Hi every one, i am a new user of this forum.
I have a problem with my inverter that i use for transform the battery energy to alternative voltage for my house.
I have an fotovoltaic plant and it is my passion.
On the board of this inverter there are 2 KA7500B (one for first stage dc-dc and one for second stage dc-ac).
There are 16 mosfets (8 IRF3205 and 8 SW740) and one LM324 also.
As first thing i found three final mosfets (SW740) in short circuit and i replaced them with others good.
Before of this operation i didn't the voltage after the transformer, while now i have 450vdc after the rectifier bridge, but still i haven't the Ac output voltage.
The capacitors after the bridge are 3x47μF 400v.
Why the voltage is so higher?
it should be about 310 vdc?
I checked the npn transistors drivers of second stage (2 x ksp44) and them are ok.
On web i found an schematic similar to my circuit, but not perfectly same.
Can you give me some suggetions for solve the trouble?
Thank you so much everyone
Kyu9971

 

Best guess at this point being your secondary DC rail voltage is so high I would suspect some part of your feedback circuit that monitors and tells the primary switching device driver circuits to regulate the voltage is bad or at least has a bad connection.

 

The problem can be the lm324 that connect both the ic pwm controller?

 

High possibility being that the feedback loop runs through it.

 

Thank you so much, tmctech,
Tomorrow morning i will try to replace it and after give you the response.
It is the only smd component on this circuit.
I have an hot air welding station, but i not believe that i have another lm324 smd.
For to try, can i to use an traditional lm324 and connect it with the wiring?

 

i replaced the ic lm324 and the ka7500 of the first stage, but the problem persists.
i have always an high voltage (450 vdc) after the rectifier bridge and i haven't AC in output.
i attached some pictures so you can see better the problem.
i have the signals on pin 9 and pin 10 of the first ka7500, about 40 khz. (i set 5 uS time base)
while on the pin 8 and pin 11 of the second ka7500 i haven't the altenative signals, but them are continue.
i believe that i should have two 50/60 hz signals
the first picture show the signal on pin 9 or pin 10 of first ka7500.
the second and third picture show track side where there is the ic lm324 that i replaced.
the fourth picture show the signals on pin 9 and pin 10 together ( i used two probes)
and finally the last picture show the component side.
do you have some ideas to solve this problem?
thank you so much
kyu9971

 

Is the reference voltage coming from the HV side going back to the PWM IC through the LM324 getting there?

If it is either the IC has its reference voltage is missing or it has a bad feedback input and needs to be replaced .

 

i am searching to understand as the feedback accross the lm324 connecting the two pwm ic.
unfortunatly my circuit is different in some parts of diagram.
i measured the output voltage on pins out of the lm324 and all four parts of ic are to voltage zero.
at the moment all the integrated circuits are replaced.
on pins 14 of both ka7500 i have 5 volts reference
in my circuit one of four parts of this ic is used for cooler fan motor.
can you give me some suggestions
thank you so much.

 

So the first Tl494 is oscillating giving 450dc across C24, but the second Tl494 is not giving signals on pins 9,10.

what is the voltage on pin 4 of the second tl494, this is the shutdown pin,high for shutdown,low to oscillate,

 

ok,
thank you so much for this help.
while the first tl494, use as output the pin 9 and the 10, the second tl494, use as output the pin 8 and 11 as you can see by diagram.
with the 12,4 voltage of battery on pin 4 i have 4,28 volts.
on the pin 8 and 11 i have 11,28 volts on both, but this signal is continue instead alternative.
i tryed with my scope on various time base set.
instead on the pin 9 and 10 of first tl494 i have two waveform (square) at 40 khz.
thank you still
kyu9971

 

pin 4 should be at zero volts for it to work......put a temporary link from pins 4 to 7.

 

i followed your suggestion and i linked pin 4 with pin 7 (gnd).
two final mosfets are broken (irf740).
luckily only these.
i replaced with others two good and now i am to start point.
high voltage dc (450vdc) on capacitor, two signals from IC1, but nothing AC voltage in output.

 

if you disconnect the outputs of the tl494 to the fets do you have complimentary signals on pins 8,11.

 

ok, i disconnect the pin 8 and 11 (IC2) from the rest of the circuit and check the signals
i must leave the link between pin 4 and 7?

 

with pin 8 and 11 disconnected to rest of the circuit i have two fixed signals (no waveform):
i connected the pin 4 with pin 7
these are the voltage on pins

pin 8 0,69 volts
pin 11 0,74 volts

 

you need to leave the pull up resitors on pins 8, 11 connected to pin 12, thats R19 and R21 they are 1K,and remove the connections to the fets, if there is still no signal the chip maybe defective or its components blown.

datasheet for Tl494 http://pdf.datasheetcatalog.com/datasheet/texasinstruments/tl494.pdf

 

In this way?

 

yes, assuming that circuit is what your inverter is like.

 

i did the test that you told me to do.
with the link from pin 4 and pin 7, not work also the first stage.
without the link from pin 4 and pin 7, i hear continued sound from the buzzer and the first stage not work also.
nothing voltage on the capacitors.
after, I connected everything as before and the result is always the same.
450 vdc on capacitors, but nothing ac voltage output
i tryed to understand as in my circuit are connect the components and follow the track i redesigned a part of final diagram (red block)
on the diagram taken from web i found some differences.
thank you so much for others suggestions
kyu9971

 

Just guessing but until you get the primary switching system regulation working the secondary AC conversion part is rather pointless being it could have a HV lockout that keeps the secondary side from working if the HV DC rail voltage is too high.

Schematic is hard to read on my laptop screen so I am not sure.