Thanks FvM for the reply. I am measuring primary side leakage inductance. (secondary side is shorted). Which frequency should I measure the leakage inductance (at 250 Hz which transformer operating frequency or 100kHz which is pulse width equivalent (10us).Typically you get negative inductance values if you measure above transformer self resonance frequency. I don't understand at first sight why you get negative inductance values at these low frequencies.
Inductance measurement has nothing to do with transformer operation mode, e.g. duty cycle.
What are you measuring, primary or secondary leakage? For full transformer characterization, I usually measure 4 parameters, primary and secondary inductance, other terminals both open and shorted.
According to instrument accuracy curves, negative inductance measurement in the post #1 results is merely an artefact. Apparently a more or less plausible leakage inductance of 1 µH has been identified in later measurements. Unfortunately you didn't tell if it's measured on the primary or secondary side.Negative inductance is merely capacitance.
Thanks FVM for the reply. I am measuring at primary with the secondary shorted for measuring through LCR meterAccording to instrument accuracy curves, negative inductance measurement in the post #1 results is merely an artefact. Apparently a more or less plausible leakage inductance of 1 µH has been identified in later measurements. Unfortunately you didn't tell if it's measured on the primary or secondary side.
1uH and 5 MHz ringing frequency makes 1 nF.
I have used two IGBT modules to SKM 200GB 12E4. two generate Bipolar Square wave. This Bridge is connected to Step Transformer.Hi,
What diode did you use?
(I think about big trr.)
Klaus
Thanks Easy Peasy for the reply. Are toroidals or U Cores better suited for this. I have tested with toroid as it has inherently lower leakage compared to U core. Also I am getting better magnetising inductance (390uH at 100kHz) with Toroidal Core. With U core I am getting very low magnetising inductance of 50uH at 100Khz. What winding structure is good for toroid. Also can you refer me to the type of transformer core shape (planar) and design materials for the same.@ Klaus - no diodes by the look of it,
the capacitance is easily measured at a few 100 Hz or less, no need for a VNA for that, what would be instructive is a look at the Z for the shorted Tx - I note that the Ridley box does this very well from 1Hz to 10MHz with little error.
One can easily see from the waveforms that excess capacitance is the cause of all the ringing - there are ways to wind to reduce this - for pulse applications a very in-depth knowledge of Tx design and construction is necessary to get clean pulses with sharp rise times ( low leakage ) - esp at the several kV you seem to be requiring ...
We have designed planars with leakages < 1nH for this purpose - the wiring to and from the Tx dominating the stray L - hence the driver must be very close to the Tx too if you want best results.
... only after the current has fallen to zero - during the power pulse & after switch off - there is significant current in play causing the source Z to be low - after the current drops to near zero, only, will there be ringing according to the parasitics - and then again - only if the bottom IGBT devices are left off - they may be ON to limit this effect ( or the Tx pri may be shorted some other way ).Coss of each polarity will interact with Lp and transformed secondary.
Yes the equivalent model is an assumption with just a load resistor at 1nH/mm and the layout, driver impedance and load capacitance are unknown affecting the results.The trouble is - the load is unknown, so measuring the slopes is all assumption.
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