Electronics > Beginners
constant current source design
<< < (5/6) > >>
Zero999:

--- Quote from: Arjunan M R on June 04, 2019, 04:45:00 am ---If I use matched pair transistors does i have to use emitter resistors?

--- End quote ---
You should be able to get away without them or using much lower values, especially if the transistors are well thermally coupled. Try it.
Arjunan M R:
I will just use 2N3904.
I am going to use a 49.9Ω emitter resistor.
When I was simulating it in LTspice I saw that if you  choose resistor with low resistance like you said(22Ω) the difference between the collector current of each transistor increases so i chose 49.9Ω.
Zero999:

--- Quote from: Arjunan M R on June 04, 2019, 01:45:55 pm ---I will just use 2N3904.
I am going to use a 49.9Ω emitter resistor.
When I was simulating it in LTspice I saw that if you  choose resistor with low resistance like you said(22Ω) the difference between the collector current of each transistor increases so i chose 49.9Ω.

--- End quote ---
LTSpice isn't very good at simulating this, because it assumes the transistors are identical and are at the same temperature.
Arjunan M R:
I have changed the temperature.
Tom45:
Since you don't need much accuracy, why not just use a simple 1 transistor current sink.

The circuit below uses a 2N3904 and 3 resistors. Testing shows that it works down to 0.2 volts.

Current was about 1 ma at 0.2 volts, up to about 1.2 ma at 25 volts.

If you don't have 5 volts available, just recompute the base bias resistor divider for whatever voltage you do have.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod