gerif
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Post by gerif on Jun 8, 2024 6:53:48 GMT
I want use LEDs for indication of states in one DIY module!
What is the best schema?
With transistor, opamp, driver or some other way? On CD4000 output, on opamp output? Though hole and SMD solution!
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Post by keurslagerkurt on Jun 9, 2024 14:57:26 GMT
It all depends on where in the circuit you want to integrate it. If your point you want to indicate is the output of an opamp, it can directly drive the LED (don't forget to always add a resistor with the LED or it will burn out!). CDxxxx chips or digital outputs in general have a hard time driving the leds, so then a simple transistor 'switch' circuit is needed.
If you can post your circuit schematic, or the relevant part, i could give more specific ideas 😄
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gerif
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Post by gerif on Jun 10, 2024 6:24:47 GMT
Many thanks for your answer! Currently I generell want to get more knowledge!
LED with resistor at OpAmp outputs is clean!
So the situation with transitors is the question! There are a lot of different types and it seems that through hole and SMD have its own type numbers!
What are the prefered types?
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Post by keurslagerkurt on Jun 10, 2024 22:18:42 GMT
In general, to drive a LED you want a 'transistor as a switch' circuit. You just want the transistor to either connect the LED fully to the power source, or not at all. (If you want a LED to have more subtle variations, depending on the height of the voltage for example, you will need more tweaking and the design will be harder)
For the purpose of just acting like a switch, pretty much any transistor will do. Be careful however that there are different 'flavors' of transistors which work different and also have different schematic symbols. My recomendation would be to use a so called BJT NPN transistor, they are easy to get by in through hole. The specific type/brand does not matter too much, these differ mainly in the region between 'completely on' and 'completely off', which is not really relevant when driving an indicator LED.
'BC547' would be a concrete example, '2N2222' as well. But loads of these specific types will act exactly the same, so just pick a cheap, readily available one 😊
If you Google 'transistor as a switch' you should find a ton of suitable circuits with just the transistor, LED, and maybe 1 or 2 resistors.
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gerif
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Post by gerif on Jun 11, 2024 4:08:23 GMT
So it is not a critical issue!
I have found the BC847 with SOT-23 45V and 100mA which is good enough for one LED.
Thank you for your support!
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