This is a new post that I copied from another post of mine. The moderator suggested that I start a new thread. My comments will be in bold & DL324’s comments will be in italics. I apologize.
Macnerd said: ↑
OK, I wish to make a slight detour & ask questions on a different but related subject.
You should probably start a new thread for your detour. That way others will know if this thread interests them.
I've googled constant current LED drivers & I've seen 2 different kinds - single transistor & double transistor.
There are many types of constant current drivers. Post a schematic of any you have questions about.
I've read on the 'net that transistors are temperature sensitive so that a single transistor would not make very good constant current drivers.
I can't think of any electronic devices that aren't temperature sensitive. If you really need a circuit that is less sensitive to temperature, there are ways to minimize sensitivity.
Based on the description of how the circuit works, the driver is basically a feedback loop.
Some have no feedback.
So, the driver isn't literally a "constant" current driver. The current goes up & down based on the voltage.
If there's enough voltage, the current source/sink will provide the designed current; assuming there's a path for it to flow. In a current source, current is constant but voltage may vary.
I also read that there's a lot of voltage lost on the FET whatever that means.
That will be some power dissipation in the FET, but it doesn't have to be a lot. The FET has some "ON" resistance whenever it's operating.
Based on my very limited knowledge of how a FET works, it gradually turns on & gradually turns off.
FETs can also be used as switches.
A BJT, on the other hand, is either on or off.
BJTs have other modes of operation; they were invented as amplifiers to replace vacuum tubes...
So, of the two 2-transistor drivers is one better than the other & why?
All circuits have compromises. Post schematics.
Macnerd said: ↑
OK, I wish to make a slight detour & ask questions on a different but related subject.
You should probably start a new thread for your detour. That way others will know if this thread interests them.
I've googled constant current LED drivers & I've seen 2 different kinds - single transistor & double transistor.
There are many types of constant current drivers. Post a schematic of any you have questions about.
I've read on the 'net that transistors are temperature sensitive so that a single transistor would not make very good constant current drivers.
I can't think of any electronic devices that aren't temperature sensitive. If you really need a circuit that is less sensitive to temperature, there are ways to minimize sensitivity.
Based on the description of how the circuit works, the driver is basically a feedback loop.
Some have no feedback.
So, the driver isn't literally a "constant" current driver. The current goes up & down based on the voltage.
If there's enough voltage, the current source/sink will provide the designed current; assuming there's a path for it to flow. In a current source, current is constant but voltage may vary.
I also read that there's a lot of voltage lost on the FET whatever that means.
That will be some power dissipation in the FET, but it doesn't have to be a lot. The FET has some "ON" resistance whenever it's operating.
Based on my very limited knowledge of how a FET works, it gradually turns on & gradually turns off.
FETs can also be used as switches.
A BJT, on the other hand, is either on or off.
BJTs have other modes of operation; they were invented as amplifiers to replace vacuum tubes...
So, of the two 2-transistor drivers is one better than the other & why?
All circuits have compromises. Post schematics.