Sporniket's log on hardware stuff

[sporniket]

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).

2021-10-26--vccs-first-prototype.jpg

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.

[exxos]

Be interesting to see how it goes :)

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

[sporniket]

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.

Be interesting to see how it goes :)

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

[sporniket]

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.

2021-10-31--current-sink-preview.jpg

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.

2021-10-31--bridge-preview.jpg

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

sel-current-sink.pdf

bridge-uc-to-modules.pdf

[sporniket]

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

Code: Select all

SEL - CURRENT SINK
SKU Mouser 		SKU Manufacturer 	Manufacturer	Qty.	U. Price (EUR)	T. Price (EUR)	Description 
588-FA-T220-64E		FA-T220-64E		Ohmite		2	2,39 €		4,78 €		HEATSINK FOR TO-220 BLK ANODIZED
726-IPP80N03S4L03AKS	IPP80N03S4L03AKSA1	Infineon	2	1,82 €		3,64 €		MOSFET N-Ch 30V 80A TO220-3 OptiMOS-T2

Code: Select all

SEL - BRIDGE CONTROLLER TO MODULES						
SKU Mouser 		SKU Manufacturer 	Manufacturer		Qty.	U. Price (EUR)	T. Price (EUR)	Description 
755-LMR932FVJ-GE2	LMR932FVJ-GE2		ROHM Semiconductor	3	0,508 €		1,52 €		Op amps - Low Power Input-Output Full Swing Operational Amplifier
594-ACASA1000S1002AT	ACASA1000S1002P1AT	Vishay			3	0,906 €		2,72 €		Resistor networks-Resistors packs 100 / 10K ohms AEC-Q200
652-3296Y-1-503LF	3296Y-1-503LF		Bourns			4	1,84 €		7,36 €		Trimpot - THT 3/8" 50Kohms Sealed Vertical Adjust
581-12063C104JAT2A	12063C104JAT2A		Kyocera AVX		3	0,296 €		0,89 €		MLCC - CMS 25V 0.1uF X7R 1206 5%

[sporniket]

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

2021-11-07--01-usb-decoy-panel-edge-vcut-removed.jpg

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.

[sporniket]

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.

[exxos]

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

[sporniket]

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.

[olivier.jan]

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/