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Old 14th January 2007, 08:52 PM   #1
EspenE is offline EspenE  Norway
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Default OPA 2134PA current draw: regulator?

Please help a newbie here:

I'm building preamp and electronic crossovers based on the OPA 2134 op-amp. Preamp is Rod Elliotts P88 design, crossover is the Active Crossover Board group buy here from DIYiaudio (Bob Ellis).

Power supply is based on 7815/7915 regulators. The preamp uses 2 OPA2134's, the 2 crossover boards use 7 each: that totals 16 op-amps.

What is the current draw for one OPA 2134? Is the regulator (the 7815 and 7915 are in TO-220 cases, both heatsinked) sufficient for all 16 op-amps?

I have tried to look in the datasheets, but I'm not sure if i understand them correctly.

According to ti's datasheet, the quiescent curret for the OPA2134 is 5mA. Is this the value I'm looking for?

And according to various datasheets on the 7815/7915 regulators, they have a max load current of 1A.

So, if I have understood everything correctly, I shold have no problems. Or is it something I have overlooked?


Thanks, Espen
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Old 14th January 2007, 09:14 PM   #2
Nordic is offline Nordic  South Africa
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5ma at idle and can deliver another 40mA / channel.. so 85mA total.... per chip
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Old 15th January 2007, 12:35 AM   #3
Minion is offline Minion  Canada
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You should be OK with those regulators but They are quite noisy compared to the LM317/337 regulators so you might want to use a PSU that uses the LM317/337 regulators if you are going for the lowest possible PSU noise......

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Old 15th January 2007, 02:39 AM   #4
thanh is offline thanh  Viet Nam
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@Minion: Is 78XX noisier than LM317 ?
I'm using 7815. If it's like that, I will change PSU
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Old 15th January 2007, 03:42 AM   #5
lineup is offline lineup  Sweden
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Quote:
Originally posted by thanh
@Minion: Is 78XX noisier than LM317 ?
I'm using 7815. If it's like that, I will change PSU

if only supply a few OP-Amps
I would try to find
LM317L + LM337L
http://www.national.com/pf/LM/LM317L.html
http://www.national.com/pf/LM/LM337L.html

These are smaller TO-92 versions of the adjustable LM3x7 regulators..
Still they can deliver more than needed current (max100mA).

I am quite sure that LM317L will have lower noise/ripple than 7815,
if you use the recommend extra capacitor in the LM317/337 circuit.

(If you can't find LM317L / LM337L in TO-92
the LM317T / LM337T in TO-220 will work just as good.)

I would use the recommended +/- 15.0 Volt DC
for your Op-Amps. At least NOT Lower.
Suitable trafo would be 2 x 15 VAC and size ~ 5VA

-----------------------------------------------------------------------------
Attachment:
LM317L with Recommended Capacitor for improved ripple filtering = C1
~ 10uF
Attached Images
File Type: png lm317l-capacitor.png (9.0 KB, 296 views)
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Old 15th January 2007, 11:22 AM   #6
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Quote:
Originally posted by Nordic
5ma at idle and can deliver another 40mA / channel.. so 85mA total.... per chip
Espen, you must estimate the load at normal conditions, signal levels.
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Old 15th January 2007, 03:21 PM   #7
AndrewT is offline AndrewT  Scotland
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Hi,
what is the maximum peak voltage each opamp can push out?
what is the load each opamp is feeding?
calculate the peak current for each opamp.
calculate the total peak current for all opamps.
Add the quiescent current to the peak current (each chip is a dual and Iq/chip is 2*5ma=10mA).
provide smoothing capacitance of about 2mF to 5mF/(Apk+Iq) before the regulators.
Build the regs with correct bypassing before and after and keep it close to the reg pins. 16 opamps may require a heatsink on the regs.

Check the 2134 datasheet and follow the recommendations for power pin bypassing and again keep it close to or on the opamp power pins.
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Old 15th January 2007, 03:34 PM   #8
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Depending on the input voltage you going to feed the regulators, you will most probably have problems driving that many opamps (Especially with excessive dissipation). Why don't you split the boards and drive 8 opamps from a 78/79 set? These cost hardly anything, really! You will keep dissipation down, although you will still need to put heat-sinks on the regulators. This is from my own experience running 6 OPA's on a single set of regulators.
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Old 15th January 2007, 08:35 PM   #9
EspenE is offline EspenE  Norway
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Quote:
Originally posted by AndrewT
what is the maximum peak voltage each opamp can push out?
what is the load each opamp is feeding?
calculate the peak current for each opamp.
calculate the total peak current for all opamps.
Add the quiescent current to the peak current (each chip is a dual and Iq/chip is 2*5ma=10mA).
p
Thanks for all the answers. I think I get it now.

Max voltage is 2-3V.
Each filter op-amp feeds into the next one (except for the last, which feeds the 47K input resistance in the power amplifiers). That means a very high load, and corresponding negible peak current - right?

So in this case - the current dissipated from each chip is more or less equal to the quiescent current - 10 mA.

This means I'm in the clear vs power rating for the 7815/7915. Though I'll add heatsinking anyway.

Espen
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Old 15th January 2007, 08:50 PM   #10
Ryssen is offline Ryssen  Sweden
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Quote:
This means I'm in the clear vs power rating for the 7815/7915.
Please go with LM317 LM337 much better result!
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