How can you enhance Sijosae splitter precision without a trimmer?

Use an opamp.

If your circuit has a completely constant current load, then you could probably optimize it by hand selection of the various resistors.

If the current load is variable, though, I suspect you're going to have difficulty making it "precise under load variation". It looks as if this circuit has a relatively high output impedance, due to the use of those 10-ohm emitter degeneration resistors. The virtual ground is going to bounce around considerably as the load changes.

We don't know his actual "modded" circuit, but the Sijosae splitters that show up in google searches look awfully soft and sloppy.

Unless the supplies are super accurate, I can't see much virtue in a precise splitter. Downstream circuits shouldn't care much.

The mod's whatever you guys say it is. Beings a Sijosae splitter seems unpopular, give me an alternative, which works with parts typically found in most parts drawers. The Sijosae splitter show below at the link uses such parts:

A virtual ground circuit to split a wall wart between positive and negative rails is what's needed. This is for a proto-board, so it's reasonable to expect a highly variable load.

Danke,

One site I read described them as significantly better than a simple resistive divider, but significantly worse than any other buffered circuit they described (typically op-amp-based). Price-wise that's about how they fall, too. I guess you get what you pay for.

We don't know the requirements of the downstream circuits, either - why precision seemed to be called for.

It's for a proto-board with a variable load, which depends upon the circuit breadboarded. This is the first circuit:

Danke,

A resistive divider and a TCA0372.

Cheers

Phil Hobbs

Stick the electrolytics on the output. Input filtering should be minimal.

If you used an op amp, you could dump the diodes and emitter resistors and 'decouple' the reference in local feedback alone.

RL

In any event, the transistors will need to be capable of dissipating full worst-case Iload x Vin/2.

RL

Unfortunately, there's nary a TCA0372 available in my parts bin. But, there's a LM317, LM337, and a 3.3 V zener diode available, along with a

Danke,

Use two warts, or two 9 volt batteries.

There's nary a LM337 available to me, so this is it. Back to the original Sijosae splitter. How does this circuit look?

Danke,

You can get a TCA0372 or L270 in a day, or wrap a class-B amp made from an NPN + PNP complementary follower inside the feedback loop of a 741. Either would be a lot better than a crude class-AB splitter made from two vregs.

Put a resistor from the bases to the emitters of the follower to take the current at low load.

Cheers

Phil Hobbs

That is close. You want 100% negative feedback not positive so check the op-amp inputs. The 10k R3 R4 are unnecessary. As Phil Hobbs wrote in a side thread have a resistor from bases to emitters so the op-amp can supply light load currents - somewhere from a few hundred ohms to a kilo-ohm should be about right. Happy splitting!

piglet

Phil Hobbs wrote:

Nobody uses 741's any more. Adding a resistor is not so simple. The basic circuit has a lot of distortion. This would create havoc in a feedback circuit at high frequency or at DC with transients in the load.

Version 4 SHEET 1 1608 1700 WIRE 704 80 592 80 WIRE 592 96 592 80 WIRE 704 96 704 80 WIRE 384 144 320 144 WIRE 448 144 384 144 WIRE 528 144 448 144 WIRE 320 160 320 144 WIRE 704 192 704 176 WIRE 448 224 448 144 WIRE 480 224 448 224 WIRE 592 224 592 192 WIRE 592 224 560 224 WIRE 672 224 592 224 WIRE 784 224 672 224 WIRE 784 240 784 224 WIRE 320 256 320 240 WIRE 592 256 592 224 WIRE 448 304 448 224 WIRE 528 304 448 304 WIRE 784 336 784 320 WIRE 592 368 592 352 WIRE 592 464 592 448 FLAG 320 256 0 FLAG 592 464 0 FLAG 704 192 0 FLAG 784 336 0 FLAG 384 144 Vin FLAG 672 224 Vout SYMBOL voltage 320 144 R0 WINDOW 3 -53 150 Left 2 WINDOW 123 24 38 Left 2 WINDOW 39 0 0 Left 2 SYMATTR Value SINE(0 10 1e7) SYMATTR Value2 AC 1 SYMATTR InstName V1 SYMBOL npn 528 96 R0 SYMATTR InstName Q1 SYMATTR Value 2N2222 SYMBOL pnp 528 352 M180 SYMATTR InstName Q2 SYMATTR Value 2N2907 SYMBOL voltage 592 464 R180 WINDOW 0 24 96 Left 2 WINDOW 3 24 16 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value {VCC} SYMBOL voltage 704 80 R0 WINDOW 0 24 96 Left 2 WINDOW 3 24 16 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V3 SYMATTR Value {VCC} SYMBOL res 768 224 R0 SYMATTR InstName R1 SYMATTR Value 50 SYMBOL res 464 208 M90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 50 TEXT 376 -24 Left 2 ;'Complimentary Follower TEXT 376 0 Left 2 !.tran 0 250n 0 TEXT 552 0 Left 2 !.param VCC = 12

