| 摘要 |
<p>A control circuit selectively energizes a load, such as an elevator or escalator brake (12). The circuit includes a transformer (28) with a primary-winding connected to a series with a semiconductor switch (40) that is driven by a pulse width modulation (PWM) controller. Power to the PWM controller is supplied through safety relay contacts (52A, 52B). When the load is to be energized, the safety relay contacts are closed and the PWM controller drives the semiconductor switch to supply energy through the transformer to the secondary circuit. A command signal to secondary circuitry (64) causes power in the secondary to be applied to the load (12). If the safety relay contacts open, the PWM controller turns off and power is no longer delivered to the secondary circuit and the load.</p> |
