Rough waveform on SG3525 with pushpull circuit with feedback

Thread Starter


Joined Jun 12, 2021
I have made a circuit using SG3525 with pushpull configuration switching with a frequency of around 100kHz, with lower frequencies <30kHz the waveform is clean without big rippless but at 100kHz the rise and fall time is the same as with lower frequencies (around 500ns) but there is a spike in the waveform, it seems when the opposite signal goes to 0, there is an inductive spike maybe from the coil of the transformer, which has a center tap and and 3 turns for each of the primary coils and secondary has 95 turns which i've tuned the feedback circuit to keep the voltage at around 360V. I also used a an rc snubber between the coils of the primary, maybe i have to adjust the values of those, perhaps the values of components for timing i chose aren't suitable? I have to say that this is a circuit for a pure sinewave inverter, the high DC voltage is then used by egs002 spwm module to generate a pure sinewave, so i have this circuit on the breadboard currently which has a lot more parasitic capacitance this could also be the problem and for the last the sg3525 ic's im using arent genuine, got them from aliexpress so maybe they're not the best quality?

I would really appreciate some help from more skilled people to give me some tips on what could be the problem.

Best regards



Joined Aug 21, 2017
Just about now I am wrestling with a TL594 (what is close relative to Your SG 3525) with booster stage of 2110. The same problem - when upper shoulder is off and lower shoulder makes transition from off to on, then upper receives a massive delta-peak, thus the all transistors become damn hot in-spite the rather massive cooler. After making LT-Spice model, it also show the same problem, as soon the 2110 is applied. It happens even when the output transformer is substituted by purely resistive load. Before the 2110 signal is perfect, after it - awful. And dampfers - it all are individually optimized along with standard methodology (take oscillogram and calculate out of it the right values of C and R). Gates contain a due resistor and later I added a ferrite mini-ring on the gate feet, but it not helped much. As soon the other driver is used, there everything works well.... So is my current experience.
Thus I guess SOME boosters are better and some are habituating more badly.

PS Answering already not asked question, bootstraping circuit I use a tantal capacitor and 4148 diode, and oscillo on them not indicates anything wrong.
PPS - Only I havent tried (yet) is Miller Killer. Probably that is the true reason?? At least the author of following reference think so. https://electronics.stackexchange.c...itance-causing-igbt-to-turn-on-in-half-bridge

He writes following:
<<A bootstrap driver is wholly unsuitable for this type of IGBT. Notice Cres vs. Coes curve in the datasheet (also see edit below): this means for a voltage step on the collector, half that voltage appears on the gate. They're pretty awful as transistors go these days; but what do you expect from a 20-ish year old design, I guess. (Plenty fine for say motor drives, which was probably the main application they were used in.)
Devices like this, must operate with low enough gate drive impedance, and slow enough dV/dt on the switching node, that the differentiator thus formed (between the C-G-E capacitor divider, and total equivalent gate resistance), does not drop enough voltage to turn on the transistor, thus causing destructive switching (shoot-through). Vge(off) could be as high as a couple volts below Vge(th), but it is for this reason that it must be considerably less: the datasheet recommends -15 V.
Turn-on dV/dt is likewise controlled by RG and the same equivalent capacitance, so you simply wire up whatever gate drive you have, and adjust RG until switching is just safe enough under all operating conditions.
Your circuit may still work, but RG must be much higher to get dV/dt low enough to support it. This is a direct consequence of VGE(off) being only a few volts below VGE(th), rather than more than 15 below.>>
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