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Why does the current increase when you run 2x flexdrive's in parallel?

Fiddy

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G'day,

This has been bugging me for a while.

Why does the current increase when you run 2 flexdrive's in parallel?

My understanding is when you add 2 drivers at the same current setting, they would be sitting at the same voltage and being in parallel they both would stay at that voltage and hence the current will too.

The only way to increase the current would be to decrease the resistance of the diode its driver, but since that value remains a fixed, i cant see how.

Although i know ive seen and done it with 2 flexdrives i cant explain it!

Im thinking some sort of trickery in the drivers do some funky stuff.


If anyone can provide an explanation i would be glad to here it :)

What i don't want to here is, "the 2 drivers current value is added together"

Fiddy.
 
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bobhaha

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As far as I understand it is, that the driver generates a current and not a voltage. By generates I mean "push" out a current. So connecting the flexdrive on to anything will always push out the same current (within the drivers limits). That said, I think it works by both drivers "pushing" the current through the diode and the diode in turns just draws the voltage it needs at that current level.

I could be wrong but that's how I understand it.
 
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kiyoukan

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the best way i was explained this was think of it like water.
if your faucet is filling a tub and you turn on another faucet its twice the rate to fill.
twice the power.
 

Bionic-Badger

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I think the flex drive increases the voltage and current output as a function of the detected current at each driver's sense-resistor. So if you have two drivers in parallel, they're both using independent sense resistors for regulating current and are able to both pump out current as needed.
 

DTR

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I remember when I tried to run NJG-18 drivers in parallel. The current did not double. In fact it stayed almost the same. I think they were sharing the load as the two drivers in parallel were drawing about the same current from my bench supply as they did individually and producing the same current to the diode.:thinking:
 
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Fiddy

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I think the flex drive increases the voltage and current output as a function of the detected current at each driver's sense-resistor. So if you have two drivers in parallel, they're both using independent sense resistors for regulating current and are able to both pump out current as needed.

that sounds like its on the money.

I remember when I tried to run NJG-18 drivers in parallel. The current did not double. In fact it stayed almost the same. I think they were sharing the load as the two drivers in parallel were drawing about the same current from my bench supply as they did individually and producing the same current to the diode.:thinking:

Very interesting DTR thats what i would expect to happen in parallel!
 

Jufran88

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To my understanding the Flexdrive is a current source (current regulator) therefore current adds up in parallel.

NJG-18 drivers are voltage sources (voltage regulator) so in parallel don't experience any change in current, but in voltage.

So, I guess it really depends what driver your using if its wired up as a voltage regulator or current regulator.
 

Fiddy

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you can provide more paths for current flow to the load, it wont do anything to the current flowing unless the load or supply voltage changes....
 

Bogart

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Laser drivers are constant current not constant voltage BTW.

That's the essence of it.

A flexdrive measures the amount of current flowing through it, and will adjust it's output voltage up or down (within it's limits) as needed to maintain a constant amount of current.

A laser diode will consume all the current you can feed it until it fries, if given enough voltage.

A flexdrive set for 500mA is going to try it's best to deliver exactly that amount.
 




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