LM5117: CC+CV mode: No load, CV mode draws high input current

Jeff Krupp

Part Number: LM5117
Other Parts Discussed in Thread: LMV431

Hello. While using the LM5117 in a CC+CV configuration, it works great in CC mode. With no load, CV mode, the circuit draws a significant input current as the output oscillates from +44V to -10V. Is this method of CV appropriate \ Any suggestions on how to stabilize it?

over 4 years ago

0 Timothy Hegarty over 4 years ago

TI__Guru 74012 points

Hi Jeff,

Take a look at Figure 2 in app note snva829 that uses an LMV431 in the CV loop. The cap in the circuit above is likely causing excessive phase lag from a small-signal standpoint,

Regards,

Tim

0 Jeff Krupp over 4 years ago in reply to Timothy Hegarty

Prodigy 60 points

Hi Tim. The LMV431 has a lower max voltage than I want as an output voltage, so I needed another way. You were right on - the capacitor was causing the problem. Also, I needed to swap the zener with an resistor to make 1.3V on the anode at the appropriate output voltage. With both of those changes, it works well now.

Thank you for your help!

0 Timothy Hegarty over 4 years ago in reply to Jeff Krupp

TI__Guru 74012 points

Hi Jeff, thanks for the reply.

Tim

Power management

Power management forum

LM5117: CC+CV mode: No load, CV mode draws high input current