Discussion on question by OYPS: Understanding MOSFET characteristics

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tlfong01

3:38 AM

This might help：High-side versus low-side switching - Lednique
http://lednique.com/gpio-tricks/interfacing-with-logic/

And for ninjas only: GPIO high-side driver fail - Lednique
http://lednique.com/gpio-high-side-driver-fail/

tlfong01

3:59 AM

Well, comparing to the power NPN BJT such as Darlington TIP120/122 with high Vce(sat), power MOSFET's ridiculously low Rds(on) is too good to be true. You might like to read the following to get a rough idea of what I am talking about:
Determine if a heatsink is required (Darlington TIP120)
https://electronics.stackexchange.com/questions/491060/determine-if-a-heatsink-is-required-darlington-tip120.

tlfong01

4:12 AM

So for low currents, say, less than 1A, you don't need to bother Rds(on). What you need to care is the current limiting series resistor of the power LED in your inefficient, power wasting circuit. And that is why I always strongly recommend the power LED newbies to at least use the much more efficient "Two NPN BJT current mirroring, negative feedback CCS (See Wiki on 'Current Source')".

4 hours later…

tlfong01

8:15 AM

@OYPS Moreover, you might need first to decide your constant current spec, say NiChia 500mA at 500mW radiant flux, or start with the Cree commercial/industrial pseudo standard of 350mA 3W. I only play with 1W toys. So no guarantee I am not speaking nonsense. :)

tlfong01

8:26 AM

And do you have any (1) Current sensor amplifier, eg MAX4172 https://electronics.stackexchange.com/questions/544378/current-mirror-real-life-examples/544445#544445 (2) UV light sensor: AliEXpress 2.7V-5.5V Uv Sensor Module
https://nl.aliexpress.com/item/4000479381883.html?spm=a2g0o.search0302.0.0.40585dc5V2oFQV&algo_pvid=7af1041d-5999-4d92-9c31-5ef7bd14188e&algo_expid=7af1041d-5999-4d92-9c31-5ef7bd14188e-8&btsid=0b0a555e16127724531018603efab8&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_, to do CCS negative feedback experiments?

8 hours later…

OYPS

4:09 PM

@tlfong01 thanks.

I will work through your links ans articles to get hang of what you are talking. Of course I am always trying to optimize my circuit, but just to a certain extent. As my general design is connected to an external power supply and not power by anything like a battery, I am not very concerned about power consumption.

But if my design is inefficient and generally wasting power, I will try to change that. I will report back after looking at your material!

OYPS

4:30 PM

@tlfong01 @tlfong01 you are talking about this?

how would this make my circuit any more power efficient?

OK ignore my question. I now understood the wiki entry. This seems to be more complex but more efficient approach to my initial problem. But i never used such a circuit before and therefore do not know how to adapt it to my use case. especially how to calculate all the resistor values. I will research on this a bit more

OYPS

5:03 PM

I additionally found this circuit example electroschematics.com/led-constant-current with a digital control, which seems to be best fit for me. any thoughts?