DC-DC converter with Propeller ProtoBoards & BS2 board

Ron Czapala

ProtoBoard Schematic http://www.parallax.com/Portals/0/Downloads/docs/prod/prop/32212-32812-PropellerProtoBoard-v1.3.pdf

I bought 6 of these DC-DC Buck Converter Step Down Module LM2596 which have been discussed and recommended in various threads.
e.g. http://forums.parallax.com/showthread.php/133974-Powering-up-the-QuickStart?p=1155881&viewfull=1#post1155881

If I wanted to power one of the Propeller ProtoBoards (or a Basic Stamp board) using one off these, would I need to disconnect the onboard LMxxxx voltage regulator or could I just feed the converter's output across the existing regulator.

On the ProtoBoards, I was hoping to feed 5V from the converter in between the LM1086-5.0 regulator and the LM1086-3.3 regulator.

On the Basic Stamp Super Carrier Board I wanted to be able to feed 5V just past the LM2940 voltage regulator.

Would this work without disconnecting the regulators on the Parallax boards?

Thanks for any help!
- Ron

Chris Savage

Ron,

The LM2940 on the Super Carrier Board should be able to handle that no problem. As for the Propeller Proto Board I have learned from experience that the LM1086 (used on the Propeller Proto Board) is a very touchy regulator and I would not be confident answering for it being used in that manner. In general if a regulator has an open-collector output and you have no VIN you can do what you're suggesting, however in the case of the Propeller Proto Board you may have to test one.

Ron Czapala

Chris Savage wrote: »

Ron,

The LM2940 on the Super Carrier Board should be able to handle that no problem. As for the Propeller Proto Board I have learned from experience that the LM1086 (used on the Propeller Proto Board) is a very touchy regulator and I would not be confident answering for it being used in that manner. In general if a regulator has an open-collector output and you have no VIN you can do what you're suggesting, however in the case of the Propeller Proto Board you may have to test one.

Thanks Chris!

As far as "testing one", do you think there is any danger in frying the DC-DC Converter or the LMxxxx regulators?
I am concerned about damaging components...
- Ron

Chris Savage

Well, if I were really going to use the 5V from the new regulator on the Proto Board I would desolder/remove/disable the 5V regulator (LM1086) for long-term stability. It should be pretty easy to remove, but if you can't, you can always clip off the three leads that go to the PCB effectively disconnecting it from the circuit. Connect your unit to the 5V line and the 3.3V would be fed from that.

As a note, in this manner the power switch would not function properly, however if you do remove or trim the leads, then you could connect to the V_IN and V_OUT lines from the old regulator making the switch work.