three terminal voltage regulators..changing the voltage.

[RogerJ]

I want to make a regulator to stabilise the vehicle battery supply (in a camper van) to between 11 to 12v max to run LED lighting..I've got coming from Ebay a few low drop out LM2940CT-5.0 5v regulators - because they were cheap, and plan to use them with 6v2 zeners in the common terminal to make 11.2volts supplies. (slightly underunning the LEDs deliberately)

My question is are there disadvantages of doing it this way as opposed to buying 12v versions so far as chip performance is concerned ?

Thanks

 

[ericgibbs]

I want to make a regulator to stabilise the vehicle battery supply (in a camper van) to between 11 to 12v max to run LED lighting..I've got coming from Ebay a few low drop out LM2940CT-5.0 5v regulators - because they were cheap, and plan to use them with 6v2 zeners in the common terminal to make 11.2volts supplies. (slightly underunning the LEDs deliberately)

My question is are there disadvantages of doing it this way as opposed to buying 12v versions so far as chip performance is concerned ?

Thanks

hi
The main problem is the required 2 to 3 volts differential between the input to the Vreg and its output.

Regular Vregs require about 2-3V higher on the Input side, so for your 11.2V, you would need ~14V on the input.
You can buy low voltage drop out versions of Vregs, having a 0.5V differential

What are you powering?

 

[Reloadron]

Afternoon Eric, The OP's mentions the LM2940 Low Dropout Regulator as his choice. Typically a 0.5 volt dropout. It's a 1 amp regulator but as you mention, alas, the OP does not mention the load current?

Ron

 

[ericgibbs]

Afternoon Eric, The OP's mentions the LM2940 Low Dropout Regulator as his choice. Typically a 0.5 volt dropout. It's a 1 amp regulator but as you mention, alas, the OP does not mention the load current?

Ron

hi Ron,
I must admit I missed that, thats why I sneaked in the edit.
If the OP's wants a stable 12V from a 10.8 thru 14V [ vehicle battery range] I would suggest a SMPS.

E.

 

[RogerJ]

Hi...The 2940 series of regulators fits the bill in every respect. The load is 4 x 180ma and the stabilaation required is not critcal. Just want to keep >12v from the LEDs to ensure long life..Hence 11.8v considered to be fine. SMPS is overkill..

What I really want to hear about is simply if putting a 6v2 zener in the series with the ground terminal of the (Ebay cheapo) 5 v regulators I've ordered is an Ok way to proceed..It just seems too simple..!

 

[Reloadron]

While I agree with Eric as to the use of a SMPS in lieu of using a regulator what you are proposing should work for the LEDs. Especially since stability is not a big concern. If this were a critical application, then no I would not go the route of using a zener and 5 volt regulator.

Ron

 

[RogerJ]

Thanks for your help and advice. I feel happier about proceeding now. It's worth pointing out to anyone reading this thread who may be thinking of using LED lighting in a small boat or camper that some folk say - and I agree - that making a common 12v driver for all the LED lighting in the vehicle/boat, even including a nice SMPS, does result in a continous small current drain off the battery. Therefore cheap simple regulators for each switched led circuit (after the switch)is the way I'm going with these Ebay bargains.

 

[KeepItSimpleStupid]

One comment I want to make is that LED's are normally current driven. Post the exact LED's your going to be using for a more comprehensive answer.

 

[RogerJ]

The LEDS I'm using are these: https://www.amazon.co.uk/gp/offer-l...ve=22282&creativeASIN=B003C2D3KW&linkCode=asm

That's a 30 LED strip,white, 12V DC (180 mA) on a 37.5cm long "pcb"

each strip is replacing a 20watt flourescent in an old Merc ambulance I'm converting. The 30 LEDs are arranged in groups of three, each with a surface mount resistors. So the current is set by the resistor and by using the specified voltage..12v in this case.

