6.14 HIGH BREAK OUTPUT RELAY BOARD
Figure 29: High Break relay output board
A High Br
eak output relay board is available as an option. It comprises four normally open output contacts, which
are suitable for high breaking loads.
A High Break contact consists of a high capacity relay with a MOSFET in parallel with it. The MOSFET has a varistor
placed across it to provide protection, which is required when switching off inductive loads. This is because the
stored energy in the inductor causes a high reverse voltage that could damage the MOSFET, if not protected.
When there is a control input command to operate an output contact the miniature relay is operated at the same
time as the MOSFET. The miniature relay contact closes in nominally 3.5 ms and is used to carry the continuous
load current. The MOSFET operates in less than 0.2 ms, but is switched off after 7.5 ms.
When the control input is reset, the MOSFET is again turned on for 7.5 mS. The miniature relay resets in nominally
3.5 ms before the MOSFET. This means the MOSFET is used to break the load. The MOSFET absorbs the energy
when breaking inductive loads and so limits the resulting voltage surge. This contact arrangement is for switching
DC circuits only.
The board number is:
● ZN0042 001
High Break Contact Operation
The following figure shows the timing diagram for High Break contact operation.
P64x Chapter 3 - Hardware Design
P64x-TM-EN-1.3 61
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