Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Boost converter feedback

Status
Not open for further replies.
M

mavrik2k

Newbie level 6
Joined
Jul 24, 2009
Messages
14
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Location
Netherlands
Activity points
1,377
hello everyone. i am new to boost converters and trying to build one.

i have heard that boost converters in feedback have really a stability issue

but i am unable to really find and good explanation and text on it. can any one please help
 

You're probably referring to the right half plane zero which occurs in every boost and buck-boost derived converter. It's like a normal LHP zero, where gain starts increasing at 20dB per decade. But unlike a normal LHP, where you get 90 degrees of phase lead, you get 90 degrees of phase lag with the RHP zero. This is pretty much impossible to compensate, and normally forces the bandwidth of the converter to be lower than the RHP zero frequency.
 

Dear mavrik2k
Hi
I suggest you to read these terrific books! :Switching power supply design by: abraham i pressman . or switching power supply cookbook by marty brown .
Best Wishes
Goldsmith
 

Dear all thanks alot for the comment
i will definitely look into the books.

regards
 

Hello every body thanks for the help. now i understand the RHPZ. but can any body tell me if we have a constant Turn off time ? would that be eliminated ?
 

Constant off time modulation increases the frequency of the RHP zero, but does not eliminate it. As far as I know, it can't be eliminated.
 
Hi Thanks for the reply.
Is there any paper or literature supporting the idea of fixed turn off, it would be a great help.
thanks
 

This white paper from venable praises it pretty heavily:
https://www.venable.biz/tp-05.pdf

I've never seen the actual math behind the RHP zero frequency for fixed off time modulation though.
 

If response time is not an issue its not difficult to make a boost stable.
also it depends to the typical duty cycle of the converter, for higher average "d" it gets worse.
for example a 12v to 15v boost is very easier to stabilize than a 12 to 100v.
for high ratio boost circuits using a transformer is recommended.
 

mtwieg said:
This white paper from venable praises it pretty heavily:
https://www.venable.biz/tp-05.pdf

I've never seen the actual math behind the RHP zero frequency for fixed off time modulation though.
Click to expand...

Hello, I'm quite interested in this. I'm trying to build boost converters and I am really having a hard time compensating it for wide conversion ranges. I am quite interested on trying out this Fixed Off-time PWM Control and I tried your link but it doesn't work anymore. Would you still have it or do you have a new link for it? Thanks.
 

kanmaedexandzelbladex said:
Hello, I'm quite interested in this. I'm trying to build boost converters and I am really having a hard time compensating it for wide conversion ranges. I am quite interested on trying out this Fixed Off-time PWM Control and I tried your link but it doesn't work anymore. Would you still have it or do you have a new link for it? Thanks.
Click to expand...

Venable recently reorganized their site, it seems. The paper can be found here:
https://www.venable.biz/uploads/files/05-Technical-Paper-Current-Mode-Control.pdf

However, since making that post a long time ago I have not actually been able to verify that constant off time modulation changes the RHP zero frequency. Simulations I've done show that it doesn't make a difference, so the paper may not be correct there. It does, however, eliminate the need for slope compensation.
 
Last edited:

mtwieg said:
Venable recently reorganized their site, it seems. The paper can be found here:
https://www.venable.biz/uploads/files/05-Technical-Paper-Current-Mode-Control.pdf

However, since making that post a long time ago I have not actually been able to verify that constant off time modulation changes the RHP zero frequency. Simulations I've done show that it doesn't make a difference, so the paper may not be correct there. It does, however, eliminate the need for slope compensation.
Click to expand...

yeah, I have the same feeling. I'm trying to find a way to fix the RHPZ problem it's really bothersome especially at high conversion ratios. The only way to remove it easily is to lower the boost inductance. I tried using the fixed off-time and it doesn't show an effect to the RHPZ. (15V to 90V boost). I see that the zero's location is omega = (Vout(1-D)^2)/(Iout*L). Changing Toff shouldn't have a bearing here it seems. Although since the duty ratio changes slower when using fixed offtime compared to fixed frequency, the zero moves slower. Not sure if this has an effect.
 

I think you have the right idea. The small-signal-averaged behavior of a CCM converter should not depend on switching frequency (at frequencies much lower than half of fs), or on transient changes in switching frequency, but rather on duty cycle and transient changes in duty cycle. That's why fixed and variable frequency modulation methods produce the same poles and zeros. It's the duty cycle that matters only. So I'm inclined to believe that the paper is incorrect.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top