Powerful 2x50 W pulse ULF class D. Scheme, description

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Powerful 2x50 watt pulse ULF class D. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Transistor power amplifiers

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Philips TDA8920

TDA8920 contains two independent ULFs with a power of 50 W each, characterized by high efficiency (at least 90%), low non-linear distortion and current consumption. The IC can be configured as

- monophonic ULF bridge with a maximum output power of 190 W, fig. one
- 2x50 W stereo amplifier, fig. 2.

(click to enlarge)

In both cases, an 8 ohm load is implied. Each of the amplifiers has differential inputs.

Amplifiers can operate in three modes, controlled by the potential of U17 at pin 17 relative to the common wire (MODE):

- energy saving (Standby, 0< U17 <1V). Typical current consumption in this mode is 0,2 μA
- mute (Mute, 2V < U17 < 3V). The amplifier is in working condition, but there is no sound signal at the output.

Typical current consumption is the same as the current in silent mode and does not exceed 50 mA
- normal operation (On, 4V < U17 < 5,5V).

To eliminate the "pop" when turned on, the amplifier is forcibly held for about 500 ms in the muting mode, during this time all transients of the capacitor charge end.

At the output of the IC, a PWM voltage is generated with a repetition frequency of 500 kHz, the average value of which corresponds to an analog audio signal. Passive second-order LC low-pass filters suppress the carrier frequency in such a way that almost pure sound voltage arrives at the speaker system. The generation frequency is set by an external resistor Rosc connected between the OSC and SGND pins and can be estimated using the formula Fosc=5*10^9/Rosc. Synchronous operation of several microcircuits at the same frequency is provided, for this it is enough to connect the OSC terminals of all parallel-operating ICs (they have a voltage with an amplitude of 1,75 V from peak to peak).

The IC has three built-in protection systems

- from overheating (when the transition temperature Tj > 150 degrees C, it automatically switches to the muting mode until cooling)
- from static electricity (model "man" - 3000 V) all conclusions are protected
- against current overload and output short circuit. The maximum "default" output current is 7A and can be reduced to the value lo(max)=7*10^4/(10^4+Rlim), [A] by an external resistor Rlim (see fig. 1 and fig. 2 ).

The main parameters:

- supply voltage ±15...±30 V
- gain 36 dB (mono-bridge), 30 dB (stereo)
- input impedance > 80 kOhm
- output noise voltage < 100 µV
- supply voltage ripple suppression factor > 60 dB
- separation between channels > 50 dB
- maximum power dissipation 60 W
- zero offset voltage at the output < 50 mV
- harmonic distortion 0,1% (1 kHz), 0,2% (10 kHz, 1 W)

Powerful 2x50 watt pulse ULF class D

The TDA8920 is available in two designs - 17-pin SOT243 (TDA8920J, fig. 3) and 20-pin SOT418 (TDA8920TH, fig. 4) for surface mounting, both shown on the right in actual size. Recommended applications are ULF high-quality TVs, Home Theater systems, and multimedia systems.

Publication: cxem.net

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