For low distortion at high frequency, or fast load transients at DC, a full complimentary driver looks much better.

Version 4 SHEET 1 1608 1700 WIRE 384 80 368 80 WIRE 512 80 464 80 WIRE 592 80 512 80 WIRE 704 80 592 80 WIRE 592 96 592 80 WIRE 704 96 704 80 WIRE 368 144 368 80 WIRE 528 144 368 144 WIRE 224 192 160 192 WIRE 256 192 224 192 WIRE 304 192 256 192 WIRE 704 192 704 176 WIRE 160 208 160 192 WIRE 480 240 368 240 WIRE 592 256 592 192 WIRE 672 256 592 256 WIRE 784 256 672 256 WIRE 512 272 512 80 WIRE 512 272 368 272 WIRE 784 272 784 256 WIRE 160 304 160 288 WIRE 256 320 256 192 WIRE 304 320 256 320 WIRE 592 320 592 256 WIRE 528 368 368 368 WIRE 784 368 784 352 WIRE 368 448 368 368 WIRE 384 448 368 448 WIRE 480 448 480 240 WIRE 480 448 464 448 WIRE 592 448 592 416 WIRE 592 448 480 448 WIRE 592 464 592 448 WIRE 592 560 592 544 FLAG 160 304 0 FLAG 592 560 0 FLAG 704 192 0 FLAG 784 368 0 FLAG 224 192 Vin FLAG 672 256 Vout SYMBOL voltage 160 192 R0 WINDOW 3 -53 150 Left 2 WINDOW 123 24 38 Left 2 WINDOW 39 0 0 Left 2 SYMATTR Value SINE(0 2 1e6) SYMATTR Value2 AC 1 SYMATTR InstName V1 SYMBOL npn 528 96 R0 SYMATTR InstName Q1 SYMATTR Value 2N2222 SYMBOL pnp 528 416 M180 SYMATTR InstName Q2 SYMATTR Value 2N2907 SYMBOL voltage 592 560 R180 WINDOW 0 24 96 Left 2 WINDOW 3 24 16 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value {VCC} SYMBOL voltage 704 80 R0 WINDOW 0 24 96 Left 2 WINDOW 3 24 16 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V3 SYMATTR Value {VCC} SYMBOL res 768 256 R0 SYMATTR InstName R1 SYMATTR Value 50 SYMBOL pnp 304 240 M180 SYMATTR InstName Q3 SYMATTR Value 2N2907 SYMBOL npn 304 272 R0 SYMATTR InstName Q4 SYMATTR Value 2N2222 SYMBOL res 480 432 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 330 SYMBOL res 480 64 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 330 TEXT 376 -24 Left 2 ;'Complimentary Driver / Follower TEXT 376 0 Left 2 !.tran 0 2u 0 TEXT 552 0 Left 2 !.param VCC = 12

piglet wrote:

The base resistor has to be a lot lower. The circuit has high distortion and severe voltage loss from input to output. I repeat the LTspice version I posted to Phil. Compare the input and output voltages.

