OPAMP ASTABLE

I never made a triangle wave generator this way, but it seems to me you could take one op amp and set it up as a Schmidt trigger. That gives you two trip points. Then you charge the cap between voltage trip points of the Schmidt trigger. You are going to want hysteresis on the op amp anyway. As I said in my other post, linear operation (as in the transition region) is your enemy. Hysteresis makes things snap cleanly.

The drawback is the frequency is a function of the power supply rails, probably why I never made one that way.

Not if you use a 555 ;-) ...Jim Thompson

Is this what you mean?

Amplitude is linear on V+ but frequency is close to constant.

The triangle would still need to be amplified to drive a transformer.

All four resistors could be the same value, namely a quad pack.

Actually, you are going to want to split phase the signal anyway to drive the transformer, presuming you don't want a DC component.

OK, dual supplies and one less resistor.

Why?

Why? Run your .ASC file, meter the rail current, observe. ...Jim Thompson

On Tue, 10 Sep 2013 20:37:42 -0700, Jim Thompson wrote:

The 5 volt supply is showing 9 mA peaks. Is that your definition of "horrendous current spikes" ?

I did a later version that avoids the beyond-the-rail opamp input swings that I mentioned initially, and adds the transformer and rectifiers. It's pretty tame, too.

Version 4 SHEET 1 1248 680 WIRE 112 -96 80 -96 WIRE 176 -96 112 -96 WIRE 352 -96 256 -96 WIRE 240 -32 208 -32 WIRE 256 -32 240 -32 WIRE 208 0 208 -32 WIRE 80 16 80 -96 WIRE 176 16 80 16 WIRE 352 32 352 -96 WIRE 352 32 240 32 WIRE 480 32 352 32 WIRE 560 32 480 32 WIRE 144 48 128 48 WIRE 176 48 144 48 WIRE 352 48 352 32 WIRE 208 80 208 64 WIRE 560 112 560 32 WIRE 176 144 128 144 WIRE 352 144 352 128 WIRE 352 144 240 144 WIRE 816 176 688 176 WIRE 880 176 816 176 WIRE 992 176 944 176 WIRE 1088 176 992 176 WIRE 1152 176 1088 176 WIRE -176 224 -304 224 WIRE -128 224 -176 224 WIRE -96 224 -128 224 WIRE 992 224 992 176 WIRE 560 240 560 176 WIRE 688 240 688 176 WIRE -176 256 -176 224 WIRE 80 272 80 16 WIRE 176 272 80 272 WIRE 352 272 240 272 WIRE 352 288 352 272 WIRE -304 304 -304 224 WIRE 1152 304 1152 176 WIRE -176 352 -176 336 WIRE -128 352 -176 352 WIRE -96 352 -128 352 WIRE 688 352 688 320 WIRE 992 352 992 288 WIRE 992 352 688 352 WIRE -176 384 -176 352 WIRE 128 384 128 144 WIRE 128 384 80 384 WIRE 176 384 128 384 WIRE 352 384 352 368 WIRE 352 384 256 384 WIRE 480 384 352 384 WIRE 560 384 560 320 WIRE 560 384 480 384 WIRE 992 416 992 352 WIRE -304 432 -304 384 WIRE 1152 432 1152 384 WIRE 240 448 208 448 WIRE 256 448 240 448 WIRE 208 480 208 448 WIRE -176 496 -176 464 WIRE 80 496 80 384 WIRE 176 496 80 496 WIRE 816 496 816 176 WIRE 880 496 816 496 WIRE 992 496 992 480 WIRE 992 496 944 496 WIRE 352 512 352 384 WIRE 352 512 240 512 WIRE 144 528 128 528 WIRE 176 528 144 528 WIRE 992 544 992 496 WIRE 208 560 208 544 FLAG 208 80 0 FLAG 208 560 0 FLAG 240 -32 +5 FLAG 240 448 +5 FLAG 144 48 V2 FLAG 144 528 V2 FLAG -304 432 0 FLAG -176 496 0 FLAG -128 224 +5 FLAG -128 352 V2 FLAG 992 544 0 FLAG 1152 432 0 FLAG 1088 176 OUT FLAG 480 32 A FLAG 480 384 B FLAG 112 -96 G SYMBOL Opamps\\LT1498 208 -32 R0 WINDOW 0 63 91 Left 2 WINDOW 3 38 123 Left 2 SYMATTR InstName U1 SYMBOL Opamps\\LT1498 208 448 R0 WINDOW 0 74 88 Left 2 WINDOW 3 53 128 Left 2 SYMATTR InstName U2 SYMBOL res 272 -112 R90 WINDOW 0 -12 79 VBottom 2 WINDOW 3 -39 33 VTop 2 SYMATTR InstName R1 SYMATTR Value 10K SYMBOL res 272 368 R90 WINDOW 0 -14 77 VBottom 2 WINDOW 3 -42 31 VTop 2 SYMATTR InstName R2 SYMATTR Value 10K SYMBOL voltage -304 288 R0 WINDOW 0 49 41 Left 2 WINDOW 3 55 73 Left 2 SYMATTR InstName V1 SYMATTR Value 5 SYMBOL res -192 240 R0 WINDOW 0 57 32 Left 2 WINDOW 3 57 62 Left 2 SYMATTR InstName R3 SYMATTR Value 2K SYMBOL res -192 368 R0 WINDOW 0 55 40 Left 2 WINDOW 3 57 70 Left 2 SYMATTR InstName R4 SYMATTR Value 2K SYMBOL cap 240 128 R90 WINDOW 0 71 45 VBottom 2 WINDOW 3 43 0 VTop 2 SYMATTR InstName C1 SYMATTR Value 5n SYMBOL cap 240 256 R90 WINDOW 0 -5 49 VBottom 2 WINDOW 3 -32 -1 VTop 2 SYMATTR InstName C2 SYMATTR Value 5n SYMBOL res 368 144 R180 WINDOW 0 -53 70 Left 2 WINDOW 3 -54 38 Left 2 SYMATTR InstName R5 SYMATTR Value 2K SYMBOL res 368 384 R180 WINDOW 0 -53 77 Left 2 WINDOW 3 -53 42 Left 2 SYMATTR InstName R6 SYMATTR Value 2K SYMBOL ind2 544 224 R0 WINDOW 0 -59 32 Left 2 WINDOW 3 -64 65 Left 2 SYMATTR InstName L1 SYMATTR Value 1m SYMATTR Type ind SYMBOL cap 544 112 R0 WINDOW 0 -54 16 Left 2 WINDOW 3 -59 52 Left 2 SYMATTR InstName C3 SYMATTR Value 22µ SYMBOL ind2 672 224 R0 WINDOW 0 69 36 Left 2 WINDOW 3 65 68 Left 2 SYMATTR InstName L2 SYMATTR Value 9m SYMATTR Type ind SYMBOL cap 976 224 R0 WINDOW 0 59 25 Left 2 WINDOW 3 63 57 Left 2 SYMATTR InstName C4 SYMATTR Value 330n SYMBOL cap 976 416 R0 WINDOW 0 59 7 Left 2 WINDOW 3 61 44 Left 2 SYMATTR InstName C5 SYMATTR Value 330n SYMBOL schottky 944 160 R90 WINDOW 0 -51 30 VBottom 2 WINDOW 3 -43 32 VTop 2 SYMATTR InstName D1 SYMATTR Value BAT46WJ SYMATTR Description Diode SYMATTR Type diode SYMBOL schottky 880 512 R270 WINDOW 0 -25 -2 VTop 2 WINDOW 3 -29 -1 VBottom 2 SYMATTR InstName D2 SYMATTR Value BAT46WJ SYMATTR Description Diode SYMATTR Type diode SYMBOL res 1136 288 R0 WINDOW 0 64 40 Left 2 WINDOW 3 61 74 Left 2 SYMATTR InstName R7 SYMATTR Value 60K TEXT -240 80 Left 2 !.tran 5m TEXT -304 -48 Left 2 ;DC/DC CONVERTER TEXT -280 0 Left 2 ;JL SEP 10, 2013 TEXT 568 448 Left 2 !K L1 L2 0.98 TEXT -288 -88 Left 2 ;OPAMP ASTABLE TEXT 360 576 Left 2 ;/ AD8566

