It is not primarily in their power handling capacities.
While power management IC's in mobile sets working on Power Electronic principles are
meant to handle only a few milliwatts, large linear audio amplifiers are rated at a few thousand
watts.
The utilisation of the Bipolar junction transistor, Fig. 1.2 in the two types of amplifiers best
symbolises the difference. In Power Electronics all devices are operated in the switching mode -
either 'FULLY-ON' or 'FULLY-OFF' states. The linear amplifier concentrates on fidelity in
signal amplification, requiring transistors to operate strictly in the linear (active) zone, Fig 1.3.
Saturation and cutoff zones in the VCE - IC plane are avoided. In a Power electronic switching
amplifier, only those areas in the VCE - IC plane which have been skirted above, are suitable. Onstate
dissipation is minimum if the device is in saturation (or quasi-saturation for optimising
other losses). In the off-state also, losses are minimum if the BJT is reverse biased. A BJT switch
will try to traverse the active zone as fast as possible to minimise switching losses.
An example illustrating the linear and switching solutions to a power supply specification will
emphasise the difference.
Version 2 EE IIT, Kharagpur