Hello.
I've got multimeter created from my project on atmega8.
It work's quite good when measuring voltage on output stage of power supply:
0-30 VDC STABILIZED POWER SUPPLY WITH CURRENT CONTROL 0.002-3 A
But I can't figure it out how to determine current on output and current limit.
First of all, here is schematic where I have probes:
**broken link removed**
Plus one probe on point 13. It's there because I based on similar multimeter. Unfortunately this other multimeter has closed source and no explanation is given.
Measuring current flow should be a piece of cake because it's basically measuring voltage drop on resistor R7. This is first problem because when I've got no receiver it shows full range of from 0.00-4.5A. But maybe it's a good symptom?
And finally, my nightmare. How to measure current limit? (Yes it's possible)
I get the idea. We need voltage from 13 point because it's related with current limiter (U3). Also we need output voltage (which is voltage reference) of U1 (in my case it's 10V).
I found some calculations but when I implemented it, multimeter behaves strangely.
Can anyone help me with this?
I can provide a source code but i don't think it's important.
I've got multimeter created from my project on atmega8.
It work's quite good when measuring voltage on output stage of power supply:
0-30 VDC STABILIZED POWER SUPPLY WITH CURRENT CONTROL 0.002-3 A
But I can't figure it out how to determine current on output and current limit.
First of all, here is schematic where I have probes:
**broken link removed**
Plus one probe on point 13. It's there because I based on similar multimeter. Unfortunately this other multimeter has closed source and no explanation is given.
Measuring current flow should be a piece of cake because it's basically measuring voltage drop on resistor R7. This is first problem because when I've got no receiver it shows full range of from 0.00-4.5A. But maybe it's a good symptom?
And finally, my nightmare. How to measure current limit? (Yes it's possible)
I get the idea. We need voltage from 13 point because it's related with current limiter (U3). Also we need output voltage (which is voltage reference) of U1 (in my case it's 10V).
I found some calculations but when I implemented it, multimeter behaves strangely.
We need voltage reference from U1 to further calculations. We can measure it after calibrations. The only value which does not change after connecting load its the value of voltage divider P2 with resistors. We need to calculate it:
Dz = P13 / (UR7 + U1ref)
P13 - probe on point P13
UR7 - Voltage drop on R7
U1ref - voltage reference on output of U1
Current limiter will work when there will be the same voltage on inputs of U3 so:
(UR7 + REF) * Dz = UR7
Knowing previously calculated divider we can state on what voltage drop UR7 with this divider current limiter will activate.
UXR7 = (REF * Dz) / (1 - Dz)
Can anyone help me with this?
I can provide a source code but i don't think it's important.