How do I kickstart ZCS half bridge inverter

[anotherbrick]

hello dear forum

I finally amplified Current Trafo output and now I have got clean high and low side gate pulses
for half bridge inverter ( at present I drive the gates with STM32 )
however I plan to operate the inverter without STM32 and in that case I need to kickstart the inverter initially
becouse without initial current flowing out of inverter I have no pulses from CT

how do I kickstart the inverter ? any advise please

thank you

 

[BradtheRad]

Sometimes you need to create imbalance of values between symmetrical sections. The imbalance might be slightly different resistors, or different transistor gains, etc. Anything to cause one side to start conducting in preference to the other side.

Do you need to pull an input briefly high or low at power-up? There's the method of installing a series capacitor and resistor across supply rails. By connecting the capacitor to ground, it pulls the input low briefly. Or by connecting the cap to supply +, it pulls the input high briefly.
Make the resistor value great enough so it doesn't prevent normal running.

 

[anotherbrick]

hello dear forum members

finally I gave kickstart to inverter with following circuit

everything fine , inverter started

this is the US horn which the inverter is driving

everything fine , inverter started

however the horn is 20 Khz nominal

as you can see amplified CT is showing a frequency of approx. 50 Khz

what can be the reason for this frequency error ?

I am trying to make a ZCS inverter - should not firing the MOSs at ZC point bring the system to resonance at nominal freq of horn ?

thank you

PS. CT amplifier and the other 2 Opamps are high freq ( 145 MHz BW )

 

[anotherbrick]

here the schematic

 

[d123]

Hi,

Do those fascinatingly mysterious zigzag, parallel and wiggly lines also come with names and numbers of any kind?

 

[Easy peasy]

there is a phase delay between zero cross in the horn ckt and zero cross at the mosfets - that is your issue ...

 

[anotherbrick]

if the problem is phase delay then does this mean that it is impossible to make ZCS mode inverter ?

because there will be always a non zero phase delay between the actual zero cross of current
and the firing of MOSs because of the delay in the electronics

am I wrong or is there another solution for ZCS ?

 

[dick_freebird]

Usually / traditionally, the "kickstart" ("motorboat",
"hiccup") mode comes from UVLO release and
subsequent re-assert, when the part is dual-fed
by a startup resistor and a diode-blocked boot
winding on the power inductor.

 

[anotherbrick]

Usually / traditionally, the "kickstart" ("motorboat",
"hiccup") mode comes from UVLO release and
subsequent re-assert, when the part is dual-fed
by a startup resistor and a diode-blocked boot
winding on the power inductor.

hello freebird ,

does UVLO mean under voltage lock out ? or something else
can you open your answer a little bit
sorry I didnot understand you - can you help a little with a schematic?it is important for me your answer

thank you