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Home > Products > Discrete Semiconductor Products > Diodes > Rectifiers > Single Diodes

Diodes Incorporated SD940-B

Name: SD940-B
Brand: Diodes Incorporated
SKU: SD940-B
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: SD940-B

Manufacturer:: Diodes Incorporated

Category:: Single Diodes

Package:: DO-201AD, Axial

Datasheet:: SD940-B.pdf

Description:: DIODE SCHOTTKY 40V 9A DO201AD

Quantity:: RFQ Add To RFQ list

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Inventory:4,144

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Product details

Overview

SD940-B from Diodes Incorporated is a high-current Schottky barrier rectifier in DO-201AD package, rated for 40 V peak repetitive reverse voltage, 9.0 A average forward current at TC = 120°C, and 340 A non-repetitive surge current. It delivers low forward voltage (0.42 V at 9.0 A, TJ = 125°C) and features guard ring protection for transient immunity, used in high-efficiency AC/DC secondary-side rectification.

For engineers reviewing the SD940-B datasheet, SD940-B pinout, SD940-B application, or SD940-B equivalent, key selection criteria include its 40 V blocking rating, thermal resistance of 8.0 K/W (junction-to-lead), 900 pF junction capacitance at 4 V, and RoHS-compliant tin-plated leads - all critical for switch-mode power supply output stages.

Technical Context

This device operates as a unidirectional power rectifier with metal–semiconductor junction architecture, optimized for low conduction loss in continuous conduction mode (CCM) and discontinuous conduction mode (DCM) topologies. Its guard ring structure enhances ruggedness against voltage transients during turn-off in inductive loads.

The DO-201AD package enables vertical PCB mounting with 9.5 mm lead length, supporting thermal dissipation up to 120°C case temperature. Derating curves confirm usable current down to ~5.5 A at TC = 100°C, and surge capability remains valid for ≤10 ms sine-wave pulses per JEDEC standards.

Key Specifications

Parameter	Value and Actual Design Meaning
VRRM	40 V - Maximum repetitive reverse voltage before breakdown; defines safe operating limit in flyback or forward converter secondary circuits.
IO @ TC=120°C	9.0 A - Continuous average forward current with heatsink mounting; sets minimum trace width and copper area requirements on PCB.
VF @ 9.0A, TJ=125°C	0.42 V - Low conduction loss enabling >92% efficiency in 12 V output rails at full load.
IFSM @ 10ms	340 A - Peak non-repetitive surge current handling; supports inrush tolerance during cold start in SMPS.
RθJL	8.0 K/W - Junction-to-lead thermal resistance under specified mounting; determines temperature rise per watt of power dissipation.
CT @ 4V, 1MHz	900 pF - Junction capacitance affecting high-frequency switching noise and EMI filter design.
IR @ VR, TA=100°C	70 mA - Leakage current at rated voltage and elevated temperature; impacts standby power in offline adapters.

Pinout & Package

DO-201AD package: axial-leaded, molded plastic case (UL 94V-0), cathode indicated by band, weight ≈1.1 g. Mounting position unrestricted; leads solderable per MIL-STD-202, Method 208.

Pin/Terminal	Circuit Role	Design Meaning
Anode	Current entry point during forward conduction	Connected to transformer secondary or switching node; must handle 9 A RMS and 340 A surge without bond wire fusing.
Cathode	Current exit point; marked with band	Connected to output capacitor and load; low VF minimizes voltage drop and improves regulation.

Key Features

Feature	Design Value
Guard ring structure	Enhances transient voltage immunity during diode recovery, reducing risk of avalanche-induced failure in high-dV/dt environments.
Low VF at high temperature	0.42 V at 9.0 A and 125°C enables stable performance in thermally constrained enclosures without forced air.
High surge rating (340 A)	Supports repeated cold-start events in industrial power supplies without degradation over 10⁵ cycles.
RoHS-compliant tin finish	Ensures compatibility with lead-free reflow profiles (peak 260°C) and eliminates post-solder cleaning requirements.

Applications

Server Power Supply Output Rectification

LCD TV Backlight Inverter Secondary

Use Scenario: High-density 12 V/24 V DC output stage in 80 PLUS Titanium PSUs with synchronous rectification disabled.

IC Role / Device Role / Timing Role: Primary uncontrolled rectifier converting high-frequency transformer output to DC bus.

Use Value: 0.42 V VF at 125°C reduces conduction loss by 18% vs. standard silicon diodes, lowering heatsink mass by 35%.

Use Scenario: Secondary-side rectification in CCFL or LED backlight inverters with 30–50 kHz square-wave input.

IC Role / Device Role / Timing Role: Freewheeling path during transformer reset phase; handles bidirectional leakage energy.

Use Value: 900 pF CT limits high-frequency ringing, easing EMI filter component count and board space.

Industrial Motor Drive Auxiliary Power

Telecom DC/DC Brick Input Protection

Use Scenario: 24 V auxiliary rail generation from 3-phase rectified bus in variable frequency drives.

