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# Query on the AMC7135

#### ron

##### New member
Gazoo, need your advice on the AMC7135. You mentioned that for the AMC7135, you have to connect the resistor in parallel in order to reduce the current flowing into the laser diode. That's confusing my calculations. Hmmm....so lets say for example:

I need to put a 20 ohm resistor for the AMC7135. Does this mean that I can put two 10 ohm resistors in parallel? Do they add up as R(t) = R(1) + R(2) (As though they were in series), or do they add up as 1/R(t) = 1/R(1) + 1/R(2)?

If the former was true, then putting two 10 ohm resistors in parallel would equal 20 ohms. Otherwise, I need to put two 40 ohm resistors in order to get a total of 20 ohms.

#### toked323

##### New member
just to say you should of asked this in the experiments and mods section o in gazoo's thread, but for 250ma you use a 33 ohm resistor in parallel with the diode and you have to gound the case of the diode if you using a flashligh host

#### Gazoo

##### Active member
Toked is correct and make sure you use a 1/2 watt resistor. But to clarify you need to isolate the diode if you are using this in a flashlight that uses its case for ground. The reason is the ground coming out of the regulator is not common to the ground going into the regulator.

FYI, putting two 10 ohm resistors in parallel will equal 5 ohms. Putting them in series would equal 20 ohms.

#### ron

##### New member
Whoops.... Did not realise that I was posting it in the wrong section. So sorry.