LM7912 regulator output is setting down to zero after the current is drawn by the load. Here I am attaching power supply circuit and DAC circuit. My project is the sensor from the field will give 8 to 48 mA output and which is read by the ADC. After it will be taken to the microcontroller and it will be sent to DAC and the output of the DAC is 4 -20 mA.
Whenever the unit is switched on for some time the output of the DAC is going 45mA which is out of our scaling. There is no linearity between input mAmps and output mAmps. Whenever the output of DAC is 45mA , the output of the 7912 regulator is 0V.
Please let me KNOW is it because of regulator or some other component.?
I can see that the requester used the schematic without reading device specifications.
78XX and 79XX have different pinouts, and the INPUT voltage including spikes must not exceed 35 V,
otherwise the internal reference burns down. Rating capacitors for safe voltages is the very basic rule.
Please do not continue without learning the specifications. Learn the basics, or you will burn more components.
Thank you for your reply. You are right the input voltage including spikes must not exceed 30V. Since it is proved project i did not check the specifications. The input voltage from the transformer is 28VAC and it is rectified and the voltage to the regulator becomes almost 42VDC. So may be i have to reduce the transformer output voltage to 18VAC. I think it will become alright.