For the dc-dc converter circuit and waveforms attached, I have the following questions for the switching current spikes. The implementation detail is as under.

Switching Frequency: 100 kHz
Duty cycle: 80 %
MOSFETS are driven by MC33152 (https://www.onsemi.com/pub/Collateral/MC34152-D.PDF) with 6.5 V peak voltage.
MOSFET: IRFP260N
Average switch current: 12 A
1st (top) waveform: switch S1 current
2nd waveform: switching signal for switch S1
3rd (bottom) waveform: switching signal for switch S2

1) Why these current spikes appear in the switch current? Are they usual or unusual? Any IEEE reference in past 5 years that have discussed the origin of these spikes.
2) How these current spikes can be reduced, if the actual reason is known?

BTW, the drain-source voltage waveform of switch S1 is clean (no apparent voltage spikes).

 

You could add an RC snubber circuit across the MOSFET.

 

Gate suppression as well as snubbers.

https://toshiba.semicon-storage.com/info/docget.jsp?did=13416

https://www.st.com/content/ccc/reso...df/jcr:content/translations/en.DM00560907.pdf


Regards, Dana.

 

Keep in mind that some of what you're seeing in those scope traces may be an illusion caused by the inductance of your scope probe's ground lead-- that is, the ringing may not actually be happening in your circuit, but instead showing up in your scope picture because the ground lead inductance is resonating with the probe's tip-to-ground capacitance, making a series resonant circuit.

When examining circuits with high-frequency signals, or signals with very fast risetimes, scope probes should always be grounded to the circuit through the shortest possible connection to avoid this problem.

For more explanation, see this thread.

 

BTW forgot to mention that I don't have current probe (cannot afford) and measuring the current in terms of the voltage across a 0.02 Ω resistor (see the attached schematic). The resistor is a parallel combination of 5 0.1 Ω, 5 W resistors.

When examining circuits with high-frequency signals, or signals with very fast risetimes, scope probes should always be grounded to the circuit through the shortest possible connection to avoid this problem.

You suggest it is primarily the probe issue.

 

You suggest it is primarily the probe issue.

I wouldn't say primarily; just that the probe grounding issue may be contributing some of what you're seeing on the scope.

 

In these ap notes some screen shots on probing.

https://www.keysight.com/upload/cmc_upload/All/Probing-6-Hints-Scopes-Dec12-2007-webcast.pdf

http://www.tek.com/dl/Probing%20Techniques%20for%20Accurate%20Voltage%20Measurements%2051W_60161_1_HR_Letter.pdf


DIY differential probe -

https://www.analog.com/en/design-ce...illoscope-differential-probe.html#cc-overview

https://hackaday.com/2016/03/31/diy-active-sub-ghz-differential-scope-probe/

https://www.baldengineer.com/links/diy-active-differential-probe-project

Many more on web.


Regards, Dana.