Witura WT-9001 IP65 Spezifikationen PDF herunterladen (Seite 48)

3.1.2.6 Relay Driver and Electromagnetic Lock

Relay Driver ULN2803AG was used to control the output of electromagnetic

lock. The ULN2803AG is a small integrated circuit that contains 8 transistor driver

channels. Each channel has an input to a resistor connected to the base of a transistor and

a 1 amp open collector output capable of handling up to about 30volts (if my memory is

correct). Each of the collectors has a reverse biased diode connected to a common Vcc

pin that provides inductive spike protection.

Typical uses are for micro-processor interfaces to relays, lamps, solenoids and

small motors. A ULN2803AG with a set of relays is a simple and effective way of

switching mains voltages for example. They are used less commonly today but were

once an almost universal means of interfacing processors to power devices.

While an electromagnetic lock is a locking device that locking door depending

on the output of relay driver. This consists of an electromagnet and armature plate. By

attaching the electromagnet to the door frame and the armature plate to the door,

a current passing through the electromagnet attracts the armature plate holding the door

shut. Unlike an electric strike a magnetic lock has no interconnecting parts and is

therefore not suitable for high security applications because it is possible to bypass the

lock by disrupting the power supply. Nevertheless, the strength of today's magnetic

locks compares well with that of conventional door locks and they cost less

than conventional light bulbs to operate. Power supplies incorporating a trickle-charged

lead-acid battery pack can be used to retain security for short-term power outages [7].

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Witura WT-9001 IP65 Spezifikationen Seite 48