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'[EE] rail-to-rail LM358N alternative'
2012\04\02@070638 by Dumitru Stama

picon face
Hello guys,
can anyone help me by suggesting a rail-to-rail alternative to LM358N ?
I need to use a +24V single power supply and LMC6482 can only go as
high as +15V.

Thank you
Spana

2012\04\02@074008 by Spehro Pefhany

picon face
At 07:06 AM 4/2/2012, you wrote:
>Hello guys,
>can anyone help me by suggesting a rail-to-rail alternative to LM358N ?
>I need to use a +24V single power supply and LMC6482 can only go as
>high as +15V.
>
>Thank you
>Spanac

LT1678 might work for you, assuming you're using it as an op-amp and
not as a comparator.

Best regards,

2012\04\02@081240 by Dumitru Stama

picon face
> LT1678 might work for you, assuming you're using it as an op-amp and
> not as a comparator.

Yes, as a differential op-amp actually. The only scarry thing about
your suggestion is the price.
Is there a cheaper alternative or almost all rail-to-rail op-amps are
this expensive

2012\04\02@093413 by Sean Breheny

face picon face
Do you need rail to rail inputs or outputs or both? Do you really need
the output to go all the way to the 24V rail or is it more that you
need it to go all the way to GND? The LM358 is a real "jelly bean"
cheap op-amp - it seems strange to want to drop-in something with
complete rail-to-rail inputs and outputs.

Sean


On Mon, Apr 2, 2012 at 7:06 AM, Dumitru Stama <spam_OUTspanacTakeThisOuTspamgmail.com> wrote:
> Hello guys,
> can anyone help me by suggesting a rail-to-rail alternative to LM358N ?
> I need to use a +24V single power supply and LMC6482 can only go as
> high as +15V.
>
> Thank you
> Spanac
>

2012\04\02@093802 by Spehro Pefhany

picon face
At 08:12 AM 02/04/2012, you wrote:
> > LT1678 might work for you, assuming you're using it as an op-amp and
> > not as a comparator.
>
>Yes, as a differential op-amp actually. The only scarry thing about
>your suggestion is the price.
>Is there a cheaper alternative or almost all rail-to-rail op-amps are
>this expensive ?

Depends if you need rail-to-rail input AND output, what bandwidth,
etc.

For example, OPA2171 is only $1.85 in small quantities, is R-R out,
and the input CM range includes the lower rail, but only within 2V of the
upper rail.

High voltage RRIO op-amps tend to be expensive, and because you essentially
need more than one input stage to deal with different CM voltages, they
often do some funny things as you change the CM voltage (like the offset
voltage shifting around a bit at the transitions).

BTW, the LTC part might be cheaper if you get it direct from Linear.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
.....speffKILLspamspam@spam@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

2012\04\02@100549 by Dumitru Stama

picon face
> Depends if you need rail-to-rail input AND output, what bandwidth,
> etc.
>
> For example, OPA2171 is only $1.85 in small quantities, is R-R out,
> and the input CM range includes the lower rail, but only within 2V of the
> upper rail.

I need it to amplify the voltage drop over a sense resistor.
If the sense resistor is 0.1 ohms and i have a 100mA current through
it then the voltage across it will be something like 0.01V. I need the
opamp to amplify it 15 times and output 150mV.
I need its output to be as close as it can to GND, the +24V supply is
just a requirement for this circuit, the voltages will never reach
that value

2012\04\02@103248 by Gál Zsolt

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face
MCP602
MCP6002

from Microchip

2012\04\02@103409 by Michael Rigby-Jones

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face


{Quote hidden}

Have you tried loading the output the output of LM358 with a resistor to ground? (e.g. ~10k).  They will typically get within ~5mv of ground which will be significantly exceeded by potential input offset voltage issues in this particular case.

Cheers

Mike

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2012\04\02@104835 by Dumitru Stama

picon face
Microchip 602 or 6002 cannot cope with +24V supply voltage.
TI's OPA look promising though, i will try to order one for testing

> Have you tried loading the output the output of LM358 with a resistor to ground? (e.g. ~10k).  They will typically get within ~5mv of ground which will be significantly exceeded by potential input offset voltage issues in this particular case.
> Mike

I am using it as a differential amplifier and the output is already
tied to negative input using a 10k resistor. I don't think it will
work

2012\04\02@110103 by Matt Pobursky

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face
Look on the manufacturer's websites for "High Side Current Sense
Amplifiers" or "Current Monitor" amplifiers.

Almost all the analog suppliers make them, they are typically low cost, low
power differential amplifiers with high CMV specifications, low input
offset voltage and moderate to high gain. Many allow the gain to be set
with a single resistor. A gain of 15 as you require is right in the middle
of the range most of them offer. They're made to do exactly what you're
looking for.

Matt Pobursky
Maximum Performance Systems


On Mon, 2 Apr 2012 17:05:48 +0300, Dumitru Stama wrote:
{Quote hidden}

> value.

2012\04\02@111504 by alan.b.pearce

face picon face
> I need it to amplify the voltage drop over a sense resistor.
> If the sense resistor is 0.1 ohms and i have a 100mA current through it then the
> voltage across it will be something like 0.01V. I need the opamp to amplify it 15
> times and output 150mV.
> I need its output to be as close as it can to GND, the +24V supply is just a
> requirement for this circuit, the voltages will never reach that value.

Then if you really are looking for an op-amp then you looking for the wrong thing.

Check out the following devices

Linear Technology
LT6100
LT6106 (goes to 36V)

Analog Devices
AD8210 - this does bi-directional current sense, but they have others in the current sense family.

Zetex
ZDS100x Current Sense devices (they have trimmed this range considerably since being taken over by Diodes Inc).

Supertex Inc
HV78xx family Current Sense chips (some go to 450V for mains use!).


If you really must use an op-amp then maybe Analog Devices AD8675 36V R-R Op-Amp might do, but I know nothing about the pricing.


-- Scanned by iCritical.

2012\04\02@114149 by alan.b.pearce

face picon face
> Look on the manufacturer's websites for "High Side Current Sense
> Amplifiers" or "Current Monitor" amplifiers.
>
Matt beat me to it, as he says there are a lot around now, beyond the ones I have mentioned.


-- Scanned by iCritical.

2012\04\02@114208 by Dumitru Stama

picon face
> Then if you really are looking for an op-amp then you looking for the wrong thing.
> Check out the following devices
> Linear Technology
> LT6100
> LT6106 (goes to 36V)
> Analog Devices
> AD8210 - this does bi-directional current sense, but they have others in the current sense family.
> Zetex
> ZDS100x Current Sense devices (they have trimmed this range considerably since being taken over by Diodes Inc).
> Supertex Inc
> HV78xx family Current Sense chips (some go to 450V for mains use!).
> If you really must use an op-amp then maybe Analog Devices AD8675 36V R-R Op-Amp might do, but I know nothing about the pricing.

Thank you for your suggestions.
I will search for a high side current amplifier too

2012\04\02@115819 by Sean Breheny

face picon face
Hi,

Which rail is the current sense resistor closer to? In other words, is
one end of the sense resistor connected to gnd?

Sean


On Mon, Apr 2, 2012 at 10:05 AM, Dumitru Stama <EraseMEspanacspam_OUTspamTakeThisOuTgmail.com> wrote:
{Quote hidden}

>

2012\04\02@120325 by Dumitru Stama

picon face
> Hi,
> Which rail is the current sense resistor closer to? In other words, is
> one end of the sense resistor connected to gnd?
> Sean

Hi,
No, is not connected to ground. I have the sense resistor, then the
load and then the ground. I guess is called "high side" sense resisto

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