I am designing a PFC boost circuit. It uses a ucc28019A ccm controller which requires a shunt resistor on the return path of the boost circuit. I am not sure where to place my shunt resistors on the pcb. I know the traces that go to the controller need to be as short as possible. As you can see from the pcb I have them placed right next to my bridge rectifier. This is convenient because the current path is from the negative output of the bridge to the source of the mosfet but the signal trace that will go to the controller is pretty long. Can someone tell me if this is going to cause me problems or if there is a better spot for the shunts?
The purple rectangle is for the heatsink.

 

Post your schematic. Like this.

I can't see the flow. Does AC come in at the top left side? Does DC go out bottom right side?
I would put the heatsink on the right side with the parts in the middle.

 

Post your schematic. Like this.
View attachment 339727
I can't see the flow. Does AC come in at the top left side? Does DC go out bottom right side?
I would put the heatsink on the right side with the parts in the middle.

Yea I forgot to post the schematic. The ac part is the same as the circuit that you posted. I placed the heatsink there to shield my controller from the EMI of the boost inductor( Lboost). I also have a gate driver driving the gate.

 

There are two loops: one formed by Cin, MOSFET, Iboost, Sense resistor, one formed by Cin, Iboost, Diode, Cout1.
You should attempt to keep both loops as small as possible. I would put the sense resistor as close to the source pin as possible, as that would keep the loop area down.
By the way, I don't think that 560pF capacitor is a good idea. Why is it there?

 

There are two loops: one formed by Cin, MOSFET, Iboost, Sense resistor, one formed by Cin, Iboost, Diode, Cout1.
You should attempt to keep both loops as small as possible. I would put the sense resistor as close to the source pin as possible, as that would keep the loop area down.
By the way, I don't think that 560pF capacitor is a good idea. Why is it there?

All the components connected to the controller are per the guidelines and application notes of the controller itself.
Keeping the loops as small as possible is quite difficult here as the circuit components are quite big. This circuit is a 400V 1200W pfc boost which means high currents and power.
About the sesnse resistor I would put it near the controlleron the right side of the heatsink but that means I have to draw traces from my bridge to the analog side of the circuit which I don't really want to do.

 

Your shunt resistor is referenced to the controller, so the voltage across it will be minimal. I would recommend placing it closer to the MOSFET.
Regarding the 560pF capacitor on the GATE, it doesn’t make much sense; the capacitance at this point should ideally be kept as low as possible.

 

All the components connected to the controller are per the guidelines and application notes of the controller itself.

There are no capacitors on the gate output in the datasheet.

 

Oh Im sorry I know what capacictor you are talking about. That capacitor might be needed for suppling the peak current required to turn on the mosfet. It's just a precautionary capacitor.

 

Oh Im sorry I know what capacictor you are talking about. That capacitor might be needed for suppling the peak current required to turn on the mosfet. It's just a precautionary capacitor.

Unfortunately, it does exactly the opposite, charging and discharging that capacitor limits the amount of current available for charging and discharging the MOSFET gate.

 

Exactly as Ian has said.

 

Speaking of gate drive: Mosfets and IGBTs live and die by their gate drive.
A 1200 watt PFC will require a humongous Mosfet. I can’t see which part number you are using because the letters in the schematic are all garbled up. It could perhaps require a pair of paralleled Mosfets. Have you calculated the required RMS gate current and whether the controller IC can handle it?

 

If you need two MOSFETs then have you considered an interleaved supply?
https://www.onsemi.com/ pub/Collateral/TND380-D.PDF
You also might want to consider bridgeless, as 5A in the bridge rectifier will dissipate 10W

 

If you need two MOSFETs then have you considered an interleaved supply?
https://www.onsemi.com/ pub/Collateral/TND380-D.PDF
You also might want to consider bridgeless, as 5A in the bridge rectifier will dissipate 10W

Hi. Im sorry I didnt see your guys' responses. I consulted a friend who works with PFC circuits and he said exactly that. One mosfet will not be enough. I decided to put 2 MOSFETS in paralel and went with this fet : IXFH40N85X.

About the interleaved PFC, it might be a bit too complicated for me rn. I will try to make this design work first.

I also looked up the capacitor that is in paralel with the gate. As you guys said it will cause problems UNLESS the capacitance of it is not bigger than the gate capacitance. Its also there just as a precaution. Dont have to connect anything there.

 

I also looked up the capacitor that is in paralel with the gate. As you guys said it will cause problems UNLESS the capacitance of it is not bigger than the gate capacitance. Its also there just as a precaution. Dont have to connect anything there.

ANY additional capacitance will degrade performance.