Product Overview
Motorola BF423 High Voltage PNP Transistor in TO-92, Marked and Unused, Sold One Piece at a Time
Condition
New, unused stock. The photographed piece is a black epoxy TO-92 with the flat face printed BF over 423, and below that the Motorola script M followed by 151. The reverse is plain black with a small round mold mark and carries no printing. All three leads are straight, full length, untrimmed and unbent, with a dull matte mottled grey finish and no solder, flux or bend marks anywhere on them. The body shows no scuffs, no cracks and no rubbed lettering. One piece was photographed loose on the bench and again in hand for scale; it is representative of the stock, and the trailing code after the script M can vary from piece to piece. We have not powered this device up, so the electrical figures below are Motorola's published ratings for the type rather than measurements taken on this piece.
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Product Overview
The BF423 is a high voltage PNP silicon transistor in the three lead TO-92 plastic package, the small black half-round case that has been the standard low power through-hole outline for decades. This one carries the Motorola script M on the face, so it is a Motorola-marked part rather than a second-source copy. Motorola's published small-signal device data gives the BF423 a collector-emitter and collector-base breakdown of -250 V, an emitter-base rating of -5.0 V, and a continuous collector current of -500 mA - a genuinely useful current for a package this size, and the figure our older listing text has carried all along. Published power dissipation is 625 mW at 25 C ambient, DC current gain is 50 or better at -25 mA and -20 V, and transition frequency is a minimum of 60 MHz. It is the PNP complement to the NPN BF422, and Motorola pitched the pair at high voltage video output stages, CRT deflection circuits and high voltage linear amplifiers. Sold each, 27 pieces on the shelf, so you can buy the two you need for a board or a dozen for a run without taking a reel.
Key Features
- Device type: PNP silicon transistor, high voltage class, complement to the NPN BF422
- Package: TO-92 (TO-226AA), three straight untrimmed leads, Motorola Case 29-11
- Published breakdown: V(CEO) -250 V, V(CBO) -250 V, V(EBO) -5.0 V
- Published continuous collector current: -500 mA
- Published power dissipation: 625 mW at 25 C ambient
- Published DC current gain: h(FE) 50 minimum at I(C) -25 mA, V(CE) -20 V
- Published transition frequency: 60 MHz minimum
- Published pinout, Motorola Style 14: pin 1 emitter, pin 2 collector, pin 3 base - confirm against the datasheet before wiring
- Case marking: BF 423 with the Motorola script M and a trailing 151 code
- Brand: Motorola, identified by the script M logo on the case
- Condition: new and unused, no lead trimming or soldering
- Sold each, 27 pieces in stock
Applications
- A monitor or television tech rebuilding a CRT deflection or video output stage, where the drive transistor has to stand off a couple of hundred volts and an ordinary small-signal PNP simply will not survive
- An audio or instrumentation builder putting together a high voltage linear amplifier stage and wanting a PNP that can sit at -250 V without derating the whole design around it
- A repair shop matching an original BF423 on a European-designed board, or pairing it with the NPN BF422 to restore a complementary output pair
- A hobbyist driving nixie tubes, VFDs or other gas discharge displays and looking for a small high voltage PNP in a through-hole package
- A bench engineer prototyping a high voltage switching or level-shift stage and wanting three or four known-marked pieces instead of a sealed reel
Frequently Asked Questions
What do the markings on the case actually say?
The flat face reads BF on the top line, 423 on the second line, and on the third line the Motorola script M followed by 151. The BF423 is the part number; the script M is the maker's logo; the 151 is identified in Motorola's published device data as a lot and date code, not part of the type number, and it varies between pieces.
Is 500 mA really right for a TO-92 part?
Yes. Motorola's published device data for the BF423 gives -500 mA continuous collector current alongside the -250 V breakdown, with 625 mW of dissipation at 25 C ambient. The current and the voltage are separate limits, not a simultaneous operating point - at anything near full current you are nowhere near full voltage, or you would be well past the power rating. Read the safe operating area curve in the datasheet before you design to the corners.
Is this an original Motorola part or a second source?
The photographed piece carries the Motorola script M on the case, which is Motorola's own semiconductor logo, so it is Motorola-marked. BF423 was made by several European and American manufacturers over the years, so if your build documentation calls out a specific source, this is the Motorola one.
Which lead is which on a TO-92 like this?
Motorola's published Style 14 pinout for this case reads emitter, collector, base across the leads with the flat marked face toward you. We are passing that on as the published figure rather than as something we have rung out on this piece, and pin order genuinely does differ between transistor families - so check it against the BF423 datasheet diagram or a component tester before you commit the part to a board at 250 volts.
Will the piece I receive look exactly like the one in the photos?
The BF423 type number and the Motorola logo will be there. The trailing code after the script M is identified in Motorola's published device data as a lot and date code, and it can differ between pieces on the shelf, and the photos are the spec for the piece we photographed rather than a guarantee of identical printing across all 27. If a matched set of identical codes matters for your job, ask us before ordering.
Why buy two or three of these here instead of a bag of 100 somewhere else?
Because almost nobody needs 100 high voltage PNPs. A CRT rebuild wants one or two, a display driver board wants a handful, and a bench spares drawer wants three. We sell the BF423 one piece at a time out of 27 on the shelf, so you pay for the count your board actually calls for instead of a forced minimum lot with 97 pieces left over. Shipping is $8 flat rate and free once your order passes $28, and orders leave our Idaho warehouse the same or next business day.
Two hundred and fifty volts of standoff and half an amp of collector current, in a body the size of a pencil eraser - Motorola built the BF423 for the corner of the circuit where an ordinary transistor quietly gives up. Take the two or three your board actually needs and leave the rest of the drawer to us.
