|
| Class "D" |
| Class D topology MOSFETS devices outputs
work as full ON/OFF, non linear switches. The heart of the system is
the comparator, where a high frequency triangle wave form is
compared to the input signal level, resulting a square wave out at
high frequency switching, when input signal is cero, Output
switching frequency is 50% duty cycle = output RMS = 0V (like zero
input signal). when input signal increase Pulse width Modulation
increase or decrease as well in the positive or negative region.
this topology some designers called PWM amplifier (Pulse width
Modulation). The switching output is called the "Carrier",
the comparator is the modulator, and the output filter is the
"Demodulator". LC filter removes the HF content or
carrier, leaving only the audio output. (and some switching noise
residuals) |
| Advantages |
| Significantly higher efficiency 80% to
90% depending upon components used, little or not heat sink required
(in comparison of class A/B |
| Disadvantages |
| Class D amps are a lot more complex
than class A/B, and requires extensive shielding and filtering, and
a phase lag compensation for stability. Power bandwidth is limited
by switching frequency and demodulator filter, usually more
expensive than class A/B at power levels below 100Watts |
| Conclusions and
comments |
| Class D topology widely used in
subwoofer amplifiers due to the limit bandwidth and high power
required to drive music Bass frequencies |
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