OpAmp to provide -15V from -38V <100ma

I have two problems to solve and hopefully this can be done with a single (dual) part.

1. Supply a "clean" -15 V at about 35ma to a transimpedance amplifier from a -38V source,

2. Provide a steady-state -38V and (2) a timed sweep from 0V to around -5V.  Here, nanoamperes of current are involved.

I considered an LDO for -15, but those I can find won't take the -38V presently coming from a converter and we don't want to create another noisy switching converter!

So I'm thinking a "high output current" amplifier (dual package) powered by our available -38V (with the + rail of the amplifier to system ground) would be an option.  One of these would produce the -15V based on bias at the inverting input, and the other driving the -38V rail with a mosfet-selected triangle generator for the timed sweep.

Does Analog Devices have a suitable part for this idea.. or other ideas that will give us these voltages?

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  • 0
    •  Analog Employees 
    on Dec 16, 2015 1:26 AM

    Hi Mark,


    Those are two interesting problems.  There are a few high voltage opamps to take a look at but I suspect none of them meet your needs for one reason or another.  Harry's recommendation is probably the best: ADA4700-1:  Single 100V precision opamp.   However,35mA would be pushing the output drive capability of the ADA4700-1 close to its limits.  ADA4700-1 wouldn't work for your second requirement since is not a rail-to-rail output.  I'm not sure what you mean when you say provide a steady -38V and a timed sweep from 0V to -5V.  Those seem mutually exclusive.

    All in all, I still think you're better off with a switcher and an LDO.  I might suggest the ADP5071 and ADP7182.  What generates the -38V.  Does the -38V have a lot of variability or just switching noise?

    Dave

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  • 0
    •  Analog Employees 
    on Dec 16, 2015 1:26 AM

    Hi Mark,


    Those are two interesting problems.  There are a few high voltage opamps to take a look at but I suspect none of them meet your needs for one reason or another.  Harry's recommendation is probably the best: ADA4700-1:  Single 100V precision opamp.   However,35mA would be pushing the output drive capability of the ADA4700-1 close to its limits.  ADA4700-1 wouldn't work for your second requirement since is not a rail-to-rail output.  I'm not sure what you mean when you say provide a steady -38V and a timed sweep from 0V to -5V.  Those seem mutually exclusive.

    All in all, I still think you're better off with a switcher and an LDO.  I might suggest the ADP5071 and ADP7182.  What generates the -38V.  Does the -38V have a lot of variability or just switching noise?

    Dave

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