For the added overcurrent protection in this little project:
https://www.eevblog.com/forum/projects/battery-voltage-to-5v-regulation/msg2280605/?all#lastPostI want to find out what the temperature sensitivity is when the zenerdiode would be replaced by a normal one.
First I simplified the schematic, so it is more easy to see what is measured in the experiment. The experiment uses the term input and output. The op amp feeds the subcircuit (input) which has an output on the non inverted input.
The subcircuits curve and the amplification determines when the positive feedback collapses.
In the experiment I've done 3 measurements:
* At room temperature: Non automated set of points by turning up the
AWG in DC mode and measuring the output with a
MM. This method is very precise and is the baseline to compare the next one to.
* At room temperature: A 50% triangle ramp with the AWG from 0 to 800 mV at 5 hz. Measuring the in and output many times with a
DSO using the 64x average mode.
* At 50 deg (using a heatgun): The same as above.
The data of the DSO was fetched using
SCPI. I manually removed data that wasn't in the ramp up. So it was known that all voltages should be rising (discarding noise). With this knowledge I took only the first voltage/time point of a certain voltage. Values in between are interpolated later on. In this way one can use the very high horizontal resolution to get very high vertical one. (Precision is another matter).
Also I used a 450 ohm resistor instead of a 500 ohm (R9) one, because of the 50,74 ohm output of the AWG. The voltage drop over the 450 ohm resistor is used to determine the drop over the extra 50,74 ohms.
Using the two datasets (Ramp and output) a new dataset for the use in Excel can be created. There the MM and DSO measurements can also be compared.
I think the DSO results are very usable! I did not even took out abnormal values, which would not be very difficult to spot.
I'm still not sure whether the fetched dataset is an averaged one or whether averaging is only used for the DSO screen.
The next step is to check for each temperature what amplification is needed to let the positive feedback collapse. If the difference is high, then a normal diode is not suited to be used in this circuit. (It may also that a Zener diode's curve at low currents also differs too much.) I will write a simulation script which will use the datasets I got to find the answers. There's even a slight possibility it won't collapse using the current component values.
BTW: The curves already tells me that temperature dependency is a bit too high to my likings. But these experiments are a good learning experience. So we shall continue!