Dual Common-Cathode Schottky Diodes: Connections and Ratings

A dual common-cathode Schottky diode contains two Schottky rectifier junctions with their cathodes connected together and separate anodes. This arrangement can feed a shared positive output from two rectifying paths, as in a suitable center-tapped supply or diode OR-ing circuit. It is not a four-diode bridge or a synchronous rectifier.

The shared connection is the defining feature. Before comparing forward voltage or package size, confirm that the internal circuit matches the required current paths. Then check the rating of each junction and the heat produced by both.

How are the two diodes connected?

Each anode has a diode path to the shared cathode.

Call the terminals A1, A2 and K. Conventional forward current can flow from A1 to K or from A2 to K. With the respective anode below the common cathode voltage, that junction is reverse biased, apart from leakage and dynamic effects.

A common-anode device joins the opposite ends and supports a different connection. A series-connected dual device has another internal circuit. Similar package outlines can contain any of these arrangements, so the words “dual Schottky” do not establish interchangeability.

The metal tab or exposed pad may connect to the shared node. Verify that connection in the actual data sheet before attaching a heatsink or conductive mounting hardware.

Where does a dual common-cathode Schottky fit?

It fits circuits that need two paths into one node.

Two useful examples are center-tapped full-wave rectification and supply OR-ing. The same internal connection can serve both, but their current sharing, blocking duration and fault behavior are different.

Center-tapped full-wave rectification

Connect each end of an appropriate transformer secondary to an anode, the common cathode to the positive output, and the center tap to the return. The two winding halves alternately supply current through their corresponding junctions.

Under ideal symmetrical operation, each junction carries approximately half the output’s average current over a complete cycle. Its conducting pulse can be much higher, especially with a capacitor-input filter. Do not confuse this cycle-average value with instantaneous load current.

Blocking voltage also requires care. In an ideal capacitor-input center-tapped rectifier, the nonconducting diode can see approximately twice the peak voltage of one half-winding. Use the per-half winding voltage and include tolerances and overshoot. The package configuration does not eliminate this stress.

Diode OR-ing

Two sources connect to separate anodes and feed a common output through the cathodes. A source with the higher effective voltage may carry most or all the load. The other path blocks backfeeding except for leakage and transient effects.

This circuit does not guarantee equal sharing between sources, and it is not a battery charge controller. If the application needs defined priority, controlled charging or very low forward loss, a different power-path architecture may be appropriate.

When one source disappears or shorts, its junction can remain hot while supporting reverse voltage. That transition deserves a leakage and thermal assessment, not just a forward-current check.

Is this synchronous rectification?

No. The two junctions provide diode rectification.

Synchronous rectification uses controlled switches, commonly MOSFETs, to replace the main diode conduction path. It requires timing and drive. A Schottky diode may assist during dead time or appear elsewhere in such a circuit, but that does not make a dual diode package a synchronous rectifier.

This distinction changes what to compare. A dual Schottky can be evaluated for diode losses and blocking behavior; a synchronous implementation also requires a controller, gate drive, reverse-current management and fault analysis. See the SMPS guide for broader conversion-stage context.

Does a 30 A label mean 30 A through either diode?

Read whether the rating applies per diode or per package.

As a specific example, Vishay’s MBR30H60CT data sheet lists 30 A total and 15 A per diode, with a forward-current derating curve tied to case temperature. That example explains the notation; it is not a specification for every common-cathode device or a substitute recommendation for a Good-Ark part.

In an OR-ing circuit, one junction may have to carry the entire load. A design that divides the load by two simply because there are two diodes can therefore exceed the per-junction limit.

In a center-tapped circuit, alternate conduction does not mean heat disappears during the other half-cycle. Both junctions warm a shared package. Average, RMS and peak current, along with cooling, determine whether the arrangement is acceptable.

How do you estimate the shared-package loss?

Add the loss of both junctions using their waveforms.

For an illustrative OR-ing load of 10 A carried entirely by one junction at an assumed 0.5 V drop, the forward loss is approximately 10 × 0.5 = 5 W. If two identical sources happen to share equally and both junctions still have the assumed 0.5 V drop, the package total is also 5 W. Real forward voltage changes with current and temperature, so actual sharing can change the result.

For an idealized center-tapped output of 10 A with one diode path active at a time, the same constant-drop assumption also gives approximately 5 W package conduction loss. Each junction averages about 2.5 W under symmetrical operation. This excludes ripple-dependent resistance, leakage and switching contributions.

The cases have similar simplified total loss but different per-junction stress. Use the manufacturer’s thermal model where available. Treating the package as two separate, independently cooled parts can underestimate the warmer junction.

What matters beyond a low forward drop?

Check reverse leakage, dynamic behavior and mounting.