Version 4 SHEET 1 1608 1700 WIRE 704 80 592 80 WIRE 592 96 592 80 WIRE 704 96 704 80 WIRE 384 144 320 144 WIRE 448 144 384 144 WIRE 528 144 448 144 WIRE 320 160 320 144 WIRE 704 192 704 176 WIRE 448 224 448 144 WIRE 480 224 448 224 WIRE 592 224 592 192 WIRE 592 224 560 224 WIRE 672 224 592 224 WIRE 784 224 672 224 WIRE 784 240 784 224 WIRE 320 256 320 240 WIRE 592 256 592 224 WIRE 448 304 448 224 WIRE 528 304 448 304 WIRE 784 336 784 320 WIRE 592 368 592 352 WIRE 592 464 592 448 FLAG 320 256 0 FLAG 592 464 0 FLAG 704 192 0 FLAG 784 336 0 FLAG 384 144 Vin FLAG 672 224 Vout SYMBOL voltage 320 144 R0 WINDOW 3 -53 150 Left 2 WINDOW 123 24 38 Left 2 WINDOW 39 0 0 Left 2 SYMATTR Value SINE(0 10 1e7) SYMATTR Value2 AC 1 SYMATTR InstName V1 SYMBOL npn 528 96 R0 SYMATTR InstName Q1 SYMATTR Value 2N2222 SYMBOL pnp 528 352 M180 SYMATTR InstName Q2 SYMATTR Value 2N2907 SYMBOL voltage 592 464 R180 WINDOW 0 24 96 Left 2 WINDOW 3 24 16 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value {VCC} SYMBOL voltage 704 80 R0 WINDOW 0 24 96 Left 2 WINDOW 3 24 16 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V3 SYMATTR Value {VCC} SYMBOL res 768 224 R0 SYMATTR InstName R1 SYMATTR Value 50 SYMBOL res 464 208 M90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 50 TEXT 376 -24 Left 2 ;'Complimentary Follower TEXT 376 0 Left 2 !.tran 0 250n 0 TEXT 552 0 Left 2 !.param VCC = 12

For low distortion at high frequency, or fast load transients at DC, a full complimentary driver looks much better.

Version 4 SHEET 1 1608 1700 WIRE 384 80 368 80 WIRE 512 80 464 80 WIRE 592 80 512 80 WIRE 704 80 592 80 WIRE 592 96 592 80 WIRE 704 96 704 80 WIRE 368 144 368 80 WIRE 528 144 368 144 WIRE 224 192 160 192 WIRE 256 192 224 192 WIRE 304 192 256 192 WIRE 704 192 704 176 WIRE 160 208 160 192 WIRE 480 240 368 240 WIRE 592 256 592 192 WIRE 672 256 592 256 WIRE 784 256 672 256 WIRE 512 272 512 80 WIRE 512 272 368 272 WIRE 784 272 784 256 WIRE 160 304 160 288 WIRE 256 320 256 192 WIRE 304 320 256 320 WIRE 592 320 592 256 WIRE 528 368 368 368 WIRE 784 368 784 352 WIRE 368 448 368 368 WIRE 384 448 368 448 WIRE 480 448 480 240 WIRE 480 448 464 448 WIRE 592 448 592 416 WIRE 592 448 480 448 WIRE 592 464 592 448 WIRE 592 560 592 544 FLAG 160 304 0 FLAG 592 560 0 FLAG 704 192 0 FLAG 784 368 0 FLAG 224 192 Vin FLAG 672 256 Vout SYMBOL voltage 160 192 R0 WINDOW 3 -53 150 Left 2 WINDOW 123 24 38 Left 2 WINDOW 39 0 0 Left 2 SYMATTR Value SINE(0 2 1e6) SYMATTR Value2 AC 1 SYMATTR InstName V1 SYMBOL npn 528 96 R0 SYMATTR InstName Q1 SYMATTR Value 2N2222 SYMBOL pnp 528 416 M180 SYMATTR InstName Q2 SYMATTR Value 2N2907 SYMBOL voltage 592 560 R180 WINDOW 0 24 96 Left 2 WINDOW 3 24 16 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value {VCC} SYMBOL voltage 704 80 R0 WINDOW 0 24 96 Left 2 WINDOW 3 24 16 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V3 SYMATTR Value {VCC} SYMBOL res 768 256 R0 SYMATTR InstName R1 SYMATTR Value 50 SYMBOL pnp 304 240 M180 SYMATTR InstName Q3 SYMATTR Value 2N2907 SYMBOL npn 304 272 R0 SYMATTR InstName Q4 SYMATTR Value 2N2222 SYMBOL res 480 432 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 330 SYMBOL res 480 64 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 330 TEXT 376 -24 Left 2 ;'Complimentary Driver / Follower TEXT 376 0 Left 2 !.tran 0 2u 0 TEXT 552 0 Left 2 !.param VCC = 12

