Hi there,
I have a straing gauge circuit containing an INA126 amplifier. The design is to use 5V however, I only have a 12V power supply available (from the wall), and was going to use an LDO to control the voltage to 5V. In theory I though this would work, in reality the voltage that the LDO outputs changes with the input voltage.
At Vin equal to 5V it outputs 5V and the linearly decreases as the input voltage increases. I have checked the current draw and it is at 5mA well below what the LDO can draw.
However, the output and ground terminals of the LDO are connected to the E+ and E- terminals of the strain bridge. If I unsolder the strain bridge the voltage goes back to outputting at the correct voltage. This leads me to believe that due to the voltage divider created by the full strain bridge the internal voltage divider inside the LDO has had its values change and therefore is no longer accurate.
I have not attempted to fix this problem yet but I believe I can buffer the output from the LDO using a simple voltage follower op amp, but I would rather not do that if there is another way to fix this.
I have attached a picture of the circuit. (Apologies about the paint drawing no Altium here to draw a proper one)
Regards,
Lance Henderson
Mechatronics Engineer
I have a straing gauge circuit containing an INA126 amplifier. The design is to use 5V however, I only have a 12V power supply available (from the wall), and was going to use an LDO to control the voltage to 5V. In theory I though this would work, in reality the voltage that the LDO outputs changes with the input voltage.
At Vin equal to 5V it outputs 5V and the linearly decreases as the input voltage increases. I have checked the current draw and it is at 5mA well below what the LDO can draw.
However, the output and ground terminals of the LDO are connected to the E+ and E- terminals of the strain bridge. If I unsolder the strain bridge the voltage goes back to outputting at the correct voltage. This leads me to believe that due to the voltage divider created by the full strain bridge the internal voltage divider inside the LDO has had its values change and therefore is no longer accurate.
I have not attempted to fix this problem yet but I believe I can buffer the output from the LDO using a simple voltage follower op amp, but I would rather not do that if there is another way to fix this.
I have attached a picture of the circuit. (Apologies about the paint drawing no Altium here to draw a proper one)
Regards,
Lance Henderson
Mechatronics Engineer
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