10

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.

Figure 16. Recommended supply and sense resistor connections.

+

-

MOTOR

HV-

HV+

GATE DRIVE

CIRCUIT

GND1

HCPL-7520

C1

0.1 µF

C2

0.01 µF

R2

39

Ω

R4

D1

5.1 V

+

-

1

2

3

4

R1

FLOATING

POSITIVE

SUPPLY