EEVblog #329 - Tracking Pre-Regulator LTspice Simulation Part 2

An alternative circuit for a power supply tracking preregulator for a linear regultor.

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[SebastianScholle]

We need more Youtubers talking about this circuit! This is a great base configuration for building a modern and efficient power supply. Thanks Dave.

[somud]

thanks dave we had to create an oscillator for an fm transmitter and the .step directive really helped us pick the perfect caps for transmission at 98khz. You are a godsend.

[sallowsandy]

Sparked an incredibly interest in LTSPICE again... thank you Dave, going to get around to building up some boost converters for practise+hands on and you help a lot to get me to think of new ideas.

[EEVblog]

It just replaces the opamp buffer that normally drives this pin. Easier to simply place a voltage source than an opamp + divider etc.

[Slabbefusk]

I tried this out with an LT1076HV as the pregulator instead. This is to have a buck that is always a bit over the linear one instead. Works perfectly. Just put in some values that worked and made it do what I wanted. Now it's time for some more precise trimming :)

[fenclu]

It's five to midnight in Poland. What a great way to end a day!

[pychneag]

Great! Thanks Dave. Love this kind of instruction.

[definitionofis]

Oh, I understand the context now.
I watched EEVblog #260 - Tracking Pre-Regulator Simulation in LTspice

It is something more complex than I was thinking, although I guess if the microprocessor can do digital to analog output it could control the FB pin directly.
I can't think all that through though. ... so nevermind me.

[davidgiga]

It's 2AM in Germany. What a great way to start a day! :P

[Galfonz]

What happens with various loads? Could something like this be used to power a stepper (or other) motor?

[MrPorrohman]

Wah, 260 is the First One! Searched for it for days. You are a Genius, by the Way. Unfortunately you dont live ner Germany, i Would have paid Tons of euros if you had Given me Some private lessons in Electronics.

[rodstartube]

hello dave, can you do a video about MIDI protocol ?

[shogoonn]

Could you please do some simulations common in the design of DC power supplies? I think, that would be useful for some of your viewers, who want to design a PSU.
1. A load current step response with behavioral current source (BI) like this: I=if(time>1m, 500m 100m), it will jump from 100 mA up to 0.5 A after 1 ms.
2. A PSRR and loop response with both AC, and voltage step analysis.
3. Optimisation of C5 to maintain a stable load change response (so the SMPS voltage doesn't drop too low).

[ValdemarCamilo]

Yum, A Nice little EE appetizer before a main course of mars rover.

[cr]

Is V2 only for simulation purposes? I don't understand why one would need 2 voltage sources to get a regulated output (couldn't a buffered voltage divider do the same thing?). What am I missing here? It's gonna be something stupid, I know it!

[EEVblog]

Already done that. "How not to blow up your oscilloscope"

[DavidLeeMenefee]

Did you say p-channel? Looks like a BJT...

[definitionofis]

I am still thinking the same as cr1901. Maybe LT3080 is not needed and neither is an op amp buffer. V2 could drive the FB pin.

Is the FB pin such tiny current that we do not need an op amp buffer either?

[EEVblog]

Wouldn't be surprised if I goofed that. My mind is often not connected to my mouth.

[pyroesp]

My bad, 2h30.
What's with the xbox live countdown then ?