I need buck (step down dc-dc converter) circuit

designing buck step down circuit

hi all! I m new in forum but I viewed this forum for a long time.
I searched but I cant find.
I need full circuit fior a buck circuit with its pwm controller and gate drive circuit. we will adjust the duty cycle

thanks man

step down dc/dc converter circuit

Hi,
Try some of these, they should help.

http://www.microsemi.com/micnotes/1305.pdf
**broken link removed**
http://analogdesign.wordpress.com/2008/03/17/buck-regulator-calculation-sheet/

Design of the inductor is the most crucial part.



Regards
Bob.

step down dc circuit

I want to adjust duty cycle with potantiometer what kind of entegre should I use

Added after 2 hours 7 minutes:

I draw this circuit but it didn't work
why didn't it work do you know

step down dc to dc converter design

Hi,
Your circuit has no voltage feedback so it cannot sense the output voltage and control it to a known value. I do not think that you have selected the best IC for a buck regulator circuit and you are certaintly not using that device correctly as you have drawn it.

I am not quite sure what you want your circuit to do, is it meant to produce a fixed or variable voltage output, you have not drawn the output voltage on your diagram, this is important to know, as is the load current required?

The TI UC3874 would be a better choice I think.
**broken link removed**

This datasheet has a suggested circuit to use. The inductor must be the correct value for these regulators to work, these are usually wound specially for your circuit, this is not difficult but switching regulators in general can be quite tricky to design and keep stable. Please tell me what you want your circuit to do and I will try to help you a bit more.

regards
Bob.

buck step-down circuit

Along with what's already been said your P-channel Mosfet is in backwards. The drain of a P-channel Fet should be more negative then the source,the body diode will conduct.

step down dc dc converter calculations and design

DrBob13 said:

Hi,
Your circuit has no voltage feedback so it cannot sense the output voltage and control it to a known value. I do not think that you have selected the best IC for a buck regulator circuit and you are certaintly not using that device correctly as you have drawn it.

I am not quite sure what you want your circuit to do, is it meant to produce a fixed or variable voltage output, you have not drawn the output voltage on your diagram, this is important to know, as is the load current required?


The TI UC3874 would be a better choice I think.
**broken link removed**

This datasheet has a suggested circuit to use. The inductor must be the correct value for these regulators to work, these are usually wound specially for your circuit, this is not difficult but switching regulators in general can be quite tricky to design and keep stable. Please tell me what you want your circuit to do and I will try to help you a bit more.

regards
Bob.

Click to expand...

my prpject is exactly that
Description of the required converter:
Output voltage: 5 V dc
Output current ½ - 2 A
Input voltage: 12 V dc
Output voltage ripple 10% at full load
Output filter current ripple 10% at full load
Control open loop
Switching frequency Minimum 20 kHz

dc to dc step down increase current

Hello again,
The design in the TI datasheet seems to be close to what you require, If you only need 2A you could increase the current sense resistor from 0.02 ohm up to 0.1 ohm, current will then limit at 2A rather than 5A as in the TI datasheet. The inductor needs to be wound with a number of small wire strands to make up a total diameter of 1mm in order to carry the current with minimum heating up. The actual design depends on what ferrite core you intend to use. It does not need to be very big, a 19mm torroid will be more than adequate, you will be OK with a 15mm core if you can wind enough wire onto it, this depends upon the magnetic characteristics of the core and its cross sectional area. Your core needs to have an area product of >0.05 cm4. This is design parameter deduced by Williamm McLyman that is commonly used to determine the minimum core size required. Keep the total magnetic flux (B) below the value recommended by the core manufacturer to prevent saturation usually below 200mT and you should have no problems.
Best Regards and good luck with your project,
Bob.

need buck

Hello again,
I found more info regarding the chip that you originally intended to use. This is an application note.

**broken link removed**

This contains info on how to use this device as a buck regulator.

:idea:

Info on winding the inductor.
Al is specified in the magnetics makers datasheet
L is the inductor value in Henrys

Number of turns = √((L * 10^9) / Al)

Take the square root of everything in the brackets, I hope this helps and your design works.
Please let me know how you get on.

Regards
Bob.

check this intersil circuit:

thanks but I need pwm circuit

a spice model of buck SMPS