Abstract: A method for operating protection circuitry for a power switch (1) uses first and second timing windows which are started in response to the power switch (1) being turned on. The second timing window is greater than the first timing window. During the first timing window, the method prevents operation of first protection circuitry (8) and during the second timing window the method prevent operation of second protection circuitry (10). At the end of the first timing window, but before the end of the second timing window, the method allows operation of the first protection circuitry (8), and at the end of the second timing window, the method allows operation of the second protection circuitry (10) whilst preferably preventing operation of the first protection circuitry (8). In an embodiment, the first protection circuitry (8) provides latched short winding protection for the power switch (1), and the second protection circuitry provides non-latched over current protection for the power switch (1).

Abstract: In a self-oscillating bridge circuit, the control of the low switch (6) is derived from the control of the high switch (7) by coupling the control circuitry (SC2) of the low switch to a terminal P in the control circuitry of the high switch by means of a diode (D1). The control of the low switch is improved by incorporating control circuitry (SC3) for rendering the low switch conducting for a short period after the high switch has become non-conducting.

Abstract: A reference voltage source comprises a first current branch (16, 36) and a second current branch (30, 34, 12). The voltage on a first terminal (6) in the first current branch (16, 26) is one junction voltage higher than the voltage on a second terminal (8) in the second current branch (30, 34, 12) owing to the presence of a transistor (80). The ratio between the current I.sub.1 through the first current branch (16, 36) and the current I.sub.2 through the second current branch (30, 34, 12) is thus determined by two non-linear characteristics having opposite temperature coefficients. A reference voltage (v.sub.z) with a small temperature coefficient and with a value which can be chosen freely can be generated by an appropriate choice of the resistance values for the resistors (58, 30, 16, 12) and by scaling the emitter areas of the transistors (34, 36, 70, 80).