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Using a zener with variable input and led - brain freeze

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exe:

--- Quote from: digsys on July 26, 2019, 11:21:03 am ---I have never used Leds that draw more than 1mA for full brightness. They cost bugger all more.

--- End quote ---

Interesting idea. I recently bought green leds, they were already bright for me at 0.15mA. Just for fun I tried to see what's the minimum current that would still make it visible. It was 5-8uA at daylight.

I wonder which color requires less current. It's not just about brightness, but also eye sensitivity is different to different colors.

PS I also have red leds that are barely bright at 20mA.  :-// . These are new, I think it was this model: https://www.tme.eu/nl/en/details/l-424hdt/tht-leds-3mm/kingbright-electronic/ I wonder how this is possible and what's the application for such low brighness? The efficiency is super-low, I only bought them because I didn't know how much brightness I needed.

aries1470:

--- Quote from: PA0PBZ on July 26, 2019, 11:52:41 am --- (Attachment Link)

--- End quote ---
Thank you for that schematic. So, what diodes are you using? would those be two "normal" diodes? since I didn't see them as zeners or schotcky.
If so, would signal diodes also do, i.e. 1N4148? Since I am going to use very minimal mA  ;D
For the NPN transistor, I have available for easy purchase the following:
(Yes, I will be doing two versions, one THT and one SMT),

It will not dramatically increase the cost, and would help "debug" where a potential problem may be when the other people do not have a basic understanding of electronics - and don;t need to either. So this will help a lot :-)

ON Semi KSC1009YTA - THT $0.074AUD - 100pcs - $7.40AUD B160V / E140V <- Will be going for this ;)
ON Semi BC546BTA - THT $0.116AUD - 100pcs - $11.60AUD B80V / E65V
ON Semi BC546CTA - THT $0.071AUD - 200pcs - $14.20AUD B80V /E65V
ON Semi KSP06TA - THT $0.139 AUD - 100pcs - $13.90AUD B80V / E80V

ON Semi MMBTA06LT1G - SMT $0.108AUD 50pcs - $5.40 B80V / E80V
FMMTA42TA - SMT $0.067AUD 50pcs - $3.35 B330V / E300V  <- Will be going for this  ;)
Infineon SMBTA06E6327HTSA1 - SMT $0.052 100pcs - $5.20 B80V / E80V

Edit:
Added more SMT options.

Edit 2:
Link was correct for FMMTA42TA, but had MMBTA06LT1G in its name. Oopps, sorry.
Thank you to everyone that has replied, as I was not aware of this option.

aries1470:
Hi guys,

Just want to confirm if all will be okay using the following:
2x 1N4148
1x  KSC1009
1x 10K Resistor
1x 100 Ohm Resistor
1x LED

will be assembling on a breadboard.
Does anyone see any issues assembling as per image from @PA0PBZ?

Thank you.

Zero999:
It looks good to me. The current regulation in real life, probably won't be as good, as the simulation, but it'll certainly be much better than the zener circuit.

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