I can test with my SMUs (K2400 and HP 4142) and try automate tempco finding, once I get few of these little wonders too.
If would also suspect the current source, though this should not be that bad. Also EMI could be a problem, when using an external unit.
There is also a chance that there is quite some temperature effect, as the TC is low only for a suitable current and this current can be vary quite a lot from device to device. Having one with 6.0x V suggest this could be one of the more extreme ones. So if possible I would also monitor the temperature via the second diode.
The normal test circuit would be similar to the one right at the beginning of the thread.
I think that the SMU is not the largest contributor to the 100+ uV wander of the zener.
I just changed the forced current to 10mA and the average wander is now 6 uV instead of 100+ uV at 5mA.
It looks like an automated measurement will be required to characterize all 10 pcs of the 2DW232 that I will be using.
The 2DW232 mounted on the banana plug is wrapped in 3 tissues tied with a twist tie.
Another thing to mention here is that it takes 30+ minutes for the 2DW232 to stabilize. In open air, it never stabilizes.
To find the optimal current for minimum tempco you have to do a temperature change, for example heating the zener with a power resistor, letting it to cool down (with a several seconds repetition time), and adjust the current for a minimal change in voltage. It is also would be interesting to see if the minimum tempco would be for one zener only or for a zener in series with the second half working as a diode (which I suspect might be the case).
Cheers
Alex
For manual finding the optimum current, one could look an the stabilization curve (the first 10-20 seconds or so) after turning the current on. For too low a current, the voltage should drift down on settling and for to high a current the settling should be upwards.
Of cause one can do the same with the SMU and PC as well.
As heater one could use the second zener as well, so the observed voltage will stay about the same and one could use an AC coupled amplifier to watch small changes.
The much better performance at 10 mA suggests that the wandering / drift was due to thermal effects and 10 mA being much closer to the point of zero TC. Only 6 µV suggests this is already rather close - e.g. a TC of a few ppm / K at most. Final performance can also depend slightly on the resistor to set the current and the environment temperature range.
For manual finding the optimum current, one could look an the stabilization curve (the first 10-20 seconds or so) after turning the current on. For too low a current, the voltage should drift down on settling and for to high a current the settling should be upwards.
Of cause one can do the same with the SMU and PC as well.
As heater one could use the second zener as well, so the observed voltage will stay about the same and one could use an AC coupled amplifier to watch small changes.
The much better performance at 10 mA suggests that the wandering / drift was due to thermal effects and 10 mA being much closer to the point of zero TC. Only 6 µV suggests this is already rather close - e.g. a TC of a few ppm / K at most. Final performance can also depend slightly on the resistor to set the current and the environment temperature range.
Short answer: the voltage never settles upwards.
The datasheet that Zlymex posted has max power at 200mW and current of 30mA.
I have tested one sample at 5mA, 10mA, 15mA, 20mA, 25mA and 30mA. The device is wrapped in three layers of tissue to kill any air current.
The voltage always decreases for many minutes until a stable voltage is reached.
The particular device in-hand operates at 6.19xxxx volts at 30 mA. I will let this device run at 30mA until it settles and report +/- deviation.
Short answer: the voltage never settles upwards.
And what happens if you connect both sides (one as a zener, one as a diode in series with zener)?
Cheers
Alex
Short answer: the voltage never settles upwards.
And what happens if you connect both sides (one as a zener, one as a diode in series with zener)?
Cheers
Alex
I am not sure what you are asking to try. Maybe draw it out by hand and post the drawing(s)?
Here is a screen capture of the statistics of the DMM7510 measuring voltage .
Keep in mind that the voltage measure cables are unshielded 24" long each. I will use shielded BNC cable eventually when I have a 2DW232 on a pcb in an enclosure.
RMS noise (standard deviation) is less than 1/2 uV.
Short answer: the voltage never settles upwards.
And what happens if you connect both sides (one as a zener, one as a diode in series with zener)?
Cheers
Alex
I am not sure what you are asking to try. Maybe draw it out by hand and post the drawing(s)?
Like that:
Cheers
Alex
I believe that is how it is connected and is how it is intended to be used. Pin 1 is the red dot which is the output. Pin 2 is grounded. Pin 3 is the case is ignored.
