BAT42 - 30V 200mA Schottky Diode DO-35 | STMicroelectronics
MPN: BAT42 β Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.12 | $0.12 |
| 10 | $0.09 | $0.90 |
| 100 | $0.05 | $5.00 |
| 500 | $0.03 | $15.00 |
| 1,000 | $0.02 | $20.00 |
BAT42 Overview
A Schottky diode is a semiconductor diode formed by a metal-to-semiconductor junction rather than a conventional PN junction, which gives it a lower forward voltage drop and essentially zero reverse recovery charge. Within the power-discrete taxonomy, the BAT42 belongs to the diode family, specifically small-signal Schottky rectifiers, sitting below power rectifiers in current capability and above RF detector diodes in robustness.
Key features include the 30 V maximum repetitive reverse voltage, 200 mA average forward current, low forward turn-on voltage (distributor listings show approximately 400 mV class conduction, per digchip data), and fast switching suited to general-purpose high-speed circuits. A guard-ring PN-junction structure protects the junction against electrostatic discharge events, improving assembly-line robustness compared to unprotected small-signal Schottky dies. The metal-to-silicon barrier construction keeps switching losses low in clamping and steering roles.
Technically, the BAT42's majority-carrier conduction eliminates reverse recovery, so trr-limited losses that plague fast-recovery PN diodes are absent. The DO-35 glass-bodied axial package provides excellent hermeticity and handles surge events listed around 4 A non-repetitive peak (per digchip summary), with an operating junction temperature up to 125 C.
Typical applications include low-voltage rectification in small power supplies, reverse-polarity protection, freewheeling/clamping for relays and small inductive loads, and signal demodulation or detection circuits where the low forward drop improves low-level signal fidelity.
When designing, derate forward current at elevated ambient temperature and respect the 30 V reverse limit with margin for transients.
This page synthesizes cross-reference alternatives, distributor sourcing links, and practical design notes not consolidated in the manufacturer datasheet, giving engineers a single verifiable reference point.
Drop-in alternatives for BAT42 β same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with BAT42 (same form factor and footprint) β differing in Package, ESD Protection, Diode Type, Application Class, Reverse Recovery.
Quick Comparison Tool β Select alternative parts for side-by-side comparison:
BAT43
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$0.08 / Unit
View Datasheet βBAT85
β Drop-In β οΈ εζ°εΎ ιͺθ―π Reference alternative (not in catalog)
BAT42
β Drop-Inβ In Stock
$0.02 / Unit
View Datasheet βBAT43
β Drop-Inβ In Stock
$0.08 / Unit
View Datasheet βBAT42 Maximum Ratings & Electrical Characteristics
| Diode Type | Small Signal Schottky Barrier |
| Repetitive Reverse Voltage (VRRM) | 30 V |
| Average Forward Current (IF(AV)) | 200 mA |
| Non-Repetitive Peak Forward Surge Current (IFSM) | 4 A |
| Junction Operating Temperature | up to 125 C |
| Switching Speed | Fast (Schottky, no reverse recovery) |
| Package | DO-35 axial through-hole |
| Configuration | Single diode |
| Technology | Metal-to-silicon Schottky junction with guard ring ESD protection |
| Mounting Type | Through Hole |
| Application Class | General purpose fast switching |
| Manufacturer | STMicroelectronics |
BAT42 Pin Configuration
| Pin 1 | Anode β Anode terminal (unbanded end of DO-35 glass body) |
| Pin 2 | Cathode β Cathode terminal (banded end of DO-35 glass body) |
Typical Applications
BAT42 is suitable for 6 applications: Low-Voltage Rectification, Reverse Polarity Protection, Relay and Inductive Load Clamping, Signal Detection and Demodulation, OR-ing and Rail Steering, Education, Prototyping and Repair.
Low-Voltage Rectification
The BAT42 fits low-current rectification duties in auxiliary and small power supplies where every few hundred millivolts of headroom matters. Its Schottky barrier conduction gives a forward drop in the 400 mV class versus roughly 0.7 V for a silicon PN diode, directly improving efficiency in 3.3 V and 5 V secondary rails at currents up to the 200 mA rating. Because it is a majority-carrier device with no reverse recovery charge, switching losses at tens of kilohertz are negligible compared with fast-recovery PN diodes. In a half-wave or bridge arrangement, verify that peak inverse voltage on each device stays below the 30 V rating with margin, and estimated dissipation at 200 mA remains near 80 mW, well within DO-35 capability.
Recommended
Reverse Polarity Protection
Series reverse-polarity protection is a classic BAT42 use case on low-voltage DC inputs such as 5 V, 9 V, or 12 V rails. Placed in series with the supply, the diode blocks reverse connection; its low forward drop of only a few hundred millivolts keeps the voltage budget intact and dissipation near 80 mW at full 200 mA load, avoiding the 0.7 V penalty of a standard rectifier. The 30 V reverse rating covers 12 V systems with ample margin, while the guard-ring ESD protection adds robustness during connector mating. Estimated: on a 12 V / 100 mA load the BAT42 wastes about 40 mW versus roughly 70 mW for a PN diode. For 24 V industrial rails, substitute the BAT43 or BAT85 for extra reverse margin.
