Reverse polarity protection on (commercial) DC Electronic Loads? - Page 1
Forum section: electronics / projects

author: jan28
author_rank: Contributor
timestamp: July 07, 2024, 08:04:58 am
content: Hello,I'm working on the design of an DC Electronic Load. The basic topology is made of N channel MOSFETS in controlled loops. The common topology.The load will have some protections for over current, voltage, temperature and power. Partially in hardware, partially done in software. Again all pretty common.Due to the body diodes of the MOSFETS a large current will flow thru the device if the user (me) connects the DUT in reverse. So I'm thinking about adding a reverse polarity protection (not just detection, actually stopping current flow). A reverse polarity will not break the electronic load, but it might cause smoke or fire from the DUT (batteries....).During the design I looked at several manuals, reviews and teardowns of Electronic Loads and did not find any protections like these.So my question is: Do (commercial) Electronic loads have a reverse polarity protection? If so, how is it implemented?I'm really interested to know how the common brands like Keysight, Silent, Rigol, Korad handle this.Thanks in advance.

author: perdrix
author_rank: Frequent Contributor
timestamp: July 07, 2024, 08:56:31 am
content: Take a look at this post I made some while ago.https://www.eevblog.com/forum/beginners/another-reverse-polarity-protection-question/msg5239122/#msg5239122I think you should be able to apply it to your problem.David

author: tszaboo
author_rank: Super Contributor
timestamp: July 07, 2024, 09:09:57 am
content: The Keithley DC load I have at work starts beeping at you immediately if you connect something in reverse. It doesn't get damaged when it's not turned on.I think at least an SCR on the output, latch up protection and clamping on the measurement.

author: jan28
author_rank: Contributor
timestamp: July 07, 2024, 09:21:16 am
content: Quote from: perdrix on July 07, 2024, 08:56:31 amDavid,Thank you for your answer. Indeed a MOSFET is the solution I have in mind for implementation. The input range for an Electronic Load is larger than the use case in your post (and I have active power rails available): It has to switch off around -0.5V (just before reverse body diodes start conducting) and has to be fully on around +0.5V (min. operating voltage of my Load) and operate up to 80V. Therefore I will add a comparator to make the transition more exact around 0V.At 10A a relatively small MOSFET still causes 0.1-0.2V drop.All measurement inputs have clamps just as @tszaboo mentioned.Jan

author: aeg
author_rank: Regular Contributor
timestamp: July 07, 2024, 11:34:30 pm
content: Kikusui PLZ72W has a series diode between the input terminal and the load transistors! But it also has a minimum operating voltage of 4V nominal (due also to the load transistors being BJTs in Darlington configuration).

author: jbb
author_rank: Super Contributor
timestamp: July 08, 2024, 01:11:50 am
content: A ‘synchronous rectifier’ control IC might be useful for controlling the anti-parallel FET. They include comparators and a gate driver.

author: jan28
author_rank: Contributor
timestamp: July 09, 2024, 08:55:58 pm
content: Quote from: jbb on July 08, 2024, 01:11:50 amI looked into this and indeed this looks like an easy solution. Found the IR11662https://www.infineon.com/cms/en/product/power/ac-dc-power-conversion/ac-dc-pwm-pfc-controller/synchronous-rectification-ics/ir11662spbf/#] https://www.infineon.com/cms/en/product/power/ac-dc-power-conversion/ac-dc-pwm-pfc-controller/synchronous-rectification-ics/ir11662spbf/#!?fileId=5546d462533600a4015355c44195164f. This one should fit my use case.Still interested how Siglent, Rigol and others handle this.

author: jbb
author_rank: Super Contributor
timestamp: July 09, 2024, 09:25:36 pm
content: I’m having 2nd thoughts about Synchronous Rectifier controller - I wonder if they will behave OK with low load currents? The IR11662 has a turn off threshold of -10mV or so, which will be some hundreds of mAYour original thought of a comparator sensing the input voltage might well be better. I don’t know what they do in commercial units.

author: thm_w
author_rank: Super Contributor
timestamp: July 09, 2024, 10:37:27 pm
content: https://www.eevblog.com/forum/beginners/reverse-polarity-protection-for-an-electronic-dc-load/https://www.eevblog.com/forum/projects/input-protection-of-dc-electronic-load/msg1397141/#msg1397141https://www.eevblog.com/forum/beginners/dc-electronic-load-polarity/Rigol just states you'll blow it up if its connected backwards, so minimal protection, whatever the FETs can take.Proper protected unit will have a relay.Bridge rectifier can be possible on units where you don't care about higher dropout voltage.Quote from: jbb on July 09, 2024, 09:25:36 pmIf I look at dl3021 spec, 0.08R minimum resistance. So I guess 125mA as you say.If you had your own FET or relay control, and don't want to actively rectify AC, then can be better. Or maybe you could just bias that turn on threshold so it says on at 0V?