Electronics > Projects, Designs, and Technical Stuff
TO220 rail splitter?
CJay:
Given that those power op-amps are not cheap, what's the betting it's actually something like an LM1875 or TDA2030...
Zero999:
--- Quote from: 0xdeadbeef on December 19, 2018, 09:53:10 am ---Hm. I feel I will repeat myself at some points but in a nutshell: the idea was not to replace the TLE2426 with some OpAmp that can deliver even less current but with a beefy TO220 one.
When looking for TO220-5 OpAmps on Mouser, it comes up only with the LM675, the LT1010 and the OPA544.
The OPA544 doesn't seem to be unity gain stable and the LT1010 (which is actually a unity gain buffer) has a significant offset error (and can only deliver only +/-150mA anyway). Actually there is a 0.3V offset when you simulate the recommended application circuit in LTSpice with the official LT1010 model.
So this leaves us with the LM675. I simulated the recommended application circuit in LTSpice and it doesn't show any significant error there but then again I can't tell how realistic the model is (taken from some opamp.lib with an author tag "rperez"). And of course there is no temperature model and no worst case model and what not.
But yes, as stated in my last posting, it looks like the total error of the TLE2426 will exceed that of an LM675 with 1% resistors for input voltages >15V.
So for a typical +/-12V or +/-15V scenario, the LM675 should give better results if the total error stays below 2% as the simulation etc. suggest(s).
--- End quote ---
Then use a standard op-amp with pair of transistors on the output.
--- Quote from: David Hess on December 19, 2018, 12:56:46 pm ---Circuit stability is often a problem. A power splitter should have low AC output impedance which implies adding an output capacitor to either or both supplies but some devices will become very unhappy with this unless it is carefully done. The standard techniques for driving a capacitive load help but raise mid frequency impedance. Swamping the output with like a 10 microfarad solid tantalum or aluminum electrolytic capacitor often provides the best performance.
--- End quote ---
Yes, I would think a large capacitor on the output is a good idea. An inductor with a resistor in parallel might also help to isolate the output capacitance from the op-amp, at high frequencies.
0xdeadbeef:
For the record: GigaJoe was right: the mystery TO220 is a TDA2030 class A/B audio amplifier.
Zero999:
--- Quote from: 0xdeadbeef on December 29, 2018, 11:24:38 am ---For the record: GigaJoe was right: the mystery TO220 is a TDA2030 class A/B audio amplifier.
--- End quote ---
That doesn't surprise me.
Incidentally, it should be easy to obtain better accuracy than the TLE2426 using the TDA2030 and 1% resistors.
Did you try reverse engineering it? If so, please post the schematic.
0xdeadbeef:
It just arrived today and I only quickly tested it. I will post a schematic of the virtual ground circuit as soon as I find the time.
The embedded step up converter is based on the XLSemi XL009 with a frequency of 400kHz and a built-in N-FET switch.
So it actually seems to be an enhanced version of the LM2577 with an official branding and not a simple counterfeit. I actually like that since thus there's a real datasheet etc.
There's a 220µF cap at the input and a 100µF cap at the output. The voltage feedback is done with a voltage divider formed by a 330Ohm SMD resistor and a 10k trimmer (W103).
Anyway, there's nothing totally surprising there I guess as these modules are flooding eBay etc.
What's quite interesting is that the DC/DC board is actually placed in a cutout of the virtual ground board. So you could even remove the DC/DC completely.
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