Graydust999
Newbie
Hello. I'm working on a single IGBT module circuit with high side switching. This is for a plastic sealing application (apply controlled power to a heat element wire). My circuit works well in simulation (LTspice) and I've built the circuit and tested successfully at lower power levels. When high power is applied the IGBT is destroyed immediately on the first gate activation (holds voltage fine until fired). I have read several application notes and studied the specs and I'm pulling my hair out.
Background: This control is typically done with SCR or triac based phase angle control. I wanted to test an IGBT based design because of their availability and high current capability. The goal was to simplify the circuit and minimize components so that our field techs can troubleshoot. I also wanted to minimize changes to our overall machine design, which is why I chose to control the secondary side of our seal transformer (not shown in the schematic, 3 phase 460VAC to single phase 160VAC). Feel free to comment on the feasibility of the IGBT vs SCR methodology, but the purpose of my post is to learn why my IGBT is failing at higher currents. It seems to me that I'm well within the safe operating range of the device. I have a large heat sink attached, but this doesn't seem to be a thermal issue (fails immediately, never gets warm). Here's the details:
IGBT model: IXYS IXGN320N60A3 (data sheet attached)
DC to DC converter for the 15VDC boost (shown in the schematic) is done with a Recom Power RK-2415S/H (4kvdc isolation).
Benchtop test circuit (works well) - 120VAC supply, rectified to 195VDC peak to peak (oscope), 1khz pwm signal to a mosfet gate. The mosfet controls voltage to the IGBT gate. Load is a 60ohm incandescent lamp. Output waveform is clean. Test successful.
Simulation in LTspice - Schematic and results attached. Note the "DC" source to the IGBT is rectified but not filtered or smoothed. Smoothing the output is challenging due to the rapid discharge to the 1ohm heater element (the capacitor would be huge). I decided to eliminate smoothing capacitors because the load in this application doesn't care about the waveform. Test successful.
High power test - 1 phase 160VAC supply from a transformer, rectified to 210VDC (meter reading, likely 227 peak), same gate control circuit as used on the bench test. Load is a 1 ohm heater wire. The seal power via PWM was set to 5% and the seal time was limited to 500ms. Voltage is held in the off-state with no problems. IGBT immediately fails (audible pop, bright blue arc flash) when the seal is triggered. At the 227VDC on a 1 ohm load, current should be 227A. My IGBT has a max Ic of 320A and Vce of 600V. I'm at room temp. Per the manufacturer's safe operating parameters, this should be okay. What am I missing?
Please note that the circuit shown is for proof of concept only and is not intended to be a robust final design (be nice if you can). I have not included a snubber circuit because the load is not inductive and, again, proof of concept only. Also, this is not my engineering area of expertise, so roast me if its warranted.
For information, our traditional seal unit (triac phase angle based) uses about 70VAC @ 70A to seal plastic. FWIW, I now believe the phase angle method is more robust, but I still want to understand this application.
I'm sure I've left out something so please just ask and I'll add detail as needed.
Thank you very much for any suggestions or thoughts you can offer!
IGBT datasheet
I see that my IGBT has a "terminal limit" of 200A, so perhaps I'm arcing across terminals. I am crossing that threshold. Would that short the IGBT? Perhaps this is the answer but I'd like to hear other opinions. If the IGBT just needs to be bigger, that's fine. I just don't want destroying them to be my test method. Thank you.
Background: This control is typically done with SCR or triac based phase angle control. I wanted to test an IGBT based design because of their availability and high current capability. The goal was to simplify the circuit and minimize components so that our field techs can troubleshoot. I also wanted to minimize changes to our overall machine design, which is why I chose to control the secondary side of our seal transformer (not shown in the schematic, 3 phase 460VAC to single phase 160VAC). Feel free to comment on the feasibility of the IGBT vs SCR methodology, but the purpose of my post is to learn why my IGBT is failing at higher currents. It seems to me that I'm well within the safe operating range of the device. I have a large heat sink attached, but this doesn't seem to be a thermal issue (fails immediately, never gets warm). Here's the details:
IGBT model: IXYS IXGN320N60A3 (data sheet attached)
DC to DC converter for the 15VDC boost (shown in the schematic) is done with a Recom Power RK-2415S/H (4kvdc isolation).
Benchtop test circuit (works well) - 120VAC supply, rectified to 195VDC peak to peak (oscope), 1khz pwm signal to a mosfet gate. The mosfet controls voltage to the IGBT gate. Load is a 60ohm incandescent lamp. Output waveform is clean. Test successful.
Simulation in LTspice - Schematic and results attached. Note the "DC" source to the IGBT is rectified but not filtered or smoothed. Smoothing the output is challenging due to the rapid discharge to the 1ohm heater element (the capacitor would be huge). I decided to eliminate smoothing capacitors because the load in this application doesn't care about the waveform. Test successful.
High power test - 1 phase 160VAC supply from a transformer, rectified to 210VDC (meter reading, likely 227 peak), same gate control circuit as used on the bench test. Load is a 1 ohm heater wire. The seal power via PWM was set to 5% and the seal time was limited to 500ms. Voltage is held in the off-state with no problems. IGBT immediately fails (audible pop, bright blue arc flash) when the seal is triggered. At the 227VDC on a 1 ohm load, current should be 227A. My IGBT has a max Ic of 320A and Vce of 600V. I'm at room temp. Per the manufacturer's safe operating parameters, this should be okay. What am I missing?
Please note that the circuit shown is for proof of concept only and is not intended to be a robust final design (be nice if you can). I have not included a snubber circuit because the load is not inductive and, again, proof of concept only. Also, this is not my engineering area of expertise, so roast me if its warranted.
For information, our traditional seal unit (triac phase angle based) uses about 70VAC @ 70A to seal plastic. FWIW, I now believe the phase angle method is more robust, but I still want to understand this application.
I'm sure I've left out something so please just ask and I'll add detail as needed.
Thank you very much for any suggestions or thoughts you can offer!
--- Updated ---
IGBT datasheet
--- Updated ---
I see that my IGBT has a "terminal limit" of 200A, so perhaps I'm arcing across terminals. I am crossing that threshold. Would that short the IGBT? Perhaps this is the answer but I'd like to hear other opinions. If the IGBT just needs to be bigger, that's fine. I just don't want destroying them to be my test method. Thank you.
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