Power Transistor BU109 NPN, TO-3

Power Transistor BU109 NPN, TO-3

Transistors

Reference: TRBU109

Part.No: BU109

€2.95

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The BU109 is a high-voltage NPN power transistor in a TO-3 package, designed for line output (LOPT) and horizontal deflection circuits in CRT televisions and similar high-voltage switching applications. Its rugged construction withstands peak voltages in the kilovolt range.

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Description
Product Details

BU109 High-Voltage Power Transistor – LOPT & Deflection Driver

The BU109 is a pioneering high-voltage NPN power transistor, engineered to drive the flyback transformer in B&W and early colour television sets. It withstands kilovolt-range peak voltages and is designed for bolting directly onto large heatsinks, making it the standard choice for horizontal deflection and line output switching circuits.

Functions & Applications

Kilovolt-Range Peak Voltage: Built to withstand the extreme transient overvoltages generated by flyback transformers in CRT television circuits.
Robust TO-3 Package: Large metal can design allows direct bolting to heavy heatsinks for efficient thermal management.
High-Voltage Switching: Optimized for line output and horizontal deflection driver applications requiring reliable, repeatable high-voltage switching.
Legacy CRT Reliability: Proven workhorse in thousands of television sets, with a track record for ruggedness and longevity when circuit protection is adequate.

Technical Specifications

Parameter	Value / Specification
Transistor Type	BJT (Bipolar Junction Transistor)
Polarity / Channel	NPN
Package / Case	TO-3
Collector-Emitter Voltage (Vceo)	1500V
Peak Voltage (Vp)	3000V
Mounting Type	Bolt-On TO-3 (Heatsink Required)

Frequently Asked Questions

Q: Why does the BU109 keep failing in my TV repair?
A: If the transistor repeatedly burns out, the fault is almost always in the flyback transformer (likely shorted) or in the high-voltage snubber capacitors around it, not the transistor itself. Always test the flyback and snubber circuit before replacing the BU109.

Q: What heatsink do I need for the BU109?
A: The BU109 must be mounted on a large, heavy-duty heatsink with thermal compound. For CRT television applications, a metal radiator with fin surface area of at least 200–300 cm² is typical.

Notes

This is a legacy high-voltage transistor designed for CRT television and similar peak-switching applications. It requires proper heatsinking and protection from transient overvoltages. Not suitable for general-purpose low-voltage switching.

Note: Price refers to one (1) piece. The component is shipped in bulk without individual packaging.

Transistor Type: BJT (Bipolar Junction Transistor)
Transistor Polarity / Channel: NPN
Transistor Case Style: TO-3

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