Onsemi MURS105T3G Ultrafast Rectifier: Key Specifications and Application Circuit Design

The Onsemi MURS105T3G is a highly efficient surface-mount ultrafast rectifier, designed to meet the demanding requirements of modern switch-mode power supplies (SMPS), inverters, and other high-frequency circuits. Its exceptional recovery characteristics and robust construction make it a preferred choice for engineers seeking to improve system efficiency and reliability.

Key Electrical Specifications

A deep dive into its datasheet reveals the critical parameters that define its performance. The device boasts a repetitive peak reverse voltage (VRRM) of 50 V and an average forward rectified current (IF(AV)) of 1 A. A standout feature is its ultrafast reverse recovery time (trr) of 35 ns (typical), which is pivotal in minimizing switching losses and reducing electromagnetic interference (EMI) in high-speed switching applications. The low forward voltage drop (VF) of 0.85 V (typical at IF = 1.0 A) further enhances efficiency by reducing conduction losses. Housed in a compact and rugged DO-214AA (SMB) package, it offers excellent power dissipation capabilities and is suitable for automated assembly processes.

Application Circuit Design Considerations

Integrating the MURS105T3G effectively requires careful circuit design, particularly in a switch-mode power supply (SMPS) output rectification stage.

1. Output Rectification: In a flyback or boost converter, the MURS105TT3G is ideal for the output rectifier role. Its fast recovery ensures that when the main power switch (e.g., a MOSFET) turns on, the rectifier ceases conduction almost immediately. This prevents reverse recovery current spikes that can overstress the switch and lead to significant power loss. The low VF directly contributes to higher efficiency, especially under high load conditions.

2. Freewheeling Diode: In inductive load circuits or as part of a power factor correction (PFC) stage, the diode protects other components by providing a path for the current to circulate when the main switch turns off. The ultrafast trr is crucial here to ensure a clean and rapid transition, maintaining circuit stability.

3. Snubber Circuits: While the diode is fast, some high-frequency ringing may occur due to parasitic inductances and capacitances. A simple RC snubber network across the diode can often be necessary to dampen these oscillations and prevent overvoltage transients that could exceed the VRRM rating.

4. Thermal Management: Despite its efficiency, power dissipation (IF(AV) VF) generates heat. Proper PCB layout is essential. The DO-214AA (SMB) package should be soldered to a sufficient copper pad area acting as a heatsink. For high ambient temperatures or maximum load conditions, thermal vias under the package can help transfer heat to other PCB layers.

Design Example: SMPS Output Stage

The core of the circuit consists of the transformer/inductor, the MURS105T3G, and the output capacitor. The cathode is connected to the transformer’s secondary, and the anode to the ground. The output capacitor smooths the rectified voltage. A small ferrite bead in series with the output can help suppress any remaining high-frequency noise, leveraging the diode’s fast characteristic to create an effective filter.

ICGOODFIND Summary

The Onsemi MURS105T3G stands out as a superior solution for high-frequency rectification, where its ultrafast recovery time and low forward voltage directly translate to enhanced efficiency and reduced EMI. Its robust SMB package ensures reliability in demanding environments. When designing with this component, prioritizing thermal management through PCB layout and considering the use of snubbers are key steps to unlocking its full potential in applications like SMPS, inverters, and PFC circuits.

Keywords:

Ultrafast Recovery

Forward Voltage

Switch-Mode Power Supply (SMPS)

Thermal Management

Reverse Recovery Time