[SOLVED] Help with inverting buck converter

[tanhong007]

I am looking for resources (books + papers) on inverting buck converter. But I can't find any over the internet or in the library. If you guys have any info about it, please let me know. Thank you very much!

 

[leo_o2]

Did you mean it output a negative voltage?
https://www.engr.colostate.edu/ECE562/EE562_newlabs/Buck_Boost_OrCAD.pdf

 

[tanhong007]

Did you mean it output a negative voltage?
https://www.engr.colostate.edu/ECE562/EE562_newlabs/Buck_Boost_OrCAD.pdf

No. It is like a regular buck converter, but move the inductor from the top to the button. I found one paper about that is from the IEEE, "Improving Current Regulation for Offline LED Driver". The author actually using an inverting-buck converter as an regular buck converter.

 

[davenn]

No. It is like a regular buck converter, but move the inductor from the top to the button. I found one paper about that is from the IEEE, "Improving Current Regulation for Offline LED Driver". The author actually using an inverting-buck converter as an regular buck converter.

top to the bottom of what ? the PCB ? ;-) that didnt really make sense
the term "inverting buck converter" is as leo suggested for producing a negative voltage from a positive supply often needed for FET gate biasing




Dave

 

[tanhong007]

top to the bottom of what ? the PCB ? ;-) that didnt really make sense
the term "inverting buck converter" is as leo suggested for producing a negative voltage from a positive supply often needed for FET gate biasing

Dave

Sorry. I think I confused u guys. Here is the Figure for the inverting-buck converter. I don't know if you guys will be able to see the attachedment or not.

 

[leo_o2]

I modified your schematic:

The common voltage node will be node "A". The principle is similar to Buck.
If voltage on the diode is neglected, following equation will describe the output voltage:
Vo=D*Vs

 

[tanhong007]

I modified your schematic:

The common voltage node will be node "A". The principle is similar to Buck.
If voltage on the diode is neglected, following equation will describe the output voltage:
Vo=D*Vs

Yes. The principle is very similar to Buck. I try to figure out what kind of advantage this topology has? And why people use this instead of Buck? When I use PSpice to do the simulation, I don't know how to do the closed loop, because I don't know how to make the model for the controller. Do you have any suggestion for this? Thank you very much for your help!

 

[leo_o2]

One of advantage is it can use NMOS as power switch instead of PMOS. In IC, NMOS will have smaller area.

 

[dick_freebird]

Your load is now however returned / referred to the supply
rail and not ground. That may be inconvenient for a general
purpose converter. If the load doesn't have to interface
with anything, though, then the cost of the switch alone
may be reason enough.

 

[mtwieg]

Right, I've used this type of buck when the load doesn't need to be ground referenced, like when driving LEDs or TECs. Having a ground referenced gate drive signal is pretty convenient.

 

[leo_o2]

If you want to build AC model, it depends on the controlling model (voltage mode or current mode). The feedback voltage should be referenced to the supply voltage.

Yes. The principle is very similar to Buck. I try to figure out what kind of advantage this topology has? And why people use this instead of Buck? When I use PSpice to do the simulation, I don't know how to do the closed loop, because I don't know how to make the model for the controller. Do you have any suggestion for this? Thank you very much for your help!

 

[tanhong007]

I tried to do the open-loop simulation on PSpice, I think the result is not right. It might be something wrong with the load part, I just give a regular resistor for it, the load doesn't interface with anything. Thank you for your help!

---------- Post added at 23:31 ---------- Previous post was at 23:29 ----------

Actually I don't really understand why this called inverting-buck. The output voltage is not negative. Is there something maybe related to the stability?

---------- Post added at 23:34 ---------- Previous post was at 23:33 ----------

If you want to build AC model, it depends on the controlling model (voltage mode or current mode). The feedback voltage should be referenced to the supply voltage.

I think my open-loop is not working right now. And I still have to do the small signal model before I get to the closed-loop.....The name "inverting" is really confusing.....

---------- Post added at 23:36 ---------- Previous post was at 23:34 ----------

Right, I've used this type of buck when the load doesn't need to be ground referenced, like when driving LEDs or TECs. Having a ground referenced gate drive signal is pretty convenient.

Yes. I did found this kind of converter used in LED field, but why they don't chose buck converter? What are the difference?