RF Circuit Battery Efficiency

[mcasey]

I'm looking to increase the efficiency of this circuit. The circuit is powered by 4 AA alkaline batteries which only lasts approximately 26 days. Any suggestions are appreciated.




Components quiescent current consumption:
https://linxtechnologies.com/wp/wp-content/uploads/lical-dec-ms001.pdf
https://linxtechnologies.com/wp/wp-content/uploads/rxm-fff-lr.pdf
http://www.vishay.com/docs/83807/lh1503aa.pdf
http://www.ti.com/lit/ds/symlink/ua78m.pdf

 

[davenn]

I'm looking to increase the efficiency of this circuit. The circuit is powered by 4 AA alkaline batteries which only lasts approximately 26 days. Any suggestions are appreciated.

parts wise, its a very minimalistic circuit. So as such, I doubt there is much you can do and still have it work properly

the only thing you could look at would be to replace the linear regulator with a switching buck regulator
the linear reg. will be very inefficient at dropping 6V down to 3.3V

 

[mcasey]

Maybe this?
http://www.ti.com/lit/ds/symlink/tps62745.pdf

 

[davenn]

Maybe this?
http://www.ti.com/lit/ds/symlink/tps62745.pdf

looks good
just make sure 300mA is enough for supplying all the other requirements

 

[kellys_eye]

Use C or D-cells instead. If battery size is an issue then some more exotic chemistry versions of the AA might do it??

 

[mcasey]

300mA is sufficient for this circuit.

Space is somewhat of an issue, but I only need 3 volts for everything except the L293. It requires 6 volts. What about switching to 2 C or D batteries, then boosting to 6v for the L293 Driver?

 

[kellys_eye]

A decent quality boost circuit will deliver the required 6V at up to 90-95% efficiency - certainly worth a go.

Look up the relative battery capacities (Ahr) for comparison to longevity. Some of the more esoteric chemistry AA's are also very energy-dense but correspondingly expensive.

Sticking to readily available batteries is a good idea.

Have you considered solar re-chargeable cells and the control circuitry?

 

[mcasey]

I'll give it a shot.

I like the idea of sticking with readily available batteries as well.

I use the device indoors only, and because it's attached to something, it's not easily moved for recharging.

 

[mcasey]

I'd like to simplify the circuit even further by eliminating the Solid State Relays. The circuit works fine without them, but the H Bridge driver draws too much current. Is there another H-Bridge I can use that doesn't draw so much current? (The outputs are pulled low when it's not in use)



http://www.ti.com/lit/ds/symlink/l293.pdf

 

[davenn]

What about switching to 2 C or D batteries, then boosting to 6v for the L293 Driver?

that's no good as you are not going to get your 3.3V

 

[mcasey]

Sorry, let me clarify; just the two switches.

 

[davenn]

Sorry, let me clarify; just the two switches.

not sure if you were responding to my comment ? and what removing those 2 switches had to do with only using 2 batteries

Do you understand why you cannot use 2 batteries ?

 

[mcasey]

not sure if you were responding to my comment ? and what removing those 2 switches had to do with only using 2 batteries

Do you understand why you cannot use 2 batteries ?

I do not understand why I cannot use 2 batteries if I use a boost circuit to get back up to 6v for the L293...

 

[davenn]

I do not understand why I cannot use 2 batteries if I use a boost circuit to get back up to 6v for the L293...

because 2 batteries WILL NOT supply your 3.3V requirements

 

[(*steve*)]

The radio module powered by the 3v3 regulator, does it need to be powered up all the time?

You can probably reduce your power demands significantly by turning it off (possibly by using a 3v3 regulator with an enable input) when not required.

The same is true for other support functions. Don't leave them powered up when not required.

If you can slow the clock speed for your microcontroller when in a standby condition you can also reduce the power required.

 

[mcasey]

The radio module powered by the 3v3 regulator, does it need to be powered up all the time?

You can probably reduce your power demands significantly by turning it off (possibly by using a 3v3 regulator with an enable input) when not required.

The same is true for other support functions. Don't leave them powered up when not required.

If you can slow the clock speed for your microcontroller when in a standby condition you can also reduce the power required.

Yes, it needs to be powered, but there is a build in power down function that draws only .1uA on the decoder and only .28uA on the receiver. I'm not sure how it works, but it is specified on the data sheets.

The reason I included the SSR Switches was to remove power from the L293 driver when it was not being used. This drastically increased battery life by eliminating the 35mA IQ. I was hoping to eliminate the SSR's and find a low power replacement driver for the L293, but can't seem to find one.

Am I correct in thinking that I should leave the SSR's in the circuit (to remove power from the L293), and focus on a more efficient regulator to make this circuit as efficient as possible?

I ordered a step down regulator to take the place of the other from ti:
http://www.ti.com/lit/ds/symlink/tps5403.pdf

I hope I'm on the right track. This forum has been most helpful.

 

[mcasey]

because 2 batteries WILL NOT supply your 3.3V requirements

The decoder and rx only require 2.0 and 2.7 volts. I should be able to power that with 2 batteries... right?

 

[davenn]

The decoder and rx only require 2.0 and 2.7 volts. I should be able to power that with 2 batteries... right?

the datasheets appear to confirm that

give it a try

 

[kellys_eye]

Why the L293?

Can't you use simple MOSFET drivers for switching?

 

[mcasey]

Why the L293?

Can't you use simple MOSFET drivers for switching?

It provides bi-directional drive currents that I need for forward and reverse rotation of the motor.