August 19, 2014 Leave a comment
What is it?
PCBs for DC-DC converters as described here. There are three sizes, for 1”x1”, 1”x2” and 2”x2” converters respectively. These footprints are industry-standard so you can use converters from a variety of manufacturers such as Traco, Recom, Murata and many others.
How big are the boards?
- 1”x1” PCB: 1.875″ x 1.475″ (app. 48 x 38 mm)
- 1”x2” PCB: 2.85″ x 1.475″ (app. 72 x 38 mm)
- 2”x2” PCB: 2.85″ x 2.5″ (app. 72 x 64 mm)
What is the status of the boards?
All the boards are in version 1.1, meaning they have been prototyped and minor tweaks made to silkscreen etc.
Does it use any special/expensive/hard-to-find parts?
The ceramic caps between the primary and secondary sides should typically be rated for 2-3kV which can be a bit difficult to find. Mouser/Digi-key obviously have them but your local parts suppliers might not. Otherwise, apart from the converter itself, not really.
Anything else I need to know?
- The external components are for EMI filtering and (usually) not required in order for the converter to work. All the caps on the primary side have 1812 SMT footprints.
- The two component positions on the secondary side can be used for decoupling (required for stability with some converters) or for voltage trim if your converter supports that. These have 1206 SMT footprints.
- Not all converters have enable-pins and some has the functionality, but wired as “always-off” instead of “always-on”. In this case you need to wire the enable-pin to the negative input voltage in order for the converter to turn on (you can of course also use the optocoupler here, but with the logic inverted).
- If you use a 4:1 input range converter and you expect to actually use that input range, you need to be a bit careful with the value and power rating of the LED resistor, at least on the two small boards. Both the LED and the resistor are 1206 SMT here. On the 2”x2” board you can fit a 1/2W or 1W leaded resistor and then there should be no problems.
- Many converters are sensitive to the capacitive loading on the output, so remember to check the datasheet for maximum allowed capacitance. If you exceed this limit it is possble that the converter will refuse to start up.
- You can sometimes find DC-DC converters as cheap surplus items. Normally that is absolutely not a problem, but remember that even if the footprints are industry standard there can be quite a few differences between manufacturers. I recommend that you do not buy anything that is so obscure that you can’t google your way to a datasheet/application note for it :D
Download design files here
Note: Always read the “intro post” for additional important information about my designs.
Always remember to refer to the manufacturer’s datasheet and application notes for specifics on pin connections, external component values etc.
EDIT 20-08-2014: Added comment on capacitive loading.