Reducing inductor ripple in buck converter

[eahmadi]

Hi There,
I'm designing CMOS buck converter. I'm trying to reduce inductor ripple. But as I design in Hspice, It can't reach between 20-40 percent of average current load. Could you possibly tell me What I can do?
Thanks in advance;
Ebi

 

[D.A.(Tony)Stewart]

lower the frequency and increase duty cycle?? You need to design each parameter, not guess.

 

[ahsan_i_h]

Try to increase the inductance.

 

[online79]

share the schematics.

 

[dick_freebird]

Integrated current mode control, using senseFET type
schemes, wants a lot of ripple to give it a sense-able
edge and reject as much VIN noise as possible. Low
ripple slope makes more trailing edge jitter. But ripple
current does cost you efficiency in the input filter
partuicularly. I think you should quantify how much
ripple current you can stand, and how much minimum
you need, and position yourself accordingly. Right up
against the bare minimum is not a good place to put
your production or your customers.

 

[eahmadi]

Hi dick_freebird
I'm designing it for ripple current between 20-40 percent of average output current. I don't want to increase amount of inductor(L=4.7uH). when I simulate in Hspice, I can't achieve to desirable ripple current. In addition, I'm designing open loop current mode buck converter without controll circuit. Is it reasonable that ripple current can be reduced after designing controll circuit and closed loop?
Thanks in advance,
Ebi

 

[BradtheRad]

Hi There,
I'm designing CMOS buck converter. I'm trying to reduce inductor ripple. But as I design in Hspice, It can't reach between 20-40 percent of average current load. Could you possibly tell me What I can do?
Thanks in advance;
Ebi

In order to reduce inductor ripple, it means you are going further into continuous conduction mode (CCM). You wish to reduce the distance between waveform crest and trough.
To do this, increase frequency. Or, reduce the hysteresis travel.

 

[eahmadi]

Hi BradtheRad,
I sweep the switching frequency and find optimize amount of it for specific input voltage and load current. I need to investigate both CCM and DCM mode. And I suppose load current below 0.25 average output current is DCM mode and over than it is CCM mode. I wanna design PWM and PFM mode together.
What is the meaning of the heysteresis travel? How can I reduce it?
Thanks,
Ebi

 

[BradtheRad]

Hi BradtheRad,
I sweep the switching frequency and find optimize amount of it for specific input voltage and load current. I need to investigate both CCM and DCM mode. And I suppose load current below 0.25 average output current is DCM mode and over than it is CCM mode. I wanna design PWM and PFM mode together.
What is the meaning of the heysteresis travel? How can I reduce it?
Thanks,
Ebi

Hysteresis travel has to do with the high and low points at which a waveform is automatically made to change direction. The automatic part is often performed by an op amp. You adjust the hysteresis action via positive feedback.

I could also have said 'hysteresis range' or 'hysteresis limits' or 'hysteresis setpoints'.

Go to the link below. It is my tutorial simulation of a buck converter. It is animated and interactive. (Your computer needs to have Java installed, in order to run Falstad's simulator Java applet.)

https://tinyurl.com/8g8e6q7

You drive the converter by pressing and releasing the switch at the left.

Watch the scope trace showing current through the coil.

With some experimentation you can find the right tempo which will produce CCM, DCM, large ripple, small ripple, high output V, low output V.

You can change values as desired. Right-click on a component, and select Edit.

 

[eahmadi]

Thanks for your help,
why you design with Java?

 

[BradtheRad]

Thanks for your help,
why you design with Java?

The Java code is invisible to me and you. I drew my circuit as though it was a schematic. It is an easy-to-use graphical interface.

The simulator was written by Paul Falstad. He has put a large number of programs for anyone to use at his website:

www.falstad.com

Since Java runs on Macs and pc's, his Java applets are cross-platform. That may be one advantage of programming in Java.

Another advantage of his electronic circuit simulator. It can export a link which contains an entire schematic, which will be loaded into his simulator, and then run on anyone's computer (if they have Java installed).