Basic Requirements for Rectifier Diodes
In switching power supplies, rectifier diodes must possess the following characteristics: low forward voltage drop, fast recovery, and sufficient output power. Based on these requirements, common types of rectifier diodes include fast recovery rectifier diodes, ultra-fast recovery rectifier diodes, and Schottky rectifier diodes. These diodes are designed to meet various circuit needs and ensure the efficient operation of switching power supplies. Many distributors offer a wide range of electronic components to cater to diverse application needs, like FAN7554
Fast Recovery and Ultra-Fast Recovery Rectifier Diodes
Fast recovery and ultra-fast recovery rectifier diodes feature moderate forward voltage drops, typically ranging between 0.8V and 1.2V. They also exhibit high reverse voltage ratings, making them ideal for low-power auxiliary power circuits with output voltages around 12V.
Compared to standard rectifier diodes, these diodes significantly reduce reverse recovery time to the nanosecond level, greatly enhancing power supply efficiency. As a rule of thumb, when selecting these diodes, their reverse recovery time should be at least one-third of the switching transistor's rise time.
Additionally, these diodes effectively suppress voltage spikes during switching, thereby minimizing the ripple in the DC output voltage. However, while soft recovery rectifier diodes produce less noise, their longer reverse recovery times and higher reverse currents increase switching losses, making them unsuitable for the demanding requirements of switching power supplies.
The need for heatsinks when using fast recovery and ultra-fast recovery diodes depends on the circuit’s maximum power load. Typically, these diodes can tolerate junction temperatures up to 175°C, with manufacturers providing technical specifications to guide designers in calculating maximum working current, voltage, and casing temperature.
Schottky Rectifier Diodes
Schottky rectifier diodes have an extremely low forward voltage drop, approximately 0.4V, even under high forward current conditions. Moreover, their forward voltage drop decreases further as the junction temperature rises, making them particularly suitable for low-voltage circuits with output voltages around 5V. The reverse recovery time of Schottky diodes is almost negligible because they are majority carrier semiconductor devices, eliminating the need to clear stored minority carrier charges during switching.
However, Schottky diodes have two main drawbacks:
- Low reverse voltage tolerance, with most products rated at around 100V.
- High reverse leakage current, which makes the device more prone to thermal breakdown.
These limitations can be mitigated by adding transient overvoltage protection circuits and controlling the junction temperature, thereby improving the reliability of Schottky rectifier diodes.
Conclusion
Fast recovery rectifier diodes, ultra-fast recovery rectifier diodes, and Schottky rectifier diodes each have specific roles in switching power supplies. Selecting the appropriate diode type based on circuit requirements not only enhances power efficiency but also reduces ripple and switching losses, providing superior performance for circuit designs.