Agilent Technologies 90B manual Summary of Basic Switching Regulator Configurations

catch diode) was not required in the two transistor regulators of Figures 10 and 11 because of their full-wave rectifier configuration.

Another item not found in the previous regulators is "flyback" diode CRF. This diode is connected to a third transformer winding which is bifilar wound with the primary. During the off periods of the switch, CRF is forward biased, allowing the return of surplus magnetizing current to the input filter, and thus preventing saturation of the transformer core. This is an important function because core saturation often leads to the destruction of switching transistors. In the previously described two transistor push-pull circuits, core saturation is easier to avoid because magnetizing current is applied to the core in both directions. Nevertheless, matched switching transistors and balancing capacitors must still be used in these configurations to ensure that core saturation does not occur.

Figure 12. Single Transistor Switching Regulator

Summary of Basic Switching Regulator Configurations

Figure 13 shows three basic switching regulator configurations that are often used in today’s power supplies. Configuration A is of the push-pull class and this version was used in the switching supplies shown in Figures 10 and 11. Other variations of this circuit are used also, including two-transistor balanced push-pull and four transistor bridge circuits.

As a group, push-pull configurations are the most effective for low-voltage, high-power and high performance applications. Push-pull circuits have the advantage of a ripple frequency that is double that of the other two basic configurations and, of course, output ripple is inherently lower.

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