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Class D amplifier circuit

Class D amplifier circuit

Class D amplifier is a type of amplifier where the power devices (MOSFET or transistor) are operated as switches. There will be only two states (ON/OFF) for these switches and no time is wasted for the transition from one stage to another. The working of a class D amplifier is as follows. At first the audio signal to be amplified compared with a high frequency triangle waveform and the result will be a square wave whose duty cycle is proportional to the input audio level. This square wave is then fed to the gate of the switching element (MOSFET) for power amplification. The then the audio signal is retrieved from the amplifier square wave using an LC filter. The LC filter filters off the high frequency switching components from the square wave the amplified audio signal will be available at its output. To know more about class D amplifier read this article: Class D power amplifier. The main advantage of class D amplifier are high efficiency (up to 95%), smaller size (small heatsinks are required for the switching element because of the low power wastage) , low cost (due to the smaller heatsinks and transformers).

BD5460 class D amplifier IC.

D5460 is a low power Class D amplifier that can be used in low power applications like handheld audio devices. BD5460 does not require an LC filter at the speaker output and can be driven using a battery, The standby current of BA5460 is typically zero and there is no switch ON / OFF clicks. The BD5460 can deliver 0.8 watts into an 8 ohm speaker at 3.6 V supply voltage. The power supply voltage range is from 2.5 to 6.5 V DC. The IC has a built-in standby function, short circuit protection, thermal shutdown and under voltage lockout.


Two class D amplifier circuits using BD5460 are shown below. The first one is a differential input class D amplifier while the second one is a single ended input class D amplifier. The 0.1uF capacitors (C1, C2, C3 and C4) are input DC decoupling capacitors. The lower cut off frequency of the amplifier depends on these capacitors. 10uF capacitors (C5 and C6) are the power supply filters. S1 and S2 are the shutdown switches. Connecting the C1 pin to the high logic will make the IC active and connecting the C1 pin to ground will put the Ic into shutdown mode.

Circuit diagram

stereo amplifier circuit BA5417