Greetings,
I ran into an issue where my current regulation wasn't working as expected, and Markd77 pointed out that I was depending on my transistor HFE to be 100. (I tested the transistors, and he was right.)
Anyway, I learned about current mirrors in the ebook here:
http://www.allaboutcircuits.com/vol_3/chpt_4/14.html
So I've replaced one side of my H-bridge with that. Both sides used to look like the red R8, and I made the change to the blue R7.
I was hoping someone could review it, and make sure my understanding is correct.
It looks like the benefit is that I can basically ignore the HFE and changes due to temperature when Q10 and Q7 are identical.
...and the drawback is that it takes 1 extra component and doubles the H-bridge current draw because the current is "mirrored" across R7.
Does that sound right?
Thanks,
-masked
(desired output is 2.63mA across "Out" leads, with polarity reversing every minute)
I ran into an issue where my current regulation wasn't working as expected, and Markd77 pointed out that I was depending on my transistor HFE to be 100. (I tested the transistors, and he was right.)
Anyway, I learned about current mirrors in the ebook here:
http://www.allaboutcircuits.com/vol_3/chpt_4/14.html
So I've replaced one side of my H-bridge with that. Both sides used to look like the red R8, and I made the change to the blue R7.
I was hoping someone could review it, and make sure my understanding is correct.
It looks like the benefit is that I can basically ignore the HFE and changes due to temperature when Q10 and Q7 are identical.
...and the drawback is that it takes 1 extra component and doubles the H-bridge current draw because the current is "mirrored" across R7.
Does that sound right?
Thanks,
-masked
(desired output is 2.63mA across "Out" leads, with polarity reversing every minute)