 

[KeepItSimpleStupid]

Kinda cool. A idea, and it may be a poor one. Use an LM317T set up as a current mode regulator. Basically remove the resistor and replace with an LM317T and 1 resistor. You do need to figure out whether the LED forward voltage is within range of the amount required by the regulator.

 

[RogerJ]

Well I'm always ready to consider an alternative approach to a problem but that's a bit impractical in this case. As I said, there are 30 LEDs on the strip. arranged as 10 groups of three LEDs in series, each with it's own current limiting resistor and the 10 groups all presented in parallel. Current feed to paralleled LED's would presumable need series resistors anyway to help ensure the current was divided equally....so nothing to be gained I think. But thanks for coming in with the suggestion..

 

[KeepItSimpleStupid]

I read it as 3 strings of 10. Oops which I should have known was wrong. Thinking cap is broken a bit today.

Look at this https://www.pololu.com/catalog/product/2120 as a possible option.

 

[4pyros]

I want to make a regulator to stabilize the vehicle battery supply (in a camper van) to between 11 to 12v max to run LED lighting.

Quick question why do you feel the need to stabilize the battery voltage?

LEDs are current devices, you maybe better off stabilizing the current to the LEDs.

 

[RogerJ]

To KeepIt Simple: That is a wizzy little ready built circuit and I can think of some uses for it. But US postal charges can be high and I'm in the UK. I see lots of stuff that I would like to get but can't for that reason..Anyway for this particular application it has a disadvantage - the input is only given as 1.5 to 12v and as the point of the exercise is to eliminate the 12 - 14.4v range across a battery under charge from an alternator...

4pyros, re your question. One of us is missing something but at the risk of insulting you - or me making a gaff - i'll say that in this instance I'm dealing with ready made led light strips made up as 10 paralleled groups of three LEDs in series - so lets say for arguments sake, 6v for the LEDs and a recommended optimal current of 18ma. The built in series resistor(s) is presumably calculated to drop 6v at 18ma at the "rated" operating voltage for the string which is 12v. If the supply voltage is higher, the current will increase and stress the LEDS causing premature failure. The range of voltage that can be expected in a 12v vehicle will range from 12.6v (fully charged battery at rest) and 13.5v - 14.4v when the alternator is charging. Given that in my original post I mentioned using a low dropout voltage regulator, and there has been some input already about stabilising the current and that that would be impractical in this case for a couple of reasons. Come back if I've missed something...

 

[4pyros]

4pyros, re your question. One of us is missing something but at the risk of insulting you - or me making a gaff - i'll say that in this instance I'm dealing with ready made led light strips made up as 10 paralleled groups of three LEDs in series - so lets say for arguments sake, 6v for the LEDs and a recommended optimal current of 18ma. The built in series resistor(s) is presumably calculated to drop 6v at 18ma at the "rated" operating voltage for the string which is 12v. If the supply voltage is higher, the current will increase and stress the LEDS causing premature failure. The range of voltage that can be expected in a 12v vehicle will range from 12.6v (fully charged battery at rest) and 13.5v - 14.4v when the alternator is charging. Given that in my original post I mentioned using a low dropout voltage regulator, and there has been some input already about stabilising the current and that that would be impractical in this case for a couple of reasons. Come back if I've missed something...

No gaff, its fine. thats why we are here.
Despite the fact that the LED strips have built in current limiting resistors the LEDs are still current devices.
Regulating the voltage would wast power and lower the available power to the LEDs.
Regulating the current to the LEDs would not wast any power and would allow you to run them at full power.
Trying to regulate a 12 volt to 15 volt input to 12 volts will always result in less than 12 volts on the low end.
Trying to regulate the current to 18ma will result in full brightness down to 12 volts.
No mater what there is always overhead involved in regulating voltage.

