Hello,
I would like to do something similar to what’s been described on this site a few times. I would like to produce +-5V from +-15V lines. I was going to use a LM3102 (or something similar) to produce +5V from the +15V input line. And in theory, I can use a slightly modified circuit to produce -5V from the -15V line. Basically connect the LM3102's Vin to Ground, and LM3102's GND to -15V, and then configure it to produce 10V relative to the -15V line.
For this negative DC buck converter, I can also use a current mirror on the LM3102’s feed back circuit to ensure that the voltage at the output is always -5V, even if the -15 volt source changes a bit (see picture from previous TI question).
However, using a simple current mirror has a few issues in my case. First, the -15V line might change to 18V or 12Vs. Furthermore, it will be used over a large temperature range. The BJTs diode voltage in the diagram (3906’s) change by 0.2V when they get hot. These two things would result in a few 100mV change in the 5V line, and I would like better regulation.
So my question is: Is there a better way to setup the feedback loop in the buck converter without building a more elaborate temperature independent current supply? Or is there a better way for me to produce the -5V from the -15V line? (Note, a negative linear voltage regulator is not an option due to power issues, nor is it an option to turn the +15V into -5 with an inverting buck as I need the current from both sources).
Thanks,
Matthew
