Blowing Transistors

[kewl_cat]

My Boss 5 blows a transistor every month or so. I remember George(Machintek) mentioning a few times that he has people that run years without popping a transistor. I personally keep a 10 pack of 2N6547's handy. The voltage is set correctly(a little on the low side but within range) and i have the amps on the drives set just under 8A. I have the rapid turned down a little on the RCK board. I recently tuned up the lube system with some new metering valves and Mobil Vactra #2. Any tune-up tricks to making these transistors last longer?

[NC Cams]

This topic was discussed on the 'Zone several weeks if not months ago.

In the discussion, a number of higher power, reverse voltage transistor options were outlined and the part numbers given. NOTE: You'll want to use the true part numbers from Motorola or the like and NOT some NTE or other aftermarket equivalents.

You might also find in the discussion that the fitting of some "flyback" diodes to/around the transistors could help prevent toasting the transistors. It seems that induced flyback voltages, indemic to stepper switching especially at higher speeds, creates "flyback" voltage that dumps reversed polarity voltage (and current) across the emitter/collector of the transistor which can and does take them out.

The fitment of "flyback" diodes involves the mounting of Schottky rectifiers across each of the switching transisors. If you look up stepper motor driver IC's on Google, you'll find examples of how to hook them up. Selecting them involves finding ones capable of high voltage potential and high current carrying capabilities.

When properly fitted, the induced "flyback voltage" (and current) get shunted around the transistor thus preventing them from getting toasted due to the momentary but normal reversed current phenomenon.

The use of the 'Zone's search engine is in your better interest as it should help you find the thread in which the proper parts to use can be found and some steps you can take to make the drive circuit a bit more robust.

[kewl_cat]

How about these transistors on Ebay?
http://cgi.ebay.com/ws/eBayISAPI.dll...7593&rd=1&rd=1

[NC Cams]

Go and read the following thread as it has a number of alternate transistors and other fixes for your problem:

http://www.cnczone.com/forums/showth...oss+transistor

[machintek]

Very important factors in transistor blowing are:
Do you have a SMS board?
What is output of T2?
Do you have snap in or screw in fuse holders on the DC side of the drive power supply?

George

[kewl_cat]

It does have a functioning SMS. T2 is 54V. All the fuseholders have been replaced with snap in except for one. You pull the lever and the fuse comes out. What type of fuse holder is it so I will know what to order. I will replace that fuse holder and go from there. Many thanks.