Moreover, the spwm signal generated from DSP also affected by the distortion as shown in waveform.
This is what I try said how the DSP signal also affected after the Dc supply is turned on, where suppose the DSP signal should be maintain, am I right?
Seeing spikes in a particular waveform doesn't mean that they are actually there.
Won't expect much noise here. The waveforms show crystal clear that the switching power stage itself generates the noise.Measure DC supply (60 V supply) noise (unconnected to the present system).
Can you ramp up the 60V or is it on/off? Ramping helps gather more information.
Scope noise would increase mostly proportionately.
A functional problem I'd expect to see it transition from none->intermittent->consistent as input voltage ramps up.
Still question the +15/-15V as that's an unnecessarily large gate drive in most applications, though probably unrelated to this particular problem.
I noticed a possible design problem. Is the PWM control voltage really only about 2V as indicated in post #5? If so, the required TLP350 input current won't be achieved. Could be a reason for drop out effects.
Hi,
Schmitt-trigger buffer:
HC types (for 3.3V supply) have poor output drive capabilities.
HCT types (for 5V supply) ... the same.
Consider to use
* LCX14 or AC14 for 3.3V supply
* Or ACT14 for 5V supply.
Klaus
I presume, you are not able to probe Vgs exactly at the MOSFET pins. Thus it's still unclear, if the oscillating waveform exists at gate or it's mainly a common mode measurement artefact. If present, it would cause multiple MOSFET edges, high switching losses and EMI.From this figure, the spike about 16.5V is occurring during the mosfit turned on. I hope this spike will be eliminated after the modification on the layout.
I suggest to increase the TLP350 LED current first and reevaluate the behavior.
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