Brochure/Catalogue

DC output:
For the control of DC voltage switching and control devices,
a switching amplier for switching the DC voltage is
connected downstream of the optocoupler (bipolar transistor
or MOSFET). For DC outputs, the specied polarity must be
observed.
2-pole DC outputs can be used as both positive and
negative switching outputs unless otherwise specied.
The abbreviations NPN (negative switching output) or PNP
(positive switching output) are often used for these terms.
With the 3-pole DC connection, the output circuit is provided
with an auxiliary voltage which is used for more precise
control of the amplier transistor.
Some applications also require this auxiliary voltage for very
fast switching, e.g. of very high frequencies. These outputs
are often only positive switching (PNP) or negative switching
(NPN) outputs and cannot do both. This is then specied in
the instruction sheet or in the data sheet for the respective
product.
Bipolar transistor (for DC outputs)
For use at low currents (≤ 0.5 A) due to having a higher
power loss than MOSFETs. However, cheaper than
MOSFETs.
MOSFET (for DC outputs)
For use with load currents.
The low contact resistance of the MOSFET generates only
very low power loss. Furthermore, a MOSFET output has
only very small leakage currents (< 10 μA).
AC output:
For the control of AC switching and control devices,
a switching amplier for switching the AC voltage is
connected downstream of the optocoupler (TRIAC or
thyristor).
Switch-on behaviour of an AC output:
Most solid state relays with triac or thyristor outputs are zero-
voltage switching outputs. This means that once a control
signal has been applied at the input, they switch on at the
next zero crossing of the AC voltage at the output. However,
this behaviour makes these outputs relatively slow in their
switch-on behaviour (up to 10 ms delay time at 50 Hz mains
frequency of the switched voltage).
To improve this, some AC outputs have an instantaneous
switching output. These outputs switch on as soon as
possible after a control signal is applied to the input (<0.1
ms). However, depending on the phase position, this can
cause high current peaks when switching on, and can cause
the electromagnetic interference emissions in the system to
increase.
Switch-off behaviour of an AC output:
Semiconductor outputs for AC voltages with triac or thyristor
all switch off at the next zero crossing of the output current
once the control signal has been removed at the input. As a
result, they cannot be used for switching DC voltages.
Thyristor (for AC outputs)
For use with load currents.
The function of a thyristor is comparable to that of a one-way
diode. For alternating currents, an anti-parallel connection of
two thyristors is therefore used.
Triac (for AC outputs)
For use with load currents.
A TRIAC combines the functional principle of anti-parallel
connected thyristors in a single component.
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Technical appendix/Glossary
W.92737920000
Solid-state relays – Overview