I have an application where the load is a user-selectable component (an electric door strike) that comes in many flavors, with each flavor requiring a specific DC voltage, most commonly either 12V or 24V. I would prefer not to have separate parts for the different voltages, and so I would like to have a jumper-selectable 12V or 24V DC/DC converter on my board.
I have played around with TI's WBENCH Designer and it seems like getting an efficient DC/DC converter for a single voltage is a piece of cake, but how do I go about adapting one to produce different outputs depending on the jumper configuration?
My first thought was simply to use WBENCH Designer to produce two different designs based on the same TI chip and then "meld" them into a single circuit with some creative hackery. I'm reasonably confident this could be made to work, but I'm also pretty sure there would be some redundant components from going this route (particularly the large and relatively expensive inductors) and naturally I'd prefer to avoid that.
Oh and obviously I'm ignoring the possibility of using a voltage divider or simple dissipating regulator because I'd prefer not to waste power, but should I be? Is there a way to use one that isn't wasteful?
Best Answer
There's a number of ways you can go about it:
Use an "adjustable" buck regulator and switch the adjustment resistors for different values through jumpers.
Use multiple buck regulators to go from your input voltage to all the output voltages in one go (all running in parallel - only one of them active at a time)
Use multiple buck regulators in a "tree" formation - one which for example goes from input voltage to say 24v, then one which takes the 24v to (for example) 18v, then another which takes the 18v to say 12v - or whatever voltage combinations you want.
Option 1 is probably the cheapest as you only need 1 regulator - picking your feedback resistors can be tricky though if you want precise voltages.
Option 2 is probably the most efficient if you want multiple voltages to be available at the same time.
Option 3 is most commonly used for a combination of buck and linear regulators - buck it down to a lower voltage then linear it down lower still to give a good clean output.
Oh, and by the very nature of the linear regulators there is no way to use them that isn't wasteful. They do have their place though as mentioned in option 3 (no switching ripple).