I am looking for a display technology (minimum 7 segment type) that can operate up to near 200 degrees f. Is there a LED, LCD, any other type of display that may work?
If LEDs are the answer? What is the most affordable way to drive them? I am assuming the drive current has to change relative to temperature.
I don’t know of any electronic display type that will work reliably for a year or more at greater than 160°F( 70°C), even those are rare. This is due to the fact that electronic displays are generally designed for reading by humans in their environment. So designing to withstand an environment that kills humans is not usually a design goal.
I’d consider using a separate display that is in the environment with the observer and have a wired or wireless link between the device and the display. For a modern high tech vibe, have the device use a smartphone as the display like the Meater thermometer, or the sadly no longer in production Mooshimeter.
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It is generally better to design your system such that the display is positioned in a more reasonable environment, as Paul states.
However, we do have the following options rated for up to 105°C (221°F):
LCD-A2X1C50TR 2.5 digit LCD
LCD-A3X1C50TR/A 3.5 digit LCD
LCD-A401C39TR 4 digit LCD
Keep in mind that all of the other components will also need this rating.
If you can assure that the temperature never exceeds 85°C (185°F), then the following character-type LCDs are also an option:
Additionally, it looks like a number of LED-based products from Lite-On and Broadcom (formerly Avago, formerly HP) are rated for 100°C (212°F) or more. I checked a few datasheets in this link, but not all.
Regarding driving them, there are too many dependencies to properly answer. In general, today, most people drive these directly with a microcontroller. Yes, one must reduce the current as the temperature rises. Their datasheets generally give a derating specification of (x)mA/°C above 25°C. This generally results in current in the low-to-mid single mA range at 100°C. One can either design the circuit to never drive at higher currents (giving a relatively dim display), or sense the temperature and reduce the drive current via PWM on the common pin (common anode or common cathode, depending on the specific part) in order to reduce the average current to the proper level.
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