C-multiplier again

Eh, the idea doesn't seem to be working out - the output is actually better without the multiplier in the cicuit! It looked good on paper, oh well. :(

Durr... I've even been known to do it with tubes. ;-)

Tim

--
Deep Friar: a very philosophical monk.
Website: http://webpages.charter.net/dawill/tmoranwms

You could do a quick test. Use the grounded base circuit you just posted, with the base lead soldered to copperclad. Apply appropriate bias and signal, and measure the result. I modeled the MPSA14. It took a 20MEG in parallel with 5nF, in series with 800pF in parallel with 100k. I then compared a single 2N4401 with the P. Hobbs model.

The results with LTspice are completely unrealistic.

The files are archived in 3CBA32DC.ZIP, posted to abse with the title "More E-F Ripple Filter Simulations".

Mike

+15V >--+--------+--/\/\--+-----> Vout 14.8v | | 4.7R | | R3 | | 2.7M | } | _| | C1 +------| \ '---||---+ | >--+---, 10uF | ,--|__/ | | | | | | | R7 '--- |----' R4 TBD 27k | 4.7R | | | --+--------+--------+----

I see your idea, not bad. It's a nice simplification of this, incorporating the current-sinking transistor into the opamp.

+15V >--+--------+--------+----/\/\--+-----> Vout 14.8v | | | 4.7R | | R3 | | | 2.7M | | } | _| | | C1 +------| \ |/ '---||---+ | >------| 10uF | ,--|__/ |\V | | | | R7 '--- |----------+ TBD | | 27k | R4 | | 4.7R | | | --+--------+----------+----

This scheme is DC regulating as well. The class-A current is set by R3 and R7, so the dc voltage drop is fixed.

--
 Thanks,
    - Win

7R

=A0|

Both give line regulation, true. John's problem seems to be that he needs(?) load regulation too.

The multi-pole BJT C-mult looks great for feather-weight and constant loads. If the ultra-clean part of the load is separable, I'd do that.

If John really needs low-dropout, 15mA, tight load regulation, and low noise, my best shot so far is to bootstrap the op-amp's supplies on the Gerber'd "filtered-reference feeding a R-R op-amp" thing he linked to, to circumvent the op amp's CMRR / PSRR feeding thru.

Or, I guess, feed the op amp with a steady voltage, e.g., to make an ultra-clean supply, start with an ultra-clean supply...

Or cascade a couple such op-amp stages, each feeding the next, each stage improving PSRR by whatever it can muster. 50-60dB? (I don't really trust op amps to have low noise and amazing PSRRs and CMRRs over frequency, but then I've not looked at all the latest and greatest.)

-- Cheers, James Arthur

If there's no voltage reference, there's no regulation.

All I want is a SOT-23 LDO regulator with 1 nv/rthz noise, 140 dB PSRR to 1 MHz, and not made by Maxim.

John

The +15v is the reference. So, maybe more accurately, these circuits don't regulate, but they preserve the +15v input's line regulation. rOut =3D 5 ohms, load regulation =3D zip.

Heathen.

-- Cheers, James Arthur

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If you don't mind, I prefer "barbarian."

John

John Larkin a écrit :

...

And a gmail account?

--
Thanks,
Fred.

Winfield Hill wrote:

[...]

Cancellation schemes give a 6dB/octave drop to a notch frequency, then a

6dB/octave rise. The depth of the notch is extremely sensitive to the emitter resistance and probably the temperature of the transistor. Some examples may show large amounts of second harmonic distortion on the output. This does not appear on the frequency analysis plot.

In this example, the notch frequency is about 2KHz with a depth of -92dB. Try changing the emitter resistance to get an idea of how critical it is.

I don't think you want to rely on this method for any more than a minor amount of cancellation, say 20 dB or thereabouts.

