systemloc
Newbie level 1
I'm slowly teaching myself to build a flyback SMPS from the ground up, including the transformer. I mostly use scrap parts I salvage.
In my latest experiment, I built a test circuit similar to Ronald Dekker's:
From: https://www.dos4ever.com/flyback/flyback.html#ind2
I used an LM556, with one half generating a pulse every 270 microseconds, and the second half to generate a variable length pulse of 5-35 microseconds, which drives the power MOSFET. (Very low duty cycle to ensure transformer fully discharges)
I took a salvaged flyback transformer from some broken electronic device, and attached the highest inductance secondary to the circuit, at 13.8V, and played around with looking at saturation and voltage on the primary.
I noticed when I drive the thing with more than 30 microseconds at 13.8V, it begins to whine at a high pitch. Of course, this is driving the wrong coil, and driving it for much longer than the 80-100 kHz it likely saw in the original circuit. I think it must whine because I'm driving it to saturation. Would excessive current cause an excessive magnetic field strength causing the wires and/or ferrite to vibrate?
I also noticed a lot of ringing in my circuit, as I haven't gotten to adding snubbers yet. I can't imagine they would contribute sufficient to cause the whine, though.
Thank you!!
In my latest experiment, I built a test circuit similar to Ronald Dekker's:
From: https://www.dos4ever.com/flyback/flyback.html#ind2
I used an LM556, with one half generating a pulse every 270 microseconds, and the second half to generate a variable length pulse of 5-35 microseconds, which drives the power MOSFET. (Very low duty cycle to ensure transformer fully discharges)
I took a salvaged flyback transformer from some broken electronic device, and attached the highest inductance secondary to the circuit, at 13.8V, and played around with looking at saturation and voltage on the primary.
I noticed when I drive the thing with more than 30 microseconds at 13.8V, it begins to whine at a high pitch. Of course, this is driving the wrong coil, and driving it for much longer than the 80-100 kHz it likely saw in the original circuit. I think it must whine because I'm driving it to saturation. Would excessive current cause an excessive magnetic field strength causing the wires and/or ferrite to vibrate?
I also noticed a lot of ringing in my circuit, as I haven't gotten to adding snubbers yet. I can't imagine they would contribute sufficient to cause the whine, though.
Thank you!!
