Parts

S8050 transistor: pinout, ratings, a 3.3 V switch and the S8550

The S8050 is E-B-C: with the flat face toward you and the leads down, the emitter is on the left and the collector on the right. That is the reverse of the BC547, so an S8050 dropped into a BC547's holes has its emitter and collector swapped.

It is a 25 V, 500 mA NPN, which makes it a common pick for a buzzer, a small motor or a relay coil driven from an Arduino or ESP32 pin. This page works through a 100 mA switch from a 3.3 V pin, shows why the 500 mA rating does not mean 500 mA from a pin, and covers its PNP partner, the S8550. Every value comes from the Micro Commercial Components (MCC) datasheets.

Datasheet: Micro Commercial Components S8050 NPN Silicon Plastic-Encapsulate Transistor (TO-92) (PDF)Ask Datasheet Guru about the S8050

Pinout by package

S8050 TO-92 · MCC1=E 2=B 3=C

Flat face toward you, leads pointing down: E, B, C from left to right.

The reverse of the BC547 and BC557 (C-B-E). A BC547 footprint takes an S8050 only turned round.

Source: Micro Commercial Components S8050 NPN Silicon Plastic-Encapsulate Transistor (TO-92), p. 1 (TO-92 outline numbered 1 2 3; 1 emitter, 2 base, 3 collector; marking code S8050)

MMS8050 SOT-23 · MCC1=B 2=E 3=C

Top view, pin 3 alone on one side: pin 1 base and pin 2 emitter on the other side.

Marked J3Y, not S8050. Rated 300 mW, not 625 mW.

Source: Micro Commercial Components MMS8050 NPN Silicon Plastic-Encapsulate Transistor (SOT-23), p. 1 (SOT-23 outline and internal structure: 1 base, 2 emitter, 3 collector; marking J3Y)

Which one do you have?

The letter after the number is the gain bin: B, C or D, from lowest to highest. A surface-mount S8050 is sold as the MMS8050 and is marked J3Y, with its own bins, L and H. The S8550 is the PNP version with the same pins. One look-alike is not a substitute: the SS8050 is a different transistor with its own datasheet, so check that sheet rather than this one.

Absolute maximum ratings

MCC rates the S8050 for 25 V collector to emitter, 40 V collector to base, 5 V emitter to base and 500 mA. The TO-92 part may dissipate 630 mW at 25 °C; the SOT-23 MMS8050 only 300 mW, because its 417 °C/W is about twice the TO-92's 200 °C/W. The 25 V is lower than the BC547's 45 V, so keep the S8050 to 5 V and 12 V circuits.

Absolute maximum ratings at 25 °C, MCC TO-92 and SOT-23 datasheets
Parameter	S8050TO-92	MMS8050SOT-23
Collector-emitter voltage, base open VCEO	25 V	25 V
Collector-base voltage VCBO	40 V	40 V
Emitter-base voltage VEBO	5 V	5 V
Collector current, continuous IC	500 mA	500 mA
Power dissipation at 25 °C PD	625 mW	300 mW
Thermal resistance, junction to ambient RθJA	200 °C/W	417 °C/W
Junction temperature TJ	−55 to 150 °C	−55 to 150 °C

Gain bins and saturation

Limits at 25 °C (min/max)
Parameter	S8050TO-92	MMS8050SOT-23
DC current gain hFE(1)IC = 50 mA, VCE = 1 V	85 to 300	120 to 350
DC current gain hFE(2)IC = 500 mA, VCE = 1 V	50 min	50 min
Gain bins at 50 mA hFE(1)rank letter after the number	B 85-150, C 120-200, D 160-300	L 120-200, H 200-350
Saturation voltage VCE(sat)IC = 500 mA, IB = 50 mA	0.6 V max	0.6 V max
Base-emitter voltage in saturation VBE(sat)IC = 500 mA, IB = 50 mA	1.2 V max	1.2 V max
Collector cut-off current ICEOVCE = 20 V, base open	0.1 µA max	0.1 µA max
Transition frequency fTIC = 20 mA, VCE = 6 V, f = 30 MHz	150 MHz min	150 MHz min

Figure 1. The bins overlap, so an S8050C and an S8050D can measure the same. At 500 mA every bin is only guaranteed 50.

