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Gain (hFE) – The replacement should have a gain equal to or better than original and it should be as close to original specification as possible.
Gain-bandwidth (fT) – replacement should have a transition frequency equal to or faster than original and it should be as close to original specification as possible.
Below is a table of application requirement and important specification that you can use for guidelines when comes to transistor substitution.
Application Requirement and Important Specifications 1. General purpose low level amplifier and switching transistors. Spec- hFE, IC (max), fT, VCEO 2. Power switching applications. Spec- VCEO, VCBO, hFE, IC (max), PD (max) 3. Low level IF/RF amplification. Spec- IC (max), fT, VCEO 4. Audio amplification. Spec- IC (max), PD (max), hFE, VCEO 5. High voltage transistors. Spec- VCEO, VCBO, IC (max), fT
Remember, replacement transistor should not run hot and if problem still persist, try another replacement number or get original number if possible. Do not overlook that surrounding components also may caused transistor to run hot even if original number is used.
Jestine Yong is a electronic repairer and a writer. For more repair information, please visit http://www.noahtec.com