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Simple LDO regualtor

On Sun, 07 Oct 2012 16:50:35 -0700, John Larkin wrote:

--- Why?

To make it oscillate?

Stop that from happening like this:

Version 4 SHEET 1 880 680 WIRE -240 -16 -384 -16 WIRE 16 -16 -240 -16 WIRE 224 -16 16 -16 WIRE -240 16 -240 -16 WIRE 224 96 224 -16 WIRE 16 112 16 -16 WIRE -240 128 -240 96 WIRE -16 128 -240 128 WIRE 64 144 48 144 WIRE 160 144 144 144 WIRE -16 160 -64 160 WIRE 224 240 224 192 WIRE 304 240 224 240 WIRE 336 240 304 240 WIRE -64 256 -64 160 WIRE 48 256 -64 256 WIRE 64 256 48 256 WIRE 160 256 144 256 WIRE 224 256 224 240 WIRE 224 256 160 256 WIRE -384 272 -384 -16 WIRE -240 272 -240 128 WIRE -64 304 -64 256 WIRE 224 304 224 256 WIRE 304 304 304 240 WIRE 48 336 48 256 WIRE 80 336 48 336 WIRE 160 336 160 256 WIRE 160 336 144 336 WIRE -384 416 -384 352 WIRE -240 416 -240 336 WIRE -240 416 -384 416 WIRE -64 416 -64 384 WIRE -64 416 -240 416 WIRE 16 416 16 176 WIRE 16 416 -64 416 WIRE 224 416 224 384 WIRE 224 416 16 416 WIRE 304 416 304 368 WIRE 304 416 224 416 WIRE -384 464 -384 416 FLAG -384 464 0 FLAG 336 240 Vout SYMBOL res 208 288 R0 SYMATTR InstName R1 SYMATTR Value 33 SYMATTR SpiceLine "" SYMBOL voltage -384 256 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 WINDOW 3 24 96 Invisible 2 SYMATTR Value2 "" SYMATTR SpiceLine "" SYMATTR Value PULSE(4 6 .001 .01) SYMATTR InstName V1 SYMBOL pnp 160 192 M180 SYMATTR InstName Q1 SYMATTR Value 2N3906 SYMBOL res 48 240 M90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 10k SYMATTR SpiceLine "" SYMBOL res -80 288 R0 WINDOW 0 -39 32 Left 2 WINDOW 3 -72 62 Left 2 SYMATTR InstName R3 SYMATTR Value 31250 SYMATTR SpiceLine "" SYMBOL Opamps\\LTC1050 16 80 R0 WINDOW 0 -104 -6 Left 2 WINDOW 3 -136 25 Left 2 SYMATTR InstName U1 SYMBOL References\\LT1634-2.5 -240 304 R0 WINDOW 3 12 -45 Left 2 WINDOW 0 15 -76 Left 2 SYMATTR InstName U2 SYMBOL res -256 0 R0 SYMATTR InstName R4 SYMATTR Value 15K SYMATTR SpiceLine "" SYMBOL res 160 128 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 100 SYMATTR SpiceLine "" SYMBOL cap 144 320 R90 WINDOW 0 65 33 VBottom 2 WINDOW 3 64 35 VTop 2 SYMATTR InstName C1 SYMATTR Value 1n SYMATTR SpiceLine "" SYMBOL cap 288 304 R0 SYMATTR InstName C2 SYMATTR Value 1000µ SYMATTR SpiceLine "" TEXT -376 440 Left 2 !.tran .1

-- JF

Reply to
John Fields
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Hey, John -

Change C2 to 1nF and... Change your simulation to: .tran 0 .1 0 10u

I don't know whether it's an artifact of simulation or not having a small enough step to see what's going on.

Not trying to be argumentative.

John S

Reply to
John S

BTW, John...

It seems to work better in LTSpice if R5 is changed to 3.3k.

What do you think?

John S

Reply to
John S

Wow! Please disregard. With a 1uF output capacitor, it makes a decent sine wave generator. Sorry about not considering all the possibilities.

John S

Reply to
John S 

--
Thanks, John. 

With C2 equal to a minimum of 100µF, it looks like the output gets 
stable pretty quick.
Reply to
John Fields

pretty

Yes, but I found that various values of output capacitance could cause oscillations. I am not equipped to handle that. Please let me know if you find a solution.

John

Reply to
John S

On Thu, 11 Oct 2012 15:13:18 -0500, John S wrote:

pretty

--- Anything > 100µF works fine here.

