Class D Amplifiers are known for their high efficiency and high power levels compared to conventional amplifiers.
In this project another unique property has been demonstrated: an excellent sound-quality, even better than most class-AB-amplifiers.
This feature made this amplifier a good choice for critical audio-listeners who don't like the huge heat and power-consumption of class-A.
The amplifier presented here is designed for high powers, but with the right supply and impedance it can be dimensioned for lower powers more applicable for smaller rooms, without reducing its quality. You do not need to upgrade your high-end loudspeakers. |
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The Class D Amplifier LPC1 is
developed by
Rebix Electronics
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Operation
The operation of Class D amplifier is complete different to Class A and AB or B.: In a Class D power is generated by modulating the duty-cycle ratio of a constant frequency square-wave signal from a switching converter. This square-wave or PWM-signal is amplified with logic gates and power-switches. The duty-cycle ratio results in a low-frequency-component (after filtering) with the same maximum power-level in respect to supply-voltage as Class A or B, but with a efficiency of >90%.
Power-efficiency
Well known is the power efficiency of a class B; with a sine-wave at full power it delivers about 70 % of the supply-power, With a square-wave this rises to 100% and a full-power triangle-or saw-tooth -signal results in just 50 % efficiency. These kind of signals are common in AC-line-regulators, Power-supplies and CRT-deflection-units, but not in most music. At signal levels lower than the maximum level, the power-efficiency drops proportionally to zero.
In music signals the ratio between the peak level and the average (RMS-) level is 20 dB or more (the sound from commercial radio stations excepted) so the average power-efficiency off a class B amplifier will mostly not exceed 5-10 percent.
A Class D amplifier has theoretically no energy-loss. Current drawn 90 degrees out of phase with output voltage (by complex loads like loudspeakers near their resonance-frequency) needs no power at all, in contrast to conventional amplifiers.
Mostly used for power-audio is Class G or H because of the higher efficiency than class A or B at an Ohmic load. At a complex load however these amplifiers do still dissipate power greater than output-power, in contrast to class D. Class G and H power amplifiers still need fans for removing heat and collecting dust. The LPC1 can deliver power to 1 or 2 kW without fans.
A digital amplifier ?
The LPC1 is not a digital amplifier. In the LPC1 the pulse-width of the PWM-signal is essentially generated linear, which gives the possibility for extra fast feedback from the analog output to the PWM-modulator, removing the distortion. In some really "digital amplifiers" the PWM-signal is converted completely digital, where a fast feedback is not possible, resulting in more distortion.
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