I've already asked this in another thread but it was sort of off topic so I'm giving it its own thread.
I want to build a HB LED driver using the Texas Instruments TPS40211:
http://focus.ti.com/lit/ds/symlink/tps40211.pdfIf you look at page 34, Figure 36, there is an application circuit for this. R6 is the current sense resistor and C5, C6 and R4 is the compensation network. R23 is for loop injection when fiddling with the optimal compensation. But what is R13? I'm assuming it has something to do with the compensation but how can I determine its value and what exactly is the function of it? I would be very grateful for answers on this one.
but how can I determine its value and what exactly is the function of it?
the value is 30.1K Ohm in page 35. i'm "assuming" the function is to separate high voltage/current from feedback/compensation network. and also r6 and r23 (and probably including the r13) will form current/voltage sense/divider, not r6 alone.
but how can I determine its value and what exactly is the function of it?
the value is 30.1K Ohm in page 35. i'm "assuming" the function is to separate high voltage/current from feedback/compensation network. and also r6 and r23 (and probably including the r13) will form current/voltage sense/divider, not r6 alone.
Yes, that is the value for this particular design. But the fact that it's 30.1k 1% and not 33k 5% suggests that it's value isn't really chosen to be just "really big". Also, it's not a divider. R6 is a current shunt resistor for sensing the current through the LED string. If we removed the compensation network I don't see any reason why it would be included since the input impedance of the inverting EA input is large that 30.1k is nothing in comparison.
Looks to me like a current measurement resistor.
10 ohm will give you 10 mV for every mA.
That's not the resistor I mean. I mean the 30.1k, 1% resistor. It doesn't seem to be needed when using a voltage divider for voltage feedback.
did you consider my assumption as voltage separator? ie to avoid voltage in sensing/respond side to affect voltage in the feedback side?
and have you tried removing it and see how the circuit behave?
After a bit of research, it seems to me that R13 is simply part of Rin as in an inverting amplifier op-amp configuration and the compensation network would be Rf. Thus, the total amount of gain would be Zf/R13 (if we ignore R23).