Application Information
Power Supplies and Bypassing
The recommended supply
connections are shown in Figure 16.
A floating power supply (which in
many applications could be the
same supply that is used to drive
the high-side power transistor) is
regulated to 5 V using a simple
zener diode (D1); the value of
resistor R4 should be chosen to
supply sufficient current from
the existing floating supply. The
voltage from the current sensing
resistor (Rsense) is applied to the
input of the HCPL-7520 through
an RC anti-aliasing filter (R2 and
C2). Although the application circuit
is relatively simple, a few recom-
mendations should be followed
to ensure optimal performance.
The power supply for the
HCPL -7520 is most often
obtained from the same supply
used to power the power
transistor gate drive circuit. If a
dedicated supply is required, in
many cases it is possible to add
an additional winding on an existing
transformer. Otherwise, some
sort of simple isolated supply can
be used, such as a line powered
transformer or a high-frequency
DC-DC converter.
An inexpensive 78L05 three-terminal
regulator can also be used to
reduce the floating supply voltage
to 5 V. To help attenuate high-
frequency power supply noise or
ripple, a resistor or inductor can be
used in series with the input of the
regulator to form a low-pass
filter with the regulator’s input
bypass capacitor.
HV+
GATE DRIVE
CIRCUIT
+
FLOATING
POSITIVE
SUPPLY
-
R4
R2
MOTOR
39
Ω
+ R1 -
R
SENSE
D1
5.1 V
C1
0.1 µF
1 V
DD1
2 V
IN+
C2
0.01 µF
3 V
IN-
4 GND1
HCPL-7520
HV-
Figure 16. Recommended supply and sense resistor connections.
10
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