exxos's Atari, Amiga & retro forum

Recently on this thread I talked about designing my electronic load. I want a "not burning hot" dissipation, and assemble little modules ( scaling and offsetting the dac output from a microcontroller to command the gate of the mosfets ; scaling and offsetting the voltage output of a current sensor to feed an adc to that same micro-controller ; the connector circuit to the device under test, with a 3A fuse and the current sensor) because I want to distribute the cost of pcb over time, and eventually reuse modules to have, for instance, 2 independent current sinks, one for a 5V rail, another for a 12V rail *wink* ;)

I have studied the load explained on eevblog #102...



...and another one by Great Scott...



...and then I learn about so called "logic level" mosfets and "rail-to-rail"/"full swing" op-amps, and relearned about op-amps generally.

Today I received the first prototype pcb of the so called "Voltage Controlled Current Sink", a grandiose name for a pair of mosfets attached to their heatsink, and a pair of connectors positioned in symmetry to allow more freedom to assemble with the other part (still in the drafting notebook).


I will revise it a little, as I finally do not like so much having one single connector for each 3A lines, so I will divide into 3 connector each. And now that I see it, my copper plane for the sources of the fets looks a little bit silly near the mosfet. The mounting holes are also a bit to close from the edge.

Be interesting to see how it goes :)

I'm using a 300watt 22R rheostat for my testing so far :)

exxos wrote: 26 Oct 2021 21:01 I'm using a 300watt 22R rheostat for my testing so far :)

Yes, I remember having read that one of your testing got your rheostat glowing red.

exxos wrote: 26 Oct 2021 21:01 Be interesting to see how it goes :)

Thanks for the interest, gives me one more reason to finish :)

This last week-end before payday, I reworked the pcb of my current sink ; as I told, I divided the high-current ports into 3 connector each, and the DUT- entry is re-labeled 'GND', that I have forgotten in my head, comparing to the schematic on eevblog. Before connecting to DUT+, one will have to add the current sensor (I will use one of those https://fr.aliexpress.com/item/1005001698417485.html, the 20A version) and a fuse.


I also work on the circuit that convert a DAC output (e.g. 0V to 3.3V) into a small range ( 0 <= Vmin to Vmax <= VCC ) to the mosfet gate, and then the circuit that convert the voltage of the current sensor ( from VCC/2 to VCC/2 + 0.1V per amp) into the range 0V to Vmax<= VCC for an ADC input. I thought to have 1 board for each circuit, but components are so tiny that it fit in the planned 5cm×5cm board.


Here are the schematics, for those that are interested...

I ordered and got my components, here is the BOM, with the price at the time of writing :

One of my goal is to power my H5 with this type of USB-C PD module :


Of course I will need a proper USB-PD wall plug (up to around 60W to be extravagant, but 30W would be enough) and a proper cable. And I don't plan to power the 12V rail.

At first I want to use the basic 5V@3A, hopefully as is. Then, as I add some upgrade, I may have to use higher voltage (9V or 12V), thus needing a converter circuit. The overall goal is to have a very small footprint, to get rid of the metal plate, replaced by a 3D printable armature for support, or just some nylon spacers, to free most of the space over the area usually covered by the legacy psu.

With my latest sessions of work, like here, I've grown fed up with my current soldering iron (a basic one, 25W, no temperature setting). I planned to wait 6 monthes-1 year before having one of those TS100 or alike, because I prioritize a good enough scope for this Xmas.

But today I found one of those cheap things on A--Express for 10€ (50% off) : 80W, temperature setting, and a set hakko-900 style tips... That will do for the time being. The drawback to me is no earthing.

I always disconnect the earth on my soldering iron because it causes more damage otherwise.

exxos wrote: 08 Nov 2021 15:27 I always disconnect the earth on my soldering iron because it causes more damage otherwise.

Ha, so finally it will be an advantage instead of a drawback :) (anyway I didn't planned to touch the tip when it's live :D )

edit : reformulation.

If you haven’t ordered yet, I would really recommend getting a Pinecil instead : similar to TS100, but can use USB-C and only 24USD. I’ve been using it for a few months, and it’s really awesome for the price.
And if you are in «Region Parisienne » and want to test, feel free to PM me.
https://pine64.com/product/pinecil-smar ... ring-iron/