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Old 10th June 2004, 03:44 PM   #1
Hemal is offline Hemal  Kenya
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Question Distorted Square Wave

Hi, I was hoping sum1 could help me out, I tried making a car amp using a toroid transformer from a kenwood amp, it works fine except that the FET's (IRFP50N06 x 4) heat up real quick with a small 240v 100W light bulb connected to the sec. The oscilloscope shows a "square" wave at the gates that is rounded at the edges. The secondary provides about 70v (35-0-35)
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Old 11th June 2004, 06:55 AM   #2
Immo_G is offline Immo_G  Australia
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Which IC are you using for the power supply, sg3525 ? tl494 ? I don't think the 3525 really can drive multiple fets well, and i'm going to try a tps2812 mosfet driver as a buffer, to see how it goes.
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Old 17th June 2004, 11:27 AM   #3
Tensop is offline Tensop  Lebanon
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the driving side of the pwm combined with track length and the capacitance of the mosfet will all add up when it comes to turn on/off switch states can you get a pic of the waveform? on mine (3525/2x fets per phase) there was quite a bit of rounding, from memory the capacitance added up to somewhere between 9 and 30nF
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Old 18th June 2004, 10:17 AM   #4
Tensop is offline Tensop  Lebanon
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buuuuut you also said that the mosfets are getting hot
disconnect the transformer, connect each of mosfets ouputs to the cro and see if they are overlapping.. that would cause the heat and the rounded edges(to some degree)
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Old 25th June 2004, 12:05 PM   #5
Hemal is offline Hemal  Kenya
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Hey I finally figured out wat da prob was, The KA3525A is good enough to drive da MOSFETS but da return traces 4da Sources of da MOSFETS 2ground were inadequte, nothin heavy gauge wiring couldn't solve. Now im running heavier loads (3 bulbs) and everythin runs coool! The MOSFET's stay at room temperature.

Thnx 4ur help n gud luck y'all.
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