blasphemy000
New member
Dear Friends:
I am currently in the planning/designing phase of building a Switch-Mode TIG welder and I have some questions. Before anybody asks, I have built several lower-power <500W SMPSs in the past, as well as one 1000W SMPS(The miniature version of this welder). I've built a couple really tiny <10W SMPSs as well, but this welder will be my largest power supply I've ever built so I am taking many precautions. I do have a scope and a home-brew differential probe as well as several 100X probes and as soon as my next paycheck comes in I will be purchasing a real differential probe to help with the building of this beast. I am fully aware of the high voltages involved in such a power supply and the lethality of such voltages and current. Anyways, on to the project.
Input voltage will be supplied from 240VAC mains voltage, rectified, then filtered by 8x1000uF/400VDC capacitors. I ABSOLUTELY MUST HAVE a very robust soft-start circuit to charge these so that the inrush current is minimal and the voltage surge to the H-Bridge is minimal as well. Any ideas here? This will give approximately 340VDC across the H-Bridge.
Output voltage will be ~30-40VDC with a maximum of ~250-300A.
Output regulation will be variable voltage/constant current as is required by a TIG or Stick welder.
Current feedback will be supplied by TWO current transformers:
One on the secondary side to provide feedback for the normal operating range.
And one on the primary side to provide a shutdown mechanism should the transformer's primary current exceed the maximum limit.
To prevent a high OCV(Open Circuit Voltage) and to also prevent the PWM controller from running at max duty-cycle when idle, I am also incorporating an opto-isolated voltage feedback circuit on the output to limit the duty-cycle to the minimum when there is no load on the output.
The main switching transformer will be wound on double-stacked Ferroxcube EE80/38/20 cores.
The secondary side will be wound with 1.0mm X 54mm copper strip. 2-Turns.
The primary side will be wound with 30 strands of 0.75mm wire. 14-Turns.
This was calculated using the program from here(http://www.diysmps.com/forums/showthread.php?275-SMPS-transformer-design-tool).
The output inductor will be wound on a single EE80/38/20 core using copper strip. How do I calculate the amount of turns for this?
Output rectification will be a full-bridge provided by 8xSTTH200L06TV1 ultra-fast diode packs. 2 in parallel for each of the 4 diodes.
The STTH200L06TV1 diode packs contain 2x120A ultra-fast diodes(so 240A per package) and can easily be bolted to a very large heat-sink.
Does anybody know of an ultra-fast diode or diode pack that will handle more power so that I would only need 4 instead of 8?
Topology is a full H-Bridge running at 25KHz in hard-switching. Pulse-Width-Modulation will be provided by a TL494(Because I'm almost a master at using this chip and its VERY easy to control.) giving a maximum duty-cycle of 44%.
Gate drive will be provided by IR2110s that will be opto-isolated from the TL494 using an SFH6732: http://www.vishay.com/docs/83685/sfh6731.pdf
This chip provides two isolators per chip and features a totem-pole output to ensure fast triggering.
I'm using the opto-isolators so that the TL494 and its associated circuitry can be earth grounded to provide isolation for the user controls since the IR2110 will be directly hooked to the H-Bridge.
Switching transistors will be IGBTs. My original plan was to use 8 of these: IRG4PF50WDPbF
I have since changed my plan and I intend to use 8 of these instead: HGTG30N60A4D
I decided on the change of device due to the fact that the latter IGBT(according to the datasheet) will handle it's full 60A@110*C rating below 30KHz whereas the former IGBT will only handle its full rating of 28A@100*C below 1KHz where the current capability begins to fall off sharply and is down to 10A at 25KHz.
According to the transformer calculator the peak primary winding current will be just under 50A at peak output current.
I calculated the transformer using a 300A output current but if I am able to squeeze out 250A of usable current I will be happy with this unit. If I can get a peak output current of 300A, I'm only shooting for a 20% duty-cycle at that amperage. This means that the power supply should be able to sustain 300A of output current for 2 minutes, then have a cool-down period of 8 minutes. This is how the welding industry rates the duty-cycle of their welding power supplies. At 250A I'm shooting for at least a 40% duty-cycle. At 200A I'm shooting for 70% DC. And below 175A I'm shooting for 100% DC, meaning that my power supply should be able to supply 175A or less continuously without overheating or damaging components.
I will incorporate a thermal overload protection using several temperature sensors placed as close to the switching IGBTs and the output diodes as possible to get the most accurate temperature readings.
