3 phase inverter problem with IGBT module and TLP250 optocoupler

[steve_rb]

Hello,

I have a circuit and I am trying to find its problem. I have square pulses at the tlp250 input (pin3, 5 V peak-to-peak) but I have no output at all (pins 6 and 7 of TLP250). There are six TLP250 to drive the BSM10GN60 IGBT module. Three of them has their Vcc connected together but the other three Vcc are not connected together and are separate. The same for the GND. I am not an expert in electronics but all circuits I saw so far usually they use one Vcc for all parts. I don't understand why they have used separate Vccs. Saying this I realized three TLP250 have only 3 V in their Vccs (pin 8 with respect to pin 5) and the other three only 2V. Datasheet for TLP250 says Vcc should be 10-36 V. I am sure I am having problem here because I replaced one of the TLP250s but still the same and no output. I don't have schematics and I tried to find where all these Vccs came from but so far couldn't find the power supply generating these Vccs. I have the following questions:

1- Do you think circuit might have designed with 3 and 2 V as Vcc for optocouplers? Or do you think Vccs are defective and I should find the cause.
2- Do you have any complete similar circuit to send me so that I can have an idea where to find for the Vccs?
3- Do you have any advice for me how to diag. this circuit?

 

[schmitt trigger]

The top IGBTs in a 3-phase bridge require floating supplies as its emitter goes up and down in voltage.
The bottom IGBTs have all of its emitters are tied to the common return.

A voltage of 2 to 3 volt is way too low, it is a defective power supply (or you have a short and it is entering current limit).

 

[steve_rb]

Yes. Thank you. I already found the defective part and fixed the problem.