| 摘要 |
An electromagnetic doorholder for retaining a door in an open position by magnetic interaction with an armature secured to the door. The doorholder includes a core having a face confronting the armature and a coil of wire surrounding the core. A cup having an inside diameter somewhat greater than the coil outside diameter receives the coil, the core extending from the face to the cup bottom. A power control circuit including a resistor circuit controls electrical power supplied to the coil, the power control circuit being mounted on a circuit board situated between the coil rear surface and the cup bottom. The resistor circuit being situated in sufficiently close proximity to the cup bottom for transfer of heat from the resistor circuit to the cup. The power control circuit also includes a low resistance circuit coupled to the resistor circuit, the low resistance circuit including a fusible link, the fusible link being selected to carry current when the power input terminals are coupled to a lower voltage power source and to stop carrying current when the power input terminals are coupled to a higher voltage power source.
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