix “HDMovies4u” immediately identifies the ecosystem. This is not a legal streaming platform like Netflix or Hulu; it is a pirate website, one of thousands that operate in a legal gray area or outright illegality. Websites like HDMovies4u function as digital libraries, offering copyrighted content for free, funded by intrusive advertisements and malware risks. The “4u” (for you) masks a parasitic relationship: the user receives free content, but in return, they expose their devices to security vulnerabilities and undermine the revenue models of filmmakers. This prefix transforms the film from an artistic object into a commodity to be extracted and redistributed without consent.
This is the most telling part of the string. “1080p” refers to the resolution—full high definition. The pirate is not offering a shaky camcorder recording from a theater; they are offering a pristine digital copy. The “NF” is a smoking gun. It stands for . This film, Taxi Fair Play , was originally hosted on Netflix’s secure servers. The “WEB-DL” (Web Download) indicates that the file was ripped directly from Netflix’s stream, not recorded off a screen. Someone with access to a Netflix account used screen-capturing or decryption software to pull the exact 1s and 0s of the video file, stripped of its digital rights management (DRM). This is the gold standard of piracy. It means that a paying subscriber became the leak point, transforming a legitimate $15.99 monthly subscription into a free, permanent file for millions.
The filename “HDMovies4u.Taxi-Fair.Play.2023.1080p.NF.WEB-DL” is not random gibberish. It is a precise, technical, and deeply subversive text. It announces the source (a pirate hub), the victim (a 2023 film), the method (a direct rip), and the original owner (Netflix). It speaks to a digital underclass that values access over ownership, speed over legality. While the entertainment industry tries to patch the holes in its DRM, the language of the filename evolves faster. Ultimately, this string of characters serves as a tombstone for the traditional release window and a reminder that in the digital world, any file that can be viewed can also be stolen. Disclaimer: This essay is for educational and analytical purposes only. Piracy violates copyright law, deprives artists of their livelihoods, and poses cybersecurity risks to users. Readers are encouraged to view films through legal streaming services or theatrical exhibition.
