Hello, I need to do negative power supply from -70V to -5V, 0.5A, is the possibility to use LM5017 converter ,or something similar?
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It depends. Is it possible to share the VIN variation?
The Fly-buck applications of the LM5017 use a transformer to develop isolated output called VOUT2. If the positive side of the secondary output was connected to the intput ground, the negative side of the secondary output could be set to -5V by proper adjustment of VOUT1 and transformer turns ratio. It is not as simple as a buck regulator but it solves the feedback issue from the -5V output to the -70V referenced controller.
Thank you for replays, I need circuit without transformer, to save space, is the another variants? thank you.
Valery,
I am not aware of a negative buck that will step from a negative input to a less negative output and regulate the output with respect to the ground. The problem is providing feedback from the -5V output to the LM5017. You will need a negative reference operating below ground and a level shift circuit that sends feedback to the FB pin of the LM5017 which is referenced to the -70V input.
What is the accuracy requirment of the -5V output? If it must be accurate within a few percent, then a TL431 device will be needed to monitor the -5V and control a feedback current to the LM5017.