DatasheetsPDF.com

AN1042D

ON Semiconductor
Part Number AN1042D
Manufacturer ON Semiconductor
Description High Fidelity Switching Audio Amplifiers Using TMOS Power MOSFETs
Published Nov 12, 2013
Detailed Description AN1042/D High Fidelity Switching Audio Amplifiers Using TMOS Power MOSFETs Prepared by: Donald E. Pauly ON Semiconductor...
Datasheet PDF File AN1042D PDF File

AN1042D
AN1042D

Overview
AN1042/D High Fidelity Switching Audio Amplifiers Using TMOS Power MOSFETs Prepared by: Donald E.
Pauly ON Semiconductor Special Consultant http://onsemi.
com APPLICATION NOTE With the introduction of complementary bipolar power transistors in the late 1960s, switching amplifiers became theoretically practical.
At low frequencies, bipolar transistors have switching efficiencies of 99% and will directly drive a low impedance speaker filter.
The requirement for switching frequencies above 100 kHz resulted in excessive losses however.
Bipolar drive circuitry was also complex because of its large base current requirement.
With the advent of complementary (voltage/current ratings) TMOS power MOSFETs, gate drive circuitry has been simplified.
These MOS devices are very efficient as switches and they can operate at higher frequencies.
A block diagram of the amplifier is shown in Figure 2.
An output switch connects either +44 or –44 volts to the input of the low pass filter.
This switch operates at a carrier frequency of 120 kHz.
Its duty cycle can vary from 5% to 95% which allows the speaker voltage to reach 90% of either the positive or negative supplies.
The filter has a response in the audio frequency range that is as flat as possible, with high attenuation of the carrier frequency and its harmonics.
A 0.
05 ohm current sense resistor (R27) is used in the ground return of the filter and speaker to provide short circuit protection.
The negative feedback loop is closed before the filter to prevent instabilities.
Feedback cannot be taken from the speaker because of the phase shift of the output filter, which varies from 0° at dc to nearly 360° at 120 kHz.
Since the filter is linear, feedback may be taken from the filter input, which has no phase shift.
Unfortunately, this point is a high frequency square wave which must be integrated to determine its average voltage.
The input is mixed with the square wave output by resistors R4 and R5 shown in Figure 2.
The resultant signa...


Similar Datasheet


@ 2014 :: Datasheetspdf.com :: Semiconductors datasheet search & download site. (Privacy Policy & Contact)