HCPL-7840-360 データシートの表示（PDF） - Avago Technologies

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HCPL-7840-360

Isolation Amplifier

Avago Technologies 

Application Information

Power Supplies and Bypassing

The recommended supply con-nections are shown

in Figure 17. 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-7840 through an RC anti-aliasing filter (R2 and C2).

Although the application circuit is relatively simple, a few

recommendations should be followed to ensure optimal

performance.

The power supply for the HCPL -7840 is most often ob-

tained from the same supply used to power the power

transistor gate drive circuit. If a dedicated supply is re-

quired, 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

POWER

SUPPLY

–

R2

39 Ω

D1

5.1 V

MOTOR

•••

+ R1 –

RSENSE

HV–

•••

C1

0.1 µF

C2

0.01 µF

HCPL-7840

Figure 17. Recommended supply and sense resistor connections.

14

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