Hi All,
I have a current transformer with 1:100 turns ratio in my fly-back converter. It is designed such that a current of just over 2.5A will trigger a current limit at approximately 3V input to a DSP. I have attached a schematic to this post.
Unfortunately, the output voltage is not at all what I expect. When the switch is off, the voltage is a positive DC signal. When the switch turns on and current flows through the current transformer, the voltage drops right down and often falls below zero and becomes a negative signal. I have also attached an image of the observed waveform, with switching frequency of 650kHz. The CTX is able to operate at 1MHz.
What I would expect is zero DC voltage when the switch is off, and a positive going peak that hits 3V when the switch is on. I was suspicious that I connected the transformer with the wrong polarity, but the waveforms suggests that something else is afoot here.
Does anybody have any suspicions of what may be occuring here? Picture 4 is the current transformer output at the sense resistor.
I have a current transformer with 1:100 turns ratio in my fly-back converter. It is designed such that a current of just over 2.5A will trigger a current limit at approximately 3V input to a DSP. I have attached a schematic to this post.
Unfortunately, the output voltage is not at all what I expect. When the switch is off, the voltage is a positive DC signal. When the switch turns on and current flows through the current transformer, the voltage drops right down and often falls below zero and becomes a negative signal. I have also attached an image of the observed waveform, with switching frequency of 650kHz. The CTX is able to operate at 1MHz.
What I would expect is zero DC voltage when the switch is off, and a positive going peak that hits 3V when the switch is on. I was suspicious that I connected the transformer with the wrong polarity, but the waveforms suggests that something else is afoot here.
Does anybody have any suspicions of what may be occuring here? Picture 4 is the current transformer output at the sense resistor.
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