Current output gadget for PSU front - Page 1
Forum section: electronics / projects

author: JebCrag
author_rank: Newbie
timestamp: November 06, 2023, 06:02:40 pm
content: Sharing this for the sake of sharing - I wanted to make an easy-to-use "thing" to plug into the front of my power supply, which would provide a BNC output jack to monitor current. The idea was that if I was in the middle of something and suddenly wanted to monitor current waveforms (inrush or other transients not reported by PSU front panel), then I could plug this into my PSU and not have to do much or any re-wiring, as the banana jack would be duplicated on the front.It's a pretty straightforward arrangement of banana plugs/jacks, an INA290 current sense amplifier and shunt resistor (various combinations of gain and resistance to suit different situations), and a separate voltage connection for flexibility when monitoring low-voltage channels (bring in e.g. 5V from another common channel), in a 3d-printed two-piece case.It works well enough for a first prototype, if I return to it I'll try and make it smaller and reduce component costs (perhaps running off the spade terminal area rather than the banana jacks on the PSU), and put more work into the circuit itself - I'm getting more noise than expected on the signal, and I don't know if that's inherent to the amplifier or poor layout/assembly on my part.My original idea was to have 5-10 of these with different configurations for current range, some without the external voltage supply etc. to quickly suit whatever need came up without fuss.

author: coppercone2
author_rank: Super Contributor
timestamp: November 07, 2023, 03:31:13 am
content: If you could find a really small cable gland to put for the top wire it would be really good.Otherwise I make a clamp by drilling a thin hole in something, cutting it in half carefully with a thin blade, and clamping it with screws.it kind of a homer simpson look with the wire sticking out of thereor 3d print a well around it so you can fill it with rubberhttps://www.electronicsweekly.com/blogs/electro-ramblings/industry-comment/connect-introducing-worlds-smallest-cable-gland-2018-12/

author: jonpaul
author_rank: Super Contributor
timestamp: November 07, 2023, 06:33:45 am
content: Off the shelf CT?j

author: coromonadalix
author_rank: Super Contributor
timestamp: November 07, 2023, 06:54:42 am
content: nah keep your idea as it is, others will adapt it like they want ...banana jacks are perfect, if you plug it and dont move it very oftenfor sure plastic will bring noise, transients etc .. will not help ...a ct ... could be goodbut i would only put one simple shunt resistor in serial 1 ohm or 0.1ohms for larger current and use some amplifiers, nothing fancyINA290 current sense amplifier is not perfect for fast responses / transients etc ...you need one to one reading, meaning amplify or divide the signal, no conditioning like the current sensor would doa ct would isolate your scope etc ... you play with turns ratio to lower or amplify the signals / pulses say 1:1 1:5 ... 5:1 ...EDITi do something like this with an pico scope, the usb is isolated and the picoscope supply too, i use what they call : non invasive current sensorshttps://www.sparkfun.com/products/11005or like theses but not at this current ranges lollhttps://flexscada.com/product/hall-effect-current-sensor-ac-75a-dc-100a/

author: JebCrag
author_rank: Newbie
timestamp: November 07, 2023, 01:42:34 pm
content: Quote from: coromonadalix on November 07, 2023, 06:54:42 amThanks for the feedback - I've attached a test signal to give a sense of the results (raw and with 32x averaging), green trace is BJT base voltage and magenta is collector current. The current shown in magenta is 2mA p-p, the monitor in this one is configured for 250mA full-scale. Do you think a CT would give fundamentally better results here? I'm open to designing one operating on a different principle in the same form-factor, but I'm wondering if a better next step would be to do some output filtering for the noise and limit the bandwidth, use a metal case, generally try and improve things.Edit:Quote from: coromonadalix on November 07, 2023, 06:54:42 amCould anyone suggest a better-suited amplifier for this purpose? I selected this one because of the accuracy specs listed and voltage ranges (could hit64V32Vsupply, and common-mode input), but op-amp-search fatigue really set in and I didn't look too far. I figured a dedicated current-sense amplifier would do a better job than I could otherwise with a regular opamp, and limited my search to those.

author: jonpaul
author_rank: Super Contributor
timestamp: November 08, 2023, 07:50:12 am
content: exactly what is the goal?What load, PSU anticipated?PSU linear/SMPS?DC current monitor?Observe load current transients?AC HF like EMI?mains freq ripple?j

author: Terry Bites
author_rank: Super Contributor
timestamp: November 10, 2023, 11:26:05 am
content: The LTC6102 is fast and quiet, whats not to love? OK... the price.

author: JebCrag
author_rank: Newbie
timestamp: November 10, 2023, 10:39:17 pm
content: Quote from: jonpaul on November 08, 2023, 07:50:12 amTo monitor changing current values coming from the bench PSU into the DUT. It's meant to be versatile (e.g. phase measurement between V and I), but a clear example would be measuring inductor current into a buck converter (1MHz switching frequency max), to see whether continuous conduction is being maintained under load. If it could do that, I think it would be useful to me as a "probe" for tweaking designs, or as an educational tool.Quote from: Terry Bites on November 10, 2023, 11:26:05 amI'll check this out in more detail, but I'm seeing a bandwidth of 200kHz, compared to 1.1MHz for the INA290. Am I missing something there?