2N2907A PNP transistor: pinout, ratings and a 12 V high-side switch

Read the print on the flat face: 2N2907A, sometimes PN2907A, with a maker's logo and date code. Both makers cited here list only the A version, and this page covers that part. The SOT-23 version is the MMBT2907A, marked K2F. All of them are PNP, so on diode test the black probe goes on the base.

Both makers rate it for 60 V collector to emitter and 600 mA continuous, with 800 mA peaks. The TO-92 part can dissipate 625 mW at 25 °C; the SOT-23 one only 310 to 350 mW, depending on the copper under it. A PNP datasheet prints every current and voltage with a minus sign. The tables here give magnitudes.

Gain holds up well: at least 100 from 1 mA to 150 mA, and still 50 at 500 mA. Note the test voltage, though. Both sheets measure gain at 10 V across the transistor, not the 1 V a 2N3906 sheet uses, so the figures flatter a saturated switch a little.

The two sheets differ on saturation. At 150 mA with 15 mA of base current, Diotec promises 0.3 V across the transistor and Diodes 0.4 V. At 500 mA, Diotec says 1 V and Diodes 1.6 V. Only Diodes gives the base-emitter voltage, 1.3 V at most at 150 mA. The worked example uses the worse figure each time.

A 150 mA load on 12 V: emitter to +12 V, load from the collector to ground, and a resistor from the base to a driver that pulls it to ground to turn the load on. A microcontroller pin cannot be that driver directly, because its high level never reaches 12 V and the transistor would never turn off. Put a small NPN such as a 2N3904 in front, or use an open-drain output rated for 12 V. 150 mA is a point both datasheets test at, so every limit below is printed.

On a 5 V rail the same 150 mA needs R ≤ 247 Ω, so 220 Ω and 16.8 to 22.7 mA of base current. That is more than most microcontroller pins should sink, which is one more reason to drive it from an NPN.

The sheet says 600 mA, and the saturation table goes up to 500 mA, so it is tempting to switch half an amp with it. Work out the heat first. At 500 mA with 50 mA of base drive, the collector drop is 1 V on Diotec's sheet and 1.6 V on Diodes', and the base adds up to 50 mA × 2.6 V. That is 630 mW to 930 mW, against a 625 mW rating that only holds at 25 °C.

In a 40 °C enclosure, at 200 K/W, the junction has 110 °C of room before it reaches 150 °C. The 500 mA case needs 126 °C to 186 °C. The 150 mA example needs 17 °C.

For continuous loads much above 150 mA, use a part in a bigger package. The IRF9540N on our IRF540N page is a P-channel MOSFET that does the same high-side job at several amps, given a gate drive of about 10 V.

• Switching the positive side of a load up to about 150 mA on 12 V or 24 V rails, where a 2N3906 would be out of saturation.
• The PNP half of a complementary pair with a 2N2222A: push-pull drivers for a MOSFET gate, a speaker or a small motor.
• Fast switching at moderate current: Diodes gives 45 ns turn-on and 100 ns turn-off at 150 mA.

• Put a resistor from base to emitter (10 kΩ is common) so the switch stays off while the driver is starting up or disconnected.
• For a relay coil, put a diode across the coil, cathode to the collector side. Without it the coil's turn-off spike lands on the 2N2907A.
• Check the base resistor's wattage. At 12 V and 1:10 drive it carries about 210 mW, which a small 1/8 W resistor will not take for long.
• Measure a suspect switch from the rail: on, the emitter-collector drop should be a few hundred millivolts. A volt or more means it is short of base current or carrying too much load.
• The SOT-23 MMBT2907A has half the dissipation of the TO-92 part. Do not copy a TO-92 design onto it without redoing the heat sum.

1. Set the meter to diode test. Put the black 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 a PNP; on a TO-92 2N2907A it is the middle lead.
2. Reverse the probes: both junctions should read open, and the outer leads open both ways.
3. With the flat face toward you, the emitter is the left lead and the collector the right.

The transistor testing lesson goes through it step by step, and the BJT as a switch lesson explains why the 1:10 drive ratio matters. For the meter itself, see continuity and diode test.

Use a 2N2907A for high-side loads up to about 150 mA on 12 V, with 680 Ω (1/2 W) for 1:10 drive and a 2N3904 or 2N2222A pulling its base down. For much more current, or in a hot box, move to a P-channel MOSFET or a TO-126 or TO-220 transistor rather than pushing the TO-92 part toward its 600 mA rating.

The 2N2907A is sold loose, often in the same bins as the 2N2222A, so check the print before you fit it. Our guide to buying electronic components in India compares ten online sellers and covers how to spot fakes.