How do I connect this PWM-controlled supply board properly?

[Demon]

I bought a bunch of these last summer on AliExress to pulse 7-segment LEDs.

Do GND and NEG share the same connection?




I think it is (Darrel once corrected me about sharing grounds as a reference), but I'd like to avoid frying these.

[richard]

Do GND and NEG share the same connection?

what does your multimeter say ?

if they are galvanically isolated then they don't

find the data sheet and/or a schematic to be sure
or
at least a picture of the other side of the board so the possibility of an opto coupler can be established

[Demon]

Nope, not connected together. No BEEP on DMM.

I have no idea what "galvanically connected" means.


But I did find 2 of the circuits on Proto Supplies:






One connection is GND earth, the other is GND power...?


Proto doesn't have the FR-120N, but I have found a picture of all 3 circuits elsewhere. They seem identical on the top except for the MOSFET used (2 share the same opto-coupler).




EDIT: The PWM comes from a PIC. The PIC and this board both will run on the same 5V supply.

I've just very rarely dealt with a earth GND before.

[richard]

I have no idea what "galvanically connected" means.

galvanically isolated means there is no physical (metallic or otherwise conductive) connection between the terminals .

the terminals are optically coupled therefore galvanically isolated. therefore the gnd and the neg do not need to be connected and probably should not be connected

[Demon]

I've found more data from the listing.



This is meant to power motors; hence the use of the flyback diode we're supposed to add on the power connection, and the priority to isolate both sides.

I'm going to be powering LEDs, no mechanical devices. I don't really care about isolation, since both sides are getting power from the same source.

And that's how I answer my own question (I think).

[Ioannis]

The idea of using optocoupler is to have electrically separate circuits. If you connect the two reference points together as a common ground then what is the point of using an optocoupler? Connect directly the PWM to the MosFet and save few parts.

Ioannis

[Demon]

... what is the point of using an optocoupler? ...

I was trying out Richard's idea of using pre-made circuits. It wasn't the same design as what he used (no boost), but I thought it would be a good exercise.

https://www.picbasic.co.uk/forum/sho...110#post154110


This circuit isn't to power the project. I'm just trying to use 2 pots and PWM 5 volts to control the brightness of LED strings and the intensity of 7-segment LEDs (one pot controls the dash lights using 1 circuit, another the radio display using a 2nd circuit).

I'm trying to reproduce this effect:

[Ioannis]

I do not quite follow what you are after. But anyway, the purpose of the optoisolation is to isolate circuits that are in different voltage levels for either safety of the users or the safety and protection of the circuits.

If none of these are of concern at your application, then I see no point in using that module. Connect directly the PWM signal to the MosFet and control whatever load you have.

Ioannis

[Demon]

Using JLCPCB opens up other options for me. It gives me access to very low-cost components with very small footprints that can be integrated in my circuits.

These PWM circuits are just for ease of testing now. I'll be switching to a dual logic-level MOSFET to drive the console lights and radio display.

The hard part is finding a device that is available at Digikey/Mouser/Newark in through-hole footprint, as well as the desired SMD footprint at JLCPCB.

I'm just starting to look for a good L-V MOSFET now. Any suggestions?