Better Alternatives to 7805 ?

[Art]

Hi Guys,
Is there a less power consuming device than the 7805 regulator out there?
What is everyone using to power their 5 Volt pic projects nowadays?

I'd like a very conservative way to regulate say 25-30 Volts (similar to the 7805),
but only need low current 5 Volt supply.
Cheers, Art.

[Byte_Butcher]

Hi Guys,
Is there a less power consuming device than the 7805 regulator out there?

Sure, there's lots of good switching regulator circuits out there that are WAY more efficient than using a linear regulator (especially with high input voltages)

What is everyone using to power their 5 Volt pic projects nowadays?

I usually use a 7805....

I'd like a very conservative way to regulate say 25-30 Volts (similar to the 7805),
but only need low current 5 Volt supply.

78L05?

Seriously, what is your dissatisfaction with using a 7805?

Efficiency? ANY linear regulator is grossly inefficient with a high input to output voltage ratio...
Consider the math. If Vin = 25v and Vout = 5V, and you expect 100mA of current, then the output power is 5v * 0.1A = 0.5W
Power wasted in the regulator is Vin - Vout * Iout. So... 25 -5 * 0.1 = 2.0W.
I think that about sums it up, eh? With 25 V in and 5V out, 20 % efficiency is the BEST you can expect from a linear regulator.

Time to look at switching regulators if you want high Vin and low Vout with decent efficiency.

If I've missed the mark and it's not about raw efficiency, then what's the problem? What's your application and current requirements? Maybe someone can suggest a better regulator method.


steve

[ronsimpson]

How much current?

[Art]

It doesn't have to be a linear regulator.
One example suggested on an electronics forum was an ICL7660 switched
capacitor regulator which apparently can be better than 99% efficient for low-power supplies.

Sounds better than a 7805 to power a battery monitor
(ie. I don't want a battery monitor to chew up much of it's own power).

The current I'm talking about I don't know exactly, but it's a 16F876, I2C EEPROM, and 2x16 LCD display.
Surely that is a low power circuit. I might even be able to sleep the chip when I'm currently pausing.
Art.

[Acetronics2]

It doesn't have to be a linear regulator.
One example suggested on an electronics forum was an ICL7660 switched
capacitor regulator which apparently can be better than 99% efficient for low-power supplies.

Art.

Hi, Art

the 7660 NEVER has been a regulator, but a voltage doubler ... Better Try the ICL 7663 !!!

for 25 v you'll need a pre-regulator ( switching ! )

the 78L05 also is to consider ...

Alain

[HenrikOlsson]

You could have look at the Recom DC/DC switching regulators. The R-78xx series is pin compatible with the linear 78 series regulators. I've never tried them myself though, I just stumbled across them a couple of weeks ago.

[Melanie]

The Recom units are a work of Art. They require no heatsink, run cold all the way up to their maximum rated current and happilly handle all kinds of rubbish pumped into them as an excuse for input DC Supply.

They have TWO dissadvantages... (1) They require a minimum load current otherwise they can go into spurious oscillation. A PIC on it's own isn't enough load... I've had to put a 330R Resistor across the 5v Rail just to draw sufficient idle current for them to be stable. (2) The price... I hate the price... even buying, 100, 500 or 1000 pieces at a time, they're just way too expensive.

If you need something better than a 78L05 but don't like the inefficiency of the standard junk 7805, why not try a 78M05 with a small clip-on Heatsink. Not as efficient as the Recom - but you can have twenty of those for the price of one Recom!

[Gusse]

LM2936 is much better than 7805 for small current applications

• ultra low quiescent current (Iq <= 15µA for Io = 100µA)
  - e.g in Sleep mode in battery powered devices

• fixed 5.0V with 50mA output
  - 50mA should be enough for PIC, EEPROM and LCD

• needs only 10uF cap for output (stability)

• input voltage up to 40V (HV up to 60V)

Works fine for me.

BR,
-Gusse-

[Normnet]

See MAX666CPA

Not cheap but very simple and power efficient.
For 5 volts no external components required.
No heat sink. No power loss?
Includes low battery detector.

Norm

[Byte_Butcher]

These are rather too much I think for your low current application because the chip alone draws several mA, but I've used the CS5171 with good success. Input voltage is up to 30V. I've used them to get 5 volts at a few hundred mA from a 10v - 15v input source.

http://www.onsemi.com/pub_link/Collateral/CS5171-D.PDF

I don't really have any experience with "small" converters of only a few mA so I can't recommend a "favorite" chip for that...


steve

[Gusse]

The current I'm talking about I don't know exactly, but it's a 16F876, I2C EEPROM, and 2x16 LCD display.
Surely that is a low power circuit. I might even be able to sleep the chip when I'm currently pausing.
Art.

Regulator with max. 50mA output should be enough, even if you would like to have illumination on LCD. Realistic current consumption should be in a range of 20-30mA.
In case of illumination, then LED(s) must be PWM controlled (HPWM or similar).

BR,
-Gusse-