I just built a small heater / regulator board for ovenzing components. I should also be usable for temperature cycling. The heater outputs up to around 0.6W, runs on 12V.
It is designed with a voltage sensor and opamp that compares the sensor output to a fixed (setpoint) voltage divider. The opamp output drives a small power transistor. Pretty much like the LTZ1000 datasheet circuit but with a few tweaks. I have used the LM35 temperature sensor as sensing element, and compared it to a reference voltage, derived from a zener. The LM35 has an output of 10mV / C. I gave it a separate buffered output, amplified it by a factor 10, so I can easily monitor the temperature with a voltmeter (ie 5.0V = 50C) The heater resistors give about 0.4W output on average and the regulator loop switches on/off about once per second at best. It has been running since last night. Short term stability has been about 0.002 - 0.004C peak to peak (2-4 milli Celcius (mC) ) over a few minutes, at a nominal temperature of 33C. The temperature has varied by around 10mC as I have tried different component values. I have not really measured the drift so far, as I have been tinkering too much with the circuit. It seems to be no more than one or two mC so far. I am prettu sure that If I place the sensor and heater behind copper plate or heatsink, the other side of the plate would consistently see less than 1 mC rms oscillations. Long term drift should only depend on the LM35, a resistor pair and the zener reference. If someone is interested, I will get back when I have built a few more boards, tuned the component values, made some longer tests. _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