Mike

Version 4 SHEET 1 1140 1108 WIRE -1072 -432 -1088 -432 WIRE -944 -432 -992 -432 WIRE -896 -432 -944 -432 WIRE -832 -432 -896 -432 WIRE -720 -432 -832 -432 WIRE -656 -432 -720 -432 WIRE -496 -432 -576 -432 WIRE -480 -432 -496 -432 WIRE -832 -416 -832 -432 WIRE -944 -400 -944 -432 WIRE -1088 -352 -1088 -432 WIRE -480 -320 -480 -432 WIRE -944 -304 -944 -336 WIRE -832 -304 -832 -336 WIRE -832 -304 -944 -304 WIRE -720 -304 -720 -432 WIRE -752 -288 -768 -288 WIRE -624 -272 -688 -272 WIRE -544 -272 -624 -272 WIRE -1088 -256 -1088 -272 WIRE -832 -256 -832 -304 WIRE -800 -256 -832 -256 WIRE -752 -256 -800 -256 WIRE -832 -224 -832 -256 WIRE -720 -224 -720 -240 WIRE -768 -176 -768 -288 WIRE -736 -176 -768 -176 WIRE -480 -176 -480 -224 WIRE -480 -176 -736 -176 WIRE -480 -160 -480 -176 WIRE -832 -128 -832 -144 WIRE -480 -64 -480 -80 FLAG -1088 -256 0 FLAG -896 -432 Vin FLAG -496 -432 Vout FLAG -480 -64 0 FLAG -720 -224 0 FLAG -832 -128 0 FLAG -800 -256 U1P FLAG -736 -176 U1N FLAG -624 -272 U1O SYMBOL npn -544 -320 R0 SYMATTR InstName Q1 SYMATTR Value 2N4401 SYMBOL voltage -1088 -368 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 15 SYMBOL voltage -976 -432 R90 WINDOW 0 49 39 VRight 0 WINDOW 123 -48 40 VRight 0 WINDOW 39 0 0 Left 0 WINDOW 3 -2 123 VRight 0 SYMATTR InstName V2 SYMATTR Value2 AC 1 SYMATTR Value SINE(0 0.1 1200) SYMBOL res -496 -176 R0 SYMATTR InstName R1 SYMATTR Value 4.681 SYMBOL res -672 -448 M90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R2 SYMATTR Value 4.7 SYMBOL opamps\\1pole -720 -272 R0 SYMATTR InstName U1 SYMBOL res -848 -432 R0 SYMATTR InstName R3 SYMATTR Value 2.7e6 SYMBOL res -848 -240 R0 SYMATTR InstName R4 SYMATTR Value 27k SYMBOL cap -960 -400 R0 SYMATTR InstName C1 SYMATTR Value 10µf TEXT -824 -528 Left 0 ;'Op Amp Ripple Cancellation TEXT -832 -488 Left 0 !.ac oct 100 0.1 4e6

You'd need a trimpot to make up for the tolerance of the 4.7r resistors. And yes, the dynamics are terrible here. And it's a power hog.

Feedforward is great when you want a 3:1, or even sometimes 10:1, fix to some problem. Like for temperature compensation or some other situation when negative feedback isn't available.

John

|

=A0|

|

=A0|

=A0|

=A0|

4 4.7R

=A0|

. .

Well, apart from THAT, Mrs. Lincoln, how'd you enjoy the play?

-- Cheers, James Arthur

John Larkin wrote:

I'd stay away from a trimpot. If you try to get exact balance, it may work in the lab. But if you ship it to the customer and there is some noise problem, it may work one day and not work the next. That would be impossible to troubleshoot.

Also, it is impossible to do a worst-case tolerance analysis on this method. If you cannot guarantee that you know how it will work under all conditions, give it to Joerg and let him fix it:)

Anyway, I have solved your problem. This approach gives -180dB at 1KHz, with a -200dB notch at 1MHz. The IR drop is 18.8 * ImA, so if you have a

10mA drain, you end up with 14.8V. An additional benefit is very good brownout protection. It will keep your lamps lit for a long time!