I believe that is how it is connected and is how it is intended to be used. Pin 1 is the red dot which is the output. Pin 2 is grounded. Pin 3 is the case is ignored.
OK, thanks, that was my understanding as well, however from the discussion in this thread it was not quite clear.
Cheers
Alex
For manual finding the optimum current, one could look an the stabilization curve (the first 10-20 seconds or so) after turning the current on. For too low a current, the voltage should drift down on settling and for to high a current the settling should be upwards.
Of cause one can do the same with the SMU and PC as well.
As heater one could use the second zener as well, so the observed voltage will stay about the same and one could use an AC coupled amplifier to watch small changes.
The much better performance at 10 mA suggests that the wandering / drift was due to thermal effects and 10 mA being much closer to the point of zero TC. Only 6 µV suggests this is already rather close - e.g. a TC of a few ppm / K at most. Final performance can also depend slightly on the resistor to set the current and the environment temperature range.
It appears to be the opposite of your hypothesis.
For too-high current, the voltage drifts down. For too-low current, the voltage drifts up.
Now that that is sorted out, the zero T-C current for this device is between 7mA and 8mA in open air. Covered in tissues the zero T-C current is between 6mA and 7mA.
That's better!
An 6-8 mA current for zero TC sounds very good. However the optimum current seems to be quite temperature dependent if it already changes so much from open to air and covered.
It is interesting to see an negative TC and thus falling voltage at high current. The normal zener refs like 1N829 are the other way around with a negative TC at low currents and a positive at high currents.
It might be interesting to do full characterization with 1 or 2 samples, as this units seem to be different from the more normal western zeners and the DS does not give much information. Is the diode in forward direction reasonably normal and working as a temperature sensor ?
I will mount a second device and take the same tests for currents causing rising and falling current. And I will have a try at measuring a single diode.
An 6-8 mA current for zero TC sounds very good. However the optimum current seems to be quite temperature dependent if it already changes so much from open to air and covered.
It is interesting to see an negative TC and thus falling voltage at high current. The normal zener refs like 1N829 are the other way around with a negative TC at low currents and a positive at high currents.
It might be interesting to do full characterization with 1 or 2 samples, as this units seem to be different from the more normal western zeners and the DS does not give much information. Is the diode in forward direction reasonably normal and working as a temperature sensor ?
A second mounted sample works exactly the same. High current causes voltage to fall. Low current causes voltage to rise.
I will mount a second device and take the same tests for currents causing rising and falling current. And I will have a try at measuring a single diode.
I mounted a device with the red dot at HI of the SMU. The device case is at LO of the SMU.
1mA of forced current creates 0.73 V. 1mA of reverse current creates -5V.
5mA creates 0.78V. -5mA creates -5.26V
I think that explains the device behavior.
1mA of forced current creates 0.73 V. 1mA of reverse current creates -5V.
5mA creates 0.78V. -5mA creates -5.26V
I think that explains the device behavior.
Seems to me that you're measuring a combination of temperature coefficient and dynamic resistance there, and the two measurements are not even the same difference in temperature. I don't know how to draw any conclusions from it.
1mA of forced current creates 0.73 V. 1mA of reverse current creates -5V.
5mA creates 0.78V. -5mA creates -5.26V
I think that explains the device behavior.
Seems to me that you're measuring a combination of temperature coefficient and dynamic resistance there, and the two measurements are not even the same difference in temperature. I don't know how to draw any conclusions from it.
The observation is that there are two devices; a 5V zener in series with a 0.7v diode. Nothing more complicated than that.
So a low TC can be obtained with both diodes in series, as an 5.4 V zener with posistive TC and one working as a normal diode with negative TC. At some current (about 5-10 mA) the TCs will compensate, since the TC depends on the current. For a normal diode the TC gets smaller (less negative) with more current. For this zener it seems the TC is also getting smaller (a little faster than that of the diode) at high current as the overall TC seems to turn negative on high currents.
Having the two diodes in series makes it possible to use the normal diode as a temperature sensor - for compensation of residual temperature dependence (not just linear) or a regulated temperature. With the diode as a sensor one might be able to get quantitative values for the TC at maybe 5 and 10 mA.
