Transistor oven.

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Glenn Gundlach 20 years ago

I did exactly that for a log amp about 10 years ago. Used a MAT-04 with one transistor as the temp sensor, 2 transistors as the heaters and the

4th as the log element. The circuit was actually from Jim Williams. I used 1/2 AD708 as the heater driver and the other half as a lamp driver. The LED is red when under temp and turns green at temperature. Using multiple meters on the unit as temp readout and drive level, placing a finger on the package causes the drive to increase with no measurable change in the temp monitoring point. IIRC 469 mV corresponds to 69 C. From room temp to operate takes 10-15 seconds. The heaters run on 12 volts with the drive limited to 30mA to not damage the transistors during initial warm up. Actual maintenance current is only a few mA when warmed up. GG

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Herb 20 years ago

Hi. I wish to use a monolithic transistor array in a circuit where the die temperature is temperature stabilized. I am hoping to find a circuit design for a 'transistor oven' whereby one transistor is used as a temperature sensor eg by monitoring the Vbe, and one of the transistors (possibly the same one) as a heater to raise the temperature to ~50C. I would appreciate if someone would suggest a circuit to achieve this. I am looking for a circuit with the minimum of external components. Temperature accuracy of +/-5% sould be sufficient. TIA HMV

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Ian Stirling 20 years ago

Consider the problems of differential heating - if you heat it using internal components, then you're going to have fairly significant thermal differentials across the die.

+-5% means nothing. +-5% in F, C, K, R, ...

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Jim Thompson 20 years ago

Die mount over an insulator. Metal can package, evacuated.

Resistor (heater) pattern around edge of die.

It's been nearly 40 years now, but I believe we were doing about

0.05°C stability.

...Jim Thompson

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Rene Tschaggelar 20 years ago

There is only one physical temperature unit, and this is Kelvin. All the others are history biased convenience units.

Rene

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Gerhard 20 years ago

See "Self-Heated Transistor Thermostats Individual Components" Electronic Design, Feb 9, 1998. It employs a TIP41 as the heater-sensor.

Gerhard van den Berg

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Jim Thompson 20 years ago

Well-insulated is most of the trick.

And proportional control is a necessity. Heaters banging on and off wreak havoc in analog circuits.

...Jim Thompson

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Ian Stirling 20 years ago

Right. I'm not arguing that this is impossible - but that it does sound a tad unlikely that this is the sort of scheme proposed.

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Spehro Pefhany 20 years ago

Why would *stability* require calibration?

Best regards, Spehro Pefhany

"it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com

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josh lawton 20 years ago

I think the temperature must be higher unless you really want to limit the application. I would take transistor and short across vdd. Regulate the current to obtain the desired temperature.

Herb wrote:

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josh lawton 20 years ago

I would love to see how you can reach this without some calibration.

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Jim Thompson 20 years ago

0.05°C was the measured _variation_

As Spehro points out, it is only the _absolute_value_ that needs calibration.

...Jim Thompson

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josh lawton 20 years ago

I think you must interpet things differntly. I assume .05?C stability is the tolerance. I would assume the circuit is stable, otherwise why build it?

Spehro Pefhany wrote:

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Transistor oven.

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