Dear Team I: Moon Wreckers,

Below are comments on your Task 12 PDS Schematic

—

Team I:

Comments:

Y. Nadaraajan comments:
The schematics seems to be lacking the connectors necessary. Check the ratings for your load components carefully before selecting the parts. You will need heat sinks for the 12V regulator is you are plnning to continuously draw 3A. Also the 12V regulator is not going to be effective if your input voltage is also 12V

L. Navarro comments:
No design document, so this feedback is entirely based on this submission. You have a 12V power source which feeds two LDO regulators, with 12V and 5V outputs. The 12V regulator may not be regulating at all, since it requires an input voltage of at least 12V+600mV (worst case) before it ceases to regulate against further reductions in input voltage–that’s by the very definition of what the dropout voltage is. Your conclusions in terms of joint temperature for this regulator are correct though: this regulator is not at risk of overheating–even without a heatsink–since its series element will be saturated to minimize the voltage drop between the input and the output. As for the 5V regulator, your analysis is incorrect: at your estimated current draw of 0.9A it will be consuming 6.3W, not the 0.045W you calculated. The problem is that you incorrectly assumed a voltage drop of only 50 mV across the regulator, which violates Kirchhoff’s Voltage Law (5V+50 mV != 12V). In any case, this regulator will overheat without a proper heatsink. Consider replacing it with a DC-DC converter for higher efficiency. Or at least use a mitigation strategy, e.g. use a series power resistor between the power supply and the regulator to reduce the power dissipated at the junction–and a heatsink, of course. If you stick with this regulator, please note that you indicated a 1.8V regulator in your schematic–don’t buy the wrong part!

—

The MRSD Instructors