The basic circuit creates havoc in a feedback circuit. It requires an op amp with a GBW 25 times the operating frequency. Compare the input voltage, the output voltage, and the output of the op amp. Then lower the GBW of the op amp to 1MHz and view the distortion. The basic circuit demands high performance from the op amp. For comparison, look at the full complimentary driver just above for input and output voltages and distortion.

Version 4 SHEET 1 1608 1700 WIRE 784 32 256 32 WIRE 592 80 320 80 WIRE 704 80 592 80 WIRE 592 96 592 80 WIRE 704 96 704 80 WIRE 320 112 320 80 WIRE 256 128 256 32 WIRE 288 128 256 128 WIRE 400 144 352 144 WIRE 448 144 400 144 WIRE 528 144 448 144 WIRE 192 160 128 160 WIRE 288 160 192 160 WIRE 128 176 128 160 WIRE 704 192 704 176 WIRE 448 224 448 144 WIRE 480 224 448 224 WIRE 592 224 592 192 WIRE 592 224 560 224 WIRE 672 224 592 224 WIRE 784 224 784 32 WIRE 784 224 672 224 WIRE 784 240 784 224 WIRE 592 256 592 224 WIRE 128 272 128 256 WIRE 448 304 448 224 WIRE 528 304 448 304 WIRE 784 336 784 320 WIRE 320 368 320 176 WIRE 592 368 592 352 WIRE 592 368 320 368 WIRE 592 384 592 368 WIRE 592 480 592 464 FLAG 128 272 0 FLAG 592 480 0 FLAG 704 192 0 FLAG 784 336 0 FLAG 192 160 Vin FLAG 672 224 Vout FLAG 400 144 U1O SYMBOL voltage 128 160 R0 WINDOW 3 -53 150 Left 2 WINDOW 123 24 38 Left 2 WINDOW 39 0 0 Left 2 SYMATTR Value SINE(0 2 1e6) SYMATTR Value2 AC 1 SYMATTR InstName V1 SYMBOL npn 528 96 R0 SYMATTR InstName Q1 SYMATTR Value 2N2222 SYMBOL pnp 528 352 M180 SYMATTR InstName Q2 SYMATTR Value 2N2907 SYMBOL voltage 592 480 R180 WINDOW 0 24 96 Left 2 WINDOW 3 24 16 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V2 SYMATTR Value {VCC} SYMBOL voltage 704 80 R0 WINDOW 0 24 96 Left 2 WINDOW 3 24 16 Left 2 WINDOW 123 0 0 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V3 SYMATTR Value {VCC} SYMBOL res 768 224 R0 SYMATTR InstName R1 SYMATTR Value 50 SYMBOL res 464 208 M90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 50 SYMBOL opamps\\universalopamp2 320 144 R0 SYMATTR InstName U1 SYMATTR Value2 Avol=1Meg GBW=25Meg Slew=25Meg TEXT 376 -24 Left 2 ;'Complimentary Follower With Feedback TEXT 376 0 Left 2 !.tran 0 2u 0 TEXT 552 0 Left 2 !.param VCC = 12

Was:

S.B.

Then lower the GBW and slew rate of the op amp to 1MHz and view the distortion.

Of course they don't--I was teasing Don about his fixation with his junkbox.

Which is why you put a BFC on it, the way you would any regulator, including the TCA0372.

Cheers

Phil Hobbs

Check the op amp input polarity.

You don't need R3 and R4, but with the feedback correctly inverting you can slow the op amp down some with an input resistor and local feedback cap around the op amp. you can degenerate the DC gain a couple of tens of mV.

The electrolytics do the transient response, the op amp only has to do low frequency DC. No point having the circuit oscillate unnecessarily an light or no load - this would just consume power..

A resistor in the collectors of the transistors will improve their ability to dissipate power and avoid a potential silicon short.

RL