I left the cancellation method in for comparison.

Mike

Version 4 SHEET 1 1140 1108 WIRE -1072 -432 -1088 -432 WIRE -944 -432 -992 -432 WIRE -896 -432 -944 -432 WIRE -832 -432 -896 -432 WIRE -720 -432 -832 -432 WIRE -656 -432 -720 -432 WIRE -496 -432 -576 -432 WIRE -480 -432 -496 -432 WIRE -320 -432 -336 -432 WIRE -224 -432 -240 -432 WIRE -160 -432 -224 -432 WIRE -48 -432 -80 -432 WIRE -832 -416 -832 -432 WIRE -944 -400 -944 -432 WIRE -224 -400 -224 -432 WIRE -48 -400 -48 -432 WIRE -1088 -352 -1088 -432 WIRE -480 -320 -480 -432 WIRE -224 -320 -224 -336 WIRE -48 -320 -48 -336 WIRE -944 -304 -944 -336 WIRE -832 -304 -832 -336 WIRE -832 -304 -944 -304 WIRE -720 -304 -720 -432 WIRE -752 -288 -768 -288 WIRE -624 -272 -688 -272 WIRE -544 -272 -624 -272 WIRE -1088 -256 -1088 -272 WIRE -832 -256 -832 -304 WIRE -800 -256 -832 -256 WIRE -752 -256 -800 -256 WIRE -320 -240 -336 -240 WIRE -224 -240 -240 -240 WIRE -160 -240 -224 -240 WIRE -48 -240 -80 -240 WIRE 0 -240 -48 -240 WIRE 48 -240 0 -240 WIRE -832 -224 -832 -256 WIRE -720 -224 -720 -240 WIRE -224 -208 -224 -240 WIRE -48 -208 -48 -240 WIRE 48 -208 48 -240 WIRE -768 -176 -768 -288 WIRE -736 -176 -768 -176 WIRE -480 -176 -480 -224 WIRE -480 -176 -736 -176 WIRE -480 -160 -480 -176 WIRE -832 -128 -832 -144 WIRE -224 -128 -224 -144 WIRE -48 -128 -48 -144 WIRE 48 -128 48 -144 WIRE -480 -64 -480 -80 FLAG -1088 -256 0 FLAG -896 -432 Vin FLAG -496 -432 Vout FLAG -480 -64 0 FLAG -720 -224 0 FLAG -832 -128 0 FLAG -800 -256 U1P FLAG -736 -176 U1N FLAG -624 -272 U1O FLAG -336 -432 Vin FLAG -224 -320 0 FLAG -224 -432 Vout2 FLAG -48 -320 0 FLAG -48 -432 Vout3 FLAG -224 -128 0 FLAG -224 -240 Vout4 FLAG -48 -128 0 FLAG 0 -240 Vout5 FLAG -336 -240 Vout3 FLAG 48 -128 0 SYMBOL npn -544 -320 R0 SYMATTR InstName Q1 SYMATTR Value 2N4401 SYMBOL voltage -1088 -368 R0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR InstName V1 SYMATTR Value 15 SYMBOL voltage -976 -432 R90 WINDOW 0 49 39 VRight 0 WINDOW 123 -48 40 VRight 0 WINDOW 39 0 0 Left 0 WINDOW 3 -2 123 VRight 0 SYMATTR InstName V2 SYMATTR Value2 AC 1 SYMATTR Value SINE(0 0.1 2.111e3) SYMBOL res -496 -176 R0 SYMATTR InstName R1 SYMATTR Value 4.681 SYMBOL res -672 -448 M90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R2 SYMATTR Value 4.7 SYMBOL opamps\\1pole -720 -272 R0 SYMATTR InstName U1 SYMBOL res -848 -432 R0 SYMATTR InstName R3 SYMATTR Value 2.7e6 SYMBOL res -848 -240 R0 SYMATTR InstName R4 SYMATTR Value 27k SYMBOL cap -960 -400 R0 SYMATTR InstName C1 SYMATTR Value 10µf SYMBOL cap -240 -400 R0 SYMATTR InstName C2 SYMATTR Value 10000µf SYMATTR SpiceLine Rser=20m Lser=2.5nh SYMBOL res -336 -448 M90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R5 SYMATTR Value 4.7 SYMBOL cap -64 -400 R0 SYMATTR InstName C3 SYMATTR Value 10000µf SYMATTR SpiceLine Rser=20m Lser=2.5nh SYMBOL res -176 -448 M90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R6 SYMATTR Value 4.7 SYMBOL cap -240 -208 R0 SYMATTR InstName C4 SYMATTR Value 10000µf SYMATTR SpiceLine Rser=20m Lser=2.5nh SYMBOL res -336 -256 M90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R7 SYMATTR Value 4.7 SYMBOL cap -64 -208 R0 SYMATTR InstName C5 SYMATTR Value 10000µf SYMATTR SpiceLine Rser=20m Lser=2.5nh SYMBOL res -176 -256 M90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R8 SYMATTR Value 4.7 SYMBOL cap 32 -208 R0 SYMATTR InstName C6 SYMATTR Value 10µf SYMATTR SpiceLine Rser=2m Lser=2.5nh TEXT -824 -528 Left 0 ;'Op Amp Ripple Cancellation TEXT -832 -488 Left 0 !.ac oct 100 0.1 4e6

