04-16-2019 04:35 PM
Hi All.
The attached circuit has two zener diodes, one 3V3 and the other 6V2.
Both diodes (BZX384) show a linear negative temperature coefficient
between 20 and 180 degrees Centigrade, whereas the 3V3 should be
-2.4mV/degree C and the 6V2 diode +2.3mV/degree C.
I have not changed the models. I hope someone can tell me I am an
idiot or I will have lost faith in the temperature modelling.
Thanks,
Keith
04-18-2019 06:51 AM
Hi Keith,
Thank you for your post.
Please may I ask what you are trying to do? Also, please may I ask for more details on your setup.
Kind regards,
YD
04-19-2019 11:24 AM
Hi Yusuf.
I wanted to create a constant voltage, similar in action to a zener diode,
with near to zero temperature drift. To create this I was going to use the
combination of a zener diode and bipolar transistor. I have looked at using
shunt voltage references, but they all rely on a low impedance ground
because of the circuitry contained within. They are not suited to being
operated in series with a resistor in the anode and cathode.
Whilst pursing this task, the circuit I designed did not have the thermal
characteristics I was expected. Following on from this, I swept the
temperature of a BZX384 6V2 to find it's temperature coefficient
was negative rather than positive. The same negative coefficient
applied to the 3V3 diode. The circuit I presented was my test
circuit which need not be any more complicated for this purpose.
However, I should have only placed one probe on circuit so the resulting
graph had a much limited range of about 100mV.
Basically, I should have just asked the community where the
temperature coefficient was stored the the BZX384 model, and, if not
included, what should it be.
Thank you,
Keith
04-19-2019 11:27 AM
Hi Yusuf.
I wanted to create a constant voltage, similar in action to a zener diode,
with near to zero temperature drift. To create this I was going to use the
combination of a zener diode and bipolar transistor. I have looked at using
shunt voltage references, but they all rely on a low impedance ground
because of the circuitry contained within. They are not suited to being
operated in series with a resistor in the anode and cathode.
Whilst pursing this task, the circuit I designed did not have the thermal
characteristics I was expected. Following on from this, I swept the
temperature of a BZX384 6V2 to find it's temperature coefficient
was negative rather than positive. The same negative coefficient
applied to the 3V3 diode. The circuit I presented was my test
circuit which need not be any more complicated for this purpose.
However, I should have only placed one probe on circuit so the resulting
graph had a much limited range of about 100mV.
Basically, I should have just asked the community where the
temperature coefficient was stored the the BZX384 model, and, if not
included, what should it be.
Thank you,
Keith