Splitting and stepping down voltage

[swuster]

I'm currently attempting to design a circuit that can step down an 18.5V lipo battery into independent voltages of 12V and an indeterminate number of 5V lines, which will be powering various pieces of equipment. At this point I'm still pretty much in the early conceptual stages, so I'm not too worried about the precise specifications. What's the best way for me to step down the voltages as efficiently and safely as possible? I was thinking of using an op amp buffer system (LF353 or something similar) or just plain getting a regulator (LM78XX) maybe wiring a capacitor or two in parallel with the output and ground. Unfortunately the 18.5 V to 5V, and even the 18.5 V to 12 V drop are probably way too high and would cause overheating, especially when you take into affect the possibility of an overcharged battery. I could step the power down gradually with multiple regulators but it seems a roundabout solution. Any suggestions?

 

[vk6kro]

It depends on the current involved.

If the system only uses a few tens of milliamps, you can certainly drop voltage down using linear regulators. It is perfectly OK to drop from 18 volts to 5 volts.
However, it is not very efficient as heat will be generated in the regulator and you may need to mount the regulators on heat sinks to get rid of this heat.
They are electrically quiet, though, so they do not generate interference in nearby equipment.

If large currents were involved, you probably need to be looking at bucking switch mode DC-DC power supplies.
Whether the extra efficiency warrants the extra circuit complexity and cost is something you will need to weigh up.

 

[berkeman]

I'm currently attempting to design a circuit that can step down an 18.5V lipo battery into independent voltages of 12V and an indeterminate number of 5V lines, which will be powering various pieces of equipment. At this point I'm still pretty much in the early conceptual stages, so I'm not too worried about the precise specifications. What's the best way for me to step down the voltages as efficiently and safely as possible? I was thinking of using an op amp buffer system (LF353 or something similar) or just plain getting a regulator (LM78XX) maybe wiring a capacitor or two in parallel with the output and ground. Unfortunately the 18.5 V to 5V, and even the 18.5 V to 12 V drop are probably way too high and would cause overheating, especially when you take into affect the possibility of an overcharged battery. I could step the power down gradually with multiple regulators but it seems a roundabout solution. Any suggestions?

Google or Wiki "buck" DC-DC converter circuits. Or go to Maxim, National Semiconductor, Linear Technology, etc., and do a search. Any of those will get you in the ballpark.

 

[vk6kro]

I found an interesting website for ICs and modules dealing with power control:

http://www.datasheetdir.com/Step-down

And have a look at the index on the left column in this view:
http://www.datasheetdir.com/company-TI

This leads to an amazing selection of ICs although prices are not given, so you have to follow that up with suppliers.