Now the power supply bumps are soft and slow and peak at about 25 mA. It's a power converter, so it needs input current.

I, being a cautious sort, ran at small time step (10ns). Ip-p=23mA

...Jim Thompson

I, being a cautious sort, use bypass caps.

And I've tested the AD8566, and it has no windup, no rail stickies, no shoot-through. Fortunately, there are people at ADI who design better opamps than you do.

Wasn't me that announced that the scheme was for low noise.

You still have those circulating currents.

How about current spikes?

You just can't resist being the snot-nosed little brat. Slinging slurs unbacked by facts.

You're mentally ill _and_ rude. What a combination! ...Jim Thompson

It will have milliampere power supply ripple with microsecond slew rates. A conventional CMOS power driver or synchronous switcher would likely have amps in nanoseconds. The di/dt ratio would be in the ballpark of 10^8. You don't think

You whine about anything I post, even if you have to spout nonsense to do it.

Circulating currents? You mean the transformer primary drive?

I said no shoot-through. If it drives a non-DC load, it will have "current spikes", namely the load current. What do you do, design batteries into your opamp chips? Maybe you only ever load your circuits with Spice probes.

More nonsense.

You received lots of advice from other folk. You ignored it. ...Jim Thompson

You've given up on facts and numbers. You do that a lot.

The best idea is Vlad's suggestion to use a PV generator to bias my photodiodes. We're looking into that. Maybe we can live with a negative supply that's good for 20 uA and is 0.4% efficient.

More snot nosed crap. You must have to carry a towel with you to handle such quantity.

Yes, I liked Vlad's idea. ...Jim Thompson

Please view in a fixed-width font such as Courier.

. . . . . . OA . . |\ . | \ . | >---+----- . -|-/ | | . | |/ === ) . Comparator | | ) . | | ) . |\ | [R] ) . | \ Ci | | | . --| >----[Ri]--+---||---+--------+----- . | | / | | . | |/ | |\ | . | -|-\ | . | | >---+ . | | / | . | |/ OA | . | | . | | . | | . | | . ------------------------- . . . . . .

Sorry I didn't 'get' Vlad idea. "Consider photovoltaic thingy." What's that mean?

George H.

For example: TLP191B

After all the folderol, low-noise required followed by current spikes don't matter, why not just buy a charge pump off-the-shelf? ...Jim Thompson

Nice, I didn't realise these existed.

Bit pricy if you need several in series I suppose.