Emergency power supply circuit for a dynamo-supplied load

摘要

An electric circuit is described for the short-term power supply of a dynamo-supplied load in the event of dynamo failure, according to Patent ... (Application P 3145775.4). On the one hand, the load is connected via a capacitor in the dynamo circuit so that both half cycles of the dynamo current reach the load. However, the load is additionally connected in an emergency circuit, which is blocked by a semiconductor switching element during normal dynamo operation. The semiconductor switching element is controlled by the combination of a large capacitor and a small capacitor which are connected together with their polarities in reverse parallel via a high-resistance resistor, the small capacitor normally being connected by means of its negative terminal to the control electrode of the semiconductor switching element and blocking said switching element. In the event of dynamo failure, the large capacitor discharges via the control electrode of the semiconductor switching element, so that the latter is switched on for the duration of the capacitor discharge and connects the load to the emergency power source. In this case, the capacitor which is located between the dynamo and the load acts as a return-flow block and prevents the return flow of the current from the emergency power source to the dynamo. Once the capacitor has discharged, the voltage at the control electrode of the semiconductor switching element falls below the threshold value of the switching element again and the current from the emergency power source to the load is automatically interrupted.