Non-linear load compensation

Wouldn't a better driver be the solution?

If you only need a couple of volts of voltage swing, a video driver or a fast op amp intended for use as a video driver might be viable options.

Tell us more about the amplifier you are using at the moment.

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Bill Sloman, Nijmegen

The device you are looking for is a resistor.

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 Thanks,
    - Win

or a capacitor.. Mark

It's not really going to happen, is it?

I have an apple tree that produces bananas and, every so often, produces pears but I wanted grapefruits. This is due to the tree graft coming from a weeping willow.

What I am looking for is a nice entertaining game in plastic, preferably yellow, that will give me some oranges, but forget about the oranges for now because that just confuses things.

PS: for design reasons, I would prefer not to use something that will solve my problem etc.

Thanks, all help really appreciated, glad to be part of the group, perhaps we can get together for a hug later.

Bestest

DNA

You're worried about the voltage across the load.

Why?

The load doesn't seem to care.

The non-linearity sounds something like a solenoid actuating.

If there are parts of the circuit that need a clean voltage, isolate the nonlinear portion of the load.

It's possible that what you're just seeing is the load current passing through zero out of phase with the measured voltage. Some drivers don't like this.

RL

Sounds like a woofer.

Sounds like friction against the voice coil of a woofer, which 'sticks' when velocity hits zero. Sticking friction is a higher force than sliding friction.

Huh? What does that mean? Do you want the current to not follow the demands of the load? Do you want the driver amplifier to be unaffected by the transient? Do you want the load current to be a perfect sinewave, or the load voltage to be a perfect sinewave?

Or do you want to readjust the voice coil in the woofer so it doesn't rub the magnet?

a capacitor there would help absorb the hump

use something that behaves like a capacitor then....

what you don't say is how you're driving it

is it a voltage drive or a current drive

is there room for some feedback to modulate the drive so the glitch becomes less significant?

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Bye.
   Jasen

Well gosh bill ReadTheFinePost, OP aleardy ssaid under 100 Hz, hardly a need for normal video drivers.

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 JosephKK
 Gegen dummheit kampfen die Gotter Selbst, vergebens.  
  --Schiller

Well gosh josephkk, ReadTheFinePost, OP wants to minimise cross-over distortion, which can be helped by using a driver with a very high bandwidth and slew rate, such as a nice, cheap, widely available video driver. This won't get rid of the glitch, but it can feed back the error signal fast enough to make the glitch very, very small.

Try engaging your brain before descending on your keyboard.

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Bill Sloman, Nijmegen

Back off and remember that crossover issues are usually bias problems not bandwidth problems. 100 MHz amplifiers are not necessarily the solution to

100 Hz problems. Fully discrete class "A" amplifiers with appropriate negative feedback can do the required task easily.

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 JosephKK
 Gegen dummheit kampfen die Gotter Selbst, vergebens.  
  --Schiller

Class A amplifiers don't suffer from cross-over distortion. Properly biassed class B amplifiers are almost as good, but you end up with quite a lot of bias current, and you have to worry about the junction temperatures of all the transistors involved in determining the bias current.

A driver which can slew two Vbe drops in less than a microsecond is a less elegant solution, but it can work pretty well, and doesn't demand the same level of skill in thermal design.

In fact, it isn't clear that the OP was having trouble with cross-over distortion as such - he complained about a non-linear load - and lots of gain-bandwidth in the feedback loop is probably the more general solution.

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Bill Sloman, Nijmegen

In article , wrote: [....]

Actually that makes it a class AB not just a class B, but the point is mostly correct. You can also reduce the needed idle current at the cost of losing some peak to peak swing by increasing the emitter balasting resistors.

The idle current for least distortion is just about where the gain for no signal is equal to the gain where only one transistor is in use.

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kensmith@rahul.net   forging knowledge

[snip]

[snip]

If you use Sziklai-connected darlingtons in the output stage, then only the Vbe of the drivers are in the loop for quiescent current control. Since these aren't working as hard as the output devices, they don't get as hot and you can thermally link the transistor used for the Vbe multiplier to the two drivers and end up with a pretty stable quiescent current over all output levels.

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T

If it\'s not broken, don\'t fix it.

Been there, done that. My home-built amplifier in the basement works exactly that way, and has done since about 1975.

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Bill Sloman, Nijmegen

Each to their own, I would use a class AB if i had to go that way. Crossover glitch is a typical property of class B and class C amplifiers. It is not difficult to a little class AB and still remain power efficient.

--
 JosephKK
 Gegen dummheit kampfen die Gotter Selbst, vergebens.  
  --Schiller

Sounds like your load has like back-to-back diodes in series with it, so below some value the load is disconnected. There's a whole lot of issues here:

(1) If the load is disconnected and it's not drawing power, that's probably bad-- you're going to get distortion. The best way to fix this is not to kludge something, but to find a way to make the load more reasonable.

(2) You're asking for a resistor that conducts more at lower voltages, then much less or not at all at higher voltages. That's close to what a negative resistance does, only a negative resistor would be linear. Depending on the power level of the load, anytwhere from two to a tmillion tunnel diodes might be coerced into doing what you need. (Kidding-- tunnel diodes are getting hard to find).

(3) If you absolutely positively need this, a pair of comparators and a MOSFET or two will do this.

(4) A better question might be: WHY do you want to smooth out this glitch? It's not going to affect the signal power delivered to the load, it's only going to smooth out the voltage waveform.

(5) The best way would be to forget about a changing load, but instead work on the source. Lowering the source impedance with negative feedback is the common way to do this.