CAPZero Family
Safety
CAPZero meets safety requirements even if placed before the
system input fuse. If a short-circuit is placed between D1 and
D2 terminals of CAPZero, the system is identical to existing
systems where CAPZero is not used.
X Capacitor
R1
With regard to open circuit tests, it is not possible to create a
fault condition through a single pin fault (for example lifted pin
test) since there are two pins connected to each of D1 and D2.
If several pins are lifted to create an open circuit, the condition
is identical to an open circuit X capacitor discharge resistor in
existing systems where CAPZero is not used. If redundancy
against open circuit faults is required, two CAPZero and R1 / R2
configurations can be placed in parallel.
Discharge Operation
To meet the safety regulations, when the AC supply is
disconnected, CAPZero will discharge the X capacitor to the
safety extra low voltage (SELV) levels according to the above
functional description. Although there are no specific safety
requirements below SELV, CAPZero still continues the discharge
until the X capacitor is fully discharged. As such CAPZero can
be safely used at low input voltages such as the common
industrial 18 VAC and 24 VAC supply rails while retaining X
capacitor discharge when the AC source is disconnected.
R2
≥4
mm
PI-5610-041310
Figure 4.
Typical PCB Layout.
4
Rev. D 11/11
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