Old 11-10-2012, 05:17 AM #49
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Default Re: PT-121 Testing

I dropped the sense because I needed to drop the reference voltage. That should be a perfectly fine change.


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Old 11-10-2012, 02:14 PM #50
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Default Re: PT-121 Testing

Yeah, but the sense resistor (assuming you mean those parallel 0.005 resistors + 1k) is connected to a feedback look that'll adjust the voltage output--and therefore the current output--as needed. If the voltage drop across Output + to Output - is less than before (say it's 2.5V instead of 5V) the Vo output will be reduced to reflect this due to the feedback. You don't need to change the sense resistors for this to happen.

If you change the value of those sense resistors, the amount of current measured will change because it's relying on 1mV/Amp measured across that particular resistance; you'll need to compensate with the feedback gain so it can regulate the current again. This is an unnecessary change unless you just want to reduce the amount of power being burned off at those resistors, which is very small anyway.

If you mean the resistor at VoAdjust, that mostly just sets the maximum output voltage possible. I believe you just set to something greater than your (V_diode + V_sense). The real work, however, is being done with the op-amps/sense resistor and track pin.
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Old 11-10-2012, 05:53 PM #51
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Default Re: PT-121 Testing

I don't have the 1k resistor in parallel - I have another way of measuring current. In my simulations (on LTSpice), reducing the value of those sense resistors AND using a 2.5V shunt diode instead of 5V shunt diode SHOULD keep everything the same. I am sure that that should work unless the opamp can't deal with that low of a sense voltage, which I am sure it can.
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Old 11-10-2012, 06:30 PM #52
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Default Re: PT-121 Testing

Ah sorry, I was misinterpreting what you did.
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Old 11-10-2012, 06:45 PM #53
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Default Re: PT-121 Testing

No worries.
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Old 02-25-2015, 08:38 PM #54
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Default Re: PT-121 Testing

Any chance to get the schematics back?
I'm looking for a constant current driver to drive a laser diode and this one looks promising.
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