Author Topic: voltage regulator that does not waste (as much)  (Read 1179 times)

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Offline WhomBomTopic starter

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voltage regulator that does not waste (as much)
« on: October 21, 2010, 03:10:17 PM »
Hi guys, i've been busy with a totally over the top led desk lamp lately. That is how i first met voltage and current regulators.
Now i'm wondering; are there voltage regulators out there that do not burn off at least 1,2V? With the ones i have now (LM317) i have to input at least 1,2V more than i can output, it would really help my quadruped if i could find any that only waste 0,5V.

I thought to have found them in the category low drop out regulators, but now i'm not so sure... can anyone help?

Offline madsci1016

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Re: voltage regulator that does not waste (as much)
« Reply #1 on: October 21, 2010, 03:17:27 PM »
There are Low drop out linear regulators out there, but what you want is a switching voltage regulator, it's much more efficient at regulating voltage.

What are the spec of the lamp? Voltage and current requirements?

Offline Soeren

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Re: voltage regulator that does not waste (as much)
« Reply #2 on: October 21, 2010, 04:38:25 PM »
Hi,

Now i'm wondering; are there voltage regulators out there that do not burn off at least 1,2V? With the ones i have now (LM317) i have to input at least 1,2V more than i can output, it would really help my quadruped if i could find any that only waste 0,5V.
The LM317 need to drop 1.25V over a current limit resistor, but it has a drop of it's own (probably only around 2V in your app though).

I thought to have found them in the category low drop out regulators, but now i'm not so sure...
You're confusing the regulators own drop out voltage and the voltage dropped over an external resistor (which is the regulators internal bias- or regulation voltage - often around 1.25V as a bandgap reference is usually employed).

As madsci mentioned, you wanna go with a switcher, but more specific, a switcher made for driving LEDs would be the easy choice. They're made for a diverse range of currents and serial or parallel connection of the LEDs.

If your supply voltage is very very stable and only about half a volt over the LED voltage, a single resistor could be used (won't work with batteries though).

Since you're using an LM317 now, at least you're under 1.5A, but we need precise specs (number of LEDs, their voltage drop, their needed current and your supply voltage) to point you towards the solution.

The more info we get, the better answers we provide  :)
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
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Offline photomark

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Re: voltage regulator that does not waste (as much)
« Reply #3 on: October 22, 2010, 05:33:48 AM »
If you can get your unregulated voltage as close as 0.5v of your regulated voltage and it is stable at that then why do you need a voltage regulator at all as it seems like it is already well regulated   

Offline WhomBomTopic starter

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Re: voltage regulator that does not waste (as much)
« Reply #4 on: October 22, 2010, 11:40:13 AM »
Thanks for the answers so far.  My lamp features a 1W red, blue, green and white led. I regulate their currents with a LM317 per led, and dimm them through a transistor hooked to my arduino. The lamp is plugged into the wall outlet so power wasting isn't really a concern.

However, for my quadruped it is.
I want to regulate the voltage so that my servo's are always equally strong, the situation now is that with 6 Nimh cells fully tanked up at +/-1,4V per cell my servos receive 8,4V. Any more and they will burn and die. By the time the cells are getting empty the voltage is about 1,1V per cell -> 6,6V on my servo's. The contrast between servo force at 6,6V or 8,4V is just too big to have my quadruped walking fluently at any battery level. Hence the plan to regulate voltage.
I am willing to add one cell if it can fix this problem, but with a +/-1,2V loss through the regulator this results in 7,2V when the cells are full (9,6V regulated) and 6,5V if they are empty (7,7V-1,2V loss). It would stop the excess force at full battery but wouldn't fix the low battery force shortage.
So my options are; adding 2 cells and waste like 1,5 of them or find a regulator with just 0,5V loss. The first one I already dismissed  :P

It should be able to handle at least 4A, but i'd be more comfortable with 6A or even 8A for planned servo upgrading..

Offline Soeren

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Re: voltage regulator that does not waste (as much)
« Reply #5 on: October 22, 2010, 11:46:19 PM »
Hi,

Thanks for the answers so far.  My lamp features a 1W red, blue, green and white led. I regulate their currents with a LM317 per led, and dimm them through a transistor hooked to my arduino. The lamp is plugged into the wall outlet so power wasting isn't really a concern.

