8. DC Chopper

For AC, there is a straightforward and almost lossless way to transfer electrical energy from one (voltage) level to another level, i.e. the classical electromagnetic transformer. For DC such a standard solution is not available. Energy transfer from a higher to a lower level is indeed possible using a resistance network, but this comes at the expense of high losses. The chopper is an elegant power-electronic solution that does not lead to any significant losses. Starting from a fixed DC voltage, it adapts the load voltage by periodically switching the input DC voltage (or current), and as such adapting the average load voltage. Two advantages are that some chopper circuits also allow energy transfer to a higher voltage level, and that the chopper principle eases electronic control. Another way to control the average current is by using periodic switching of a series resistor, but this method is not energy-efficient. For low-power applications (e.g. telecommunications, computer power supply), yet another alternative using resonant circuits is quite common (see Sect. 8.5). In the first section, the basic chopper circuits will be discussed. The next section shortly discusses the power-electronic switches used in choppers. In other sections, chopper applications in traction and DC drives are illustrated. The final section gives a brief overview of the principles of resonant chopper circuits.