Abstract: A circuit configuration for a self-oscillating blocking-oscillator switched-mode power supply includes a transformer having a primary winding. A bridge rectifier has an output terminal. A semiconductor switch element is used for clocked application of an alternating voltage rectified by the bridge rectifier and unsmoothed to the primary winding. A control device has input terminals. The control device triggers the semiconductor switch element according to at least one primary current signal to be applied to one of the input terminals of the control device. A one-way rectifier configuration has an input side connected to the output terminal of the bridge rectifier and an output side connected through an RC element to the one input terminal of the control device.

Abstract: A circuit arrangement for a free running blocking oscillator type switched power pack includes a control means for pulse width modulated drive of an electrical switch element. The control means receives as controlled information, among other things a zero axis crossing detector signal at one input post and a control voltage and a further input post that is dependent upon the output voltage of the switched power pack. To guarantee reliable operation yet yield low power consumption, particularly during the standby mode, it is proposed that a detector means with whose assistance an internal reference voltage is reduced during standby mode be provided in addition to a capacitive coupling of the two input posts. The result is that the undesirable rise in the output voltage in the standby mode and the further boost by the capacitive coupling of the input posts is effectively avoided.

Abstract: A blocking oscillator contains a switching transistor which is driven by an integrated circuit. This circuit receives its supply voltage during the blocking phase from a winding at the primary side. A further winding at the primary side supplies the regulating variable for the integrated circuit during the flow phase. The supply input of the integrated circuit is connected by way of a further transistor and a diode to the control winding and a Zener diode biases the base of the further transistor. In the start-up phase in which the voltage of the supply winding (control winding) is built up, the circuit supplies the required operating voltage and switches off again in the steady state of the power unit.

Abstract: A blocking oscillator power pack is based on a conventional design in which the transformer supplied by way of a rectified line alternating voltage is provided with a first secondary winding which supplies an electrical device, as a load, by way of a further rectifier and with a secondary winding which serves for the supply of a control circuit. As a final control element, the control circuit contains a switching transistor by way of which the current in the primary winding of the transformer is adjusted. It has been shown, however, that an undesired rise of the secondary current is also possible due to a failure of the control circuit. In order to suppress such rise, a protective circuit is provided which remains inactive given intact operation of a control circuit.