5V, 5W Version Posted

A project log for LM5161 Based DC-DC Bias PS

4W, +5, +12 bias PS using TI's LM5161.

Brian CornellBrian Cornell 03/07/2021 at 18:050 Comments

I made a 5V, 5W buck derivative that is smaller than the flybuck design but uses the same input/output filter design for low noise/ripple applications. The inductor core is a Magnetics MPP C055048A2. with 38 turns of 24 AWG. Peak efficiency with a 12V input is ~ 89% at approximately 300mA load. Full load (1A) efficiency is ~ 82%. Lower largely due to DCR losses in the output inductor.

The output voltage will drop ~ 230mV at full load due to these losses. Don't try to move the feedback sense to after the output LC: the phase shift is too great and will result in an unstable control loop (there is no sensible way to compensate with this controller). If tight regulation is required and the application can tolerate a bit more ripple the filter inductor can be removed. Alternatively you could go with an inductor that has a lower DCR but with the associated size/cost penalty.

This design works with a 10-20V input but could easily handle higher input voltages. It includes a bias supply connection which is optional, even up to 20V (the controller uses an internal LDO when the bias supply is left open). Above 20V the bias supply should be used - refer to the data sheet for more information.