Hi all,

I have an unregulated 15-24V dc input and a requirement for the following:

• 12V, 500mA motor drive via h-bridge (doesn't need to be particularly well regulated)
• 7V, 50mA logic supply
• 2.5V, 20mA microprocessor supply

There are many ways to solve this problem, can anyone suggest an optimum.

Tim

P.S. Search function wasn't working when I posted this. Hope I'm not duplicating someone else's question.

 

First, filter the DC source if not already.
Then, use 3 voltage regulator ICs in series.

DC source----------7805--------+5----------BA17807T--------+7----------- UC382T-3--------------+2.5

(Or use equivalent replacements)

 

Since you're familiar with Linear products already, you might consider the LT3509. It has dual outputs, each capable of 800mA.

Open the LT3509 macromodel test fixture, and save it in the LTSpice directory as
"LT3509 test 12v.asc"
change R1 to 140k, and R2 to 10k.
You now have a 12v regulator capable of >500mA. Save it again.
Then save that file as:
"LT3509 test 7v.asc"
Then change R1 to 77.5k (you can get close to that by using 150k and 160k resistors in parallel)
You now have a 7v regulator. Save it again.
Then you can just use a small linear regulator (like an LM317L 100mA TO92 regulator) to get the 2.5v out from the 7v supply.

The 12v supply will be around 92% efficient, the 7v about 80% (due to the low current output vs the overhead). The LM317L will only dissipate around 90mW.

 

Thanks for the inspiration people, will get cracking.

Tim

 

Am sorry for the huge and stinky mental fart in my previous post.

Should be

DC source----------7812--------+12----------BA17807T--------+7----------- UC382T-3--------------+2.5

 

Hi Externet

How would you suggest filtering the DC source?