Silicon Schottky devices can have appreciable leakage at elevated temperature. A junction that has just carried the load can remain hot when the circuit suddenly reverse biases it. ST’s OR-ing thermal-runaway note examines how reverse leakage can create a heating feedback loop under particular conditions.

That possibility does not mean every Schottky will run away. It means the forward-to-reverse transition, ambient conditions and leakage characteristics belong in the design review.

Schottky junction capacitance also charges and discharges during switching. There is no PN minority-carrier recovery mechanism, but the surrounding inductance and capacitance can still create current spikes and ringing. Comparing only a forward-drop number misses these effects.

For mounting, confirm footprint, pad dimensions, tab potential and any required insulation. An insulating interface changes the thermal path. A heatsink at the common-cathode potential cannot automatically be connected to the system return or chassis.

Three connection mistakes to rule out

First, do not infer the circuit from a catalogue name alone: search results can mix common-anode and common-cathode devices. Second, do not treat the tab as electrically neutral. A tab connected to the common cathode may require insulation from a conductive heatsink or chassis. Third, do not treat alternate operation as independent cooling.

For a replacement, make a terminal map from the original data sheet and trace the board nodes. Then check the junction that carries the worst-case load and the package’s combined heat. This catches connection and rating errors before an apparently similar device is installed.

How can you check a suspected failed device?

Test both anode-to-cathode paths separately.

With power removed and stored energy safely discharged, identify the terminals from the data sheet. Diode mode may show conduction from each anode toward the common cathode and blocking in the reverse direction. In-circuit resistors, transformers and parallel devices can affect the readings.

A shorted junction or an unexpected open can identify a fault candidate, but a meter cannot prove the rated blocking voltage, hot leakage or switching behavior. A specific numerical forward reading is not a universal pass criterion.

Before replacing it, inspect the load and cooling arrangement. Fit a part with the correct internal configuration, suitable per-junction ratings and matching package connections; then verify representative operating conditions.

FAQ

What does dual common cathode mean?

Last updated: October 11, 2026

The package contains two diode paths whose cathodes are joined, with separate anodes. Each anode can supply forward current into the common cathode node. This is an internal connection description, not a guarantee of physical pin order or package current. Check the device drawing for terminal numbering, viewing direction and any tab connection before wiring or replacing it.

Can a common-anode device replace a common-cathode device?

Not as a direct substitution. Joining the opposite ends changes the current paths and the circuit node that is shared. Similar package shapes can therefore hide incompatible internal connections. A change would require circuit and polarity review, not simply rotating the part. Always compare the internal schematic and footprint along with the voltage, current and thermal requirements.

Does diode OR-ing make two supplies share current equally?

No. Source voltages, path resistance and diode characteristics determine the distribution. One source may supply nearly the whole load, so its junction must be evaluated for that case. When a source disappears, another junction can become reverse biased while still hot. Check both the full-load forward case and the relevant hot blocking condition; do not divide current by two just because the package is dual.

Is a dual Schottky package a synchronous rectifier?

No. Its junctions provide diode rectification. Synchronous rectification uses controlled switches, commonly MOSFETs, with appropriate timing and drive. A Schottky can serve a supporting path in such a design, but that does not change the package into a synchronous rectifier. Moving to synchronous operation changes the control and fault behavior as well as the main conduction loss.

Can I join the anodes to increase current?

Only after evaluating sharing and thermal limits for the exact device. Parallel junctions do not necessarily carry equal current, and both heat the same package. The manufacturer may specify total and per-junction limits that remain applicable. Check forward characteristics, layout resistance and cooling; connecting two terminals together is not proof that usable current doubles.

How do I test the two junctions with a multimeter?

Identify A1, A2 and the common cathode from the data sheet, remove power and discharge stored energy. Test each anode-to-cathode path in both directions using the meter instructions. Parallel board paths can change readings, so ambiguous results may require isolation. Diode mode can reveal certain shorts or opens, but cannot verify blocking voltage, hot leakage, rated current or dynamic performance.

Choose the connection before the package

Confirm A1, A2 and K, identify the worst-case load path, and evaluate both junctions and the shared thermal path. For broader rating interpretation, use the rectifier selection workflow; for demanding thermal loads, continue with high-current Schottky rectifiers.

Continue through this engineering topic

For the complete selection, design, verification, and troubleshooting path, explore the Schottky Diode Selection Hub.

• Practical guide: High-Current Schottky Rectifiers: Losses, Cooling and Current Ratings
• Practical guide: Low VF Schottky Rectifiers: Forward Drop, Leakage and Real Power Loss
• Practical guide: SMD Schottky Barrier Rectifier: Reliable Low-Voltage Power Conversion For Modern Electronics
• Ask Good-Ark technical support about this application