Timeline for High voltage high speed low current amplifier
Current License: CC BY-SA 4.0
18 events
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| Mar 11, 2019 at 19:01 | history | bumped | CommunityBot | This question has answers that may be good or bad; the system has marked it active so that they can be reviewed. | |
| Jul 10, 2018 at 22:24 | answer | added | rbraddy | timeline score: 1 | |
| Jul 10, 2018 at 22:13 | comment | added | jonk | @CezarChirila Just as a start, look at CFBs like the THS3096 and VFBs like the LM7171. I don't know how you will add discretes to get the additional closed-loop voltage swing and current compliance. I'd love to learn from a good answer here. So I'll +1 to see if it gets any traction from my betters. | |
| Jul 10, 2018 at 21:52 | comment | added | Cezar Chirila | @jonk thank you for your help! I'll look into that direction | |
| Jul 10, 2018 at 21:52 | comment | added | Cezar Chirila | @BrianDrummond Unfortunately I need triangle, square and sinusoidal. But your idea is not bad, I could just make a simple separate circuit for that. It shouldn't be hard, just some mosfets with small gate charge and a discrete driver. | |
| Jul 10, 2018 at 21:17 | comment | added | jonk | @CezarChirila For an ideal BJT 1st stage, I believe there exists a relationship between GBW and slew-rate. I think it works out to \$SR=\frac{I_\text{q}}{C_\text{splitting}}\$ and \$GBW=SR\cdot\frac{1}{4\:V_T}\$. (No, I do NOT want a long debate saying SR and GBW are at best loosely related. I'm discussing an ideal 1st stage, central to slew rate. There is an appnote somewhere on this topic, memory serving.) Best wishes on finding this to be an easy achievement. I think you'll spend some time on this problem. | |
| Jul 10, 2018 at 20:57 | comment | added | user16324 | If you need a square wave of a fixed amplitude, forget about amplifiers, switch a 160V supply instead. Fast enough switching is challenging enough. | |
| Jul 10, 2018 at 20:57 | comment | added | jonk | @CezarChirila The slew rate of a BJT input opamp is completely determined by the 1st stage quiescent current and its pole-splitting capacitance. I don't believe added stages are of any utility in getting better slew rates. You may get higher GBW adding stages. But not increased slew-rate, so far as I understand it. Assume a quiescent 10 mA for the 1st stage alone, I get that you still need (much) less than 2.5 pF of pole-splitting capacitance. | |
| Jul 10, 2018 at 20:51 | comment | added | Cezar Chirila | Also how can I improve the slewrate of a high voltage amplifier? Using a separate input stage? | |
| Jul 10, 2018 at 20:49 | comment | added | Cezar Chirila | My bad, it is 160V Peak-to-Peak. Thank you for answering. So what do you think, should I head in this direction, using discrete / ICs and a high voltage power supply? Or using a simple amplifier and a transformer on the output, such as this example here: sound.whsites.net/articles/line-amps-f12.gif ? I'm used to low frequency electronics / digital circuitry. | |
| Jul 10, 2018 at 20:40 | comment | added | jonk | @CezarChirila For slew-rate, I'd start with assuming a sine wave and not a triangle. If your specification is \$160\:\text{V}_\text{PK}\$ I get about \$8000\:\frac{\text{V}}{\mu\text{s}}\$. If it is \$160\:\text{V}_\text{PP}\$ then half that or about \$4000\:\frac{\text{V}}{\mu\text{s}}\$. And this number goes rapidly up for anything even starting to look a little squarish. | |
| Jul 10, 2018 at 20:36 | comment | added | jonk | @CezarChirila That example is 130 V "peak to peak". That's the total excursion. And it's based upon using the entire \$\pm 35\:\text{V}\$ output swing capability of two devices. You aren't clear in your writing, but I'd normally take your 160 V and think you mean "peak" and not "peak to peak." Either way you answer, that part won't get there by itself (added parts could help, though.) | |
| Jul 10, 2018 at 20:33 | comment | added | Cezar Chirila | At page 3, there is a proof of concept circuit using 2 of those ICs in parralel to drive a floating load. (130V Drive Across a Floating Load) But the slew rate is bad, 6V/µs. It is no where near what I need. | |
| Jul 10, 2018 at 20:23 | comment | added | The Photon | The very first sentence in that datasheet says it has +/- 40 V maximum power supply, so that won't get you to 160 V. | |
| Jul 10, 2018 at 20:21 | comment | added | Cezar Chirila | Could I maybe use something like this? I don't mind the floating output. ti.com/lit/an/snva516/snva516.pdf | |
| Jul 10, 2018 at 20:19 | comment | added | Cezar Chirila | It's not going to be a perfect square as that is impossible (infinite slew-rate). But for a triangular wave at 8MHz I would need about 4800V/us, Am I right? (for a 150V output from zero) | |
| Jul 10, 2018 at 20:05 | comment | added | jonk | Have you computed the slew-rate this is going to require? (You write "even square" and this could imply a rather fast edge.) | |
| Jul 10, 2018 at 20:01 | history | asked | Cezar Chirila | CC BY-SA 4.0 |
