LDO DC-DC Regulator Help Needed!!!!
LDO DC-DC Regulator Help Needed!!!!
(OP)
Hi,
This post is just to see if someone can clarify a confusion I am having at the moment...
I want to design a DC-DC converter which takes a 12V, 20mA DC input and converts it into a 5V, 0.5A DC output.
I have looked at LDO voltage regulators like the LM2940CT-5.0 and LM7805. My confusion is over the Quiescent / Ground Current that is needed to power the Regulator and supply the 5V DC output rail.
Am I ok to use a LDO Voltage regulator to drop 12V to 5V DC??? Or am I overlooking the fundamental fact that my LDO can get 20mA only from an external Power Supply and then needs to generate a much higher power output (5V @ 0.5A), so I need to use a different topology to boost the input DC voltage??? Something like Boost Converter???!!!
Power wise, on the input side, you have 12V x 20mA = 250mW and output side has 5V x 500mA = 2.5W (so 10x input power available!!!)...
Any guidance would be appreciated...
Regards,
Harry
This post is just to see if someone can clarify a confusion I am having at the moment...
I want to design a DC-DC converter which takes a 12V, 20mA DC input and converts it into a 5V, 0.5A DC output.
I have looked at LDO voltage regulators like the LM2940CT-5.0 and LM7805. My confusion is over the Quiescent / Ground Current that is needed to power the Regulator and supply the 5V DC output rail.
Am I ok to use a LDO Voltage regulator to drop 12V to 5V DC??? Or am I overlooking the fundamental fact that my LDO can get 20mA only from an external Power Supply and then needs to generate a much higher power output (5V @ 0.5A), so I need to use a different topology to boost the input DC voltage??? Something like Boost Converter???!!!
Power wise, on the input side, you have 12V x 20mA = 250mW and output side has 5V x 500mA = 2.5W (so 10x input power available!!!)...
Any guidance would be appreciated...
Regards,
Harry





RE: LDO DC-DC Regulator Help Needed!!!!
No, you will not get 2.5W output from 250 mW input unless you have a battery hidden in there.
Best to you,
Goober Dave
Haven't see the forum policies? Do so now: Forum Policies
RE: LDO DC-DC Regulator Help Needed!!!!
With .24W input (12 x .02) you can only get 48mA @ 5V (.24/5) assuming 100% efficient (which won't happen either).
And you don't really need a LDO regulator either.. Any 5V regulator will work but you need more input power to achieve the 5V @ 500mA.
RE: LDO DC-DC Regulator Help Needed!!!!
http://eng-tips.com/viewthread.cfm?qid=345793
Best to you,
Goober Dave
Haven't see the forum policies? Do so now: Forum Policies
RE: LDO DC-DC Regulator Help Needed!!!!
RE: LDO DC-DC Regulator Help Needed!!!!
Parts count/complexity is typically less but of course there is a more heat dissipation to deal with.. Any cheap heat sink would solve that though for these current levels though.
RE: LDO DC-DC Regulator Help Needed!!!!
When you say "am I overlooking the fundamental fact that my LDO can get 20mA only from an external Power Supply and then needs to generate a much higher power output?" You are spot on. It can't be done. As others have already pointed out.
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: LDO DC-DC Regulator Help Needed!!!!