I want to step down 5V to 3.3V at around 250mA.
As far as I see it, there are two options to consider:
- Buck: more space, higher cost
- LDO: less space, lower cost, more difficult to remove heat(?), less efficient(?)
What I am wondering is will the LDO be more efficient and better at doing this job? I've heard things like 6V to 5V solutions usually use LDO's instead of buck regulators because they are more efficient, but I'm wondering if this works for 5V to 3.3V?
Best Answer
Dropping 5 to 3.3 V at 250 mA will mean having to lose 0.425 Watt in the LDO, you will need a massive heat sink to make that work.
An LDO will never be more efficient than a buck converter, unless you need so little current that the power used by the regulator itself becomes an issue.
I have a mis-designed PCB right now where I tried doing exactly what you are proposing to turn 5 V into 3.3V at 200 mA and even though I have a large'ish copper plane as a heatsink the LDO still reaches 80 deg C in a few seconds.
I'm currently redesigning my power supply to use a MC34063A converter in stead.