lm358-like opamps

On 3/15/2012 5:20 PM, Bill Martin wrote:
> On 03/15/2012 05:10 PM, mike wrote:
>> On 3/15/2012 4:41 PM, Bill Martin wrote:
>>> Hi,
>>> anyone have a favorite brand/flavor of lm358 or equivalent opamp to
>>> recommend for a simple, low performance integrator to generate a voltage
>>> ramp? 0.5 to 2.5 volts, supply voltage available up to 18V. About one to
>>> two seconds duration, no repeating..one shot style. Looking at just
>>> Mouser, there seem to be 23 parts in soic-8 to choose from...
>>>
>>> Thanks,
>>> Bill Martin
>>
>> Since you have no requirements for linearity...or anything else...
>> I'd just use a cap and a resistor.
> That was version 1.
>>
>> The only application I can think of for a device that has "no repeating"
>> is some kind of trigger for something that goes boom.
> Oh, I hope not. It just shuts down due to power being turned off. :-)
>>
>> Precise requirements/specifications are your friend.
>
> Ok, a sort-of-linear ramp is desired. I may then torture that into
> something exponential, but opposite of how r-c time constant works.
> The game is simple: Feed as much power to a small dc brushed motor as
> possible without making the drive "slip". So, the faster it's turning,
> the more pwm I can shove at it without increasing average current too
> much. It's a toy circuit...driving a 1/24 scale electric dragster.
>
> Bill
>
PWM power supply chip with soft start?
Feed output back to soft start circuit?

If the drive "slips" make a better drive.
If you mean "wheels spin", can you do something
with a position sensor on the suspension?
Maybe a spring on a wheel out the back that
detects a "wheelie" and reduces the current?
That'll give you optimization for the current
track conditions.
Having the front wheels on the ground, especially
if they're doing any steering, is just a waste
of energy.  ;-)

Bill Sloman <bill.sloman@ieee.org> writes:

> On Mar 16, 12:41&nbsp;am, Bill Martin <w...@wwmartin.net> wrote:
>> Hi,
>> anyone have a favorite brand/flavor of lm358 or equivalent opamp to
>> recommend for a simple, low performance integrator to generate a voltage
>> ramp? 0.5 to 2.5 volts, supply voltage available up to 18V. About one to
>> two seconds duration, no repeating..one shot style. Looking at just
>> Mouser, there seem to be 23 parts in soic-8 to choose from...
>
> The Linear Technology LT1013 has rather tighter specifications.

Bill, that's a $5 against a $0.05c part. Well, nearly.

He wants cheap and nasty; LM358(a) is it.

If he wants it gold plated he can pay the extra 0.5 cents and spring for
a LM258A! :)

> The single version - the LT1006 - is a whole lot more tightly
> specified and quite a bit more expensive again. You might balance the
> extra cost against the saving on a smaller integrating capacitor.

I doubt it!

-- 

John Devereux

On Mar 16, 7:14=A0am, John Devereux <j...@devereux.me.uk> wrote:
> BillSloman<bill.slo...@ieee.org> writes:
> > On Mar 16, 12:41=A0am,BillMartin <w...@wwmartin.net> wrote:
> >> Hi,
> >> anyone have a favorite brand/flavor of lm358 or equivalent opamp to
> >> recommend for a simple, low performance integrator to generate a volta=
ge
> >> ramp? 0.5 to 2.5 volts, supply voltage available up to 18V. About one =
to
> >> two seconds duration, no repeating..one shot style. Looking at just
> >> Mouser, there seem to be 23 parts in soic-8 to choose from...
>
> > The Linear Technology LT1013 has rather tighter specifications.
>
> Bill, that's a $5 against a $0.05c part. Well, nearly.
>
> He wants cheap and nasty; LM358(a) is it.
>
> If he wants it gold plated he can pay the extra 0.5 cents and spring for
> a LM258A! :)
>
> > The single version - the LT1006 - is a whole lot more tightly
> > specified and quite a bit more expensive again. You might balance the
> > extra cost against the saving on a smaller integrating capacitor.
>
> I doubt it!

Texas Instruments are now second sourcing the LT1013, and that seems
to be a roughly $1 part. Big film capacitors cost that kind of money.

--
Bill Sloman, Nijmegen