I have worked on quite a few amps that had ferrite cores around the drain legs of the power supply FET's. Are these strictly necessary? I have had some cores I could reuse, but sometimes they don't survive the FET removal process. I have not ever been able to find exactly what cores are being used. I looked through digikey and here are ones that I came up with that seem to fit physical dimensions of a TO-220.
Ferrite Cores
Do any of these look like appropriate substitutes for cracked cores? Does it even matter? I seem to see these cores on IRF3205's most frequently.
Ferrite Cores
Do any of these look like appropriate substitutes for cracked cores? Does it even matter? I seem to see these cores on IRF3205's most frequently.
The ferrite beads may help VERY slightly reduce RF emissions which may help it meet a spec but they are not going to affect the operation of the amp. I used to replace them but I no longer replace them.
they add inductance in the current path common to input and output parts, and the it slows down the speed of switching.
Thanks. I understand their purpose, but wanted to know their necessity in repairs. They are rarely mentioned in rebuilds though. Got my answer.
I ussualy remove them. It is better to put them at the drain terminal. In the source, it slows down the rise and fall times, reducing the EMI, at the expense of increased switching loses, and heating the device. Still worse, if them are not covered, and touch drain and source pins, making a powerfull shortcircuit, as the ferite becomes conductive.
Linear Tech used this to design their low noise controllers -- obviously at the expense of heating the switching device -- but virtually eliminating EMI.
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