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Table 5.3
Inductor Value vs. Application
Application Network
Impedance
@130kHz
Inductor Impedance
@130kHz
Inductor Value
Single building AC mains
1-20 Ohms
≥
100 Ohms
≥
120µH
Dedicated cable
≤
100 nodes
≤
100m
50-100 Ohms
≥
500 Ohms
≥
680µH
Dedicated cable
>100 nodes
>100m
50-100 Ohms
≥
2000 Ohms
≥
2.4mH
There is one further constraint on the value of the inductor. When the inductor is combined
with the input capacitance of the switching supply, the LC resonant frequency should be at
least one octave away from the communication frequency range (110 kHz-140kHz). The
unintentional series resonance between the inductor's reactance and the power supply's
capacitive reactance can produce a low impedance at communication frequencies if this
frequency range is not avoided.
One way to reduce the size and cost of an inductor used to raise a power supply's input
impedance is to purposefully parallel resonate it at the communication frequency with a
capacitor, as shown in figure 5.6. If this option is chosen, resistive damping must be
included so that impulsive power line noise does not excite excessive filter ringing, which
could degrade the reception of weak signals. The 330 Ohm parallel, and 3.3 Ohm series,
resistor values have been selected to optimize receive impedance and impulsive noise
damping. Note that even though only a 100µH inductor is shown in figure 5.6, a series
impedance of
≥
200 Ohms from 125kHz to 140kHz is maintained due to the parallel resonant
effect. Also, note that the inductor must be rated for the peak AC current drawn by the
power supply; the 3.3 Ohm resistor should have a power rating consistent with the AC
current drawn by the power supply, and its voltage drop should be verified as acceptable.
Coupling
Circuit
PLT-22
Txcvr
Neuron
Chip
Power
Mains
Switching
Power
Supply
330ž ±5% 1/4W
3.3ž ±5%, 1/2W,
wire wound or carbon
composition
0.015µF ±10%
100µH ±10%
Figure 5.6
Reducing Attenuation Caused by a Switching Power Supply with a
Resonant Circuit
L
ON
W
ORKS
PLT-22 Transceiver's User Guide
5-11
Содержание LONWORKS PLT-22
Страница 6: ...iv Echelon...
Страница 14: ...1 8 Introduction...
Страница 67: ...LONWORKS PLT 22 Transceiver s User Guide 5 7 Figure 5 3 Capacitor Input Power Supply Schematic...
Страница 92: ...6 10 Design and Test for Electromagnetic Compatibility...
Страница 110: ...7 18 Communication Performance Verification...
Страница 114: ...8 4 References...
Страница 118: ...A 4 Appendix A...