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
Surely you mean 23000.
The LM358 is still out there, and cheap.
-- My liberal friends think I'm a conservative kook. My conservative friends think I'm a liberal kook. Why am I not happy that they have found common ground? Tim Wescott, Communications, Control, Circuits & Software http://www.wescottdesign.com
Since you have no requirements for linearity...or anything else... I'd just use a cap and a resistor.
The only application I can think of for a device that has "no repeating" is some kind of trigger for something that goes boom.
Precise requirements/specifications are your friend.
That was version 1.
Oh, I hope not. It just shuts down due to power being turned off. :-)
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
The Linear Technology LT1013 has rather tighter specifications. 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.
-- Bill Sloman, Nijmegen
If you want to limit torque then you want a constant current drive. Set it to just below the point of slippage then let it go.
One can easily be made with an LM393 triangle generator + PWM comparator and an LM358 half as the current feedback error amplifier. The setpoint can be constant, or controlled from a second error amplifier to control speed or voltage or some other variable.
Tim
-- Deep Friar: a very philos>> >>> Hi,
Ha, you got that right!,. I have crap loads of them.
Jamie
How do you plan on detecting if it is slipping or not?
Going to have a generator reference on the front wheels?
Jamie.
It's not going to be that advanced. I would have to mount the board on the "moving parts" to really do traction control. Just doing "educated guessing", once there is enough run data to tune it up.
Bill
This is very much the idea here. Full traction control would be nice, but not really needed to be better than what's out there now in way of motor control.
Version 1 does pretty well with just an r-c curve to control the pwm ramping up, but it's really not the right shape for the ramp. Backwards, actually! pwm is done by a nifty little chip from Supertex, meant to be controlling cooling fans in electrical racks. Darn thing comes Soooo close, but doesn't quite do everything needed.
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, 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! :)
I doubt it!
-- John Devereux
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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
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