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Author Topic: Dielectric fluid filled PCB enclosure for heat dissipation  (Read 1115 times)
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jtw11
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« Reply #15 on: March 16, 2013, 10:37:55 am »
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I'm using the suppressors to deal with flyback when switching inductive loads, as per my other thread you've helped in - hence the power dissipation.

The MOSFETs have an on resistance of only a few mOhms, and are only switching ~5A at the 10s of kHz.

The IGBTs are driving inductive loads, at currents of ~10A up to around 75Hz. The h-bridge is a VNH2SP30, so no - no bipolars here thankfully! Stepper chip uses MOSFETs in the bridges too.

The problem will arise in the future I foresee, with up to 20 high side switches potentially, so this thread was more to get a feel to see if the solution was viable re cooling.

Cheers!
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dc42
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« Reply #16 on: March 16, 2013, 02:24:39 pm »
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It's worth measuring the resistance of the inductive load, then you can work out what proportion of the stored energy will be dissipated in the load and what will be dissipated in the TVS diode. Also, consider what fall time of the current you need in the inductive load. The higher the voltage rating of the TVS diode, the faster will be the fall time - but the greater the proportion of energy dissipated in the TVS diode.
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