TDA2050

14/18

Doc ID 1461 Rev 3

Appendix A

A.1

Music power concept

Music power is (according to the IEC clauses n.268-3 of Jan. 83) the maximum power which

the amplifier is capable of producing across the rated load resistance (regardless of non-

linearity) 1 sec after the application of a sinusoidal input signal of frequency 1 kHz.

According to this definition our method of measurement comprises the following steps:

●

Set the voltage supply at the maximum operating value

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Apply a input signal in the form of a 1 kHz tone burst of 1 sec duration: the repetition

period of the signal pulses is 60 sec

●

The output voltage is measured 1 sec from the start of the pulse

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Increase the input voltage until the output signal shows a THD=10%

●

The target of this method is to avoid excessive dissipation in the amplifier.

A.2

Instantaneous power

Another power measurement (maximum instantaneous output power) was proposed by the

IEC in 1988 (IEC publication 268-3 subclause 19.A). We give here only a brief extract of the

concept, and a circuit useful for the measurement. The supply voltage is set at the maximum

operating value.

The test signal consists of a sinusoidal signal whose frequency is 20 Hz, to which are added

alternate positive and negative pulses of 50 µs duration and 500 Hz repetition rate. The

amplitude of the 20 Hz signal is chosen to drive the amplifier to its voltage clipping limits,

while the amplitude of the pulses takes the amplifier alternately into its current-overload

limits. A circuit for generating the test signal is given in Figure 22.

The load network consists of a 40 µF capacitor, in series with a 1 ohm resistor. The

capacitor limits the current due to the 20 Hz signal to a low value, whereas for the short

pulses the effective load impedance is of the order of 1 ohm, and a high output current is

produced.

Using this signal and load network the measurement may be made without causing

excessive dissipation in the amplifier. The dissipation in the 1 ohm resistor is much lower

than a rated output power of the amplifier, because the duty-cycle of the high output current

is low. By feeding the amplifier output voltage to the Xplates of an oscilloscope, and the

voltage across the 1 ohm resistor (representing the output current) to the Y=plates, it is

possible to read on the display the value of the maximum instantaneous output power.

The result of this test applied on the TDA2050 is:

Peak power = 100 W typ