[SOLVED] Bandgap Vref temperature compensation methods

Hi,

To make a bandgap reference using discrete components is easy, I see.

To make it independent of temperature is extremely difficult, as well.

Using matched beta transistors (+/- 98% for all four), and 50ppm/ºC resistors is obviously a waste of time, even as a fun hobby. Extrapolating, the version I put together would have about 150mV change from 1.23V over 25 degrees in both temperature directions, from 25ºC as the zero TC.

I saw that you can use e.g. LM35 to compensate for the drop in Vout, however, that would require an enormous circuit to a) level shift, and b) drop LM35 output/ºC to approx 2mV/ºC - not even for the sake of science.

Related: In the (TI) LM35 datasheet, the transistors in the simplified schematic have no "hats" across the C and E - what sort of BJT are they (like super beta have a wide "hat" on datasheet schematics)?

Is there some other method of compensating for the 2mV/ºC drop?

For people who don't want to use a reference IC and prefer to build them, is it more common practice to use the Brokaw cell that the Widlar 4 transistor bandgap because of this "problem"?

I don't know how you would use this in a bandgap circuit, but a zener diode combines two effects: zener effect and avalanche effect. One has a positive temp coefficient, the other a negative temp coefficient. So according to Wikipedia:

In a 5.6 V diode, the two effects occur together, and their temperature coefficients nearly cancel each other out, thus the 5.6 V diode is useful in temperature-critical applications.

Click to expand...

https://en.wikipedia.org/wiki/Zener_diode

Install a resistor divider to get a desired reference voltage.

Hi Brad,

Thanks. That's like the LM134/LM334, that recommends adding a diode to compensate for temperature drift.