BAT54S L44 Smd Schottky Diode Sot-23

BAT54S If your board needs a small Schottky diode pair wired in series, and the old part on the board is marked L44, this is the part to order. It holds two Schottky diodes in one tiny SOT-23 body, wired one after the other. It fits small, low-voltage boards where space is tight and the signal must switch fast. It does not fit jobs that need more than 30 V, more than 200 mA of steady current, or a different wiring inside the body. Check the checks below before you order, so the wiring, the size, and the limits all match your board.

This is an original, high-quality part.

What it does

A Schottky diode lets current flow one way and blocks it the other way, with a smaller voltage drop than a plain silicon diode. That small drop means less power is lost as heat, which matters on small boards. This BAT54S SOT-23 part holds two such diodes in series. Current enters one diode, leaves it, and passes straight into the next diode. The middle pin is shared by both diodes, so the three pins give you the start, the shared middle point, and the end of the pair.

Repair techs use this kind of part for fast switching, for clamping a signal line so it cannot swing too far, and for guarding a sensitive input. Its recovery time is only 5 ns at most, so it can switch on and off very fast without smearing a fast signal.

Key features

• Two Schottky diodes in series in one SOT-23 body
• Small size for densely packed boards
• Low forward voltage: 0.32 V at most at 1 mA, 0.8 V at most at 100 mA
• Fast switching: 5 ns recovery time at most
• 30 V reverse voltage limit
• 200 mA steady forward current limit
• 600 mA short surge current limit
• Low reverse leakage: 2 µA at most at 25 V
• Small capacitance: 10 pF at most, so it loads a fast signal line only a little

Checks before you order

• Marking: the body must show L44. L44 points to the series-wired BAT54S part. If your old part shows a different mark, stop and check your board list again.
• Wiring inside: this part is series-wired. Pin 1 is the anode of the first diode, pin 2 is the cathode of the second diode, and pin 3 is the shared middle point. A part that looks the same size but is wired differently inside will not work in this circuit, even if its voltage and current numbers match.
• Package: your board footprint must be SOT-23 with three pads. This is a surface-mount part. It solders flat on pads. It has no wire leads.
• Voltage: the reverse voltage on your circuit must stay at or below 30 V. Above that, this part is the wrong pick.
• Current and heat: the steady current must stay at or below 200 mA, and the power must stay well inside the 290 mW limit in the table below. At 100 mA the drop is up to 0.8 V, so work out the heat from your real current before you order.
• Signal speed: if your line is a slow power line, a plain rectifier may do. This part earns its place on fast signal lines, where its 5 ns recovery and 10 pF capacitance matter.

Specifications

All figures below are for the BAT54S series part at +25 °C unless noted. No figure here was guessed.

Other names for the same part (good to know)

Shoppers and repair techs call this same part by a few names. L44 diode is the short code printed on the tiny body, because the full part number does not fit on it. BAT54S is the full part number. Buyers also search for it as a 30V Schottky diode. KL4 is another code some makers print on the same BAT54S part. Dual series Schottky diode and Schottky diode SOT-23 are the plain names buyers use for this part. If you see L44 on a tiny SOT-23 body, and your circuit needs a series pair, this page is the right match. Do not judge by the code alone — check the body size and the series wiring too.

Frequently Asked Questions

What does L44 mean on this diode?

L44 is the short code printed on the body of the BAT54S diode. When you see L44 on a small SOT-23 part, it tells you the part is the series-wired BAT54S.

What does dual series mean?

It means two diodes sit in one body, wired one after the other. Pin 1 is the start, pin 2 is the end, and pin 3 is the shared middle point where the two diodes join.

Can I use a single diode in the same size instead?

No, not without changing the circuit. A single diode has only two ends, so it cannot give you the shared middle point that a series pair gives. Match the wiring inside, not just the size.

What voltage and current can this part handle?

It handles up to 30 V in reverse and up to 200 mA of steady forward current, with short surges up to 600 mA and total power up to 290 mW. Stay inside all of those limits at the same time.

Which way round does this part go?

Match the pins to your board print: pin 1, pin 2, and the shared pin 3. There is no band to read on this part as there is on a leaded diode, so the pin order is what matters. Put it in the wrong way round and the circuit will not work as planned.

What is the price of this part?

Check the live price on the website. The price shown on the product page is the current one.

You can view and download the datasheet for this part from the Datasheet button on this page.

Use note kept from the old page: this part was listed before for densely packed boards and for fast, low-power switching work, and that use still stands.