High Voltage OP amp

Sep 03, 2022 Last reply: 3 years ago 7 Replies
T

I am servicing a power amplifier which uses a dual, 8 pin DIP OP amp. Unfortunately, the rail Volts on the OP amp (LF353) is +/- 22 Volts. I am familiar with this particular amplifier and OP amp failure is quite a frequent thing. I need a suggested replacement. I am quite happy to use single OP amps, or SOICs, as I can employ a Brown Dog carrier to adapt to the existing layout. Ideally, a bit more performance over the LF353 would be nice.



And no, it is not possible to drop the rail Voltages. They must remain at +/-22 Volts.



TIA



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K

Hello, TI's OPA552UA has up to +/-30V rails and a bit better slew rate (24V/uS)although it's a bit noisier. You may find a dual version of this at TI.

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P

What's the required output swing? A baby board with one or two zeners in the supply leads (plus a 100 nF-ish bypass between them) is pretty easy, at least if you get these things in a lot.

Cheers

Phil Hobbs

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T

**I need maximum output Voltage swing. Hence the designer (now deceased) chose a +/- 22 Volt supply. Hence the need for higher Voltage OP amps.
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T

**Thanks for that. I can probably live with a higher noise level. I like the idea of a higher speed OP amp.

I found a couple available locally, though there is a long lead time for more. I can live with that.

Thanks for the tip.

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P

Trevor Wilson wrote: =================

** That is a mistake, all versions of the Sumo 9 used nominal +/-20V rails fed from series regs with 20V zeners.
** Which MUST be a FET input op-amp.

**Course it is, they are meant to be 19.5V each anyway.
** Humbug.

..... Phil

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P

Sure, but typically not everything in a circuit needs to swing the full supply range. You're losing at least a couple of V_BEs on each end now--in fact the LF353 datasheet minimum output swing is +-3 V from the rails (+-12 on +-15 supplies) even at light loads.

There are nice things in the 40V range such as the MC34072, which typically swings +14 to -14.7 off +-15 if fairly lightly loaded. It's also a lot quieter than the LF353, not that you probably care much in a power amp.

Cheers

Phil Hobbs

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T

**Oops. You are correct. The negative rail is fed from a 20 Volt zener and the positive rail is fed from a series transistor, with the base tied to a 20 Volt zener, in series with a forward biased diode.
**Yes. There is that.

**True enough. I had neglected to examine the schematic before I posted. According to the schem, it is +/- 20 Volts.
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