Low noise DC/DC transformer driver? LT1533 replacement - Page 1
Forum section: electronics / projects

author: Martinn
author_rank: Frequent Contributor
timestamp: October 12, 2022, 03:55:21 pm
content: In a recent project, I needed +-15 V from a 9V battery. I used an off the shelf DC/DC module and hope I can get rid of the switching noise by filtering the outputs.When you read Jim Williams' application notes, you sooner or later come across the LT1533https://www.analog.com/en/products/lt1533.html, which would help a lot here. Unfortunately it is unobtainium.Does anyone have an idea how to generate nonoverlapping gate drive signals or better know a chip with the FETs already integrated?Maybe a push-pull controllerhttps://www.ti.com/product/UC2524A?A microcontroller seems excessive (unless you have one anyway and don't need the power supply to start it).I imagine one could simply put a handful of turns on a small ring core and get custom, low noise voltages out of it.- Martin

author: Zoli
author_rank: Frequent Contributor
timestamp: October 12, 2022, 05:05:55 pm
content: MAX253/845: it needs 5V for the control part, but the output is OK up to 12V; most similar to LT1533, simple to design/build.It fits your request of integrated FET non-overlapping outputs; take inspiration of the recommended transformers(inductance, size, etc.)Alternative - UCC25800-Q:https://www.ti.com/product/UCC25800-Q1It has sine output, easiest to filter; relatively complicated, but better then the LT1533.All the above are in stock ATM.More current unobtanium: SN6501/6505; good to know about them for the future.For something quick and simple, try the MAX's; if you have time to mess around, go with UCC25800. Expect to spend some time with the transformers.Good luck, and have fun going down the rabbit hole

author: Kleinstein
author_rank: Super Contributor
timestamp: October 12, 2022, 05:56:24 pm
content: I would not call the SM6505 really low noise. They are more like that type of low noise that makes it reasonable to meet EMI limits, but not really suitable for a sensitive circuit.Probably to ease on EMI limit the chip use spread spectrum / frequency modulation with some 50 Hz range modulation, that can cause beat signals with mains.A possible other option would be a discrete build resonant royer converter, though this also needs some fiddling with the transformer.

author: Martinn
author_rank: Frequent Contributor
timestamp: October 16, 2022, 06:42:44 am
content: Quote from: Zoli on October 12, 2022, 05:05:55 pmI see... quite a number of "transformer drivers" at Maxim:https://www.maximintegrated.com/en/products/power/isolated-power/transformer-drivers.html/tab1?fam=transformer-drivers&tree=masterBut I am not sure whether they are "low noise" or simply general purpuse DC/DC drivers.When ordering form JLCPCB, VPSC might be an option:https://lcsc.com/brand-detail/12739.html- they have both drivers and matching transformers. But again probably not low noise.LT has a handful of low noise push-pull drivers:https://www.analog.com/en/parametricsearch/11497#/p5362=Push-PullResonant royer: Has been mentioned so often recently I finally had to give it a try. I remembered a box of ferrite components I bought >20 years ago (unfortunately I don't do much custom magnetics) and put a few turns on a N27 toroid.It works, somehow, but I'd have to put much more effort in calculation and design before I'd use this outside a breadboard.Thanks - Martin

author: branadic
author_rank: Super Contributor
timestamp: October 16, 2022, 04:31:42 pm
content: Although the LT1533 was the replacement for the discrete push-pull driver in later Fluke 7000 voltage references, the circuit is still something to look at. You can find the reverse-engineered schematics here:https://www.eevblog.com/forum/metrology/(3300)-wavetek-7000-the-hidden-gemstone/msg3452668/#msg3452668-branadic-

author: Zoli
author_rank: Frequent Contributor
timestamp: October 16, 2022, 11:40:17 pm
content: Typically, the non-overlapping drivers are by definition low-noise, if you manage to avoid ringing. I've played around with SN6501/MAX253&Würth_760390015 a bit, and on low power(<0.2W) I couldn't distinguish the noise from the scope(SDS1204X-E, 1:1, external 50Ω).I gave up, since I need more powah(~6W from 24V); my hopes are with MAX22256/8/25256 when they'll be in stock. And to add, resonant Royer are PITA rectified; everything is nice, efficiency and power transfer is good until you start to rectify, when everything goes downhill. Estimate: to have 1W rectified output, you need 10W designed input, just to keep the noise low compared to the transformer drivers.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 17, 2022, 08:56:58 am
content: The royer converter may need a series inductor on the secondary to do some kind of passive power factor correction. Than the rectification should not be that bad. I agree that it can be tricky, as the load can interfere with the resonance.

author: moffy
author_rank: Super Contributor
timestamp: October 17, 2022, 11:48:28 am
content: Jim Williams in AN118:https://www.analog.com/media/en/technical-documentation/application-notes/AN118fb.pdfused a Royer converter to get a 250v DC supply with 100uv noise/ripple. He also designed the LCD backlight based upon the Royer architcture. Looks like when properly designed they are quite versatile.P.S. The backlight design is described in:https://www.analog.com/media/en/technical-documentation/application-notes/an65fa.pdf