AMC7135 based drivers

[Vikas Sontakke]

Could somebody explain generic AMC7135 based drivers? Are these LDO type regulator which keep current constant to the load but burn up the excess voltage? Isn't the load current the same as the battery current for this type of drivers?

- Vikas

 

[Probedude]

Yep, that's exactly what what it is, a linear constant current regulator set to 350mA, 6V max input.
The in/out differential is very low, like 120mV.
Here's the datasheet.
http://www.micro-bridge.com/data/ADD/AMC7135.pdf

 

[fxstsb]

Yep, that's exactly what what it is, a linear constant current regulator set to 350mA, 6V max input.
The in/out differential is very low, like 120mV.
Here's the datasheet.
http://www.micro-bridge.com/data/ADD/AMC7135.pdf

Some lights are now using around 1 amp. I have not been up to speed on what is what in circuitry but wonder if there is one that will sin 1 amp?

 

[Probedude]

Some lights are now using around 1 amp. I have not been up to speed on what is what in circuitry but wonder if there is one that will sin 1 amp?

I've seen boards that use several of these AMC7135 chips in parallel to boost current output.

 

[Vikas Sontakke]

This certainly implies AMC7135 based lights are optimized for single rechargeable Lithium battery. Even if they claim to run on 2 CR123A or 2 RCR123A batteries, they are just waste of energy. Aren't most of the DX/KD drop-ins are based on AMC7135 and claimed to support 3-9V?

Singe AMC7135 supports 350 and lots of board have 3 on them to give 350, 700 and 1000 mA to emitter.

Are there any drop-in's which truely support 3 through 9 volts and increasing the voltage drops the input current?

- Vikas

 

[bshanahan14rulz]

Do amc7135 based drivers actually push a constant 350mA, or do they limit current to 350mA (or multiples of 350mA)

Like, if DD is supplying 2.5A and I make an amc7135 driver with 8 chips for 2.8A, will the amc driver only perform as well as DD or will it actually deliver more current?

 

[rmteo]

They are current limiting devices. If your given DD setup is 2.5A, adding any number of AMC7135 will not give you any more than 2.5A - in fact, it will be somewhat less than 2.5A due to the voltage drop.

 

[Justin Case]

Assuming an FET for the pass device, RDS(ON) is Vdrop/Iout = 120mV/350mA ~ 0.3 ohms.

 

[Justin Case]

This certainly implies AMC7135 based lights are optimized for single rechargeable Lithium battery. Even if they claim to run on 2 CR123A or 2 RCR123A batteries, they are just waste of energy. Aren't most of the DX/KD drop-ins are based on AMC7135 and claimed to support 3-9V?

Singe AMC7135 supports 350 and lots of board have 3 on them to give 350, 700 and 1000 mA to emitter.

Are there any drop-in's which truely support 3 through 9 volts and increasing the voltage drops the input current?

- Vikas

It is highly doubtful that any AMC7135-based driver would be claimed to run at 9V, unless it was by mistake. The absolute max Vin spec is 7V, above which you'll probably fry the IC. And a Vin of 3V won't run the AMC7135 in regulation for your usual 1050mA output AMC driver. You need Vin > Vf + 120mV, and Vf is going to be around 3.5V for a typical single-die LED at ~1A drive current.

What you seek is a buck driver, and there are plenty of those.

 

[Fulgeo]

Do amc7135 based drivers actually push a constant 350mA, or do they limit current to 350mA (or multiples of 350mA)

Like, if DD is supplying 2.5A and I make an amc7135 driver with 8 chips for 2.8A, will the amc driver only perform as well as DD or will it actually deliver more current?

I as understand it the AMC7135 is a low dropout current regulator rated at for 350 mA constant sink current. On some test on another thread it was measured to be 330 mA to 350 mA per chip as long as the source voltage is above 3.9 volts. That being said they can only limit current. If you have a DD set up that delivers 2.5A an 8 chip driver can not deliver over your 2.5A. You are going to lose a few tenths of an amp actually, especially if you have not removed the diode from your driver(s). Think of them more like a rev limiter.

 

[Justin Case]

No. Vbatt for regulation has to be greater than the load voltage drop (LED Vf @ the drive current for the board) + dropout voltage of the board (120mV). If you have a 3xAMC7135 board that delivers a nominal 1050mA and an LED with Vf=3.4V@1050mA, then Vbatt > about 3.5V. If Vf is 3.8V, then Vbatt > about 3.9V. Thus, the required Vbatt for regulation depends on Vf.

You can see this variation in required Vbatt here:

http://www.candlepowerforums.com/vb/showthread.php?t=192925

The high Vf Cree Q5 requires a Vbatt of about 3.9V. The lower Vf Seoul P4 needs about 3.6V (actually, most likely ~3.5V, but the test used a relatively coarse measurement interval of 0.2V).

Also, removing the diodes only matters if Vf is low enough to make a difference. The criterion is that Vf > min Vdd (2.7V) + diode voltage drop (about 0.6V) ~ 3.3V. Thus, if you are trying to drive a typical Cree Q5 or Seoul P4 at the usual ~1A drive current, then quite possibly the LED Vf isn't going to be low enough for diode removal to matter. However, if you are using a 1xAMC or 2xAMC driver (350mA or 700mA drive current), then Vf could be low enough to benefit from removal of the diodes.