LDO Deep Dive - Power Regulation in PCB Design: Part Two

[@harrydymond4488]

The error circuit is not using positive feedback. The error amplifier is driving a PMOS transistor and there is in effect an inverting action from the output of the error amplifier to the output of the transistor. So, although the feedback signal is going to the positive terminal of the error amplifier, this is still negative feedback (due to the inverting action of the output transistor)

[@Zachariah-Peterson]

Thanks for catching Harry, yes you're correct I slipped up on that one

[@jasmenelee]

Brilliant, especially the graph showing the Input/Output Voltage vs Short circuit current for LDO voltage selection.

[@danielrioux54]

At 10:20 when you present the impact of output current on the minimum input/output differential voltage you are using the LT1086H, listed at 0.5 A and not LT1086, listed at 1.5 A. The minimum input/output differential voltage for the LT1086 at maximum output current (1.5 A) is even lower than the LT1086H at maximum output current (0.5 A). Past 66% of its maximum current the LT1086 exhibits a shard in crease of its minimum input/output differential voltage which is not seen in the LT1086H past 66% of its capacity. You missed an important issue.

[@victortorres2080]

Hello Friend, good videos on the topic of "Power Regulators", hoping to see soon the PCB design with LDO, Buck, etc and their respective real considerations.

[@tomyr95]

You're videos are awesome! You're a rockstar! Thank you!

[@rolandoaguilera3114]

Typically a flyback converter is used when stepping down from a rectified AC voltage (Vac x sqrt(2) -> 25/12Vdc)

[@asad5986]

For the Error amplifier, is the FET specifically a MOSFET? At 8:43. Why would the current drop? If voltage increases and resistance is constant, wouldn't current increase? Around 14:30ish, why not just use multiple LDOs to step down, instead of a buck regulator? Wouldn't you be able to get rid of the disadvantages the buck regulator brings?

[@Zachariah-Peterson]

I Yes generally a MOSFET, although some circuit diagrams will show a BJT. About the current drop, I'm not sure about this, I would have to look into it. About the multiple LDOs, yes I've seen multiple LDOs in series but the current can get limited to a low value at each stage, so just be careful with that. This is something you might see with processors that need multiple core voltages.

[@MrAlistar28]

thank you so much for these videos

[@AltiumAcademy]

You are so welcome!

[@leeslevin7602]

Brilliant. Thank you.

[@AltiumAcademy]

Glad you liked it!

[@samamani5423]

thank you..

[@jameslmorehead]

Why cover linear regulators as specifically only LDOs? LDOs are just a subset of linear regulators. Of which, LDOs are the least forgiving of linear regulators. This would probably have been better covering the venerable LM7800 series. Then look at the LDO version.

[@Zachariah-Peterson]

Well then maybe we'll just have to do something on the LM7800 series. Also we felt LDOs was a decent place to start because they are so frequently used in so many systems, including digital, RF, etc.

[@MuhammadAhsan-rr4js]

why no making 25V->3.3V buck converter??

[@km-electronics1]

Buck regulators are noisy. Going Buck => LDO in series can significantly lower noise.

[@noname-gp6hk]

@@km-electronics1 thanks, I came to the comments with the same question.

[@pcbworks]

well

[@dunk_law]

RIP circuit maker.