10Hz PSU 0–12 V sine (DC-offset), up to 10 A, externally driven - Page 1
Forum section: electronics / projects

author: DigitalDesigner
author_rank: Contributor
timestamp: September 16, 2025, 01:27:12 am
content: Hi,I’m working on a project where I need to supply power to a system in a low-frequency sinewave signal (up to 10Hz maximum) at fairly high current. This is a one-off, needed quickly, so I’m looking for something off-the-shelf. I’m open to brick/module, SMPS eval board, benchtop unit, or anything similar.Requirements:1) Input: Either mains or 12 V (car battery or equivalent)2) Output: 0–12 V (sine with DC offset), up to 10 A. Obviously if the max output voltage higher, that is perfectly ok.3) Frequency: ≤ 10 Hz (adjustable)4) Control: Prefer external signal generator drive; programmable control also fine5) Adjustability: Frequency, minimum/maximum levels6) Budget: ≤ £200 (stretch max)I’m not sure whether this is best achieved with a benchtop PSU, if there are dev kits of switcher ICs (I could not find any with an external voltage control) or some other solutions.Can anybody suggest any solution within those constraints?Thanks in advance for your ideas!

author: PCB.Wiz
author_rank: Super Contributor
timestamp: September 16, 2025, 02:22:49 am
content: Quote from: DigitalDesigner on September 16, 2025, 01:27:12 amThey will not advertise that per-se, but any adjustable power module will vary the output voltage if you inject a current into the feedback loop.ie you need to modify one slightly, with a current injection resistor.Any function generator can then provide the offset DC sine to drive that.≤ 10 Hz (adjustable) is low enough most switching modules should manage ok.You may need a minimum load, to have the output cap discharge quickly enough to follow your 10Hz sine.

author: DigitalDesigner
author_rank: Contributor
timestamp: September 16, 2025, 04:22:50 am
content: Thank you PCB.Wiz,Do you mean a simple resistor in series between the signal generator and the FB pin of the switching regulator? If so, now do I select the resistor value?Thank you

author: PCB.Wiz
author_rank: Super Contributor
timestamp: September 16, 2025, 06:07:07 am
content: Quote from: DigitalDesigner on September 16, 2025, 04:22:50 amYes. you select that value by looking at what else they have in the feedback.For example, if you find a switcher with appx 6V out, 15Vin, and it has 1.25V feedback reference and 10k and 39k resistors, that gives you 125uA of bias current, and 100uA/V gain.If you then feed that with a 39k + 10k to ground current injection resistor pair, as VIN on the added 39k varies from 0-12V, VOUT varies from 12.248V to 249mV.This assumes the switcher can vary over the whole 0-100% duty cycle, that detail may limit your output swing.Possibly something like this - claims 20A 16Vhttps://www.aliexpress.com/item/1005008785628197.htmlThat looks to have 2 switching fets for synchronous output, tho the caps look a bit light for 20A continuous, & no mention of duty cycle range.This one gives a part number, and has larger capshttps://www.aliexpress.com/item/1005007244304404.htmlWith a bootstrap fet drive, you cannot get to 100%, so you may need to limit upper swing to 90-98% regionAddit : this one has a fan, and more headroom, at 25A rating, and has LED displays for I and V.https://www.aliexpress.com/item/1005008985661835.html

author: Smokey
author_rank: Super Contributor
timestamp: September 16, 2025, 06:24:26 am
content: I have not tried this, so I don't know if it would actually work, but...Could you not abuse the sense terminals of a bench supply to externally modulate the voltage output with a function generator? The sense terminals are inside the voltage loop, so they should have a super fast response.I've never heard of anyone trying this, but I can't immediately say why it wouldn't work.Just to close the loop.... Yes, it does work!https://www.eevblog.com/forum/testgear/high-current-awg-using-power-supply/

author: inse
author_rank: Super Contributor
timestamp: September 16, 2025, 09:38:19 am
content: The sense inputs are often connected to the output via resistors not to cause the output to go berserk in case the sense is disconnected.They also might have limited compensation range, so you either have to study the manuals in detail or do practical tests whether your control method works satisfactory.

author: DigitalDesigner
author_rank: Contributor
timestamp: September 18, 2025, 04:07:08 am
content: Thank you PCB Wiz for the detailed explanation!@Smokey, I thought what @inse mentioned, but wasn't sure. Thank you for your suggestion though.

author: Someone
author_rank: Super Contributor
timestamp: September 18, 2025, 04:36:52 am
content: Quote from: inse on September 16, 2025, 09:38:19 amYep. Some power supplies have/had analog "programming" inputs which can be used for this sort of low frequency following... but they tend to be single quadrant! (like other suggestions abusing regulators)

author: inse
author_rank: Super Contributor
timestamp: September 18, 2025, 05:41:13 am
content: Single quadrant is sufficient as long as the load always draws current and no major inductive/capacitive element is involved.But afaik we are only talking about 10Hz…

author: mawyatt
author_rank: Super Contributor
timestamp: September 18, 2025, 01:33:24 pm
content: Some supplies allow the output to be controlled by a "Time Sequence" setup within the supply. This could produce a crude stepwise approximation of an offset Sinewave in 1 quadrant at very low frequencies.If one wishes to tinker inside the supply, finding the reference voltage the loop utilizes to set the supply output voltage, here the reference voltage could be replaced (or forced) by an external Sinewave (or arbitrary waveform) from an AWG. This might prove simpler than attempting toinjectan outside signal in the voltage feedback loop.Best