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KIA78R05PI Output 3.45 Volts

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Mr_Max

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Hi everyone

I have three 5V LDO regulators labeled KIA78R05PI I have tested the 3 of them with heat sinks Vout is 3.45 volts with no load and as stated in the datasheet
when control pin is pulled high or open the regulator is on so it's supposed to give 5 volts, am I missing something ? could the 3 of them be wrongly labeled ?!
 

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audioguru

Well-Known Member
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It is a low dropout regulator that must have a 47uF capacitor soldered close to its output and ground pins. I hope it is not on a solderless breadboard.
 
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Mr_Max

Member
It is a low dropout regulator that must have a 47uF capacitor soldered close to its output and ground pins. I hope it is not on a solderless breadboard.
I have tried a 100uF capacitor still Vout is 3.45 its the value of the capacitor critical ?! yes it's a solderless breadboard, I'll test it after soldering the capacitor.
 

audioguru

Well-Known Member
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I think KIA is a Korean manufacturer with such poor Engrish that the datasheet is missing the very important maximum allowed effective resistance of the capacitor and its wires (including the poor contacts of your solderless breadboard).

You do not need a low dropout regulator because your supply voltage is much higher than your output voltage so use an ordinary 7805 that is made in the West so you can see its recommended capacitors on its datasheet.
 

tomizett

Active Member
If you're just measuring a no-load voltage with a meter 10Mohm then maybe it's just leaking enough to read 3V when "off"? Try placing a small load of 10k or so at the output.
 

Mr_Max

Member
I think KIA is a Korean manufacturer with such poor Engrish that the datasheet is missing the very important maximum allowed effective resistance of the capacitor and its wires (including the poor contacts of your solderless breadboard).

You do not need a low dropout regulator because your supply voltage is much higher than your output voltage so use an ordinary 7805 that is made in the West so you can see its recommended capacitors on its datasheet.
Thanks for the suggestion, I'm making a mini UPS for my router, those 12v feed the router in addition to 5v via L7805 to the charging circuit of batteries, I noticed that while charging the output to the router sometimes drops to 10.8v
that's why I needed a 5v LDO regulator
 

Mr_Max

Member
If you're just measuring a no-load voltage with a meter 10Mohm then maybe it's just leaking enough to read 3V when "off"? Try placing a small load of 10k or so at the output.
Thanks for the suggestion, I have tried that but still the output is 3.45v, although as stated in the data sheet, the regulator is on when control pin is open or pulled high, and close when pulled down, the later is true, when pulled down the output is zero volts
 

Ian Rogers

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Thanks for the suggestion, I'm making a mini UPS for my router, those 12v feed the router in addition to 5v via L7805 to the charging circuit of batteries, I noticed that while charging the output to the router sometimes drops to 10.8v
that's why I needed a 5v LDO regulator
?

You wouldn't need a LDO until at least 6V .. I use a LDO 0n 7v even that's a tad high!
 

Mr_Max

Member
?

You wouldn't need a LDO until at least 6V .. I use a LDO 0n 7v even that's a tad high!
I understand that input to the 5v regulator is 12v, but those 12v feed the router in addition to the charging circuit, which causes the output voltage to drop under load to 10.8v, the router operates on 12v 500ma
I don't know the exact effect on the router, in terms of increased CRC errors or connection stability during blackouts, which causes sync speed drops, if it has no effect, then I believe it would be fine.
The mini UPS has 6 cells Li-Ion battery pack, charging circuit, Adjustable step up DC-DC converter , (1N5844 1N5822) O-Ring.
 

tomizett

Active Member
Thanks for the suggestion, I have tried that but still the output is 3.45v, although as stated in the data sheet, the regulator is on when control pin is open or pulled high, and close when pulled down, the later is true, when pulled down the output is zero volts
My mistake - I miss-read the original post.
 
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