driving large module gates

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pager48

Joined Nov 25, 2018
161
Are there specialty shielded cables for driving the gates of ISOTOP or power brick MOSFETs or IGBTs in noisy environments?

Would a regular RG-58 coax work better than an ordinary unsheilded cable?
 
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crutschow

Joined Mar 14, 2008
34,285
Depends upon the nature of the noise and how fast you need to drive the transistors.
In general, a coax will work well for shielding, but it needs to driven by a source capable of driving the cables characteristic impedance, (typically 50Ω or 75Ω) to the desired gate voltage if you are operating the transistors at a high frequency.

Likely better would be to send a low voltage signal down the coax and then amplify that at the transistor gate to the desired voltage.
 

cmartinez

Joined Jan 17, 2007
8,220
Pulsetrain the cable is ~12cm length. Only grounding the braid gives shielding?

Its probably better to isolate gate driver with fiber optic and place it next to the module than using a coax.
You don't need coax for that ... ordinary shielded cable should do the trick, especially at such low frequecies. Also, noise originating from the circuit's power supply will be far more influential than external EMI at those distances.
 

cmartinez

Joined Jan 17, 2007
8,220
Such as using all the wires for one connection from a RJ - STP cable?
You could do that, but it would be overkill. Is the cable directly connected to the IGBT's gate? Or is it connected to a driver, and then to the transistor's gate? In short, what voltage is being used on the cable?

Things get more complicated when you're talking frequencies above 10 KHz when switching Mosfets and IGBT's. But I've switched said transistors at 7 KHz with no problem whatsoever.
 
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