L5 short?
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Author:  gerryk [ Mon Oct 29, 2018 3:43 am ]
Post subject:  L5 short?

I am approaching the end of the main PCB build and before I carry on to apply power, I want to check something... should I see a short circuit between all terminals on L5? I see that 1 & 3 are both earthed or at least common, so that it seems like it is to be expected, but feels strange to me.

Author:  jimveatch [ Mon Oct 29, 2018 5:26 am ]
Post subject:  Re: L5 short?

Hi Gerry,

Yes all of L5's terminals are at the same DC potential: 13.8V. L5 provides Vdd to the MOSFET drain terminals. It's setup so that the current for Q1 and Q2 flows in the opposite physical direction than the current for Q3 and Q4 which means that the net current in the core is very close to zero even when the amp is drawing 10 amps. This, in turn, keeps L5's core from saturating so it can do it's job of blocking the RF present at the MOSFET drains from making it's way to the DC power terminals.

If you had inadvertently crossed the loops of L5 (which happens from time to time) you wouldn't see continuity between all of the terminals and the amp wouldn't work.


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