As for the final output stage, after the output from the switching transformer is rectified and filtered it will then pass through another large IGBT H-Bridge using these devices: CM300-12NF from Powerex. These are dual IGBT modules so I will only need 2 modules to create a full-bridge. The datasheet says these devices can handle 300A DC and much more when pulsed. This output stage is so that I can provide a simple logic-level toggle switch to change the output from DC+, DC-, or AC output. When the output is in AC mode the frequency will be variable from 20-250Hz and the duty-cycle of the output stage will be fixed at the maximum amount allowed by the devices, with some added dead-time for insurance, to ensure that the maximum amount of current is passed through the output stage. The output current will still be controlled by varying the DC of the switching transformer.
The output IGBT modules will be driven by these gate drivers, also provided by Powerex: BG2B-5015
These attach directly to the modules and are the recommended drivers for these modules.
I think this is all of my plan, but if I've forgotten anything or have any more questions I will be sure to post a follow-up. Sorry for such a long post. I just wanted to detail out my project as much as possible so you guys can all get an idea of what I am undertaking here. I also hope everyone understands that this project will be very slow-going as I am not made of money and many of these high-current devices are very expensive, especially the IGBTs for the chopper stage and the output rectifier diodes.
Here is the design of the switching H-Bridge circuit board. I've tried to make it as compact as possible and I am planning on getting the board made with as thick of traces as possible(4oz). The board measures 4in by 3in and is double sided, although the only traces on the top side are for the gate drive. The switching transformer will be mounted directly below this bridge board to keep the leads between the transformer and the bridge as short as possible. They should be < 1/2inch long. The gate driver board will then mount directly above(on top) the bridge board to keep the gate drive leads as short as possible as well. Also the gate-drive leads will be made with double-shielded wire if possible. The IGBTs mount on top of the board with their backs facing outwards. The heatsinks will consist of 4in x 4in square tube with the fins on the inside of the tube. I will utilize two tubes, one for each side of the board, and the tubes will run the entire length of the welder's case with forced-air cooling blowing through the insides of the tubes. The air will intake at one end of the welder and blow out the other end. Anyways, here is the bridge board, green is the bottom layer of copper and brown is the top. If you don't quite get my idea for cooling, I will soon be posting a drawing of how I envision it.
View attachment Bridge Board.pdf
I am currently in the planning/designing phase of building a Switch-Mode TIG welder and I have some questions. Before anybody asks, I have built several lower-power <500W SMPSs in the past, as well as one 1000W SMPS(The miniature version of this welder). I've built a couple really tiny <10W SMPSs as well, but this welder will be my largest power supply I've ever built so I am taking many precautions. I do have a scope and a home-brew differential probe as well as several 100X probes and as soon as my next paycheck comes in I will be purchasing a real differential probe to help with the building of this beast. I am fully aware of the high voltages involved in such a power supply and the lethality of such voltages and current. Anyways, on to the project.
Input voltage will be supplied from 240VAC mains voltage, rectified, then filtered by 8x1000uF/400VDC capacitors. I ABSOLUTELY MUST HAVE a very robust soft-start circuit to charge these so that the inrush current is minimal and the voltage surge to the H-Bridge is minimal as well. Any ideas here? This will give approximately 340VDC across the H-Bridge.
Output voltage will be ~30-40VDC with a maximum of ~250-300A.
Output regulation will be variable voltage/constant current as is required by a TIG or Stick welder.
Current feedback will be supplied by TWO current transformers:
One on the secondary side to provide feedback for the normal operating range.
And one on the primary side to provide a shutdown mechanism should the transformer's primary current exceed the maximum limit.
To prevent a high OCV(Open Circuit Voltage) and to also prevent the PWM controller from running at max duty-cycle when idle, I am also incorporating an opto-isolated voltage feedback circuit on the output to limit the duty-cycle to the minimum when there is no load on the output.
The main switching transformer will be wound on double-stacked Ferroxcube EE80/38/20 cores.
The secondary side will be wound with 1.0mm X 54mm copper strip. 2-Turns.
The primary side will be wound with 30 strands of 0.75mm wire. 14-Turns.
This was calculated using the program from here(http://www.diysmps.com/forums/showthread.php?275-SMPS-transformer-design-tool).
The output inductor will be wound on a single EE80/38/20 core using copper strip. How do I calculate the amount of turns for this?
Output rectification will be a full-bridge provided by 8xSTTH200L06TV1 ultra-fast diode packs. 2 in parallel for each of the 4 diodes.