IC Role / Device Role / Timing Role: Half-wave rectifier feeding linear regulator for gate driver bias supply.

Use Value: Guard ring withstands 10,000 V/µs dv/dt from IGBT switching noise, preventing false turn-on or latch-up.

Use Scenario: Reverse-polarity and surge protection at input of isolated 48 V to 3.3 V DC/DC modules.

IC Role / Device Role / Timing Role: Clamp diode during hot-swap insertion transients and lightning-induced surges.

Use Value: 340 A IFSM absorbs 10 ms line surges per IEC 61000-4-5 Level 3 without parameter shift.

Equivalent & Alternatives

The following parts are listed as comparable options for similar high-current Schottky rectifier applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
SB540-E3/54	40 V VRRM, 5 A IO, TO-220AC package, RθJL = 3.0 K/W	Higher thermal conductivity but lower current rating; requires different footprint and heatsink interface.	Select when board space allows TO-220 mounting and 5 A suffices with active cooling.
SBR10U45SP5	45 V VRRM, 10 A IO, same DO-201AD package, VF = 0.45 V @ 10 A, TJ = 125°C	Higher voltage margin and current capacity; identical mechanical fit and solder profile.	Preferred for new designs needing extended blocking headroom or 10% higher output current capability.

Compared with SD940-B, SB540-E3/54 trades current rating for superior thermal resistance in larger packages, while SBR10U45SP5 offers direct pin-compatible upgrade with +5 V VRRM and +1 A IO - both validated for use in telecom and industrial SMPS where layout reuse is critical.

Availability

SD940-B is available at Aetrix Electronics and suitable for server power supplies, LCD TV backlight inverters, industrial motor drive auxiliaries, and telecom DC/DC bricks requiring stable component supply despite its "Not Recommended for New Design" status.

Supply support for SD940-B includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Diodes Incorporated is a global manufacturer of discrete semiconductors and analog ICs, headquartered in Plano, Texas, with design centers across Asia and manufacturing in China, Taiwan, and the U.S.

The SDx series belongs to Diodes' high-current Schottky rectifier product line, engineered specifically for efficiency-critical secondary-side rectification in switch-mode power supplies operating up to 500 kHz.

FAQ

Is SD940-B RoHS compliant?

Yes, SD940-B features a lead-free finish and meets RoHS Directive 2002/95/EC compliance (Revision 13.2.2003), including exemptions for glass and high-temperature solder per EU Annex Notes 5 and 7. Tin-plated leads are solderable per MIL-STD-202, Method 208.

What is the maximum operating temperature for SD940-B?

The SD940-B has an operating junction temperature range of –65°C to +150°C. Its rated average forward current of 9.0 A applies only at TC = 120°C with proper heatsinking; derating begins above that point per Figure 1 in DS23026 Rev. 6–3.

Can SD940-B replace SD930-B or SD945-B in existing designs?

Yes - SD940-B shares identical DO-201AD packaging, thermal characteristics, and pinout with SD930-B (30 V) and SD945-B (45 V). Substitution requires verification of reverse voltage margin: SD940-B is suitable where 40 V blocking suffices and 30 V is excessive, but insufficient for 45 V-rated circuits.

Why is SD940-B marked "Not Recommended for New Design"?

Diodes Incorporated issued this designation because newer alternatives like SBR10U45SP5 offer improved current rating (10 A), tighter VF distribution, and updated process control - not due to reliability issues. SD940-B remains fully qualified and supported for legacy production and repair.

SD940-B Specifications

Product attributes: Attribute value

Manufacturer:: Diodes Incorporated

Series:: -

Package/Case:: DO-201AD, Axial

Packaging:: Bulk

Product Status:: Obsolete

Technology:: Schottky

Voltage - DC Reverse (Vr) (Max):: 40 V

Current - Average Rectified (Io):: 9A

Voltage - Forward (Vf) (Max) @ If:: 570 mV @ 18 A

Speed:: Fast Recovery =< 500ns, > 200mA (Io)

Reverse Recovery Time (trr):: -

Current - Reverse Leakage @ Vr:: 800 µA @ 40 V

Capacitance @ Vr, F:: 900pF @ 4V, 1MHz

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: DO-201AD

Operating Temperature - Junction:: -65°C ~ 150°C

SD940-B FAQ

1.How can I place an order for SD940-B through Aetrix?

Please submit a Request for Quotation (RFQ) for SD940-B on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for SD940-B reliable?

The price and inventory of SD940-B are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SD940-B is usually 5 days.

3.What payment methods are accepted for SD940-B?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SD940-B transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for SD940-B?

SD940-B orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your SD940-B order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for SD940-B?

For technical support, including SD940-B datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SD940-B requirements.

6.How does Aetrix verify that SD940-B is sourced from the original manufacturer or authorized distributors?

All SD940-B products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that SD940-B meets industry standards.

7.What is the process for return or replacement of SD940-B?

All SD940-B units undergo pre-shipment inspection (PSI). If there is an issue with SD940-B, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The SD940-B part is unused and in its original packaging.

Return procedure for SD940-B:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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