Heating device for automobile cold-starting aid - uses power transistor with heat output provided by thermal losses

摘要

The device uses a power transistor e.g. an FET, with the heat generated during operation dissipated via the medium to be heated. The transistor may be energised intermittently with the switching duration and/or frequency being variable. Pref. the device forms part of an automatic choke for an automobile engine and uses an FET (10) in direct thermal contact with the walls of the fuel feed line leading to the carburettor. The source and drain of the FET are connected between a voltage source and earth, its gate coupled to a control circuit (16) incorporating a resistive voltage divider (R1,R2). This has a variable resistor (R2) controlled by the output of a comparator (18) comparing measured and reference values (M,S) for the temp. of the heated medium.