2camjohn
Member
In order to monitor the current flowing through a motor in one of my circuits, I got some current shunt measuring ICs.
The chip i have chosen is the INA139
These chips are supposed to give a voltage output, relative to the current flowing through a shunt resistor.
However Im having trouble getting any kind of sensible output.
I copied the typical circuit as shown in the schematic and connected my oscilloscope between VCURRENT and GND.
Please see the attached schematic.
The load is turned on when CB1 is shorted high.
Also there is a 100uf capacitor in parallel with the battery which is not shown on the schematic.
After trying a wide selection of shunt resistors, changing the gain, using a resistor instead of the motor etc etc I cant get anything close to an indication of the current flowing through the load.
At best I get some transient noise when the load is switched on, it looks very much like the signals you get by touching the oscilloscope probes but with less amplitude.
So before I start again from scratch, I was wondering if anyone could spot anything obvious in my schematic?
Or if anyone can recommend an alternative high sided current monitor which is straight forward to get working(must be small like sot23)?
Or any other methods of monitoring current?
Or if anyone knows any good websites where I can read up on this sort of thing, i feel like ive already read every post in this forum related to current monitoring, seems like a fairly simple concept so i dont have a clue where the problem lies.
The chip i have chosen is the INA139
These chips are supposed to give a voltage output, relative to the current flowing through a shunt resistor.
However Im having trouble getting any kind of sensible output.
I copied the typical circuit as shown in the schematic and connected my oscilloscope between VCURRENT and GND.
Please see the attached schematic.
The load is turned on when CB1 is shorted high.
Also there is a 100uf capacitor in parallel with the battery which is not shown on the schematic.
After trying a wide selection of shunt resistors, changing the gain, using a resistor instead of the motor etc etc I cant get anything close to an indication of the current flowing through the load.
At best I get some transient noise when the load is switched on, it looks very much like the signals you get by touching the oscilloscope probes but with less amplitude.
So before I start again from scratch, I was wondering if anyone could spot anything obvious in my schematic?
Or if anyone can recommend an alternative high sided current monitor which is straight forward to get working(must be small like sot23)?
Or any other methods of monitoring current?
Or if anyone knows any good websites where I can read up on this sort of thing, i feel like ive already read every post in this forum related to current monitoring, seems like a fairly simple concept so i dont have a clue where the problem lies.
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