Buck Converter, 50 - 180 V input, 48V output, 30W

Posted by: Gregor Simeonov on 01/23/2012

Hello,

I am desgining a non-isolated step-down converter (buck) with a wide DC voltage input range and a fixed 48 V output. The input range is 50 to 180 V DC, switching frequency is flexible but around 100 kHz is preferable. The converter should be rated for 30 W.

I am looking at Power Integration's offline controllers due to the high input voltage capabilities, specifically the LinkSwitch and TopSwitch families. However, I could not find any reference designs or application notes for non-isolated converters. I was wondering if I can get some recommendations on which product to look into and possibly a link to a non-isolated design. Thank you!

Comments

Hi,

The buck topology won't apply here because of the input to output voltage and the maximum duty cycle of our product (typically around 64%).

Would buck- boost be acceptable? Do you have any efficiency constraints - want to make sure a PI solution will meet you needs before you invest a lot of time

Cheers PI-Chekov

Thanks for the reply.

I can change the output voltage to Vout = 38 V. With a 64% maximum duty cycle this means that my minimum input voltage is 60 V. This is acceptible. The voltage is always going to be stepped down so a boost isn't required. If the buck-boost topology is capable of providing the required voltage range, and has the same number of components then we can consider it.

Regards,
Gregor

ALso, the the system must be capable of starting up from the minimum input voltage.

With a 30w requirement at 38v you'll need to select a TOPSwitch part with a current limit roughly double (38/30). I'd go with a TOPSwitch-HX or JX. Connect the f pin, x pin and v pin to source turning the device into a three terminal configuration.

If you PM me with your email address I'll email a circuit config this evening EST (on a plane at the moment).

Cheers PI-Chekov