Unlike the BC547, whose gain groups are measured at 2 mA, the S8050's bins are measured at 50 mA, close to how it is used. At 500 mA MCC guarantees a gain of only 50 in every bin, and it specifies saturation with the base current at a tenth of the collector current: at most 0.6 V across the transistor and 1.2 V on the base at 500 mA.

Worked example: switching 100 mA from a 3.3 V pin

A 100 mA load on a 5 V rail, switched from an ESP32 or any other 3.3 V pin: load from +5 V to the collector, emitter to ground, a resistor from the pin to the base. The pin goes high to turn the load on.

1. Pick the base current. 100 mA / 20 = 5 mA. That ratio is ours: it is 2.5 times below the guaranteed gain of 50, and it keeps the pin current low.

2. Take the worst-case base-emitter voltage. MCC gives V_BE(sat) as 1.2 V at most, so R ≤ (3.3 V − 1.2 V) / 5 mA = 420 Ω.

3. Round down to a standard value. The next E12 value is 390 Ω, giving 5.38 to 8.46 mA of base current. MCC gives no minimum V_BE, so the upper figure takes it as 0 V.

4. Check the gain. 5.38 mA × 50 = 269 mA, well over the 100 mA the load needs, so the transistor stays saturated.

5. Check the heat. At most 100 mA × 0.6 V plus 8.46 mA × 1.2 V = 70 mW, about 14 °C above the air at 200 °C/W.

Figure 2. The low-side switch, drawn as ngspice checked it. Its base current lands inside the worked range of 5.38 to 8.46 mA, the voltage across the transistor stays under 0.6 V, and the load gets almost the full 5 V.

From a 5 V Arduino pin the same sum gives R ≤ 760 Ω, so 680 Ω and 5.59 to 7.35 mA of base current.

Figure 3. Base resistor and base current for the 100 mA load from a 3.3 V and a 5 V pin.

Worked example in numbers

Base resistor: 390 Ω
Base current: 5.38 to 8.46 mA
Transistor heat: 70 mW
Junction rise: 14 °C

Why 500 mA is not a 500 mA switch from a pin

The 500 mA on the front page is the most the transistor may carry. To be sure of saturation at that current, MCC drives the base at 1:10: 50 mA of base current. From a 3.3 V pin that needs about 42 Ω in the base, and no microcontroller pin can supply 50 mA.

With the 390 Ω from the example, the gain floor of 50 guarantees only 269 mA. A 500 mA load would pull the transistor out of saturation. At 1 V across it, the point where MCC measures that gain, it turns 500 mW into heat: 80 % of the 630 mW rating and about 100 °C above the air.

Figure 4. The 100 mA switch uses about a ninth of the rating. A 500 mA load that the pin cannot saturate uses most of it.

For loads over about 200 mA from a microcontroller, use a logic-level MOSFET. Our MOSFET guide for Arduino and ESP32 picks one by gate voltage.

The pin order against the BC547 and 2N2222

Figure 5. The S8050 and the PN2222A share a pin order; the BC547 is the other way round. Some TO-92 2N2222s are C-B-E, so check the 2N2222 page before you swap one in.

What it is good for

Switching a buzzer, small motor, relay coil or LED string of up to about 200 mA from a 3.3 V or 5 V pin.
The NPN half of a push-pull pair with the S8550, both E-B-C.
Small amplifier stages on 5 V and 12 V supplies, inside its 25 V rating.

Tips and checks

Put a diode across a relay coil or motor, cathode to the positive rail. Without one the coil's spike at turn-off can exceed the S8050's 25 V.
Add a 10 kΩ resistor from base to ground so the load stays off while the microcontroller boots and its pins float.
With the load on, measure collector to emitter. A few hundred millivolts means saturated; a volt or more means the base current is too small for the load.
Check the print before you solder: an S8050, an SS8050 and a BC547 can come from the same bag and do not share pins or ratings.
A meter's hFE socket measures at a few milliamps, not at the 50 mA of the bins, so its reading will not match the bin. Use it to tell a working part from a dead one.

