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3-3. Applications of SBDs

SBDs are used for applications requiring low forward voltage (V_F) and short reverse recovery time (t_rr).

Rectification on the secondary side of a power supply circuit
SBDs are used for rectification on the secondary side of various step-down voltage converters such as flyback, forward, push-pull, half-bridge, and full-bridge converters. SBDs pass electrical power while they are conducting. Therefore, when an SBD is on, a power loss occurs because of a voltage drop equal to its forward voltage (V_F). An SBD also suffers a large switching loss during a reverse recovery time (t_rr), i.e., during a transition from the on-state to the off-state. SBDs with low V_F and low t_rr are ideally suited for converter applications where the voltage applied to an SBD on the secondary side is lower than its maximum rated reverse voltage (V_R).

Our website provides videos describing the operations of these converters:

[e-Learning] DC-DC Converter - Basics of Switching Power Supplies (6)
[e-Learning] Resonant Half Bridge Converter - Basics of Switching Power Supplies (7)

Reverse-connection protection
A diode is inserted in series with a power line when there is a possibility that the user of a mobile device might place a charger or a battery in the wrong direction. When a diode is connected in the right direction, a voltage drop that occurs across the diode causes a power loss. A low-VF SBD is the ideal choice when the voltage across a reverse-connected SBD is lower than its VR.

Figure 3-3 Reverse-connection protection

IC protection
Some ICs have a maximum input voltage rating of GND-0.3 V to VDD + 0.3 V. A low-V_F SBD is the ideal choice when its input voltage might exceed the maximum rated voltage because of ringing.

SBDs are also used in various devices to support the recent trend toward low operating voltage and low power consumption. For example, SBDs are used to compose low-voltage (e.g., 1.5-V) diode logic and undervoltage detection circuits (voltage monitoring circuits).