Full Bridge Class D Amplifier

590

07:30:58

Full Bridge Class D Amplifier. A triangular wave is compared against the input Signal. The result is a PWM Signal and thereby digitized. The triangular wave usually has a high frequency (e.g. 250kHz). As a result the output Transistors just need to change between "on" and "off" minimizing losses. Due to the high frequency of the PWM signal it's possible to remove the high frequency components with a low-pass(in the simplest case the Speaker itself) and retrieve the amplified input Signal.

The Diodes placed in parallel to the MOSFETs are used to reduce the switch-off time.

The configuration shown is a Full Bridge to increase Power output at a given operating Voltage. The principle is comparable to the H-Bridge used in DC-Motor Circuits

published 7 years ago

Karma247

7 years ago

Very nice. Great description too. 👍

hurz

7 years ago

needs quite a lot more work. Filter is impractical from corner frequency and ringing. mosfets on high side cant be very performante. 250kHz is 4us periode. The diode are actually god given and called body diode you cant get rid. They are part of the mosfets. So all in all it need a lott work to make it perfect. Not talking about missing deadtime control.

Pico8000

7 years ago

Thanks for your Comments. @hurz the circuit just illustrates the concept. With 250kHz the simulation is just painfully slow for me so I choase a lower frequency. The 250kHz are around a freq. commercial ICs would use. Therefor I didnt spended much time designing the filter. If you wanna do so keep in mind, that the Speaker represented as resistor in this circuit is also a complexe impedance. So if you take just the series inductivity into account you end up calculating a 6 element Filter so I rather builded something what kind of worked for just showing the principle. Deadtime controll is not integrated for the same reasons.

Pico8000

7 years ago

You can use the internal Body Diodes as Diodes but with increasing switching speed you may want to use external Shottkys. Internal body diodes are usally bad diodes you get by connecting bulk to source internally. This internal connection is what in fact defines what connection is Source and which is Drain.

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