High Voltage Transistors

Some simple explanation about high volatage transistors

High voltage transistors is a transistor with higher specification than the normal transistor. It is usually located in the area of power transformer such as the switch mode power transformer and flyback transformer. In television, monitor, oscilloscope, radar that uses the flyback transformer to generate high voltage, a high volatage transistor are required to perform the job. It's location mainly beside the flyback transformer and attach to a heat sink in order to transfer heat faster. Otherwise it may blow in a very short time due to the hard work of this transistor in switching.

Typical part number of high voltage transistor that used in monitor and Tv is BU2520DF, C3997, C5148, C5047, C5589 , C5802 and etc. Usually their rating of volt, amp and watt is in the 1500 volt and above, 10 amp, 50 watt and more. Their sizes are much more bigger than the common signal transistor.

If this high voltage transistor blow or spoilt, you have to find the exact replacement in order for the equipment to function in tip top condition. Replacement usually don't work very long-perhaps in the few weeks or few months time and it will blow again. Unless you know the storage and the fall time of the transistor. Higher volts, amp and watts will not guarantee that your transistor will last long. Sometimes it will blow in a split of seconds the moment you switch on the equipment.

You have to go to that particular manufacturer to get the transistor datasheet and find out the spec of the transistor. Look for the fall time and storage time value. The original and the replacement value should have tolerance of not more than 20%. If not the replacement transistor will run hot and eventually blow the transistor. This will waste your precious time . As to why sometimes even the nearest specification transistor also won't work well is because the particular equipment such as monitor, the yoke coil and the flyback transformer are designed based on the specification of the transistor. Thus, only original part number transistor that can be install in that particular equipment.

I have seen even the original number with different batch of transistor when install in the monitor causing the display to curve in (pincushion out) and the transistor runs very hot. I've checked all the circuit and components that connected to the transistor to be ok. Even replacing the flyback transformer also didn't help. The transistor's temperature keep rising and if i don't switch off the monitor, i believe it will eventually blow the transistor. I took out the transistor and compared with the original number and discovered that the replacement logo is a little bit different from the original transistor logo. When i called the supplier about the logo, they said that the transistor that i bought is of a newer version, thought from the same factory.

After long hour of searching for the original transistor i managed to find one. Unbelieveable, the original transistor that i replaced runs cool and the picture is perfectly fine. Guess what is the high voltage transistor number? It was C5148!