User Guide

4 System Design
4.1 BA390X lamps
BA390X panel lamps draw a current of between 18 and
22mA when their terminal voltage is between 14 and
30V. If the terminal voltage falls below 14V, the current
consumed and the lamp brilliance are reduced.
There are three design steps:
1. Select a Zener barrier, galvanic isolator or certied
voltage source with output safety parameter equal
to or less than the BA390X maximum input
parameters i.e.
Uo = 30V dc
Io = 159mA
Po = 1.2W for gas hazards
0.683W for dust hazards
2. Ensure that the cable capacitance and inductance
are less than the maximum gures specied by
the intrinsic safety certicate for the device
powering the lamp(s).
3. Ensure that the voltage across the BA390X
terminals is equal to or greater than 14V.
Fig 3 shows a simple application in which a single BA390X
lamp is powered by a Zener barrier. The lamp may be
turned on and off by switching the power supply on and
off, or by a switch in series with the lamp in the safe area.
The lamp may also be controlled by an IP20 protected
manually operated switch in the hazardous area.
BA390X
Barrier
Single channel 28V 93mA
300 Zener barrier
Hazardous area Safe area
Power
supply
Optional
mechanically
operated switch
Fig 3 BA390X powered from a Zener barrier
Considering the voltage drops
Minimum operating voltage of BA390X 14.0V
Maximum voltage drop caused by barrier 7.3V
(22mA x 330*)
Maximum voltage drop caused by cables 0.2V
(22mA x 10 cable resistance) _____
21.5V
* maximum end-to-end resistance of barrier
The power supply must therefore have an output of greater
than 21.5V but less than the maximum operating voltage
of the Zener barrier, which is typically 26.5V.
Alternatively a BA390X lamp may be powered from a
galvanic isolator which can power two lamps in parallel as
shown in Fig 4.
BA390X
Hazardous area Safe area
Galvanic
isolator
21.4V
158
Optional
mechanically
operated switch
BA390X
Fig 4 Two lamps powered by a IIB galvanic isolator
Considering the voltage drops when powering two BA390X
lamps in parallel.
Open circuit voltage of galvanic isolator 21.4
Less maximum voltage drop caused by isolator 6.9
(44mA x 158*)
Less maximum voltage drop caused by cables 0.4
(44mA x 10) _____
Voltage at BA390X lamps 14.1V
* maximum output resistance of galvanic isolator
4