3 ms·

I've built one for ~ $30 in parts from Radio Shack using an LM317 current limiter. But the data sheet for the LM317 says the minimum operating current is 2.0 m

I've built one for ~ $30 in parts from Radio Shack using an LM317 current limiter. But the data sheet for the LM317 says the minimum operating current is 2.0 mA, yet the amount delivered to the brain should be 1 mA. How did it work?

learc83 15y ago
It requires a 2 mA to operate; that doesn't mean you're forced to actually draw 2 mA from the output.
- amstr 15y ago
  According to http://clinicaltrials.gov/ct2/show/NCT00763230 http://clinicaltrials.gov/ct2/show/NCT00763230 , 2 mA is quite safe and actually more effective than 1 mA.
  - ChristianMarks 15y ago
    Correct.
- martincmartin 15y ago
  Sorry if I'm being dense, but where is that 2 mA measured? It only has three pins: input, output, and reference. There's no ground pin. The reference presumably draws almost no current, as drawing significant current would affect the measurement. So the current on the input & output must be the same, and the same as what we're feeding into the electrodes. No? Does this just mean you can't use the simple circuit composed entirely of the LM317 and a single resistor between the output pin and the reference?
  - learc83 15y ago
    Sorry my mistake, I was talking without looking at the datasheet. From the datasheet >all quiescent operating current is returned to the output terminal. This imposes the requirement for a minimum load current. If the load current is less than this minimum, the output voltage will rise. I've used an LM317 drawing less than 2mA, so I assumed it was possible (in hindsight I must have used the solution, below). The solution is very simple however, make a separate parallel circuit that will draw at least 2mA. This can be accomplished just by placing a resistor of appropriate value between the Vout and ground.
    - ORLIN1 15y ago
      i get from LM317 min 0,7mA and not get lower different types (small,large case) of LM317 havemaybe different parametrs

learc83 15y ago

It requires a 2 mA to operate; that doesn't mean you're forced to actually draw 2 mA from the output.

amstr 15y ago
According to http://clinicaltrials.gov/ct2/show/NCT00763230 http://clinicaltrials.gov/ct2/show/NCT00763230 , 2 mA is quite safe and actually more effective than 1 mA.
- ChristianMarks 15y ago
  Correct.
martincmartin 15y ago
Sorry if I'm being dense, but where is that 2 mA measured? It only has three pins: input, output, and reference. There's no ground pin. The reference presumably draws almost no current, as drawing significant current would affect the measurement. So the current on the input & output must be the same, and the same as what we're feeding into the electrodes. No? Does this just mean you can't use the simple circuit composed entirely of the LM317 and a single resistor between the output pin and the reference?
- learc83 15y ago
  Sorry my mistake, I was talking without looking at the datasheet. From the datasheet >all quiescent operating current is returned to the output terminal. This imposes the requirement for a minimum load current. If the load current is less than this minimum, the output voltage will rise. I've used an LM317 drawing less than 2mA, so I assumed it was possible (in hindsight I must have used the solution, below). The solution is very simple however, make a separate parallel circuit that will draw at least 2mA. This can be accomplished just by placing a resistor of appropriate value between the Vout and ground.
  - ORLIN1 15y ago
    i get from LM317 min 0,7mA and not get lower different types (small,large case) of LM317 havemaybe different parametrs