Current/Voltage Regulator

[o_DEATH_ANG3L_o]

Does anyone know of a different chip besides the LM317 that does the same thing but will accept a lower voltage input. The reason I ask is because the LM317 has a drop of 2 volts. I was making my Dorcy Metal Gear last night and was testing it with Daedal's circuit. Everything fit nicley in the Dorcy but with only 4.5 volts from the Dorcy, the LD was only drawing like 40 mA. So I had to leave the LM317 out. So with a 5 ohm resistor, a 47 uF capacitor, and the silicone diode, with an input of 4.5 volts, the LD draws a nice and comfortable 160 mA. I would like to have this regulator in their for added security. If anyone knows a different regulator that would work with 4.5 volts, please share your thoughts. Thank You.

 

[chimo]

Yes, I don't have the link handy but see my posts in Experiments/Mods about my home-made GB Laser. My LDO has a 1V drop.

 

[catdog]

Check out this link:
worldtorch.com/LDO-regulator-schematic.php

They use a LM334 which can operate with a drop of only 0.1V! The reference voltage is about 0.065V (compared to LM317 reference of 1.25V), so resistor selection is critical and is possibly difficult to find. (e.g. 0.065V / 160mA = 0.4 Ohm resistor)

 

[rog8811]

Kenom posted info on ....was it resistor girl? on ebay, I had a look yesterday, she listed fraction ohm resistors.

 

[chimo]

That takes care of the losses across the sense resistor but it will also need a low Vcesat transistor to keep efficiency high. These LDs are running att a much higher current than a 5mm LED.

Here's the link I mentioned above. http://www.laserpointerforums.com/forums/YaBB.pl?num=1188569731;start=all

Check out this link:
worldtorch.com/LDO-regulator-schematic.php

They use a LM334 which can operate with a drop of only 0.1V!  The reference voltage is about 0.065V (compared to LM317 reference of 1.25V), so resistor selection is critical and is possibly difficult to find.  (e.g. 0.065V / 160mA = 0.4 Ohm resistor)

 

[Daedal]

The LDO that I use is the LM2991

Check it out

--DDL

 

[o_DEATH_ANG3L_o]

Thanks guys. So I should go with a LM334 or LM2991? All I want is to be able to use Daedal's circuit with an input voltage of only 4.5 volts. That way I can still have control of the current going to the LD. Like I said I tried it with the LM317 and I only got like 40 mA with no resistance.

 

[Daedal]

The LM334 has a cap of 10mA I thought... :-?

And the LM2991 needs a different circuit...

--DDL

 

[a_pyro_is]

If you only got 40mA output, either it's not wired correctly, or the 317 is bad.

 

[a_pyro_is]

Death, can you post a pic of your 317 circuit?

 

[Gazoo]

If you only got 40mA output, either it's not wired correctly, or the 317 is bad.

With only 4.5 volts input, like he posted, this is about all one can expect..

 

[catdog]

That takes care of the losses across the sense resistor but it will also need a low Vcesat transistor to keep efficiency high.  These LDs are running att a much higher current than a 5mm LED.

It doesn't have to use a bipolar transistor, and there are plenty of examples on the web of it using a MOSFET instead. There are also examples of it being used for high power LEDs operating with over 1 Amp. Hopefully I am allowed to post this link:
candlepowerforums.com/vb/showthread.php?t=75204

Note that I have not built a regulator using the LM334 - I only investigated it for use with my bluray diode (since it requires a higher voltage than a red laser, and I wanted to use a minimum number of batteries).

The LM334 has a cap of 10mA I thought... :-?

And the LM2991 needs a different circuit...

The use of an external transistor allows the current to be much larger than 10 mA. I thought that the LM2991 was effectively a negative lm317? Therefore you still have a 1.25V drop across the sense resistor? Care to post your schematic?

 

[Benm]

Does anyone know of a different chip besides the LM317 that does the same thing but will accept a lower voltage input.

Well, not actually a chip, but a little circuit using an opamp and transitor.. i posted it before: http://www.laserpointerforums.com/forums/YaBB.pl?num=1189529869

It is by no means the simplest circuit to build, but features current control using a simple pot, and can drive a LD with 0.9 volts drop at 200 mA whilst retaining full regulation.

Running your LD from 3 NiMH's is no problem at all, alkalines will be fine too until they're almost completely empty.

 

[chimo]

[quote author=chimo link=1191266847/0#4 date=1191273495]That takes care of the losses across the sense resistor but it will also need a low Vcesat transistor to keep efficiency high.  These LDs are running att a much higher current than a 5mm LED.

It doesn't have to use a bipolar transistor, and there are plenty of examples on the web of it using a MOSFET instead.  There are also examples of it being used for high power LEDs operating with over 1 Amp.  Hopefully I am allowed to post this link:
candlepowerforums.com/vb/showthread.php?t=75204

Note that I have not built a regulator using the LM334 - I only investigated it for use with my bluray diode (since it requires a higher voltage than a red laser, and I wanted to use a minimum number of batteries).

The LM334 has a cap of 10mA I thought...  :-?

And the LM2991 needs a different circuit...

The use of an external transistor allows the current to be much larger than 10 mA.  I thought that the LM2991 was effectively a negative lm317?  Therefore you still have a 1.25V drop across the sense resistor?  Care to post your schematic?[/quote]

Very valid comment on the MOSFET - I was just referring to the circuit in your link.

That's a great CPF thread, there's lots of great discussion and circuit analysis in there too! I recall reading it when that thread was developing.

If the OP wants a linear regulator with a lower drop out voltage than the LM317, the MC33269 from ONSemi is functionally equivalent but with a 1V dropout. It will give about 1.5V extra battery headroom.

 

[o_DEATH_ANG3L_o]

If you only got 40mA output, either it's not wired correctly, or the 317 is bad.

I did say that the input voltage I was using was only 4.5 volts, thus resulting in only 40mA being drawn from the LD. That is with no resistance. But my main concern here is just basically using a different regulator as close as possible to DDL circuit with the same wiring and configurations. You know just keep the same circuit but use a different regulator that would allow an input of 4.5 volts whilst still being able to maintain control over the current.

 

[Gazoo]

I will be testing an AMD7135 that Kenom is sending me. It has a typical dropout voltage of 120mv's. Many of the regulators DX is selling use this regulator and in fact it is this one:

http://www.dealextreme.com/details.dx/sku.3160

I will post an update after I receive it and get a chance to check it out.