HCPL-7800 View Datasheet(PDF) - Avago Technologies

Part Name

Description

Manufacturer

HCPL-7800

Isolation Amplifer

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 ap-

plications 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-

7800(A) 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 -7800(A) 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 ad-

ditional 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

-

MOTOR

***

+ R1 -

RSENSE

D1

5.1 V

R2

39 Ω

C1

0.1 µF

C2

0.01 µF

***

HV-

Figure 17. Recommended Supply and Sense Resistor Connections.

HCPL-7800

13

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