The STTH200L06TV1 diode packs contain 2x120A ultra-fast diodes(so 240A per package) and can easily be bolted to a very large heat-sink.
Does anybody know of an ultra-fast diode or diode pack that will handle more power so that I would only need 4 instead of 8?
Topology is a full H-Bridge running at 25KHz in hard-switching. Pulse-Width-Modulation will be provided by a TL494(Because I'm almost a master at using this chip and its VERY easy to control.) giving a maximum duty-cycle of 44%.
Gate drive will be provided by IR2110s that will be opto-isolated from the TL494 using an SFH6732: http://www.vishay.com/docs/83685/sfh6731.pdf
This chip provides two isolators per chip and features a totem-pole output to ensure fast triggering.
I'm using the opto-isolators so that the TL494 and its associated circuitry can be earth grounded to provide isolation for the user controls since the IR2110 will be directly hooked to the H-Bridge.
Switching transistors will be IGBTs. My original plan was to use 8 of these: IRG4PF50WDPbF
I have since changed my plan and I intend to use 8 of these instead: HGTG30N60A4D
I decided on the change of device due to the fact that the latter IGBT(according to the datasheet) will handle it's full 60A@110*C rating below 30KHz whereas the former IGBT will only handle its full rating of 28A@100*C below 1KHz where the current capability begins to fall off sharply and is down to 10A at 25KHz.
According to the transformer calculator the peak primary winding current will be just under 50A at peak output current.
I calculated the transformer using a 300A output current but if I am able to squeeze out 250A of usable current I will be happy with this unit. If I can get a peak output current of 300A, I'm only shooting for a 20% duty-cycle at that amperage. This means that the power supply should be able to sustain 300A of output current for 2 minutes, then have a cool-down period of 8 minutes. This is how the welding industry rates the duty-cycle of their welding power supplies. At 250A I'm shooting for at least a 40% duty-cycle. At 200A I'm shooting for 70% DC. And below 175A I'm shooting for 100% DC, meaning that my power supply should be able to supply 175A or less continuously without overheating or damaging components.
I will incorporate a thermal overload protection using several temperature sensors placed as close to the switching IGBTs and the output diodes as possible to get the most accurate temperature readings.
As for the final output stage, after the output from the switching transformer is rectified and filtered it will then pass through another large IGBT H-Bridge using these devices: CM300-12NF from Powerex. These are dual IGBT modules so I will only need 2 modules to create a full-bridge. The datasheet says these devices can handle 300A DC and much more when pulsed. This output stage is so that I can provide a simple logic-level toggle switch to change the output from DC+, DC-, or AC output. When the output is in AC mode the frequency will be variable from 20-250Hz and the duty-cycle of the output stage will be fixed at the maximum amount allowed by the devices, with some added dead-time for insurance, to ensure that the maximum amount of current is passed through the output stage. The output current will still be controlled by varying the DC of the switching transformer.
The output IGBT modules will be driven by these gate drivers, also provided by Powerex: BG2B-5015
These attach directly to the modules and are the recommended drivers for these modules.
I think this is all of my plan, but if I've forgotten anything or have any more questions I will be sure to post a follow-up. Sorry for such a long post. I just wanted to detail out my project as much as possible so you guys can all get an idea of what I am undertaking here. I also hope everyone understands that this project will be very slow-going as I am not made of money and many of these high-current devices are very expensive, especially the IGBTs for the chopper stage and the output rectifier diodes.
Here is the design of the switching H-Bridge circuit board. I've tried to make it as compact as possible and I am planning on getting the board made with as thick of traces as possible(4oz). The board measures 4in by 3in and is double sided, although the only traces on the top side are for the gate drive. The switching transformer will be mounted directly below this bridge board to keep the leads between the transformer and the bridge as short as possible. They should be < 1/2inch long. The gate driver board will then mount directly above(on top) the bridge board to keep the gate drive leads as short as possible as well. Also the gate-drive leads will be made with double-shielded wire if possible. The IGBTs mount on top of the board with their backs facing outwards. The heatsinks will consist of 4in x 4in square tube with the fins on the inside of the tube. I will utilize two tubes, one for each side of the board, and the tubes will run the entire length of the welder's case with forced-air cooling blowing through the insides of the tubes. The air will intake at one end of the welder and blow out the other end. Anyways, here is the bridge board, green is the bottom layer of copper and brown is the top. If you don't quite get my idea for cooling, I will soon be posting a drawing of how I envision it.
View attachment Bridge Board.pdf