On Tuesday, March 5, 2019 at 10:58:21 AM UTC-5, John Larkin wrote:> On 5 Mar 2019 05:56:33 -0800, Winfield Hill <hill@rowland.harvard.edu> > wrote: > > >bloggs.fredbloggs.fred@gmail.com wrote... > >> > >>> Any loop, no matter its rise or fall times, could oscillate. > >> > >> Yours won't, you have 70o phase margin judging from fig2. > >> of the datasheet. Probe the top of R5 for feedback > >> gain/phase to input: > > > > Not clear if Fig 2 is of much help, it's made w/o > > high cap load. What John ought to do, is simply > > run an open-loop-gain Bode plot, with his load, > > make his own Fig 2, see what the phase margin is. > > The transient response is more useful than a Bode plot. It gets more > interesting when it's nonlinear. I saw an oscillation of the OPA552 > circuit when it was slewing hard. > > Since my load will be pulsed, I'll do some pulse-loading sims too. But > with 100uF, or even 20 uF, on the output, and microsecond pulses, I > don't expect much to happen.If it's programmable then you will need to know the settling time to 1/2 LSB step input change. That's strictly small signal.> > > > > -- > > John Larkin Highland Technology, Inc > > lunatic fringe electronics
OPA552 as power regulator
Started by ●March 2, 2019
Reply by ●March 5, 20192019-03-05
Reply by ●March 5, 20192019-03-05
On Tue, 5 Mar 2019 08:41:29 -0800 (PST), bloggs.fredbloggs.fred@gmail.com wrote:>On Tuesday, March 5, 2019 at 10:58:21 AM UTC-5, John Larkin wrote: >> On 5 Mar 2019 05:56:33 -0800, Winfield Hill <hill@rowland.harvard.edu> >> wrote: >> >> >bloggs.fredbloggs.fred@gmail.com wrote... >> >> >> >>> Any loop, no matter its rise or fall times, could oscillate. >> >> >> >> Yours won't, you have 70o phase margin judging from fig2. >> >> of the datasheet. Probe the top of R5 for feedback >> >> gain/phase to input: >> > >> > Not clear if Fig 2 is of much help, it's made w/o >> > high cap load. What John ought to do, is simply >> > run an open-loop-gain Bode plot, with his load, >> > make his own Fig 2, see what the phase margin is. >> >> The transient response is more useful than a Bode plot. It gets more >> interesting when it's nonlinear. I saw an oscillation of the OPA552 >> circuit when it was slewing hard. >> >> Since my load will be pulsed, I'll do some pulse-loading sims too. But >> with 100uF, or even 20 uF, on the output, and microsecond pulses, I >> don't expect much to happen. > >I hope it works better than this f$%$#@%* simulation which defies you to make anything work. >Of course it will work, and we'll sell lots of them. I've done many similar circuits, and all of them have worked. The OPA547 is a better opamp for this, with its programmable current limit. We'll use that one. Thanks, Lasse. https://www.dropbox.com/s/v2zqxk7yzdqz2us/ADG_OPA547_2.jpg?dl=0 -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●March 5, 20192019-03-05
On Tuesday, March 5, 2019 at 12:00:18 PM UTC-5, John Larkin wrote:> On Tue, 5 Mar 2019 08:41:29 -0800 (PST), > bloggs.fredbloggs.fred@gmail.com wrote: > > >On Tuesday, March 5, 2019 at 10:58:21 AM UTC-5, John Larkin wrote: > >> On 5 Mar 2019 05:56:33 -0800, Winfield Hill <hill@rowland.harvard.edu> > >> wrote: > >> > >> >bloggs.fredbloggs.fred@gmail.com wrote... > >> >> > >> >>> Any loop, no matter its rise or fall times, could oscillate. > >> >> > >> >> Yours won't, you have 70o phase margin judging from fig2. > >> >> of the datasheet. Probe the top of R5 for feedback > >> >> gain/phase to input: > >> > > >> > Not clear if Fig 2 is of much help, it's made w/o > >> > high cap load. What John ought to do, is simply > >> > run an open-loop-gain Bode plot, with his load, > >> > make his own Fig 2, see what the phase margin is. > >> > >> The transient response is more useful than a Bode plot. It gets more > >> interesting when it's nonlinear. I saw an oscillation of the OPA552 > >> circuit when it was slewing hard. > >> > >> Since my load will be pulsed, I'll do some pulse-loading sims too. But > >> with 100uF, or even 20 uF, on the output, and microsecond pulses, I > >> don't expect much to happen. > > > >I hope it works better than this f$%$#@%* simulation which defies you to make anything work. > > > > Of course it will work, and we'll sell lots of them. I've done many > similar circuits, and all of them have worked. > > The OPA547 is a better opamp for this, with its programmable current > limit. We'll use that one. Thanks, Lasse. > > https://www.dropbox.com/s/v2zqxk7yzdqz2us/ADG_OPA547_2.jpg?dl=0That's even easier to deal with, you end up with near 90o phase margin, more current drive, and direct current limiting: Version 4 SHEET 1 880 680 WIRE 0 32 -64 32 WIRE 144 32 80 32 WIRE 208 32 144 32 WIRE 448 32 288 32 WIRE 144 64 144 32 WIRE -64 128 -64 32 WIRE 16 128 -64 128 WIRE -64 160 -64 128 WIRE 16 160 16 128 WIRE 144 160 144 128 WIRE 208 160 144 160 WIRE 352 160 288 160 WIRE 448 160 448 32 WIRE 448 160 352 160 WIRE 144 176 144 160 WIRE -64 288 -64 240 WIRE 16 288 16 224 WIRE 16 288 -64 288 WIRE 144 288 144 256 WIRE 144 288 16 288 WIRE 352 288 352 240 WIRE 352 288 144 288 WIRE 448 288 448 224 WIRE 448 288 352 288 WIRE 144 336 144 288 FLAG 144 336 0 SYMBOL res 192 176 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R1 SYMATTR Value 10 SYMBOL res 336 144 R0 SYMATTR InstName R2 SYMATTR Value 200 SYMBOL res 192 48 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R3 SYMATTR Value 45k SYMBOL res -16 48 R270 WINDOW 0 32 56 VTop 2 WINDOW 3 0 56 VBottom 2 SYMATTR InstName R4 SYMATTR Value 0 SYMBOL res -48 144 M0 SYMATTR InstName R5 SYMATTR Value 5k SYMBOL cap 128 64 R0 SYMATTR InstName C1 SYMATTR Value 47n SYMBOL cap 432 160 R0 SYMATTR InstName C2 SYMATTR Value 100µ SYMBOL voltage 144 160 R0 WINDOW 123 24 124 Left 2 WINDOW 39 24 152 Left 2 SYMATTR Value2 AC 1 SYMATTR SpiceLine Rser=10 Cpar=10p SYMATTR InstName V1 SYMATTR Value "" SYMBOL cap 0 160 R0 SYMATTR InstName C3 SYMATTR Value 20p TEXT -96 312 Left 2 !.ac dec 100 10 100k> > > > > > > -- > > John Larkin Highland Technology, Inc > > lunatic fringe electronics
