Evening all,
I'm playing with the circuit below where I want to limit the current across the "Out" chamber leads to 2.63mA.
Fortunately, I have three 9v batteries connected to Q7\(_e\), so my voltage there is 27 minus .7 across Q7, for a total of 26.3V.
Since I want the Q7\(_b\) current to be 26.3uA (a million times smaller), I use Ohm's Law to determine that I need a 1M resistor at R7.
This works on paper, and in 2 simulators.
However, when I build the actual device, I am getting about 9mA across the chamber leads. Since my voltmeter only reads amps to 3 decimal places, I can't examine the low values at Q7\(_e_b\).
SInce the value is 3.4 times higher, it's easy to replace the 1M resistors with 3.3M resisitors. When I do that, I get the correct current in both polarities.. but that also destroys my voltage. So I'm trying to understand what could be going on in order to fix it properly.
Any ideas?
-masked
I'm playing with the circuit below where I want to limit the current across the "Out" chamber leads to 2.63mA.
Fortunately, I have three 9v batteries connected to Q7\(_e\), so my voltage there is 27 minus .7 across Q7, for a total of 26.3V.
Since I want the Q7\(_b\) current to be 26.3uA (a million times smaller), I use Ohm's Law to determine that I need a 1M resistor at R7.
This works on paper, and in 2 simulators.
However, when I build the actual device, I am getting about 9mA across the chamber leads. Since my voltmeter only reads amps to 3 decimal places, I can't examine the low values at Q7\(_e_b\).
SInce the value is 3.4 times higher, it's easy to replace the 1M resistors with 3.3M resisitors. When I do that, I get the correct current in both polarities.. but that also destroys my voltage. So I'm trying to understand what could be going on in order to fix it properly.
Any ideas?
-masked