| 摘要 |
The invention relates to a circuit arrangement for operating electric lamps, having a free-running half-bridge inverter (Q1, Q2). An auxiliary transistor (T1, T2) is in each case connected into the control circuits of the half-bridge inverter transistors (Q1, Q2), so that the emitter impedance of each half-bridge inverter transistor (Q1, Q2) is formed by a parallel circuit which consists of at least one resistor (R5) or (R7) and the control path, arranged in parallel therewith, of the corresponding auxiliary transistor (T1) or (T2). The control inputs of the two auxiliary transistors (T1, T2) are, furthermore, connected to the output of a common control circuit (IC). These measures make it possible to switch over the effective emitter impedance and therefore the feedback of the half-bridge inverter (Q1, Q2) as a function of the operating phases of the lamp (LP) and thus, in simple fashion, to vary the clock frequency of the half-bridge inverter within wide limits by virtue of the dimensioning of the resistors (R5, R6; R7, R8) of the parallel circuits (R5, R6, T1) or (R7, R8, T2) according to the invention. |
