TIDA-00120: Q1 Purpose?

Joshua Harris

Part Number: TIDA-00120
Other Parts Discussed in Thread: LM5019

This may be a dumb question, but I am scratching my head on this circuit because it appears that the VCC is powered from the panel voltage but the panel ground is isolated until VCC is created. How does the egg come before the chicken?

over 7 years ago

0 Marion Loessl over 7 years ago

TI__Expert 3925 points

Hello Mr Harris,

please excuse the delay in the response. To be honest, I can only make assumptions right now, so I will come back to you with an answer as soon as possible. Kind regards,
Marion

0 Marion Loessl over 7 years ago

TI__Expert 3925 points

Hello Mr Harris,

you are right on the isolated grounds. However the body diode of the Mosfet Q1 allows the capacitors to charge to a voltage that is high enough to power the LM5019 to power the VCC. Then Q1 is used as a switch and a signal can be generated with the MSP430 to open the Mosfet Q1 using the bipolar transistor Q8.

I hope this answers your question.
Kind regards,
Marion

0 Joshua Harris over 7 years ago in reply to Marion Loessl

Prodigy 210 points

Interesting, thank you for the information. I was thinking there must be some kind of leakage current.

Thank you!

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TIDA-00120: Q1 Purpose?