Abstract: A circuit arrangement for detecting an input voltage comprises an oscillator responsive to the voltage, the oscillator including a pair of transistors (8, 9) connected as an astable multivibrator, each of the transistors having a load which comprises a primary winding (16 or 17) of a current transformer (T) and a low resistance proof resistor (12 or 13). A current flows through a secondary winding (18) of the transformer the amplitude of which current is proportional to the input voltage.

Abstract: A circuit arrangement includes a lamp filament (1) as a load and a resistor (2) in series with the filament. For detecting the current through the load, the source of a MOSFET (6) is connected with the end of the resistor remote from the filament, the drain of the MOSFET being connected with the other end of the resistor via the primary winding of a step-up transformer (7) and a further resistor (8), a diode (9) being connected between the source and the drain of the MOSFET. If the MOSFET is turned on by an appropriate voltage at an input (11) connected to its gate, the voltage across the secondary winding of the transformer is substantially proportional to the value of the current through the filament.