The rather good stability even at 10 mA for a device with compensating current near 7-8 mA suggests that even with not so perfect current the TC is quite low.
o far the reference looks very good - 2 more points to check:
1) One point is hysteresis: So is the voltage the same starting from cold or a higher temperature.
For a test one could do a sequence like: off - 7.5 mA (optimum current) - 25 mA (to heat the device) and than 7.5 mA again.
2) The last big question is long time stability. Here the SMU might not be good enough as a current source and this would be more like testing ready made reference units with case and possibly temperature control.
So a low TC can be obtained with both diodes in series, as an 5.4 V zener with posistive TC and one working as a normal diode with negative TC. At some current (about 5-10 mA) the TCs will compensate, since the TC depends on the current. For a normal diode the TC gets smaller (less negative) with more current. For this zener it seems the TC is also getting smaller (a little faster than that of the diode) at high current as the overall TC seems to turn negative on high currents.
Having the two diodes in series makes it possible to use the normal diode as a temperature sensor - for compensation of residual temperature dependence (not just linear) or a regulated temperature. With the diode as a sensor one might be able to get quantitative values for the TC at maybe 5 and 10 mA.
The rather good stability even at 10 mA for a device with compensating current near 7-8 mA suggests that even with not so perfect current the TC is quite low.
o far the reference looks very good - 2 more points to check:
1) One point is hysteresis: So is the voltage the same starting from cold or a higher temperature.
For a test one could do a sequence like: off - 7.5 mA (optimum current) - 25 mA (to heat the device) and than 7.5 mA again.
2) The last big question is long time stability. Here the SMU might not be good enough as a current source and this would be more like testing ready made reference units with case and possibly temperature control.
Forcing current with a SMU, the voltage is never stable in the bottom 3 or 4 digits. There is no way to measure hysteresis unless a very stable circuit is built and placed in an enclosure.
My opinion is that a stable circuit will require the same heroic effort that is built into a Fluke 731B. Selected and matched tempco resistors. Lots of places for mistakes to show up.
Then the reference diodes have to be aged and characterized and only the best one is good enough.
This week's order from factory is about to close. If you want to buy one of those please PM me.
The differential resistance on the zeners should be reasonable low. So changes in the resistors are attenuated by a factor of about current setting resistor to zener resistance. This could be something in the range of 50-100 if one assumes 6 V to set the current. So the demands on the resistors are not that extreme.
For the first tests I would not assume the zeners to be as good as high end parts like LTZ1000 or LTFLU. We would be very happy it could come close to the LM399 / LM129H. So it is about resolving changes in the 10 ppm range. Some thermal shielding and soldering to a board is likely needed - alone from thermal EMF.
The measurements from VintageNut suggest he got quite good stability with the SMU as a current source. But it can depend on the individual units and environment. A dedicated reference circuit could work as well - the demands for the current setting resistors are not that high (e.g. even 100 ppm/K thick film might be good enough), at least for the hysteresis test.
Attached is a suggested simple test circuit. Paralleling R3 to R2 could be used to temporarily increase the current. The lower diode of the ref can be used to get a rough idea of the reference temperature.
Hello Kleinstein
Can you please give some analysis of how your circuit is better or different from the circuit used by zlymex on the first page of this thread?
The circuit I showed uses only 2 (instead of 3) resistors that need to be stable. Just to get a stable current for one ref. chip, even the second resistor does not really need to be a good one either.
The difference is also not that big - just replace D1/D3 with a resistor and you are back at the circuit from the first page.
For doing a transient / current step test, it might be an advantage that the current does not depend on the voltage of the ref chip under test, but on the other one. One can look at D2/D4 (e.g. 6.2 V) or at the sum of both references (12.4 V). If you want scaling to 10 V, it works slightly better (less sensitive to resistor drift) if you start from 12 V than starting from 6.2 V.
Here is the translated datasheet.
Thank you for preparing this translation, but I think the listed pinout is incorrect. For the devices I received from VintageNut, pins 1 and 2 are anodes, and pin 3 is the common cathode.
Also, I measure a resistance of ~800K between the 2 anodes. Does anyone know why that is?