Why does adding a linear regulator to this circuit cause the input voltage (V_c) to drop?
- The 9V input coming in is regulated. The voltage measured at the branch between D5 and R22 is ~8.7 V, so it should not be voltage sag due to the load of the regulator.
- If I remove REG1 from the circuit, V_c reads ~8.7 V.
- With REG1 present, V_c reads ~6.7 V. The drop in voltage is across R22.
The only other place in the circuit where V_c is used directly is to power a 2N7000 MOSFET used as an input buffer.
My best guess is that REG1 is somehow creating a voltage divider with R22, but I did not think this could happen. I don't believe my PCB has any shorts.