AN1013 Просмотр технического описания (PDF) - STMicroelectronics

Номер в каталоге

Компоненты Описание

производитель

AN1013

MONO CLASS_D AMPLIFIERS

STMicroelectronics 

AN1013 APPLICATION NOTE

To verify the linearity of the inductor, it’s suggested to verify that the inductance change versus load cur-

rent be less or equal than 10%.

Also the harmonic distortion is affected by the coil material.

The suggested coil materials are:

a) Ferrites: Gapped ferrites are suitable for this kind of application because they allow to counter fre-

quency heating and distortion problems.

The shapes of the coil we suggest are E cores, RM and PM. The Ferrite material to use could be one of

the following or others with similar characteristics ( see the producers technical sheets for the details):

THOMSON - LCC : B50, B51

SIEMENS

: T26, N27

PHILIPS

: 3C8

TDK

: H7C1, H5B2, H7A

A cheap Ferrite solution consists of Radial Lead Inductors that are easy to find already wound (i.e

TDK, Ferroxcube...). These inductors offer a good compromise in terms of features and cost but its im-

portant to verify the max. rated DC current they can sustain .

b) Molypermalloy (Magnetics): This is the coil we mount in our application board, due to the Toroidal

shape that improves the RFI characteristics of the application.

This material, however, shows a little worse (though neglegible for this application) behaviour in terms of

losses due to hysteresis, has the advantage of the distributed gaps that significantly lower the effective

permeability and increases the energy storage capability reducing also the radiated magnetic field as a

result of the elimination of the discontinuity associated with discrete air gap.

c) Ferrite powder cores: although also these material could be used for this kind of application it shows

the worse behaviour in terms of heating and losses.

A.2) Selecting supply filter capacitors:

Referring to the application note section B results that the factors to take in account for the electrolytic fil-

ter capacitors selections concern:

- RMS ripple current rating

- Ripple voltage

- Voltage rating

- ESR

Considering these factors the electrolytic filter capacitors would show electrical characteristics as follows

(for Vcc = +/-20V, Pout >20W):

- Rated voltage 50V

- Rated current > 1A

- Impedance at 20C/f = 100KHz < 100mΩ

12/13

Share Link: