PTN78000H: Placing a zener diode between the input and output

Steve Long

Part Number: PTN78000H

I'm using PTN78000H to convert 28VDC to 20VDC. In order to protect several MOSFETs that are between the 28 and 20 VDC rails, I plan to place a 15VDC Zener diode between the input and output of PTN78000H. This will pull up the output of PTN78000H when 28VDC is applied to the input. Will pulling up the output of PTN78000H damage the converter?

over 6 years ago

0 Tom Guerin over 6 years ago

TI__Mastermind 38230 points

Steve:

The placement of a 15V zener diode between Vin and Vout will likely over current the zener diode stressing it and it will short across PTN78000H Vin to Vout

Tom

0 Steve Long over 6 years ago in reply to Tom Guerin

Prodigy 20 points

I've simulated this with 33uF caps on Vin. The Zener allows current to flow from Vout to Vin during start up which charges the caps and lifts the voltage of Vout up. The zener is rated for the power that is dissipated. What I'm concerned about is will PTN78000H be degraded by lifting it's output voltage up in this manner during start up?

0 Tom Guerin over 6 years ago in reply to Steve Long

TI__Mastermind 38230 points

Steve:

Lets take this off line. My direct e-mail is tguerin@ti.com

Thanks

Tom

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PTN78000H: Placing a zener diode between the input and output