Substitutes and the PNP partner

TO-92 pin numbers as MCC draws them, flat face toward you; SOT-23 as seen from the top.
Part	Pins	Verdict
MMS8050 (SOT-23)	B-E-C (SOT-23)	The surface-mount S8050: same 25 V, 500 mA and saturation figures, but 300 mW against 625 mW, so it runs about twice as hot for the same load.Micro Commercial Components MMS8050 NPN Silicon Plastic-Encapsulate Transistor (SOT-23), p. 1; Micro Commercial Components MMS8050 NPN Silicon Plastic-Encapsulate Transistor (SOT-23), p. 2
S8550 (PNP partner)	E-B-C	The PNP complement with the same pins and ratings, for push-pull pairs and high-side switches. It replaces an S8050 only where the whole circuit is mirrored.Micro Commercial Components S8550 PNP Silicon Transistors (TO-92), p. 1; Micro Commercial Components S8550 PNP Silicon Transistors (TO-92), p. 2

S8550

The S8550 is the PNP partner: E-B-C pins, 25 V, 500 mA and 625 mW, with the same B, C and D bins at 50 mA. Its guaranteed gain at 500 mA is 40, a little below the S8050's 50. As a switch it goes on the positive side of the load, emitter to the supply, and turns on when the base is pulled low. Like any PNP high-side switch, it turns off only when the base reaches the emitter's supply, so a 3.3 V pin cannot switch it on a 5 V rail; our BC557 page works through that trap.

Finding the pins with a multimeter

Set the meter to diode test. Put the red probe on each lead in turn until you find the one that conducts to both others, about 0.6 to 0.7 V each. That is the base of an NPN (for the S8550, use the black probe).
Reverse the probes: both junctions should read open, and the outer leads open both ways.
The base-emitter reading is usually a few millivolts higher than the base-collector one, which tells the outer leads apart.

The transistor testing lesson goes through it step by step, and continuity and diode test explains what the meter is doing.

What we'd do

Use an S8050 for loads up to about 200 mA from a 3.3 V or 5 V pin, with 390 Ω in the base for 100 mA from a 3.3 V pin. Buy the D bin and check the E-B-C pin order against your board before soldering. For anything near its 500 mA rating, or above 12 V, use a logic-level MOSFET instead.

Questions people ask

What is the S8050 pinout?

Emitter, base, collector from left to right, with the flat face toward you and the leads pointing down. That is the reverse of the BC547.

Is the S8050 NPN or PNP?

NPN. Its PNP partner is the S8550, with the same pins and ratings.

How much current can an S8050 handle?

500 mA at most, and 625 mW of heat in TO-92. From a microcontroller pin, plan on about 200 mA: saturation at 500 mA needs 50 mA of base current.

Can I use an S8050 instead of a BC547?

Yes, in a circuit under 25 V, but turn it round: the BC547 is C-B-E and the S8050 is E-B-C. It handles five times the BC547's 100 mA.

What does the D in S8050D mean?

The gain bin. MCC lists B as 85 to 150, C as 120 to 200 and D as 160 to 300, all at 50 mA and 1 V.

Buying S8050 transistors in India

The S8050 and S8550 are sold loose by the hundred, often from the same drawer as the BC547 and the SS8050, so check the print on every part. Ask for the D bin by name. Our guide to buying electronic components in India compares ten online sellers and covers how to spot fakes.

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Datasheets this page was checked against

Micro Commercial Components, S8050 NPN Silicon Plastic-Encapsulate Transistor (TO-92) (Rev.3-1-01012019)
Micro Commercial Components, S8550 PNP Silicon Transistors (TO-92) (Rev.3-1-01012019)
Micro Commercial Components, MMS8050 NPN Silicon Plastic-Encapsulate Transistor (SOT-23) (Rev.3-3-12012020)

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