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I am using the LTC6090 op-amp (links to datasheet) to generate a high voltage, low current voltage.

However I've never really done anything regarding DC voltages this high before, so I was wondering which of these power supply solutions were better to provide the ±70 .

  • My plan was to buy a 140V DC power supply and use a voltage divider with high voltage resistors of 500k and tying the middle to ground.

  • The second option was to buy two 70V supplies and tying them together. Wiring the middle to ground.

My reason for chossing the first one was because I can't be certain the power supplies are even designed to be tied together like that. But I have never done this before so I thought I would ask this question to learn why doing it one way is better than the other, because in all honestly I'm not too sure.

I've done this before for batteries and low voltage supplies, does anything change when you go to ±70 or greater? Or is it you just need to make sure the voltage ratings of all your components are suitable and that's all you need to worry about?

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    \$\begingroup\$ Once you get above 48V it gets expensive. We're still buying these linear supplies. mouser.com/Power/Power-Supplies/Linear-Power-Supplies/_/… If you find anything cheaper I'd like to know. \$\endgroup\$ Commented Nov 3, 2014 at 0:05
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    \$\begingroup\$ A voltage divider isn't suitable for using as a power supply, only as an incredibly low current voltage reference. \$\endgroup\$
    – Majenko
    Commented Nov 3, 2014 at 0:22
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    \$\begingroup\$ Why don't you just build yourself a little linear +/- 70V split supply which can handle the load current you need? \$\endgroup\$
    – EM Fields
    Commented Nov 3, 2014 at 1:09
  • \$\begingroup\$ @EMFields, because I don't know how. \$\endgroup\$
    – alder
    Commented Nov 3, 2014 at 2:46

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Of course dual or split supplies are always nice, but George is right... its an expensive solution. On the other hand, your voltage divider is an often used solution for OP amp designs, if the signal is to be AC. To make it work as you described, you must add at least one capacitor, usually from the midpoint of the voltage divider to 0V, AND use a similar capacitor in series with the output to your load. Those capacitors can get pricy too, and bulky, as capacitor size generally increases with either capacitance or voltage rating. The lower the frequency you wanted to work with, the bigger that cap would get.

Now my favorite approach to single supply OP-Amp circuits is to use a second OP-amp configured as a unity gain follower. This is similar to your first idea, except that your voltage divider midpoint would get connected to this second Op-Amp's (+) input. You'll still need a capacitor there for stability, but in this case the Op-Ajmp gain serves to amplify the effective capacitance. So, now that capacitor can probably be as little as 1/uF. Next, the output of this Op-Amp becomes the "ground" for everything else, including all ground points on your original (first) OP-Amp circuit, and it also becomes the ground for your load. This arrangement is usually called a "virtual ground", and you will have effectively created a split supply. Now your circuit will no longer need a second capacitor on the output and as a bonus, the frequency response of your output will now be good down to DC. (Of course if you WANT to limit low frequency response, you can still add a capacitor to the output.)

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  • \$\begingroup\$ A schematic of the circuit you're proposing would make this answer much more clear. \$\endgroup\$
    – The Photon
    Commented Nov 3, 2014 at 2:38
  • \$\begingroup\$ Thanks @Randy, that makes sense, I think. Do you mean like this i.imgur.com/9doNjE3.png My only question is I need to power this op-amp right? If my only power source is the 140V power supply... where does it get powered from? Or did I misunderstand your answer? \$\endgroup\$
    – alder
    Commented Nov 3, 2014 at 2:39
  • \$\begingroup\$ I haven't dug into the specs, but if your OP amp is good for a +/- 70 V supply, that diagram is exactly right. Sure it seems to wast an op-amp, but certainly for audio work I've found it to be a very quiet and stable method. I'd probably drop the resistors in the voltage divider to about 50K too. Shouldn't matter with the capacitor, but large resistances can be sources of voltage noise. \$\endgroup\$
    – Randy
    Commented Nov 3, 2014 at 2:51
  • \$\begingroup\$ Just to double-check because I'm paranoid about these things, this is the final circuit, where Vdd is the +ve from the 140V power supply, and Vss is the -ve. i.imgur.com/lJuMukx.png Is that correct? \$\endgroup\$
    – alder
    Commented Nov 3, 2014 at 6:01
  • \$\begingroup\$ @alder one thing to look out for is the capacitive loading of the rail-splitter. You may not want bypass caps to ground on the main opamp. Or you might have to add some R's and C's to the rail-splitter.. look into driving capacitve loads with opamps. (Well and power dissipation of course.) What are you doing (driving)? \$\endgroup\$ Commented Nov 3, 2014 at 14:15

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