I need three dc-dc modules which cah below specs:
1. Input: 12V-16.8V
2. Out1: 12V/5A
3. Out2: 12V/3A
4. Out3: 5V/2A


I had looked into net & found that below dc-dc are ok:
http://www.digikey.com/product-search/en?keywords= UWE-12/6-Q12PB-C

http://www.digikey.com/product-search/en?keywords=UWE-12/6-Q12PB-C



1. Problem I see, they are isolated. Can I short its Vin- & Vout-, & will it still work?

2. Do these dc-dc require external heat sinks, or provided system is at room temperature they will work?
In datasheet they have placed additoanl AL baseplate

 

They have isolated outputs. You can connect Vin- to Vout- no problem
Even though they are quite efficient, some of these very small DC-DC converters get quite hot at full load. No heatsink needed but will need to have ventilation or even a small fan to keep air flowing over them.

 

For outputs 1 and 2 you have no choice but to use isolated converters, because non-isolated buck converters have a minimum voltage drop between the input and output, so you can't get 12 V out with 12 V in. For #3, there are tons of non-isolated buck regulator assemblies/modules at the major distributors, ebay, alibaba, amazon...

ak

 

thanks