Coffee cup heating

With the Cup Heater, MMD0322 you allwas have a hot coffee or tea Mug :-)
A different kind of heating element - - Normally the heating element would be a wire power resistor, with a transistor as the power switch. So the question arises, ? why not use the power ransistor as a heating element? This eliminates the procurement of the heating resistor, which is rarely found in the box in which everything can be found.

A aluminum plate 4 mm thick is provided as the heating plate. Aluminum conducts heat well and is easy to work with (saws and drills). The desired temperature can be set, with the potentiometer P1, from approx. 20C to 90C.
It is heated with a TIP142 Darlington transistor (as Silicon Heat Element) that can handle up to 125 watts, we use 25 watts. When the LED is on, the heater is in up-haeting process.