How to only allow 3v - 6v in circuit

Thread Starter

palerider2029

Joined Mar 16, 2015
18
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?
 

Thread Starter

palerider2029

Joined Mar 16, 2015
18
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
 

Thread Starter

palerider2029

Joined Mar 16, 2015
18
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.
 

Thread Starter

palerider2029

Joined Mar 16, 2015
18
Well... If, as you say, the devices operate properly at 6v, your course would seem obvious? Am I missing something? :confused:

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?
 
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 :D

Best regards
HP
 

Dodgydave

Joined Jun 22, 2012
11,285
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?
 

Thread Starter

palerider2029

Joined Mar 16, 2015
18
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.
 
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