Electronics > Projects, Designs, and Technical Stuff
Voltage boosting an opamp
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Zero999:
The buffer will improve the slew rate because it's much faster than the op-amp. The oo-amp's output only has to change a little for the buffer's output to change much more. Look at the op-amp's output voltage.
Yansi:
^ That of course makes sense.

Currently thinking about those 4 diodes in series, biasing the whole amplifier.

What would happen, if I'd replace those 4 diodes with a NPN Vbe multiplier (NPN with Rbe, Rcb resistors)? That would also give a bit more flexibility in selecting the bias voltage.

Just wondering, how could I get more stable biasing. Huh.  ???  What would be the dis/advantages of using 4 diodes vs. Vbe multiplier?
SiliconWizard:

--- Quote from: Yansi on December 29, 2016, 09:25:27 pm ---I know that some high voltage opamps do exist, but mostly expensive.

--- End quote ---

Define expensive. How many units are you going to build? Are a few dollars going to really matter? A couple references: OPA452, ADA4700-1...

And do you think the added parts, time to design, and extra PCB area for a discrete version will really yield a lower cost solution? Unless you go for large quantities, I even kinda doubt it.
Yansi:
Yes, OPA454 is exactly what I mean by EXPENSIVE NONSENSE.  OPA454 is about $7 + VAT at single quantities from Mouser.

MCP6001T is below $0.5 in single counts, and those 4 jellybean PNP/NPN transistors cost next to nothing.  So say about $2 maximum per discrete amplifier unit?

Does not pay off to use OPA454 even at single quantities. Every idiot can find a ready made solution given amount of $$$. Sure, time is valuable, but knowledge even more so.  I value knowledge more, than the time spent getting the knowledge.

Next time I will need a HV amplifier, I know sure how to make one, cheap. 

Now, don't you have anything better to do, then question the obvious from over 2 years old posts?

SiliconWizard:
Learning things is interesting, but the choice here is absolutely NOT obvious. Is gaining say $5 (and again you didn't count the extra PCB area needed and time to design, so it's likely less than that) worth the trouble? The added part count also means a larger BOM, which does not always pay off either. If it floats your boat, fine, but saying using HV opamp is idiotic doesn't make sense in general.

And I didn't notice it was initially 2 years old, as there are a number of recent posts discussing it. You're apparently still working on it 2 years after judging from your above posts? If you still think it was worth the trouble, fine. Just saying.
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