It's a shame that supercaps have such high ESRs.

John

I was thinking about that. Maxwell Technology makes unit with milliohm ESRs, but I wasn't sure there wasn't some funky noise problem, like electrolyte convection or who knows what.

Oh, and they're a few cubic inches--not surface mountable.

But as for leakage, I've seen a *really* clever dodge around that. Walt Jung, I think, in a low-noise reference IIRC.

-- Cheers, James Arthur

=A0|

=A0|

=A0|

=A0|

4.7R

=A0|

20dB sounds about right. The advantages of this approach are low drop- out voltage and superior low-frequency noise cancellation (compared to practical passive equivalents).

A big part of the dynamic limitation is the f.f. network rolling off. If you change C1 to 100uF, and tack 100uF on the output to cover the high-end, overall performance is much improved--nearly as good as a passive version using 10,000uF caps, and a lot smaller.

For super massive attenuation of input noise and ripple, other approaches are better.

If John could knock down that 50mV switcher ripple with an LC at the input, that's a bonus. But he won't--The Brat would kill him.

-- Cheers, James Arthur

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My description was crap--it was a question of notation. I'm not sure of the dB convention as applied to these circuit--some R.F. work a ways back ruined me.

In R.F., 'dB' in our shop meant a ratio of powers unless otherwise specified. So, if you said '40dB' I'd assume you meant a ratio of

10,000 in power, or, equivalently--power being V^2/R--that you meant a factor of merely 100, voltage.

I vaguely recall, but I don't remember clearly, that we used to used the symbol 'dBv' to designate when a ratio of voltages was being reported. To convert that to power comparison, we'd have to multiply those dB by 2.

Anyway, the other posts have cleared it all up. Thanks.

-- Cheers, James Arthur

No, I survived. The Gerbered board had...

Wall wart connector

Polyfuse

Transzorb

10 uF ceramic

47 uH inductor

two 10 uF ceramics and one 120 uF polymer aluminum to make "+15 volts." That's 12 dB/octave starting at about 2 KHz.

Then the LM8261 low-noise LDO reg, which has its own 15 ohms + 2x10uF

• 120uF at its output.

I also use two Hobbsonian c-multipliers in other supplies that don't need LDO or regulation.

Paranoia, groveling for nanovolts.

But I really need to measure some actual c-multiplier circuits to see what the Early slopes are like. Could be that LT Spice is grossly pessimistic. I note here that everyone, including myself, would rather sit in a swivel chair and simulate and theorize, than get up and solder and measure.

John