Understanding Transistor Data and Replacement

If, for some reason, you can’t find the exact part number for the transistor that you want to substitute, you can always refer to one of the guide book for transistor substitution , and try to identify a “near replacement”. The most general transistor substitution guides used is the Philips ECG Semiconductor Master Replacement Guide. Finding the right transistors parameters or specifications for the equipment you repair will avoid callbacks from your customers. Callbacks or repeated repairs due to wrong transistor substitution will waste your precious repair time and money! So understand each of the transistor parameters below carefully and once you master it there will be no more problem in finding substitution for transistor.

Some important transistor parameters are:

Maximum collector-to-base voltage (VCBO) – The replacement transistor should have a VCBO rating equal to or higher than the original transistor.

Maximum collector-to-emitter voltage (VCEO) – The replacement transistor should have a VCEO rating equal to or higher than the original transistor.

Maximum emitter-to-base voltage (VEBO) – The replacement transistor should have a VEBO rating equal to or greater than the original one.

Maximum collector current (IC) – The replacement transistor should be able to handle as much (or more) collector current as the original one.

Power dissipation (PD Watts) – The replacement transistor should be able to dissipate as much (or more) power as the original one.

Gain (hFE) – The replacement should have a gain equal to or better than the original transistor and it should be as close to the original specification as possible.

Gain-bandwidth (fT) – the replacement part should have a transition frequency equal to or faster than the original transistor and it should be as close to the original specification as possible.

Below is a table of application requirement and important parameter that you can use for guidelines when comes to replace your transistor.

Be in mind that the replacement transistor should not run too hot and if problem still persist, try another replacement number or get the original transistor number if possible. Do not overlook that the nearby components also may caused the transistor to run hot even if original transistor number is used. As for me the rule of thumb is always check the surrounding components first before fit in the transistor otherwise the replacement transistor will blow in seconds and you will be back to the square one. For example, whenever if there is a horizontal output transistor shorted in a monitor i will always scan thru the flyback, b+ voltage, dry joints, capacitor nearby the horizontal output transformer before put in a new transistor. Very seldom the transistor will spoilt by itself (maybe applicable for certain monitor only) usually there is components failure in the electronic circuit that causes the transistor to go shorted.