LM317 or 7805

[kalaman]

Hello there,
I have a circuit which include a PIC and some leds. The pic has to be sensitive for A/D conversations in battery application. 7805 have never made a problem. I have read each datasheets but i can't see standby current. Which regulator will be advised.

 

[ssylee]

LM317 is an adjustable voltage regulator, while 7805 is constant voltage regulator. Btw, what is it that you're trying to do?

 

[kalaman]

The most important thing is the standby current. I don't want my regulator to waste the power in stand by cases.

 

[donniedj]

An adjustable regulator requires more parts and tunning than a fixed regulator. If you can use 5v then use a fixed 5v or fixed 3.3v regulator. The standby current will be based on the type of regulator first, then the manufacturer. Standard ones will span from 3 to 10 mA for standby current. The newest will be even lower. Gate controlled version will be down to the 1uA. The lower the regulator output power the lower its standby, hence use the power level to match your circuit.

Take a look at these LDO models. Super low standby.
https://www.fairchildsemi.com/pf/FA/FAN2500.html

 

[Krumlink]

I would reccomend the LM2940. It is a LDO voltage regulator, that provides 5 volts all the way down to about 5.5 Volts (I believe). It cost more than some others, but it is your best bet for good Voltage regulation. As with any, throw a ton of caps of different chemistries on there for awesome performance.

 

[mvs sarma]

While FAN2500 is a super low standby version of LDO, the components used around for defining the output voltage to5V will draw the current.

Instead , a 5V fixed LDO version can be used.

 

[Hero999]

The only disadvantage of the FAN2500 is that the maximum input voltage is only 7V. The LM2936Z-5 is much more tough (40V and reverse polarity protection) but has a higher quiescent current, a lower output current, only 50mA.

 

[donniedj]

Quoting myself: "hence use the power level to match your circuit."

FAN2500 is a series not a single device. It includes adjustable and fixed.

The intent of modern designs is to use a voltage source proportionate to the voltage regulation. This reduce wasted power dissipation. 7v max input more than suffices for the suite of devices that run under 3v in this decade. Electronic circuit manufactures produce a continual advancement in their products. Any minimums or maximums that do not meat your requirements is not a disadvantage on behalf of the device but are competitive edges that have risen out of years of fierce and close competition forcing any designer to follow my quote above.

 

[ericgibbs]

hi kalaman,
Tell us what the voltage input supply to the regulator is going to be?

 

[nikolausc]

based on experience I would have to recommend the 7805, there is also a low power model if you are really worried about consumption

 

[kalaman]

First of all thank you for replies. I think LDO is the most important for me.

@ericgibbs
My input range is wide (12-21V).

 

[Hero999]

What's the maximum current drawn by your project?

 

[kalaman]

What's the maximum current drawn by your project?

max 400mA.

 

[audioguru]

Since your minimum input is 12V then you don't need a low-dropout regulator.
Since your max input is 21V and your max current is 400mA then a linear regulator must dissipate 6.4W of heat so it will need a pretty big heatsink.

 

[Hero999]

What is the minimum current taken by your project at any point?

The LM317 requires a minium load of 10mA and the LM217 requires a minimum load of 5mA, if you make R1 really high and your circuit always draws more than the minimum current then it'll work.