MPP Coil And Preamp Speed

[godigit1]

Tried a little bit last Knight. I got the signal connected and through the 4562. It was looking really good but then I switched between wave forms sine ramp pulse all looked good then going back to square wave I can not get a square wave through my voltage divider. Its good on the + side of r1 and neg side of r2 but not through the divider.
Cant explain it maybe bad cable I will try again and use the sample generator.
I took it to 20 KHZ before switching around. My genny is pretty slewed ot that with a square wave but the 4562 looked really good, At first it looks like something is maybe up with your chip .
More tonight and a 5532. Oh and my rise and fall tiimes stayed right with the genny there was no lag.

[green]

Trigger the scope on the leading or falling edge, 500ns or 1us/division.

[green]

Trying some things in spice. Step time to flat approximately equal to(closed loop gain/amplifier BW). Needed to parallel fdbk resistor with a capacitor to prevent overshoot with some of the amplifiers I tried. Calculated step time to flat LM4562(33/55e6)=.6us NE5532(33/10e6)=3.3us

Thinking measured step time to flat should be less than desired target TC?

Single amplifier MP had a gain of 1000. Step time to flat=(1000/10million)=100us. Amplifier TC around 20us. Carl stated in another thread, amplifier TC needs to be less than target TC. Wondering if the single amplifier MP could detect a US nickel(TC=10us)or is my thinking wrong again?

[green]

Spice files I've been using for step time. Move OP amps to try a different one.

[green]

Spice files I've been using for step time. Move OP amps to try a different one.

Tried moving amps to look at a different amp. Didn't work with the zip file, had to cut moved amplifier after moving the desired amp to circuit.

[green]

Put the LM4562 in a socket above the board to isolate the board. Appears board capacitance is slowing response. Step time to flat close to calculated(40/55e6=.73us)

MPP rev D

[godigit1]

Hi Green,

Thanks for posting the spice simulation.

In your last post the top scope shot.
I was having problem with a very large curve as well, for me it was connection problems from my breadboard and scope probes.

I was able get my voltage divider problem figured out it was a bad scope probe really strange behavior.

I tested with 10khz square wave using the set up in your post #70.

I tested 3 amps with the same set up only changing the b cursor for measurement.
The yellow channel is the genny in. Its 320ns before flat. The cursors are set between where both signals o out after that.
The frequency on the cursor scale is wrong it was all done at 10khz


Lm4562


1.54 us to flat
1.22Us lag
5532


2.12us t flat
1.80 us lag

Max412


1.90us to flat
1.58us lag

looks like you may have it figured out but let me know if I'm missing something or another way you would like to see me try to set up.
Best

[Polymer]

@ green, godigit1: Got lost on the way, too confusing for me for now ....

[green]

Hi Green,

Thanks for posting the spice simulation.

In your last post the top scope shot.
I was having problem with a very large curve as well, for me it was connection problems from my breadboard and scope probes.

I was able get my voltage divider problem figured out it was a bad scope probe really strange behavior.

I tested with 10khz square wave using the set up in your post #70.

I tested 3 amps with the same set up only changing the b cursor for measurement.
The yellow channel is the genny in. Its 320ns before flat. The cursors are set between where both signals o out after that.
The frequency on the cursor scale is wrong it was all done at 10khz


Lm4562
[ATTACH]49649[/ATTACH]

1.54 us to flat
1.22Us lag
5532
[ATTACH]49650[/ATTACH]

2.12us t flat
1.80 us lag

Max412
[ATTACH]49651[/ATTACH]

1.90us to flat
1.58us lag

looks like you may have it figured out but let me know if I'm missing something or another way you would like to see me try to set up.
Best

Thanks for the test. I get about 4divisions, 2us to flat for each of your amplifiers. I would start time when it first starts changing. Appears faster amplifier doesn't help, still fast enough for most targets. My only question, is circuit card capacitance causing the longer decay time or something else?

[godigit1]

Hi Green,
I wish I could answer your question About the pcb design capacitance. I'm still trying to learn more about that as well as op amps. Thanks for the post it definitely taught me a bit at least a light came on any ways.

I remember reading here somewhere the the Mpp op amp design has or adds a inherent 2 to 3 us to the sample time.

Looking again at your post # 81. By raising the chip and changing the gain a bit it looks like you have knocked off 1us.
Ill see if I can get the same results. This plays in to one of my other projects ive recently restarted.
Also wondering if bending the signal pins out and direct connecting to the feedback resistor off board might help? Make connections off board except for pins 4 and 8
Just thinking.
Thanks again.

[6666]

Increase the + and - voltage to max, and only use the + inputs of pre amp op amps to reduce sample time

[green]

Hi Green,
I wish I could answer your question About the pcb design capacitance. I'm still trying to learn more about that as well as op amps. Thanks for the post it definitely taught me a bit at least a light came on any ways.

I remember reading here somewhere the the Mpp op amp design has or adds a inherent 2 to 3 us to the sample time.

Looking again at your post # 81. By raising the chip and changing the gain a bit it looks like you have knocked off 1us.
Ill see if I can get the same results. This plays in to one of my other projects ive recently restarted.
Also wondering if bending the signal pins out and direct connecting to the feedback resistor off board might help? Make connections off board except for pins 4 and 8
Just thinking.
Thanks again.

The different amplifiers look similar with an input step that causes less than full scale output. Maybe you could try with the flyback(normal operation)to see if any comes out of saturation sooner.

Think you would get what I got if you connected directly to the amplifier off the board.

[SaltyDog]

Hi All,

I have scop'ed the preamp in (pin 2, yellow) to output (pin 1 blue) and notice quite a bit of distortion in the signal, especially overshoot (this is with NE5532)
See attached image ... will a faster opamp fix this?

[dbanner]

The overshoot could be the result of capacitive loading on the output pin. Or it could be the front end doesn't like the coil. The noise looks minimal.

[Carl-NC]

I'm not sure what you think is wrong, or what you mean by distortion. A little bit of overshoot usually indicates slight underdamping and that's where you want to be.