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A design I am working on requires a ±20v differential line driver, but I can't seem to find such a component. The highest voltage line drivers seem to be RS-485, which aren't high enough. Fully differential op-amps seem to top out at about ±18v.

Do high voltage differential line drivers or op-amps exist?

If not, what's the best way to make one from discrete components?

Added:

The bandwidth is pretty low, a rise time of several tens of micro seconds is fine. The ±20v output voltage swing implies 40v between the output pins.

Transmission line length is just a few inches.

The impedance is unknown, but I'm going to assume it's reasonably high impedance and low capacitance.

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  • \$\begingroup\$ We would need to know if the ±20V signal has a certain bandwidth requirement. \$\endgroup\$ – Michael Karas May 22 '18 at 11:18
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    \$\begingroup\$ You could do it with two regular opamps, maybe. When you say ±20V differential, does it mean the differential outputs swing between +20V and -20V (±40V total swing), or between 0V and +20V (±20V total swing)? Also, what are the timing requirements? \$\endgroup\$ – dim lost faith in SE May 22 '18 at 11:20
  • \$\begingroup\$ @MichaelKaras - Done. \$\endgroup\$ – Rocketmagnet May 22 '18 at 11:34
  • \$\begingroup\$ What is it for and what dictates the levels if you don't mind me asking? \$\endgroup\$ – Andy aka May 22 '18 at 11:35
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    \$\begingroup\$ @Andyaka - It's to drive some Thin Film Large Area Organic Electronics. Apparently, the transistors need these kind of crazy voltages. It's part of the ATLASS project. \$\endgroup\$ – Rocketmagnet May 22 '18 at 11:44
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Maybe consider using an LTC6091 - it's a dual op-amp that can run from supplies up to 140 volts and is able to deliver a decent current too: -

enter image description here

GBW product and slew rate should be OK for your application by the sounds of it.

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I'm a bit late, but hey...

If the requirements in terms of timings are rather lax, you can implement it with just a few passives and three BJT complementary pairs. A circuit like this could probably fit your needs:

enter image description here

Link to the LTSpice file

You just need the +20V, -20V and +3.3V supply (assuming the input is LVCMOS). Simulation shows that there isn't much power wasted (A few mA from each supplies, not including the receiver load. Also, there is no unwanted shoot-through current), and the delay is ~1.5µS with a rise/fall time <1µS. The outputs could probably source/sink ~100mA as it is.

Here is how it works:

  • There are two stages: a simple level shifter stage, and an inverter stage. The differential output is taken between the outputs of those two stages.
  • For the level shifter input stage: a "reference" point is set by the resistor divider R7-R8, based on the logic supply voltage (this reference is actually moving quite a lot, because Q3-Q4 are in emitter-follower configuration with R7-R8, but it doesn't matter).
  • When the input is high (above the reference point), Q3 conducts. This turns Q5 on and OUTPUT_A is then +20V. When the output is low (below the reference point), Q3 stops conducting and Q4 starts to conduct. This turns Q6 on and OUTPUT_A is then -20V.
  • Then comes the inverter stage, which is made of a simple PNP/NPN pair.
  • C1 and C2 are there to force both transistors of each pair to change state simultaneously. This prevents a high shoot-through current from occuring when the state changes.

This is actually quite simple. It can be made for damn cheap, and very compact provided that you choose transistor pairs in a single package (for example MBT3946).

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    \$\begingroup\$ C1,2 will cause a destructive shoot through when power is applied; don't use them. \$\endgroup\$ – EinarA May 25 '19 at 0:49
  • \$\begingroup\$ C1, C2 should indeed be replaced by either current limiting resistors if the output drive requirements are low (simplest), or active shoot-through prevention circuitry (requires more components). Look at how old RS232 transmitters were built for inspiration. The schematic is on page 2. This one has active shoot-through prevention: ti.com/lit/ds/symlink/mc1488.pdf \$\endgroup\$ – Timmy Brolin Nov 13 '19 at 12:17

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