Figure 35. Low Side dc Switch

A low side switch has a much simpler gate drive so it should be used whenever possible. The IR series of SmartFET devices (IR30XX) offer protection against over current, over temperature, and electro-static discharge. SmartFETs can also be driven directly from logic ICs.

IR manufactures many logic level HEXFET® power MOSFETs in voltages 200V and below. These logic level devices are capable of being driven directly from standard logic ICs, thus making the gate drive design very simple. They are typically used in applications where the HEXFET is used in a switching function, and not in an energy conversion function, such as in a power supply. The crossover to using IGBTs as dc switches usually occurs around 250V. Standard speed IGBTs offer the highest efficiency at higher voltages.

Figure 36. Output Rectification: Singled Ended

Common cathode is the most common output rectifier configuration and can be made up of single discretes or modules, or common cathode discretes or modules.

Reverse recovery is critical. Always a high frequency circuit, it usually requires the ultrafast switching characteristics of Schottky and HEXFRED® rectifiers. Schottkys range from 150 volts and under, HEXFREDs from 400 to 1200 volts. For under 8 amps and between 150 and 400 volt requirements, the IR line of ultrafast rectifiers works best.

A hot spot for Schottkys is in 3-volt dc outputs. IR offers 15-volt devices manufactured using its highly efficient "OR-ing" Schottky process. For small, lower power converters, the 1-amp, 15-volt 10BQ015 is ideal. The 30BQ015 is best in applications up to 10 watts.

Figure 37. Output Rectification: Double Ended

Figures 36 and 37 show the output section for a bridge or push pull configuration. The considerations for the double-ended configuration are the same as for the singled ended configuration.