What a waste of regulators where a single resistor would have done nicely ::)


I want to regulate the voltage so that my servo's are always equally strong, the situation now is that with 6 Nimh cells fully tanked up at +/-1,4V per cell my servos receive 8,4V. Any more and they will burn and die. By the time the cells are getting empty the voltage is about 1,1V per cell -> 6,6V on my servo's. The contrast between servo force at 6,6V or 8,4V is just too big to have my quadruped walking fluently at any battery level. Hence the plan to regulate voltage.
I am willing to add one cell if it can fix this problem, but with a +/-1,2V loss through the regulator this results in 7,2V when the cells are full (9,6V regulated) and 6,5V if they are empty (7,7V-1,2V loss).

You don't understand how a regulator works it seems.
The voltage drop of a regulator is the minimum extra voltage you need on the input.
Let's say you need it to provide a stable 6.0V out. The voltage drop of an LM317 used normally, as a regulator, will have a drop of 3.0V to 3.5V to ensure regulation under all (accepted) conditions.
The input needs to be, at least, 6.0 + 3.5 = 9.5V, but can be more (up to a limit of course) while still providing 6.0V out.
The 1.2V that you have gotten hung up on (should be 1.25V +/-0.05V) is the regulation bias voltage and has nothing to do with the voltage drop.


It would stop the excess force at full battery but wouldn't fix the low battery force shortage.
So my options are; adding 2 cells and waste like 1,5 of them or find a regulator with just 0,5V loss. The first one I already dismissed  :P

It should be able to handle at least 4A, but i'd be more comfortable with 6A or even 8A for planned servo upgrading..

It is typical of noobs to want lots more than needed, disregarding that it most often will have a negative effect one way or another, but hey, at least it's only money wasted in this case ;)
So, go ahead and get my favorite high power regulator, the MIC29752BWT
At 4A, the typical drop is 0.27V and at 7.5A it is 0.425V.

While it's a 7.5A (26V in max.) nominal regulator, the current limit is 9A typical and 15A max. (Don't expect it to function for regular periods at such currents though, it's just the values of the internal limiter circuit)

You set the output voltage by 2 resistors like on the LM317 (but it doesn't work exactly like the LM317, so study the datasheet.
Further you need two caps (10µF and 22µF) to complete the circuit.
Remember a heatsink!!
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline WhomBomTopic starter

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Re: voltage regulator that does not waste (as much)
« Reply #6 on: October 23, 2010, 02:40:10 PM »
You're right about the ml317 Voltage drop Soeren. I measured the 1,2V drop without a load  :-[



It is typical of noobs to want lots more than needed, disregarding that it most often will have a negative effect one way or another, but hey, at least it's only money wasted in this case ;)
So, go ahead and get my favorite high power regulator, the




That's because when we make decisions on such stuff we are not hindered by knowledge  :P

I've looked around for some high current ldo regulators an managed to find the mic29752 at a fair price, so i think i'll go with that one. But just out of curiosity would it be possible to have two or more lower current regulators in parallel?


« Last Edit: October 23, 2010, 02:43:54 PM by WhomBom »

Offline Soeren

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Re: voltage regulator that does not waste (as much)
« Reply #7 on: October 23, 2010, 10:42:55 PM »
Hi,

But just out of curiosity would it be possible to have two or more lower current regulators in parallel?
It's bad practice, as they won't be precisely the same and even if you adjust them to the same output voltage initially, sooner or later, tolerances will develop and one will carry most of the load (although the thermal protection circuit will help in that respect, assuming LM317 - don't try this with an LDO).
The right way to boost a voltage regulator is by an external power transistor and a resistor and, if over-current protection is wanted, a medium power transistor and 2 more resistors).

But it's so much "cleaner" to use a more powerful regulator, if one can be found and besides, the point was to keep the dropout voltage to a minimum. A current boost transistor will negate that somewhat.

Of course, there's still the switch mode solution, which can be down converting (buck), down converting (boost) or even both (buck-boost, SEPIC or CUK), which means that your 6 cells could give a stable output of eg. 7V over the full discharge.
Switchers however, are much more involved and either you have to calculate both the electronics and the magnetics (quite a lot of math on the latter), or pay for a ready made solution if one can be found.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

 


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