[SOLVED] need help and evaluation of a circuit

[romel_emperado]

help with my circuit

i posted an atachement. pls. evaluate this circuit if you think this would possibly work before i may buy this components..just to be sure a little.

 

[Prototyp_V1.0]

help with my circuit

Exept for controlling the motor, how do you plan your circuit to act like?

Why do you put a diode in parallell with the 22 ohm resistor next to the fet?

 

[DrBob13]

Re: help with my circuit

The 22 ohm resistor limits the charge-up current of the FET input capacitance to provoide a softer motor start, the diode provides a rapid discharge path on turn-off so that the motor turns off as fast as possible.

Note, that beyond the opto-isolator the circuit is mains live, so make sure that the 5V and 15V power supplies are fully isolated, do not use simple lab PSUs to supply these voltages even during the prototype testing, the simplest safe way to do this is the inclusion of very small galvanically isolated low power switch-mode supplies mounted on the PCB such as those made by TRACO, the whole circuit can then be supplied by a single DC PSU input if suitable input voltage switching PSUs for the 5V and 15V are selected. I have not checked the pin connections of your MOSFET driver IC but the circuit is essentially OK provided that the circuit components are adequately rated for 240V mains useage.
Bob.

 

[millwood]

help with my circuit

Exept for controlling the motor, how do you plan your circuit to act like?

Why do you put a diode in parallell with the 22 ohm resistor next to the fet?

to program the dead time.

Added after 6 minutes:

I cannot speak for the front end but in terms of the gate driver, you should follow the datasheet religiously.

a few observations:

1) I would use a 1uf electrolytic + a .1uf film capacitor for supply bypassing.

2) you have to have the low-side working or the bootstrap capacitor wouldn't get charged up and the highside wouldn't work.

3) I don't understand why you put the mosfet in serial with the ac motor through a bridge.

4) since your driver is floating, you may want to study grounding seriously.

if I were you, I would think about what you are trying to do and seek the best way to do that, not a way to get this circuit working.

 

[DrBob13]

Re: help with my circuit

All good stuff millwood, I did not spot your point 3 when I looked briefly at the circuit earlier. I assume he is intending to use a DC motor fed with direct rectified AC but as you have pointed out that is not what he has drawn.

Also as millwood gently pointed out regarding proper grounding, the Opto isolator Pin 3 (input ground) UNDER NO CIRCUMSTANCES MUST THIS GO TO THE SAME GROUND AS PIN 5 (isolated ground) or the galvanic isolation of the 6N137 is totally compromised.
Bob.