Driver Test Load for PHR-803T Schematic

DIY Driver Test Load for PHR-803T Schematic

I have been asking questions all the time since im a LPF member but i wanted to aport something to the forum. So i tried to help aporting this schematic to how to read mA with a homemade test load .

These schematics are for the purpose to regulate the mA of a Rkcstr or Flext-Drive Driver using a Voltmeter for then use it with a Phr-803T Diode.

You will need:
6 x 1N4001 Diodes
1 Ohm Resistor
Voltmeter

The Diodes and the resistor are connected in series.

Any error in these Schematics please post.

Good job of showing how to test current...
There are a few posts on the forum that also explain and show
a similar schematic..
You can't have too many of a good thing...:yh:

Jerry

Yes, the Voltmeter is connected correctly. With a 1 Ohm resistor as you have in your diagram, the voltmeter would show e.g. 120mV if your current is 120mA (1:1 correspondence). Be sure to set your voltmeter to the correct voltage range.

Your setup is correct for any constant current LED driver, rkcstr MicroDrive, drlava FlexDrive or home-made LM317 driver (except that you'd use only one battery for the FlexDrive since it's limited to 5.5V).

i've found that this helps people more often than not, set your voltmeter to "2000m" that is the corect setting to read tripple digit Ma readings. "200m" setting would work for low Ma 2 digit readings, IE 45Ma. if im mistaken please correct me, just thought that would be a usefull footnote for people wondering.

Correction is coming A DMM typically has 3 1/2 digits, meaning the first digit only displays 0 and 1 (0.000...1.999). Note that this gives you the display resolution, it does not mean that the DMM is actually that precise! The "intrinsic" setting is the 200mV/200mA one; the others just use an internal resistor network to divide the input voltage/current by the appropriate power of 10, and shift the decimal point in the display.

When using the 2000mA setting, you can thus get readings that are precise to within a few mAs. Using the 200mA setting, you'd get them precise to some 100uAs. Generally, you should use the lowest possible setting, as this will give you the greatest actual precision.

The test loads available around here use 1Ohm resistors, so that 1mA current shows as 1mV on the DMM. The disadvantage is that for currents over 200mA, you have to use the 2V setting and this means a 10-times larger display error. It doesn't really matter for practical purposes (the resistor introduces a 5% error by itself anyway), I just wanted to point it out.

It's also worth stating that six diodes are good for blu-rays but not for red or IR diodes. For those, use three diodes instead of six. Diodes introduce a voltage drop of .7V per diode. This voltage drop is used to simulate the voltage necessary to power your laser diode. Since blu-ray lasers require >5V to operate, the six diodes equals a voltage drop of 4.2V (.7 x 6), which is close enough. Red and IR diodes usually require 2.5V or less, so simulating a voltage drop of 4.2V will not work in this case, but three diodes (.7 x 3 = 2.1V) would be ideal. Four (.7 x 4 = 2.8) is close enough for government work. You want the voltage drop to be as close as possible to that of the laser diode you're using so that your current setting will be very close to accurate.

ALSO, the minimum voltage for the rkcstr is too low. You really should have a minimum of 9volts. yes i know the technical amout but real world shows 9 to be the minumum.

just a regular ole' 1ohm resistor. the wattage doesn't matter but the standard one is half a watt.
http://www.radioshack.com/product/index.jsp?productId=2062337

oops didn't pay attention. sorry. but it make it just one ohm, but it looks almost identical to that one.

chipdouglas said:

oops didn't pay attention. sorry. but it make it just one ohm, but it looks almost identical to that one.

Click to expand...

10% tolerance? in't taht too high? This means a 10% error when you read the current!

That would be a maximum of 10% error. On average, you should get 5% or less (I guess there is some attempt to get the correct resistance in the manufacturing process, but I don't know the actual error distribution). Resistors with 5% tolerance would be preferable, they're just as cheap & available. For precision junkies, even better tolerances are available.

the radio shack i go to sells them. for the record, i wasn't suggesting the 1m ohm resistor. I thought it was the 1 ohm one. but i actually just wanted bennycast to see a pic of the one he should be using.

michael

If you cant find a 1 Ohm resistor.....

Radio Shack sells 10 ohm 5% 1/4 Watt resistors in a 5 pack
item #271-005...

Just put 10 of these resistors in parallel to get 1 Ohm...

Jerry

lasersbee said:

If you cant find a 1 Ohm resistor.....

Radio Shack sells 10 ohm 5% 1/4 Watt resistors in a 5 pack
item #271-005...

Just put 10 of these resistors in parallel to get 1 Ohm...

Jerry

Click to expand...

Thank you Jerry so when i connect them in parrallel, im suposed to use the reciprocating formula Right?
and how many 1n4001 do i need, and how are they connected with the 10ohm resistors?

If you are using identical value resistors...
all you do is take 10 Ohms divided by the number of resistors 10/10=1 Ohm...

For a Red LD test load you need 4pc of 1N400X diodes and for a Blu-Ray LD
you need 6pc 1N400X diodes all in series like your drawings in the first Post...

Jerry

Thank you lasersbee, i finally got the 1 ohm resistor, i had to buy a quantity of a 100 to only use 1 resistor, unbelievable. I dont know what am i going to do with the other 99 resistors, lol. I just feel stupid because of buying all those resistors

Another question, in of those schematics is something has to go to any ground?, because i believe in the shematic nothing is grounded and maybe ill create a short of some kind