BTW, I changed the LTC1050 to an LTC2050:

Version 4 SHEET 1 880 680 WIRE -240 -128 -384 -128 WIRE 0 -128 -240 -128 WIRE 224 -128 0 -128 WIRE -240 -64 -240 -128 WIRE 0 32 0 -128 WIRE 224 64 224 -128 WIRE -240 80 -240 16 WIRE -32 80 -240 80 WIRE 160 112 112 112 WIRE -32 144 -80 144 WIRE 0 208 0 192 WIRE 224 240 224 160 WIRE 304 240 224 240 WIRE 336 240 304 240 WIRE -80 256 -80 144 WIRE 16 256 -80 256 WIRE 32 256 16 256 WIRE 128 256 112 256 WIRE 224 256 224 240 WIRE 224 256 128 256 WIRE -384 272 -384 -128 WIRE -240 272 -240 80 WIRE -80 304 -80 256 WIRE 224 304 224 256 WIRE 304 304 304 240 WIRE 16 336 16 256 WIRE 48 336 16 336 WIRE 128 336 128 256 WIRE 128 336 112 336 WIRE -384 416 -384 352 WIRE -240 416 -240 336 WIRE -240 416 -384 416 WIRE -80 416 -80 384 WIRE -80 416 -240 416 WIRE 224 416 224 384 WIRE 224 416 -80 416 WIRE 304 416 304 368 WIRE 304 416 224 416 WIRE -384 464 -384 416 FLAG -384 464 0 FLAG 336 240 Vout FLAG 0 208 0 SYMBOL res 208 288 R0 SYMATTR InstName R1 SYMATTR Value 33 SYMATTR SpiceLine "" SYMBOL voltage -384 256 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 WINDOW 3 24 96 Invisible 2 SYMATTR Value2 "" SYMATTR SpiceLine "" SYMATTR Value PULSE(0 6 .01 .001) SYMATTR InstName V1 SYMBOL pnp 160 160 M180 SYMATTR InstName Q1 SYMATTR Value 2N3906 SYMBOL res 16 240 M90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 10k SYMATTR SpiceLine "" SYMBOL res -96 288 R0 WINDOW 0 -39 32 Left 2 WINDOW 3 -72 62 Left 2 SYMATTR InstName R3 SYMATTR Value 31250 SYMATTR SpiceLine "" SYMBOL References\\LT1634-2.5 -240 304 R0 WINDOW 3 12 -45 Left 2 WINDOW 0 15 -76 Left 2 SYMATTR InstName U2 SYMBOL res -256 -80 R0 SYMATTR InstName R4 SYMATTR Value 15K SYMATTR SpiceLine "" SYMBOL cap 112 320 R90 WINDOW 0 65 33 VBottom 2 WINDOW 3 64 35 VTop 2 SYMATTR InstName C1 SYMATTR Value 1n SYMATTR SpiceLine "" SYMBOL cap 288 304 R0 SYMATTR InstName C2 SYMATTR Value 100µ SYMATTR SpiceLine "" SYMBOL Opamps\\LTC2050 0 112 R0 SYMATTR InstName U3 TEXT -376 440 Left 2 !.tran .1

-- JF

Reply to
John Fields

John S wrote:

This works.. Nice out put all the way down to 3.0 volts on the rail. Jamie

Version 4 SHEET 1 880 680 WIRE 16 -16 -384 -16 WIRE 224 -16 16 -16 WIRE 224 96 224 -16 WIRE 176 112 128 112 WIRE 16 160 16 -16 WIRE 128 160 128 112 WIRE 128 160 112 160 WIRE -16 240 -32 240 WIRE 64 240 64 224 WIRE 112 256 80 256 WIRE 224 256 224 192 WIRE 224 256 176 256 WIRE 304 256 224 256 WIRE 336 256 304 256 WIRE -384 272 -384 -16 WIRE -32 288 -32 240 WIRE 224 288 224 256 WIRE 304 288 304 256 WIRE 48 336 32 336 WIRE 80 336 48 336 WIRE -384 416 -384 352 WIRE -32 416 -32 384 WIRE -32 416 -384 416 WIRE 48 416 -32 416 WIRE 224 416 224 368 WIRE 224 416 48 416 WIRE 304 416 304 352 WIRE 304 416 224 416 WIRE -384 464 -384 416 FLAG -384 464 0 FLAG 128 32 0 SYMBOL res 208 272 R0 SYMATTR InstName R1 SYMATTR Value 33 SYMBOL voltage -384 256 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 WINDOW 3 24 96 Invisible 2 SYMATTR Value PULSE(3.5 6 .001 .01) SYMATTR InstName V1 SYMBOL References\\LT1634-2.5 144 256 R90 WINDOW 3 -43 -151 VTop 2 WINDOW 0 -27 0 VBottom 2 SYMATTR InstName U2 SYMBOL cap 288 288 R0 SYMATTR InstName C1 SYMATTR Value 10µ SYMBOL pmos 176 192 M180 SYMATTR InstName M1 SYMATTR Value HAT1072H SYMBOL res 112 16 R0 SYMATTR InstName R2 SYMATTR Value 1k SYMBOL pnp 112 224 M270 SYMATTR InstName Q1 SYMATTR Value 2N2907 SYMBOL npn 32 288 M0 SYMATTR InstName Q2 SYMATTR Value 2N3904 SYMBOL res 80 224 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 10k SYMBOL res 32 320 R0 SYMATTR InstName R5 SYMATTR Value 56k SYMBOL res 64 240 R0 SYMATTR InstName R4 SYMATTR Value 680 TEXT -376 440 Left 2 !.tran 0 .1 0 startup

