Low Leakage DC-DC Design - Page 1
Forum section: electronics / general

author: derZockerMP
author_rank: Regular Contributor
timestamp: February 13, 2025, 01:29:58 pm
content: Hello,I want to build a power supply for a precision voltage source. The power requirements are ±15V 200mA and ±120V 120mA. Is there an approach to design a circuit that generates those voltages from a common SMPS voltage of 12V, for example? I'm searching for a circuit similar to what's used in the Keithley 2400. However, they use a custom transformer. Another aspect is ensuring low winding capacitance between the windings to minimize common-mode noise.A second approach is to use a normal 50Hz mains transformer, but that's not ideal, as it would also need to be custom manufactured to include a guard shield between the primary and secondary.I already watched Marco Reps' video about this topic, but it didn't address my problem.Any suggestions or hints would be welcome.Best regards,Stefan

author: Overspeed
author_rank: Frequent Contributor
timestamp: February 13, 2025, 02:25:11 pm
content: Hello±15V 200mA and ±120V 120mAyour 200 mA and 120 mA current value are max value or the value your need at 100 % of the time ?what precision you try to reach in Voltage and current output ?RegardsOS

author: miro123
author_rank: Frequent Contributor
timestamp: February 13, 2025, 08:07:34 pm
content: What do you want to achieve . You want to learn something new or you just need a final product.In case of second one - the short answer is "there is no free lunch" invest money or time and patience.There are many ways to achieve it.1. Easy way, industries proven solution. Just prepare a lot of money -https://daitronglobal.com/data/img/2023/12/RFS50A_Catalog_En.pdf- it allows serial connection between them.2. start building yourself . Pre-request area. good knowledge of magnetcs and power electronics.b invest a lot of time. to simulate design and tests.c. made several iteration before achieving the final result.3. Custom or selfmade 50/60HZ transformer looks the easiest way

author: David Hess
author_rank: Super Contributor
timestamp: February 13, 2025, 10:34:35 pm
content: For low noise isolated supplies in multimeters, I have seen a high frequency inverter used with secondary side linear regulation. Of course it will require a custom transformer. Where maximum efficiency is not required, sine drive may be used.

author: Smokey
author_rank: Super Contributor
timestamp: February 13, 2025, 11:13:17 pm
content: 120V at 120mA = 14.4W (x 2 channels). That's a non negligible amount of power to be pushing through a boost converter if you care about noise and such.It seems like making +/-120V using a transformer off the line voltage is much more straightforward (and low noise).

author: derZockerMP
author_rank: Regular Contributor
timestamp: February 14, 2025, 06:24:32 am
content: I'm building a 5.5-digit voltage source using a 20-bit DAC. It should output a voltage between ±100V at 100mA, so a ±120V 120mA rail is necessary. The ±15V rail will power the operational amplifiers, but not much power is required—probably around 100-200mA should suffice. It also needs very low noise on the rails and isolation due to a bootstrapped output stage.Is there an initial circuit design I can reference?Best Regards

author: Smokey
author_rank: Super Contributor
timestamp: February 14, 2025, 08:29:29 am
content: I think this would work:https://www.digikey.com/en/products/detail/talema-group-llc/0100MD-1-003/4289485https://talema.com/wp-content/uploads/datasheets/MD.pdf

author: branadic
author_rank: Super Contributor
timestamp: February 14, 2025, 09:16:02 am
content: What if you use a ±115 V to ±15 V shielded toroidal mains transformer and for the ±120 V 120 mA a similar shielded toroidal mains transformer operated in reverse from the ±15 V rail?If I remember correct Echo88 had tried such transformers from MPAudio (Premium Audio Grade Transformer) and reported his results somewhere on this forum.-branadic-

author: Overspeed
author_rank: Frequent Contributor
timestamp: February 14, 2025, 04:28:45 pm
content: HelloFor the +/- 15 V why not use a Traco / XPower module OTS available from Mouser / Farnell ... and focus on the 120 V ?RegardsOS

author: Eraldo
author_rank: Regular Contributor
timestamp: February 16, 2025, 12:35:16 pm
content: Quote from: derZockerMP on February 14, 2025, 06:24:32 amFrom what I'm reading you're trying to build a precision 2 quadrant supply with up to 120v. The closest device that comes close to your description would be a source measure unit (smu). Luckily there is a very good project from djerickson called diy smu here at eevblog. He also has a website:https://www.djerickson.com/diy_smu/He uses medical grade toroidal transformer (i believe you can find the type he uses in the bom on his project files.)I would recommend reading his article and how he achieved it. It's an expensive project as you can assume. Even the 20bit dac which you mention would cost u a minimum of 60 bucksAnother of his project is the ps load which is a cheaper version without the high voltage. But to achieve reliable 5.5 digits you will need to spend quite a bit.EDIT:Jaromir also has posted an smu he build and posted the schematics here:https://github.com/jaromir-sukuba/J-SMUThis also is a great read and he has done a great job.The thread:https://www.eevblog.com/forum/projects/how-i-made-my-smu/

author: trobbins
author_rank: Frequent Contributor
timestamp: February 17, 2025, 12:39:26 am
content: If the application is 'every now and then', and perhaps 'a few hours at a time', then you could side-step common-mode concerns by using 12V monoblock batteries (eg. from a UPS). That would then collapse your design effort into a dc/dc that regulates sufficiently.I've even used cheap $10 ebay 12V inverter modules to generate 100Vdc and 500Vdc, within a regulation loop based on LM336, to use as small portable transfer references for 6.5 digit applications.