Not All LM723s are Born Equal

LM723CNChipPictureLM723JChipPicture

I made a few tests using LM723s from ST in a self-heated reference circuit. The typical drift curves over 10.5 days looked like this:

SelfHeatedReferenceWithLM723LoggerTest3OutputVoltage

Its all covered by the datasheet, saying typical stability is 500ppm/kHour at 25°C (we have ca. 90°C).

The circuitry can be seen here:

Click here to see Silly Circuits – A Heated LM723 Reference …

Still, its a bit disappointing, so I tried a military grade LM723J. OK, now it looks like this:

SelfHeatedReferenceWithLM723JLoggerTest4OutputVoltage

It drifts less, and it seems to settle down on top of that. Looks promising !

All the gory details can be seen below:

Click here to see Updated LM723 Long Term Stability Results …

 

Updated Results for the Long-Term Tests of the LM723 Self-Heated Reference

The test setup for the heated references is shown here:

LM723HeatedReferenceMeasurementSetupPicture

The reference itself sits on top of the 34401A (a metal box with a Pt1000 thermistor hinged on the lid of it). The pile of cables on the right comes out of the breakout box of the 20 channel voltage measurement card (inside the M300). Power supply and shunt resistor are at the bottom of the pile.

Test run two and three have been completed and they show some consistent behaviour. Back to test #1 (ca 4.5 days):

SelfHeatedReferenceWithLM723LoggerTest1OutputVoltage

Test #2 (10.5 days) :

SelfHeatedReferenceWithLM723LoggerTest2OutputVoltage

and Test #3 (10.5 days):

SelfHeatedReferenceWithLM723LoggerTest3OutputVoltage

It seems that the LM723 creeps up about 4mV per 10.5 days.More info here:

Click here to see some LM723 Long Term Stability Results …

Do all LM723s exhibit this behaviour ? Or are chips from other brands or MIL chips better ? Lets see … The logger is running.

 

Added Preregulators for Linear Power Supplies Pages

HP8255APowerSupplyPicture

I built quite some linear power supplies, and sometimes I wanted to make them more energy efficient without sacrificing their main advantage – low ripple and noise. So, I collected some circuitry from the web and from boatanchor service manuals to get ideas how that could be done.

Voilá : Here comes the Preregulator Gallery :

Click here to see some Preregulator Circuits for Linear Power Supplies …

First Results from the LM723 Self-Heated Reference Long-Term Tests

 

LM723ChipPictureAfter more than a month of observing my silly LM723 self-heated reference circuit the first results have arrived:

  • the first 1000h drift ist about 100ppm (the datasheet typical value is 500ppm typical)
  • there seems to be no significant room temperature dependency

Further tests will show if the drift rate slows down over time and how much.

Click here for Silly Circuits – A Heated LM723 Reference …