Swend
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Maybe you should tell us what we’re looking at. Maybe you should tell us what your input is. Maybe you should post a schematic.
What exactly is driving them, the waveform suggests it is a single pulse and the transformer is 'ringing'.
Are the tabs mounted on a a heatsink? I appreciate they are insulated but the accumulated capacitance of 40 diodes will have some effect at those frequencies.
I would also like to know how you are measuring 16KV with the scope, obviously some probe with a very high input impedance, does it have the bandwidth to handle ~500KHz?
capacitance will dominate for hi-Z loads ... and when the source is hi-Z
you can buy special diodes for EHV and higher currents - not that cheap - but do work ...
It's not surprizing to see large ripple at the rectifier output. Negative voltage as shown is however not feasible. Most likely explanation is the waveform distortion by the uncompensated voltage divider.
The voltage divider tranfer function should be checked with a square wave generator and corrected by compensation capacitors.
I suspect that the voltage is not getting shared equally by the diodes. You need to put resistors in parallel with the diodes so that the applied voltage is divided equally.
The value of the resistors to be decided by the reverse leakage current of individual diodes.
Does it work with lower frequency? Say 1kHz or 10kHz?
Is your scope probe frequency compensated?
In post #5, you show the primary side single pulse. The ringing is coming from the probe or the transformer?
Rectifier output voltage is clamped to n*diode forward voltage, e.g. a few 10 V in your design.But what makes you say negative voltages are not feasible here? I'm asking out of ignorance and for educational purposes.
Are you compensating the probe alone or with the HV divider resistors attached? You need to apply the square wave through the divider then do the compensation. I suspect you have inadvertently added an RC low pass filter in your measurement.You mean by feeding it a square wave and turn the trim-cap? Yes
Here is the output of the bridge rectifier when load resistance is 30Kohm. you have to multiply v/div with 1000 to get the correct voltage.
Is that how diodes in series are usually done?
For low frequency (say 50-60Hz), you can protect the diodes with capacitors and resistors. They help suppress spikes.
The capacitor cannot be used for high frequency. I do not know other ways to protect the diode from the reverse breakdown. It becomes really important when you have diodes in series.
Are you compensating the probe alone or with the HV divider resistors attached? You need to apply the square wave through the divider then do the compensation. I suspect you have inadvertently added an RC low pass filter in your measurement.
The scope traces look suspicious to me. Given that the scope, probe and stray capacitance is effectively the load after 100M of resistance, I would have expected the opposite to have happened, the trace would have a slow rising and falling edge. Adding extra capacitance at the bottom would make it worse, not better. Possibly the 100M resistor itself has a relatively high capacitance so it is effectively more conductive than Ohms law would suggest at that frequency.
I remember seeing the schematic for a Tektronix HV probe similar to the one in the photo. The compensation network was really complex, as you can tell from the several visible adjustments.
I concur with the rest of the posters: your uncompensated voltage divider is distorting the waveform.
Compensation ideally works only for a fixed frequency. Why the frequencies seen in post 14 for the square pulses are so low?
I remember seeing the schematic for a Tektronix HV probe similar to the one in the photo. The compensation network was really complex, as you can tell from the several visible adjustments.
Compensation ideally works only for a fixed frequency. Why the frequencies seen in post 14 for the square pulses are so low?
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