Burkhard Kainka
About the article

A Zero Current Switch

For inductive Loads

A Zero Current Switch

Relays or contactors are often used to switch AC powered inductive loads such as motors, valves or electro magnets. When the device is switched off an arc can form across the relay contacts as they open. This leads to premature relay failure if measures are not taken to suppress the spark.

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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD members can exclusively download these files for free as part of their membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service.

Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

Component list
R1 = 100 Ohm
R2 = 2.2kOhm
R3,R4 = 47kOhm
R5 = 82kOhm 1%, 0.6W 350V (Vishay MRS25000C8202FCTOO)
R6 = 220Ohm
R7 = 180Ohm
R8 = 68Ohm
R9 = 22kOhm
C1,C3 = 10µF 100V 20%, pitch 2.5mm, diam. 6.3mm
C2 = 10µF 63V, axial, 10 x 4.5mm
D1,D2 = 1N4004
D3 = 1N4007
D4 = BZX79-C13 (13V 05W)
B1 = WO6M, 600V 1.5A
T2..T5 = BC546A
IC1 = PC817 (see text)
PCB # 100270
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