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Continuous or Discontinuous Buck Design and Inductor Selection

Continuous or Discontinuous Buck Design and Inductor Selection

Continuous or Discontinuous Buck Design and Inductor Selection

(OP)
When designing buck regulators, it seems that design notes and web-based design apps always ask for the maximum current when calculating the required inductance value when in reality, it seems the minimum current is what is needed to determine the inductance value if you want to keep the regulator in continuous mode of operation all the time (which seems to be always recommended).

My general rule of thumb for products with low current draw is to design the buck regulator for discontinuous mode.  I try to avoid a situation where the regulator can or will be switching between discontinuous and continuous mode in normal operation as I am nervous (perhaps wrongly) that it could cause instability issues.

I'm generally young and not very experienced in power design but does anyone know why 'max current' always seems to be used in calculating the inductance value for buck regulators (as opposed to min) and does anyone have strong feelings about a converter switching back and forth between continuous and discontinuous in normal operation?

RE: Continuous or Discontinuous Buck Design and Inductor Selection

Generally it isn't a problem as there is some hysteresis provided by efficiency changes, or the regulation mechanism, such that the converters don't find themselves flipping back and forth every other cycle.

BTW: This is the wrong forum for this. Next time stick it in Circuit engineering.

Keith Cress
kcress - http://www.flaminsystems.com

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