78L05 3mA Quiescent Current for Remote Control Keys is to high

[tpetar]

Hi,
How to decrease or turn off 78L05 current.
78L05 in datasheet Quiescent Current is 3mA in my project is about 3,17mA.
I make IR and RF remote control keys. Both project uses the same 78L05ACD (SMD) to step down voltage from 12V to 5V. In both I use uC.
Mini Battery used is standard A27 12V with capacity of 22mAh to 6V.
uC goes to sleep when keys not used.

Is there any way to minimize quiescent current of 78L05ACD ?
A27 battery have only 6h working hours.

 

[alexan_e]

I don't think there is a way to reduce that current, actually if you are after a higher efficiency I think you should use a switching regulator, you are currently wasting 7v (from 12v to 5v) on a linear regulator.

Alex

 

[tpetar]

There is no battery on 5V or 6V A23 and A27 are on 12V.
This is batteries for remote control key. All (most) car remote control keys in world uses that batteries or familiar.

I think that swither take to much place in remote key case.

 

[mtwieg]

There's no way to decrease the Iq of a given device; it's fixed internally. You'll just need a lower power regulator.

 

[dick_freebird]

My key fob uses a single lithium coin cell. I question the
use of starting with such a high primary voltage, especially
if you insist on using linear regulators.

One approach might be to use a crude very low current
regulation, such as a diode stack (or low current zener)
and a megohm resistor for "sleep mode", and have the
uC's first task be to turn on a PMOS power switch to
energize the higher-current, better-regulated power
path only when needed. This path might have to be
diode blocked incurring some loss, and the regulation
loop closed around it. Or you could use the zener as
low-power regulator and high power reference, both.
Whether you can find a zener that stays tight from
(say) 100nA to 10mA, is on you.

 

[tpetar]

I found LP2957 and LP2957A with micro quiescent current typical 150uA at 1mA my PIC12F629 goes to sleep and consupt <1mA.
This can be solution but there is no SOIC8 package. I will try something with zener and resistor.

---------- Post added at 23:14 ---------- Previous post was at 23:08 ----------

LP2950 have 75uA Quiescent Current

 

[mtwieg]

There are tons of LDOs with quiescent currents in the 10-50uA range. I've used the LT1763 before, for example. Not sure why you want a SOIC8 package. You could probably find smaller packages (sot23).

 

[tpetar]

There are tons of LDOs with quiescent currents in the 10-50uA range. I've used the LT1763 before, for example. Not sure why you want a SOIC8 package. You could probably find smaller packages (sot23).

I know but there is no sot23 in market in my Country.
I make balans between parts in market and my circuit.

---------- Post added 15-10-11 at 00:03 ---------- Previous post was 14-10-11 at 23:57 ----------

I made PCB and make complete remote, put battery and I check voltage drop from 12,5V to 11,99V (obvious parasitic consumer is here or short circuit). Tomorrow I check remote, battery is dead 6V. And then I check remote and second DIP prototype, I realize that volt reg quiescent current is to high.

I will probably redesign PCB.

---------- Post added at 00:06 ---------- Previous post was at 00:03 ----------

So far I didnt paid attention to quiescent current of volt reg, but from now I will, especially when working with batteries. This is new school class for me.

 

[tpetar]

I make some modification on my remote control (IR and RF) design.

Both RC (RF and IR) uses 12V A27 22mAh battery (because RC plastic case what I have is make for this battery Of course I looking to find and buy some other cases with lithium 3V battery).

In IR I try 3,3V and works fine. Without 78L05 regulator quiescent current is 0,5mAh. And this is to much also for this battery. Only few (1uA or 2uA) are ok, everything else is to much for this battery. Of course calculation based on time to change battery on one year or two.

On RF is not good to degrade voltage from 12V to 3V, it will make of degradation of power.
On 3V I supose I will get about 10mW or 10m theoreticaly. At 12V its 100mW about 100m theoreticaly on open.
But I will try RF on 3V, first I must to redesign my TX to works on 3V and make 433MHz freq. I didnt use quartz, if change voltage freq will also change.

I realize that best way is to break circuit with control button. Battery consuption only when control button is pressed, in purpose of prolong battery working life.

Next I will try to use transistor as switch between 78L05 Gnd and battery Gnd and see quiescent current.