Reply to
Jamie

On 10/11/2012 4:15 PM, John Fields wrote:

Good move!

With a slight modification, it works with .01uF or greater:

Version 4 SHEET 1 880 680 WIRE -240 -128 -384 -128 WIRE 0 -128 -240 -128 WIRE 432 -128 0 -128 WIRE 432 -80 432 -128 WIRE -240 -64 -240 -128 WIRE -80 -48 -96 -48 WIRE 272 -48 -16 -48 WIRE 0 32 0 -128 WIRE 432 64 432 0 WIRE -240 80 -240 16 WIRE -192 80 -240 80 WIRE -96 80 -96 -48 WIRE -96 80 -112 80 WIRE -32 80 -96 80 WIRE 144 112 112 112 WIRE 272 112 272 -48 WIRE 272 112 224 112 WIRE 368 112 272 112 WIRE -32 144 -80 144 WIRE 0 208 0 192 WIRE 432 240 432 160 WIRE 512 240 432 240 WIRE 544 240 512 240 WIRE -80 256 -80 144 WIRE 16 256 -80 256 WIRE 32 256 16 256 WIRE 128 256 112 256 WIRE 432 256 432 240 WIRE 432 256 128 256 WIRE -384 272 -384 -128 WIRE -240 272 -240 80 WIRE -80 304 -80 256 WIRE 432 304 432 256 WIRE 512 304 512 240 WIRE 16 336 16 256 WIRE 48 336 16 336 WIRE 128 336 128 256 WIRE 128 336 112 336 WIRE -384 416 -384 352 WIRE -240 416 -240 336 WIRE -240 416 -384 416 WIRE -80 416 -80 384 WIRE -80 416 -240 416 WIRE 432 416 432 384 WIRE 432 416 -80 416 WIRE 512 416 512 368 WIRE 512 416 432 416 WIRE -384 464 -384 416 FLAG -384 464 0 FLAG 544 240 Vout FLAG 0 208 0 SYMBOL res 416 288 R0 SYMATTR InstName R1 SYMATTR Value 33 SYMBOL voltage -384 256 R0 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 WINDOW 3 24 96 Invisible 2 SYMATTR Value PULSE(0 6 .01 .001) SYMATTR InstName V1 SYMBOL pnp 368 160 M180 SYMATTR InstName Q1 SYMATTR Value 2N3906 SYMBOL res 16 240 M90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 10k SYMBOL res -96 288 R0 WINDOW 0 -39 32 Left 2 WINDOW 3 -72 62 Left 2 SYMATTR InstName R3 SYMATTR Value 31250 SYMBOL References\\LT1634-2.5 -240 304 R0 WINDOW 3 12 -45 Left 2 WINDOW 0 15 -76 Left 2 SYMATTR InstName U2 SYMBOL res -256 -80 R0 SYMATTR InstName R4 SYMATTR Value 15K SYMBOL cap 112 320 R90 WINDOW 0 65 33 VBottom 2 WINDOW 3 64 35 VTop 2 SYMATTR InstName C1 SYMATTR Value 1n SYMBOL cap 496 304 R0 SYMATTR InstName C2 SYMATTR Value .01u SYMBOL Opamps\\LTC2050 0 112 R0 SYMATTR InstName U3 SYMBOL res 416 -96 R0 SYMATTR InstName R5 SYMATTR Value 10 SYMBOL res -208 64 M90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R6 SYMATTR Value 10k SYMBOL cap -16 -64 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C3 SYMATTR Value 22p SYMBOL res 128 96 M90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R7 SYMATTR Value 1000 TEXT -376 440 Left 2 !.tran .5

Reply to
John S

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