| 摘要 |
A garage door opener with solenoid latches is provided with a circuit for energizing the coils of the solenoid latches with power from a 24-volt step-down transformer, either as 120 volt power is applied to a motor to move the door in response to detection of an initial surge of current or as a manual or radio controlled command switch is actuated. In either case, current at a higher level is applied initially to pull in the armature locking pins of the solenoid latches, and thereafter at a lower hold-in level. A transformer with a single turn primary winding or a Hall-effect device may be used to detect the initial surge of current to the motor and in response thereto pull in the locking pins. Thereafter, hold-in current is applied as long as current to the motor is sensed. In the case of sensing actuation of a command switch, a first one-shot triggered by the command switch times the total period (16 seconds) during which the solenoid latches are provided with at least hold-in current, and a second one-shot triggered by the first one-shot at the beginning of its timing period, times a short (100 ms) period during which high, pull-in current is applied. The second one-shot may also be used to inhibit application of power to the motor during the pull-in time. Still other embodiments utilize a mechanical means for sensing when power has been applied to the motor by the door opener.
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