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Old 3rd June 2006, 05:22 AM   #1
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Unhappy opamp problem

Hi guys - i am building regulated psu but need an opamp ....
Opamp has to be stable on gain 2-3, be low cost, has output voltage +/-16V minimum and supply voltage +/-20V minimum. Are there any opamps that have this characteristics....I have looked at NE5532 (also at few other low cost) but this one has low voltage output (+/-13V - not enough)....
regards
daniel

p.s. thanks for any help
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Old 3rd June 2006, 06:27 AM   #2
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What are you going to use it for?

Maybe a LM317 and LM337 would suit you?
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Old 3rd June 2006, 06:53 AM   #3
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Try MC33172 from ON semi they have a +/-22V supply rating
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Old 3rd June 2006, 07:13 AM   #4
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Default Re: opamp problem

Quote:
Originally posted by sparkle
Hi guys - i am building regulated psu but need an opamp ....
Opamp has to be stable on gain 2-3, be low cost, has output voltage +/-16V minimum and supply voltage +/-20V minimum. Are there any opamps that have this characteristics....I have looked at NE5532 (also at few other low cost) but this one has low voltage output (+/-13V - not enough)....
regards
daniel

p.s. thanks for any help
5532 will swing +/-16V on +/-18V supplies...where do you see this +/-13V limitation?

OPA2604 will also run off of high rails (+/-22V), and ought to be able to get within 2V of those rails with output swing, but might not meet your low-cost requirements.
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Old 3rd June 2006, 08:45 AM   #5
AndrewT is online now AndrewT  Scotland
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Hi,
the datasheet for the 5534/2 is standardised for +-15Vdc supplies. A few of the graphs are for other voltages.
Most other data sheets follow the same standardisation.

You should extrapolate above +-15Vdc to get projected maxima but be careful with max supply. It is usually quoted as absolute maximum.

However I have an amp that runs 5534 at the input on a voltage divider from the main rails. On low/zero bias the opamp supply rises from the normal +-18Vdc to +-22Vdc and the opamp survived and seems to be OK.
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Old 3rd June 2006, 01:26 PM   #6
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Thumbs up whoa.... so many replies....

peranders... i am trying to modify psu from LC audio that uses LM329 as a reference, 2 ne5532 opamps (well, one dual ne5532 actually) and IRF640, IRF9640 series pass device. Input is 15VAC and output is -13 / 0 / 13V. Sorry the sch is at my work (here I have only printed version).... the problem is that I need -15/ 0 / +15V for the headphone amplifier i am making and i don't want to use good old LM317/337 dual regulated psu....i want better and i would like to modify this psu from LC audio to run it on +/-15V. And that means that I would have to use opamp that could have output voltage of more than 15V to be safe - i didn't know that NE5532 has more than 13V at output...

So what You are saying is that if I run NE5532 on +/-20V supply voltage i would have more than 15V at the output - my input is no more than 6.9V (LM329 reference)......
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Old 3rd June 2006, 02:03 PM   #7
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Default Re: opamp problem

Quote:
Originally posted by sparkle
Hi guys - i am building regulated psu but need an opamp ....
Opamp has to be stable on gain 2-3, be low cost, has output voltage +/-16V minimum and supply voltage +/-20V minimum. Are there any opamps that have this characteristics....I have looked at NE5532 (also at few other low cost) but this one has low voltage output (+/-13V - not enough)....
regards
daniel

p.s. thanks for any help
the gain of the error amp for a regulated power supply is usually much higher than 2-3x -- there is typically a compensation network which reduces the gain at higher frequencies -- you want a lot of gain to reduce the ripple content of the power supply output, and to help you bridge some transients -- on the other hand you don't want so much gain at high frequencies that the error amplifier goes into oscillation. high frequency impinging upon the power supply rails can come from many sources -- crud on the power supply line, radiated noise from computers, switches and relays -- once it gets going the power supply wires (which have inductance, capacitance and resistance) act like an LC tank circuit.

if you bootstrap the regulator it can see the full absolute value of the voltage rating. you can also use a zener diode so that the regulator only sees a differential between the power pins that it can handle -- this is what some tube manufacturers did for their preamp power supplies (like the Audio Research SP8). the zener has its own issues (i.e. noise).

just starting out ? -- this is a very easy circuit to implement -- i've found that there are a number of ham radio guys who use it in their receivers -- from Wenzel Associates --- http://www.wenzel.com/documents/finesse.html
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Old 3rd June 2006, 02:12 PM   #8
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Anyone else see a potential issue with no gate stopper resistors on the pass FETs in the LC regulator?
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Old 3rd June 2006, 04:16 PM   #9
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jackinnj - i would really like to stick with dual serial regulator.... finesse is shunt regulator... i know that it is really good but it is shunt... i need +/-15V serial regulator - that is why i decided on something like LC audio regulator.... thanks for Your nice and informative reply


BobEllis - yes i saw that there are no gate stoppers.....don't know why.....oh well......
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Old 3rd June 2006, 04:46 PM   #10
mlloyd1 is offline mlloyd1  United States
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yep

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Quote:
Originally posted by BobEllis
Anyone else see a potential issue with no gate stopper resistors on the pass FETs in the LC regulator?
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