Hi folks,
I am building a dimmable 300w PFC LED driver using TI's TPS92075 and their design spreadsheet with the buck/boost topology.
It takes 120v, dimmed with a regular dimmer, and is supposed output a calibrated max of 2.4A @ ~95vdc for a string of 3 100w, 30-32v LED chips. (=<240w; these are Chinese LEDs, so it is recommended not to run them at full power)
I sized all my components for at least 300w, hoping to reduce heat and consequently the need for fan cooling.
However, when powering it up, outputting ~80v, 2a, my efficiency is roughly the same as it would be if I used a linear regulator. Consequently the MOSFET and the inductor get very hot after only a short time. Also, to get 2a, I have to reduce the resistance of the current sense resistor, presumably because the energy needed to get the full 2.4a is getting wasted in inefficiencies. Also, if I tweak the current up much higher than 2a, my MOSFET short-circuits. I have no clue why!
Everything else functions great, the TPS92075 is truly an amazing chip!
Drive MOSFET: IPA60R460CE
Inductor: PM2120-221K-RC (MOUSER link)
Diode: BYV29FX-600
Schematic: attached
I currently have the TPS92075 in a breadboard, so I can fine tune the angle sense, as well as add overheat/overvoltage protection. The switching circuit, as well as the AC filter capacitors I have soldered, so my breadboard is not causing added resistance problems there. The TPS92075 is getting powered by an external isolated bench supply at the moment. There is a solid ground connection between the two, and noise is not enough to cause problems. I have monitored the MOSFET's gate to make sure it is getting a clean signal with enough voltage, and everything looks very good through the oscilloscope; the MOSFET is getting at least 10v and a nearly perfect cut-on to the gate.
I'm thinking that maybe I somehow sized the inductor wrong. Though that doesn't explain why the MOSFET blows when I go much over 2a. Unfortunately, I don't have a /10 probe for my oscilloscope, so the highest voltage I can measure with it is at best 80v. Thusly, I can't measure to see if the drain voltage is going too high or too low. Though I highly doubt the MOSFET's 600v top limit is getting exceeded.
Thanks guys, any help/ideas will be greatly appreciated.
I am building a dimmable 300w PFC LED driver using TI's TPS92075 and their design spreadsheet with the buck/boost topology.
It takes 120v, dimmed with a regular dimmer, and is supposed output a calibrated max of 2.4A @ ~95vdc for a string of 3 100w, 30-32v LED chips. (=<240w; these are Chinese LEDs, so it is recommended not to run them at full power)
I sized all my components for at least 300w, hoping to reduce heat and consequently the need for fan cooling.
However, when powering it up, outputting ~80v, 2a, my efficiency is roughly the same as it would be if I used a linear regulator. Consequently the MOSFET and the inductor get very hot after only a short time. Also, to get 2a, I have to reduce the resistance of the current sense resistor, presumably because the energy needed to get the full 2.4a is getting wasted in inefficiencies. Also, if I tweak the current up much higher than 2a, my MOSFET short-circuits. I have no clue why!
Everything else functions great, the TPS92075 is truly an amazing chip!
Drive MOSFET: IPA60R460CE
Inductor: PM2120-221K-RC (MOUSER link)
Diode: BYV29FX-600
Schematic: attached
I currently have the TPS92075 in a breadboard, so I can fine tune the angle sense, as well as add overheat/overvoltage protection. The switching circuit, as well as the AC filter capacitors I have soldered, so my breadboard is not causing added resistance problems there. The TPS92075 is getting powered by an external isolated bench supply at the moment. There is a solid ground connection between the two, and noise is not enough to cause problems. I have monitored the MOSFET's gate to make sure it is getting a clean signal with enough voltage, and everything looks very good through the oscilloscope; the MOSFET is getting at least 10v and a nearly perfect cut-on to the gate.
I'm thinking that maybe I somehow sized the inductor wrong. Though that doesn't explain why the MOSFET blows when I go much over 2a. Unfortunately, I don't have a /10 probe for my oscilloscope, so the highest voltage I can measure with it is at best 80v. Thusly, I can't measure to see if the drain voltage is going too high or too low. Though I highly doubt the MOSFET's 600v top limit is getting exceeded.
Thanks guys, any help/ideas will be greatly appreciated.
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