VS-40CPQ100-N3

The VS-40CPQ100-N3 is a dual 20A Schottky barrier rectifier in a common-cathode configuration, providing a total current rating of 40A at 100V reverse voltage. Manufactured by Vishay Semiconductors, this device belongs to the high-performance Q-series Schottky product line, optimized for very low forward voltage drop while maintaining moderate reverse leakage at high temperatures.

Using proprietary Schottky barrier technology with a guard ring structure, the VS-40CPQ100-N3 achieves a forward voltage of typically only 0.61V per leg at 20A and 125 degC junction temperature. This exceptionally low VF translates directly into higher efficiency in power supply output rectifiers, where conduction losses are a significant portion of total power loss. The guard ring structure enhances device ruggedness and long-term reliability by suppressing edge effects and improving breakdown uniformity.

The TO-247AC 3-lead package houses two independent Schottky diodes sharing a common cathode connection. This configuration is particularly suited for center-tapped transformer full-wave rectifier circuits, push-pull converter output stages, and as parallel diodes when higher current capability is needed. The package provides low thermal resistance (0.63 degC/W for the whole package) when mounted to an appropriate heatsink.

Schottky diodes are majority-carrier devices with effectively zero reverse recovery time, making them ideal for high-frequency switching applications where recovery losses would otherwise significantly degrade efficiency. The -N3 suffix indicates Vishay’s halogen-free, RoHS-compliant, 100% lead-free product designation.

The VS-40CPQ100-N3 Schottky rectifier operates on the principle of the Schottky barrier formed at a metal-semiconductor junction:

1. Schottky Barrier Formation: Unlike conventional PN-junction diodes, a Schottky diode is formed by the junction of a metal layer with a semiconductor (typically N-type silicon). The difference in work functions between the metal and semiconductor creates a rectifying barrier that allows current flow in one direction (from metal to semiconductor, i.e., anode to cathode) while blocking current in the reverse direction.

2. Forward Conduction: When forward-biased (anode positive, cathode negative), electrons in the N-type semiconductor easily surmount the Schottky barrier and flow into the metal contact. Since only majority carriers (electrons) are involved, there is no minority carrier injection or storage effect. The forward voltage drop is determined primarily by the barrier height and the series resistance of the drift region. At 20A and 125 degC, VF is typically 0.61V per leg.

3. Reverse Blocking: When reverse-biased, the Schottky barrier blocks electron flow from the metal back into the semiconductor. A small reverse leakage current flows due to thermionic emission over the barrier and tunneling effects. This leakage increases significantly with temperature (1.25mA at 25 degC rising to 15mA max at 125 degC). The 100V VRRM rating sets the maximum repetitive reverse voltage.

4. Zero Reverse Recovery: Because Schottky diodes are majority-carrier devices with no stored minority charge, they exhibit virtually zero reverse recovery time (trr). When switching from forward conduction to reverse blocking, the current stops almost instantaneously. This makes Schottky diodes far more efficient at high switching frequencies than PN-junction diodes, eliminating the losses and noise associated with reverse recovery.

5. Guard Ring Structure: The integrated guard ring is a PN junction formed around the perimeter of the Schottky contact. It reduces electric field crowding at the edges of the metal contact, improving breakdown voltage uniformity and long-term reliability. The guard ring also protects against surface-related failure mechanisms.

6. Thermal Considerations: With a maximum junction temperature of 175 degC, the VS-40CPQ100-N3 can operate at higher temperatures than standard silicon rectifiers. However, Schottky leakage current increases exponentially with temperature, so thermal design must ensure TJ stays within rated limits to prevent thermal runaway in continuous conduction modes. Proper heatsinking is essential.

Package: TO-247AC 3L (3-lead through-hole plastic package). Body dimensions: ~15.5mm width x ~20.5mm length. Standard 0.1-inch (2.54mm) lead pitch. Large mounting tab for efficient thermal dissipation. Tab is at cathode (common) potential. Total weight approximately 6 grams.

• Switching Power Supply Output Rectification: Secondary-side output rectifiers in forward, push-pull, and half-bridge SMPS topologies, where the low VF and zero recovery loss significantly improve overall efficiency, especially at high switching frequencies and low output voltages common in server, telecom, and datacom power supplies.
• DC-DC Converter Freewheeling Diodes: Synchronous and non-synchronous buck converters, POL (point-of-load) regulators, and distributed power architectures, where Schottky diodes serve as freewheeling/clamp diodes or as backup diodes in parallel with synchronous MOSFETs to handle dead-time conduction and fault conditions.
• Reverse Battery / Polarity Protection: Reverse polarity protection in automotive, telecom, and portable electronic systems, where the low VF of the Schottky diode minimizes power loss and voltage drop under normal operation while blocking reverse current if the power source is connected incorrectly.
• High-Frequency DC-DC Modules: High-density DC-DC converter modules operating at frequencies from several hundred kHz to multi-MHz, where Schottky’s zero recovery characteristic is essential for maintaining efficiency and managing switching losses that would otherwise dominate at elevated frequencies.
• Battery Charging Systems: Output rectifiers in battery chargers for consumer electronics, power tools, and industrial battery systems, where low forward voltage reduces heat generation and improves charge efficiency, especially in low-voltage battery chemistries like Li-ion and NiMH.
• Server and Telecom Power Systems: High-efficiency server power supplies, telecom rectifiers, and -48V distributed power systems where energy efficiency and thermal management are critical design priorities, and the common-cathode dual configuration perfectly matches center-tapped transformer secondary windings.
• OR-ing Diode Applications: N+1 power supply redundancy and load sharing applications where multiple power sources are ORed together, with the Schottky diode providing low-loss isolation between supply rails while preventing fault propagation from one supply to another.
• Low-Voltage High-Current Power Supplies: Low output voltage (5V, 3.3V, and below) high-current power supplies where even small reductions in forward voltage drop translate into significant efficiency gains and thermal improvements that directly impact system reliability and cooling requirements.