Specifications

Chapter 5 – Power Supplies for PL Smart Transceivers
158 PL 3120/PL 3150/PL 3170 Power Line Smart Transceiver Data Boo
k
Energy Storage Capacitor-Input Power Supplies
A particularly cost-effective example of an energy storage power supply is the capacitor-input power supply. The
most attractive feature of this supply is that both the V
A
and V
DD5
supplies can be built with just a few components
for approximately US$1.00.
Figure 5.2 illustrates the operation of a capacitor-input power supply. As shown in the figure, a capacitor in series
with the AC mains causes AC current to flow through a zener diode, which acts as a shunt regulator. This regulator is
selected to limit the V
A
supply voltage to ≤16V. An energy storage capacitor is connected across the shunt regulator
to provide current capacity required for transmission. Note that unused source current flows through the shunt
regulator. This maximizes the zener diode temperature when the supply load is at a minimum. Because the regulation
voltage of a >10V zener diode has a strong positive temperature coefficient, a pair of forward-biased silicon diodes,
which have negative temperature coefficients, have been added in series with a slightly lower-voltage zener diode.
Note that this type of capacitor-input power supply would inherently attenuate communication signals, due to its low
impedance, if not for the addition of a series inductor, as shown in Figure 5.2
.
Figure 5.2 Capacitor-Input Power Supply Theory of Operation
Due to the low available current, the use of capacitor-input power supplies is generally limited to PL 3120 and PL
3170 based devices which require minimal I/O and application current (e.g., latching relays, SCR triggers, low-
power LEDs). Figure 5.3 presents a schematic for a C-band device based on a PL 3120 or PL 3170 Smart
Transceiver IC powered by a capacitor-input power supply. Figure 5.4 shows the A-band version. These devices are
designed to operate with an enclosure internal air temperature range of 0-70°C.
The C-band versions provide enough stored energy to transmit a 92.2ms packet under worst-case conditions prior to
recharging. The A-band option provides sufficient stored energy to transmit one complete 140.7ms packet under
worst-case conditions prior to recharging. Under typical conditions, the C-band and A-band versions support a
maximum transmit duty cycle of ≥65%. Under worst-case conditions, they each support maximum transmit duty
cycles of ≥10%. Note that the use of any of these capacitor-input power supply options requires that the
configuration data of the device be programmed to enable power management, as described in Chapter 8.
Energy
Storage for
Transmission
Current
Source
Shunt
Regulator
Output
Voltage
AC Line
Voltage
V
A (8.5V-16V)
V
DD5 (5V)
78L05
AC Line
Voltage
78L05
Raise Input Z
Partial
Temperature
Compensation
V
Input Capacitor
(5V)
DD5
V
(8.5V - 16V)
A