What you could try is a zener shunt regulator but you would need a series load resister but you may get better results than trying to use a liner regulator.
Andy

 

[KeepItSimpleStupid]

OP: You didn't read between the lines: https://www.pololu.com/catalog/product/2120/specs

The MAX operating voltage is 16 V. In an automotive environment, I would use a backwards diode and a Transorb or TVS as power protection. You could use one set for multiple supplies or one for each. The closer it is to the input of the supply the better. The backwards diode protects against the -200 V spikes. The Transorb will protect against the 50 V spikes on the car's electrical system.

I order for the UK occasionally and the shipping isn't too bad. I ordered some PICAXE components and Vitamins from the UK and even some IC chips and the shipping wasn't bad. It does depend on the vendor just like it does with conventional US shipping. Some US establishments will only ship one way. One of the things you can always ask to do is to "Ship Complete".

 

[RogerJ]

I missed that..the description says " The tiny (0.4"×0.7") module can support input voltages from 1.5 V to 12 V" and I didn't read past that point. Confusing...
Unless I've got this wrong as well the max current quoted is 300ma.. Each LED light strip needs 180ma. doesn't pan out too well..

The5 x LM2940CT-5.0 5v regulator chips were just $2 in your money and the 6v2 zeners just pennies.

Anyway youve alerted me to the existance of tiny smps and there are plenty advertised on Ebay...a variety of specs. I hadn't heard of transorbs or tvs's but Ive Googled them and am enlightened ..Thanks. I'll look into that aspect...

 

[RogerJ]

No gaff, its fine. thats why we are here.
Despite the fact that the LED strips have built in current limiting resistors the LEDs are still current devices.
Regulating the voltage would wast power and lower the available power to the LEDs.
Regulating the current to the LEDs would not wast any power and would allow you to run them at full power.
Trying to regulate a 12 volt to 15 volt input to 12 volts will always result in less than 12 volts on the low end.
Trying to regulate the current to 18ma will result in full brightness down to 12 volts.
No mater what there is always overhead involved in regulating voltage.

What you could try is a zener shunt regulator but you would need a series load resister but you may get better results than trying to use a liner regulator.
Andy

I lost my detailed reply in the clipboard here's a quicker one.

Given a load that is a resistor, or appears to be (ie a LED in series with R) It makes no difference as far as wasted power is concerned how it is regulated.

ie. Put 12v regulated cross 12ohms and 1 amp will flow - effectively 1 amp regulated..

Cause 1 amp to flow from a regulated current source into 12ohms and 12v will appear across it.....effectively 12v regulated

In other words the result is the same.

If the supply voltage to either type of regulator goes up the same power is disapated in the regulator (excess voltage x set current)

!My V regulators with .5v drop and set to 11.2v will deliver that down to 11.7v off the battery. By then the battery needs charging!

One chip will run all four strips (approx 700ma) as it's good for 1 amp

Current regulators would be good for a single LED or a single series chain of them where no resistor is used. A current reg is a "better" resistor" but wastes power in exactly the same way..

 

[KeepItSimpleStupid]

If you put something in a car, the tansorb and reverse polarity protection is mandatory. Here is a datasheet for a 16 V device, but it's in SMT technology. Finding them in stock though seems to be difficult. You can try www.digikey.com and www.mouser.com in the states.

Now it might be possible to get a schematic and/or reverse engineer the SMPS to get a higher current. e.g changing the output device and resistors that determine current limiting. Talk to them.

 

[RogerJ]

I guess you can tell I'm going to go with the 12v (11.2v in my case) voltage regulator.
I see there's another long thread on a similar subject going (hooking up 12v dc LED to automotive wiring) about 12v LED strips in an automobile. Didn't read it all but gathered there may be a different problem there.
However I've since found these: http://www.reuk.co.uk/buy-12-VOLT-REGULATOR.htm ready built little gagdets and bought a couple to see what they are like.. .5v dropout using the 2940. They might be of interest to the other poster. I might use them for other LED lights.

On the point of spike/surge protection, would a fuse, followed by a reversed power diode in parallel with a fat 15v zener do the job ?