OPA549 psu at 31.1v will it be stable? - diyAudio
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Old 29th August 2012, 07:47 PM   #1
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Default OPA549 psu at 31.1v will it be stable?

I got a trafo which is rated at 22-0-22 and its designed by a industrial guy. He said that on load it will deliver the rated values. The trafo is EI and rated at 9Amps and almost weighs 10kg. I have opa549 and I have this good trafo at this moment. After rectification I will be getting 31.1 V may be on over or under voltage fluctuations Its possible to get something 32 at max. So I doubt that is OPA549 stable at this voltage? what is the maximum limit.

what if I drive the opamp in 4 ohms imp? what should be the supply voltage to drive 4 ohms drivers?
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Old 29th August 2012, 09:49 PM   #2
AndrewT is offline AndrewT  Scotland
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apply mains power to your transformer. Measure the input voltage and the output voltage.
It is a small step to then determine the worst case (highest mains voltage & low load current) smoothing capacitor voltage.
Compare that worst case voltage to the 549 specification.

BTW,
this is not stability. This is overvoltage to the power pins.
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Old 29th August 2012, 10:20 PM   #3
Bone is offline Bone  United Kingdom
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Max Voltage on a 549 is +/-30v so this will be over spec. See datasheet http://www.ti.com/lit/ds/symlink/opa549.pdf.
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Old 30th August 2012, 03:55 AM   #4
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can I use a regulator LT1083 to reduce the voltage? Is there anyway to reduce like 4 volts using some sort of method?
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Old 30th August 2012, 04:14 AM   #5
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Quote:
Originally Posted by rhythmsandy View Post
I got a trafo which is rated at 22-0-22 and its designed by a industrial guy. He said that on load it will deliver the rated values. The trafo is EI and rated at 9Amps and almost weighs 10kg. I have opa549 and I have this good trafo at this moment. After rectification I will be getting 31.1 V may be on over or under voltage fluctuations Its possible to get something 32 at max. So I doubt that is OPA549 stable at this voltage? what is the maximum limit.

what if I drive the opamp in 4 ohms imp? what should be the supply voltage to drive 4 ohms drivers?
Is the weather hot by you? The line Voltage varies with the weather (AC load). At our house I've seen line Voltage as low as 99 though it's typically 121 or so. Your 31.2 is already over the 'absolute maximum' recommended by TI. If your line Voltage goes up it will be even worse. While you can often exceed the manufacturers ratings you do so at your own risk.

Haven't you downloaded the data sheet? Burr Brown's sheets were always very good as were Motorola's (now ON Semiconductor) and Analog Devices (Excellent). The 'applications information' is well worth the time to read and understand. Any examples of how to use it are always helpful.

Your amplifier into a 4 ohm load with +/- 30 Volt supplies will need 3-4 Amps PER CHANNEL to run continuously at full power with a sinewave. Your 9 Amp will be fine for music even at 4 ohms though temporary peaks up to 16 Amps but the average will be within the transformer rating. The nice thing about larger transformers is that they have a lower output resistance which suffers less droop under load. Have you considered toroidal transformers? Antek makes some pretty fine units at very reasonable prices. They take less space, are less lossy and weigh less than conventional EI core units.

G
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Old 30th August 2012, 08:30 AM   #6
Mooly is online now Mooly  United Kingdom
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Maximum ratings are just that. Stability doesn't come into it, you are exceeding the rated limits of the devices and substrate die.

A simple regulator/ripple filter could easily be made to loose a few volts but you always have the issue of the heat generated under full load. Example, 5 volts across the series pass device at 5 amps is 25 extra watts to get rid of.
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Old 30th August 2012, 08:55 AM   #7
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can this chip deliver 100RMS into 4ohms if the psu has 9 amps of current?
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Old 30th August 2012, 09:52 AM   #8
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Quote:
Originally Posted by rhythmsandy View Post
can this chip deliver 100RMS into 4ohms if the psu has 9 amps of current?
Understanding Class-D amplifier power supply requirements

Article is for Class D, but the maths are still appropriate.

As for the amp, I'd just build a Sysmasym or BabyAKSA. Both very simple and will do exactly what you want without all the tedious mucking around with regulated supplies.
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Old 31st August 2012, 07:03 PM   #9
juma is offline juma  Germany
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Quote:
Originally Posted by rhythmsandy View Post
... Is there anyway to reduce like 4 volts using some sort of method?
Yes, the "method" is capacitance multiplier made with HexMosfets - it will "eat" 4V of each rail and lower the ripple voltage by about 50dB
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Old 31st August 2012, 09:13 PM   #10
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nice... method but need to source the IRF..
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