MC34063 Question about converting positive voltage to negative voltage

[YOSHIZAKI]

This is a 5V to -12V circuit, the IC used is MC34063.
I don't know why the output is -12V, but the Ref voltage divider is divided into positive 1.25V

[selcuk]

Vout measurement is referenced to circuit ground. Feedback measurement is referenced to GND pin of the IC. And GND pin is not connected to the circuit ground but to the Vout. You can connect feedback voltmeter reference to circuit ground.

[YOSHIZAKI]

I can first see that the output is a negative voltage, and then think that the negative voltage becomes positive because the GND of the IC is not connected to the circuit ground. But is there any more intuitive way for me to judge the positive and negative voltages? Or how you imagined it?

[selcuk]

I didn't comment about the IC. I'm just saying that you have two voltmeters. You need to connect their references (negative probes) to the same potential to compare them. The output voltage is -12V and the feedback net is at -10.75V. There is a 1.25V difference between them.

[Miti]

Print the schematic on paper and write all the voltages relative to the circuit GND. See what you get.

[Terry Bites]

Vo=-Vref(1+R1/R2) so for a -12V output R1/R2 =8.6 . No mystery there.
See fig 13 of attached. Their R1 is your R2 and vice versa.

[TimFox]

I wish manufacturers of flexible ICs such as this one would avoid naming a pin "ground" if there is a good reason to connect that pin to something else than the ground plane.
I once designed a circuit using a shunt regulator chip (precision version of the common TL431) where the PCAD model had a "GND" pin for the negative terminal, but I was using it as a two-terminal device to make a negative reference voltage with respect to the ground plane.
The PCB layout guy connected that pin to ground, instead of how I drew it on the schematic as a Zener diode (with pin numbers).
(Incidentally:  why are there zero precision three-terminal reference chips for a negative reference voltage?)

[YOSHIZAKI]

Thank you for your reply. I followed your suggestion and wrote down the positive and negative voltages, now it's clear.