I've been using fixed 3volt LDO regulators, but I want to be able to allow any voltage from 3v - 6v. Are there similar components that will allow this?

 

You need to provide more information...

 

I've got multiple battery configurations: 3v to 7.4v
I want to run an LED light between 3v - 6v depending on the output of the batteries not less not more.

If 3v output is 3v (1 x cr123)
If 3.7v output is 3.7v (1x 18650)
If 6v output is 6v (2 x cr123)
If 7.4 volt output is 6v. (2 x 18650)

Best if the component allows >500ma of current.

I've been limiting the voltage to 3v using this component, but this does not allow the LED to perform at the brighter 6v settings when I install the other battery configurations.
http://www.digikey.com/product-detail/en/MCP1702T-3002E/CB/MCP1702T-3002E/CBCT-ND/1979827

 

Do you have specs for the LED? Sounds like you need a constant-current source.

 

The LED's already have drivers.
One is 3v - 9v
The other is 6v only

Thank you for trying to help me. I really appreciate it.

 

Have you considered a buck/boost switching regulator. These can provide a regulated output voltage which can be greater or less than the input voltage. Not really worth building as there are many available on ebay at very low cost.

This type of thing:

http://www.ebay.co.uk/itm/2-24v-Inp...f&pid=100005&rk=2&rkt=6&sd=400858208676&rt=nc

 

Well... If, as you say, the devices operate properly at 6v, your course would seem obvious? Am I missing something?

Regards
HP

 

Have you considered a buck/boost switching regulator. These can provide a regulated output voltage which can be greater or less than the input voltage. Not really worth building as there are many available on ebay at very low cost.

This type of thing:

http://www.ebay.co.uk/itm/2-24v-Input-DC-DC-2A-Adjustable-Step-Up-Boost-Power-Supply-Converter-Module/301475077594?_trksid=p2047675.c100005.m1851&_trkparms=aid=222007&algo=SIC.MBE&ao=1&asc=20140122125356&meid=af28ab514864442ebae5c6991613231f&pid=100005&rk=2&rkt=6&sd=400858208676&rt=nc

I was hoping for a simple surface mount component, some type of IC. I'm not very familiar with what is out there.

 

Well... If, as you say, the devices operate properly at 6v, your course would seem obvious? Am I missing something?

Regards
HP

Since I use 3v batteries I really need to limit the output to 6v, but still allow the 3v bulb to function normally if the input is only 3v.

If I used a 6v regulator would it still function at 3v?

 

If I used a 6v regulator would it still function at 3v?

It would not reliably pass the 3v 'through' if that's what you mean -- I strongly recommend you take the former poster's advice (Re: the linked devices)

Best regards
HP

 

I was hoping for a simple surface mount component, some type of IC. I'm not very familiar with what is out there.

A diode "OR" arrangement may be useful -- though you'd need to select diodes exhibiting a low forward (bias) 'drop'...

Really though, no need to be 'afraid' of the boost converters - they're 'self documenting' as it were

Best regards
HP

 

Here's how you could do it :-

Tempco is ~ -7mV per degree C.

 

Since I use 3v batteries I really need to limit the output to 6v, but still allow the 3v bulb to function normally.

Here's how you could do it :-
View attachment 82208
Tempco is ~ -7mV per degree C.

Thank you for taking the time to show me this.

 

use a J113 fet in constant current mode,

uses just 2 components one transistor and one resistor .

 

use a J113 fet in constant current mode,

uses just 2 components one transistor and one resistor .

Would you mind being a little more specific?
I like that the J113 comes in an sot-23 package.

 

you can use the Jfet with a resistor between the Gate and Source like this

http://www.vishay.com/docs/70596/70596.pdf

 

you can use the Jfet with a resistor between the Gate and Source like this

http://www.vishay.com/docs/70596/70596.pdf



View attachment 82252

This is a constant current? But does not cap the voltage at 6v?

 

In simplest terms I basically need gate that will allow any voltage through up to 6v, and then switch off if higher voltages are present.

 

If you want to shut off above a certain voltage you need a Comparator circuit, not a constant current,
the constant current keeps the same level irispective of the voltage variation.

What are you trying to make?

 

If you want to shut off above a certain voltage you need a Comparator circuit, not a constant current,
the constant current keeps the same level irispective of the voltage variation.

What are you trying to make?

It is a head mounted flashlight system. It can use 6v surefire incandescent or LED lamps, or 3-9v Solarforce lamps with a variety of battery types.
I'm trying to regulate the voltage to protect the surefire lamp from 7.4v battery configurations while still allowing the solarforce lamp to run at 3v if the user decides to use that style of lamp.