Hi all,
Thanks to SgtWookie I was able to work out building my h-bridge for a variable current circuit.
I just did the equations for made-up limit of 10Ω, on the grounds that the conductance in my electrolysis chamber will never approach that of the 10Ω element in my house water heater.
...also, it makes the math easy: 27V/10Ω = 2.7A.
I came up with the attached schematic which seems to handle any resistance down to about 10Ω at which point it draws ~2.7A
Since I want to run at a constant 2.64mA, and I'm still waiting for my current limiting diode to arrive, I popped in a 10.2k resistor to simulate the correct current draw.
It works - but: I noticed the bridge was pulling 64.33mA total to drive my 2.64mA load, and from what I've learned on the forums, I knew I could do better. The drive transistors don't need nearly as much current to run this small load, so I swapped out my resistors in the schematic as follows:
Viola! It now draws only 8mA - a savings of 56ma. hooray. (I got as low as 2.65 when I refactored without the LEDs).
From my tests, it looks like this circuit WILL restrict the current to the desired 2.64mA. So my question is this: Why wait for a CLD to arrive in the mail, when it looks like I can already create a constant current with this modification?
The only drawback I see is that I've limited current by depriving the drive transistors of base current, so when the chamber resistance drops below 10.2k and the collector wants more than the 2.64mA (probably about 6mA) then the drive transistors will be in forward-active mode, and presumably heat up a bit.
Is this bad? or is it an acceptable way to limit current?
Thanks in advance,
-masked
Thanks to SgtWookie I was able to work out building my h-bridge for a variable current circuit.
I just did the equations for made-up limit of 10Ω, on the grounds that the conductance in my electrolysis chamber will never approach that of the 10Ω element in my house water heater.
...also, it makes the math easy: 27V/10Ω = 2.7A.
I came up with the attached schematic which seems to handle any resistance down to about 10Ω at which point it draws ~2.7A
Since I want to run at a constant 2.64mA, and I'm still waiting for my current limiting diode to arrive, I popped in a 10.2k resistor to simulate the correct current draw.
It works - but: I noticed the bridge was pulling 64.33mA total to drive my 2.64mA load, and from what I've learned on the forums, I knew I could do better. The drive transistors don't need nearly as much current to run this small load, so I swapped out my resistors in the schematic as follows:
Viola! It now draws only 8mA - a savings of 56ma. hooray. (I got as low as 2.65 when I refactored without the LEDs).
From my tests, it looks like this circuit WILL restrict the current to the desired 2.64mA. So my question is this: Why wait for a CLD to arrive in the mail, when it looks like I can already create a constant current with this modification?
The only drawback I see is that I've limited current by depriving the drive transistors of base current, so when the chamber resistance drops below 10.2k and the collector wants more than the 2.64mA (probably about 6mA) then the drive transistors will be in forward-active mode, and presumably heat up a bit.
Is this bad? or is it an acceptable way to limit current?
Thanks in advance,
-masked
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