Recommended
Relay and Inductive Load Clamping
The BAT42 serves as a freewheeling or clamp diode across small relays, solenoids, and fan motors switched by transistors. When the driver turns off, the stored inductive energy forces the diode to conduct, clamping the flyback voltage to a diode drop above the rail and protecting the switching transistor. Its fast Schottky action begins clamping immediately without forward-recovery delay, an advantage over slower rectifiers for sensitive drivers. The roughly 4 A non-repetitive surge rating absorbs the initial coil current pulse, though the clamp is single-shot per switching event at 200 mA continuous coil current. Estimated: a 12 V / 40 mA relay coil releases energy harmlessly through the clamp each cycle, keeping DO-35 average dissipation minimal.
Recommended
Signal Detection and Demodulation
In AM detection, envelope detectors, and RF measurement probes, the BAT42's low turn-on voltage enables rectification of small signal levels that a PN diode would miss entirely. The metal-to-silicon barrier begins conducting at a few hundred millivolts, so envelope peaks bias the diode on earlier, improving detection sensitivity and linearity at low drive levels. The DO-35 glass body adds low parasitic capacitance and hermetic stability for signal-path roles. Note that for very weak signals (tens of millivolts) or VHF work, a dedicated zero-bias detector diode outperforms the BAT42, which is best above roughly 100 mV and at audio through low-MHz frequencies. Estimated detection threshold sits near the 400 mV class forward knee.
Recommended
OR-ing and Rail Steering
Diode-OR combining of two supplies, battery backup feeders, or wall-adapter versus battery inputs uses the BAT42 to steer current while preventing back-feed between sources. The low Schottky forward drop keeps the delivered rail voltage close to the source, important for battery-powered equipment where 0.3 V of savings extends usable capacity. At 200 mA maximum per device, parallel BAT42 units can share higher loads if each leg carries its own diode to force current sharing. Estimated: at 100 mA per leg the drop costs roughly 40 mV-to-50 mW of budget versus about 70 mW for a PN diode. Check that the blocked source voltage stays below 30 V, or specify the BAT43/BAT85 for higher rails.
Recommended
Education, Prototyping and Repair
The BAT42 is a staple for breadboard prototyping, STEM education kits, and through-hole repair work because its DO-35 axial body is easy to handle, solder, and identify via the cathode band. Technicians repairing vintage audio gear, test instruments, and small power bricks frequently encounter the BAT42 on the bill of materials; the Vishay second-source under the same part number keeps replacement stock available worldwide. Its forgiving 4 A surge rating and guard-ring ESD protection tolerate handling and soldering without special precautions. When substituting during repair, the BAT43 offers extra voltage margin at a similar cost, and the identical footprint means no lead-forming changes are needed on legacy PCBs.
Recommended
Recommended Products Summary
Engineering reference data for BAT42 β comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | BAT43 (ST) | BAT85 (ST) | BAT42 (Vishay) | BAT43 (Vishay) |
|---|---|---|---|---|---|
| Package | DO-35 axial | DO-35 axial - same | DO-35 axial - same | DO-35 axial - same | DO-35 axial - same |
| Brand | STMicroelectronics | STMicroelectronics | STMicroelectronics | Vishay Intertechnology | Vishay Intertechnology |
| Reverse Voltage (VRRM) | 30 V | 40 V class | 40 V | 30 V | 40 V class |
| Forward Current | 200 mA | 200 mA | 200 mA | 200 mA | 200 mA |
| Junction Temperature | up to 125 C | up to 125 C | up to 125 C | up to 125 C | up to 125 C |
| Switching Character | Schottky, no reverse recovery | Schottky, no reverse recovery | Schottky, no reverse recovery | Schottky, no reverse recovery | Schottky, no reverse recovery |
| Mounting | Through Hole (axial) | Through Hole (axial) | Through Hole (axial) | Through Hole (axial) | Through Hole (axial) |
Key Differentiators
- Lower reverse voltage keeps cost minimal for low-voltage rails (vs BAT43 (ST))
- Higher surge capability within the same family (vs BAT42 (Vishay))
- Dual-source availability under an identical part number (vs BAT42 (Vishay))
Design Notes
Respect the 30 V reverse rating with margin. On inductive or transformer-coupled nodes, leakage-inductance spikes can momentarily exceed the apparent DC stress; a conservative rule is to keep steady-state reverse voltage below roughly 24 V for the BAT42 and move to the BAT43 or BAT85 (40 V class) above that. Reversing the diode orientation in a protection role defeats the function - always match the cathode band to the original layout polarity during rework.
Estimated: at the full 200 mA rating with a forward drop in the 400 mV class, dissipation is about 80 mW, which the DO-35 glass body handles through its axial leads into the PCB without heatsinking. Derate forward current at elevated ambient temperature per the datasheet derating curve; for designs operating continuously above about 75 C ambient, verify junction temperature stays below the 125 C maximum using lead-length dependent thermal resistance data.
As a through-hole part, keep axial lead length short on high-frequency clamp nodes to minimize loop inductance; excess lead inductance degrades the fast-clamping benefit that motivates choosing a Schottky. For surge duty (relay coils), a few millimeters of lead length is acceptable, but avoid long pigtails. In dual-source BOM strategies, STMicroelectronics and Vishay BAT42 share the DO-35 footprint, so no layout change is required when alternating suppliers.
Compliance Information
Compliance status not stated in the provided web data; consult the STMicroelectronics BAT42 product page and datasheet for current RoHS/REACH declarations.
