Electrical Power Transfer with “No Wires” - Energy Harvesting Autonomous Sensor Systems - page 190

MAX 666
SENSE

C
1 uF

R1
27.5 K

V IN

N4148

V OUT2

R4
150 K

SHDN

C1
47 uF

Q1

V SET

GND

Core

Z1
6.2 V
1N4738A

C
33 uF

R3
940 K

AC

R5
100 K

R2
6.75 K

Inductive Energy
Tr ansfer Core

Voltage
Doubler
(Single Stage)

Q2

Power Storage and Supply Circuit

Linear Regulator

HT12E

A0
A1
A2
A3
A4
A5
A6
A7
VSS

VDD
DOUT
OSC1
OSC2
/TE
AD11
AD10
AD9
AD8

AM-RT4-433FR

750 K

V cc
GND

ANT

IN

RF Load

FIGURE 6.9
Schematic drawing of the magnetic energy harvesting system.

throughout the discharge of C1. When the voltage across C1 dropped below
around 4 V, the voltage drop across R3 caused Q1 to turn off and hence in
turn deactivated Q2 from the latched stage. When this happened, the ground
lines of MAX666 and AM-RTFQ1-433 were disconnected from C1, and the
discharge of C1 was stopped. As the secondary coil of the transformer con-
tinued to induce V emf to the voltage doubler and increased the voltage on C1,
the cycle started again.

6.1.3 Experimental Results

An experimental platform, which consisted of a 220/230 V ac power supply
connected to a bank of load resistances of 60 , was set up as shown in

Figure 6.10 to emulate the electrical current of 1 to 4 A flowing in the power
line [167]. Since the primary side power line was AC, the induced emf would
be AC voltage. This experimental setup was used as a testing platform to
evaluate the performance of the magnetic energy harvesting system.
Figure 6.11 shows the waveforms of the induced AC voltage V emf output
of the stray magnetic energy harvester and the output DC voltage of voltage
doubler circuit. It can be observed that the induced voltage signal is a distorted
sinusoidal wave rather than a smooth sinusoidal wave. The reason for this
phenomenon may be due to the magnetic hysteresis effect and the magnetic
saturation of the toroid core.