I have designed a circuit to keep the heating element at a constant temperature. The digital part of the circuit is being feed from a 5V LDO which is powered by two 18650 batteries in series and the heating element is directly connected to the output batteries. Also heating element wire(approximately 2ohm) is controlled with an N channel low side mosfet by the microcontroller.
What i noticed is that the LED and the seven segment display(connected to 5V output of LDO) seems to flicker when controller toggles the mosfet because of the voltage drop on the supply. Is there anything i can do to isolate these rails so that current draw for the load does not affect the 5V components?
The highest supply voltage for the system is 8.4V and currently the load roughly uses 2A. The problem is becomes more significant when the supply voltage gets lower. I don't think that any inrush current situation occurs because voltage continues to stay below 5V at the output of LDO when the load is on after few seconds. Also i tried with both batteries(which i am sure that can supply a lot more than 2A) and a lab bench power supply with no luck. I read that bulk capacitors can fix instant voltage drops but can they prevent constant voltage drop? If so where should i place these bulk capacitors?
Is there anything i can do to isolate these rails so that current draw for the load does not affect the 5V components?
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I read that bulk capacitors can fix instant voltage drops but can they prevent constant voltage drop? If so where should i place these bulk capacitors?
For an easy thing to try, install a resistor to isolate the sensitive device from the noisy supply. Add a reservoir capacitor as shown below.
This won't make up indefinitely for sagging supply voltage. You may wind up needing to boost voltage to the control device (as well as regulate voltage). Such as a boost converter or voltage multiplier.