Mutually supplementary gain control circuit

Abstract

The invention discloses a complementary gain control circuit applied to a class D audio power amplifier, comprising a voltage dividing unit, a first comparing unit, a ramp wave generating unit, and a second comparing unit through all of which the duty ratio can be adjusted according to the differential voltage of high voltage and low voltage so that the power gain loss can be made up and class D audio power amplifier in different voltage still can keep fixed output power or power gain.

Description

technical field [0001] The invention relates to a complementary gain control circuit, in particular to a circuit capable of maintaining a fixed output power or power gain of a Class D audio power amplifier under different power supply voltages. Background technique [0002] The working principle of the class D audio power amplifier is to use the audio signal to modulate the carrier, so that the output signal is a PWM (PulseWidthModulation) switching signal, so when the input voltage is zero voltage, the PWM duty cycle (dutycycle ) is 50%, and when the input voltage is a positive voltage, the duty cycle is greater than 50%, and if the input voltage is a negative voltage, the duty cycle is less than 50%. The voltage is the power supply voltage, and its low voltage is zero voltage, so when the PWM signal has a fixed modulation ratio (that is, a fixed duty cycle), the output power will drop as the power supply voltage drops; [0003] The current customary open-loop (open-loop) ...

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Problems solved by technology

[0003] The current customary open-loop (open-loop) class D audio power amplifier, as mentioned above, when a fixed input signal (that is, a fixed duty cycle), its output power drops with the drop of the power supply voltage. The overall power gain of the power amplifier also decreases with the decrease of the power supply voltage, so when the class D amplifier uses battery power, the power gain of the amplifier will decrease with the decrease of the battery voltage, and when the output power drops to a certain level At this time, it is often mistakenly thought that the battery power is insufficient and the battery should be replaced. At this time, if the battery still has power, it will cause waste of the battery. In order to make good use of the battery power or maintain a stable volume output, the Class D audio amplifier needs to have Stable power gain;

[0004] Generally, Class A and B audio power amplifiers use a negative-feedback method, that is, a closed-loop method, so that the voltage gain does not change with the power supply voltage to achieve stable output power. For Class D power amplifiers, the negative feedback circuit will be relatively complicated if the closed-loop method is used. This is because the output signal of the Class D amplifier is a PWM switching signal, which contains extremely high harmonics, and, in order to be able to extract The audio signal is used for feedback, and its unnecessary high-frequency harmonics must first be filtered by a low-pass filter, which causes problems such as increased cost, high-frequency harmonic interference, and increased difficulty in circuit layout (layout);

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