Background:
I am reviewing my prototype PCB to iron out previous issues. The pcbPCB is a bluetoothBluetooth data capture unit for liquid levels and flow. I am a software programmer by trade and I have some formal digital electronics training, the rest I learn as I go along, I would really appreciate it if some of the buffs over here could point me in the right direction.Circuit breakdown:
Supply
10 - 15Vdc -> Buck/Boost -> 12VDC -> 5VDC -> 3.3VDCLoad: +-500mA
1. two 5v5V MCUs 2. 5v. 5V RDM6300 RFID reader. 3. 3.3v3V HC-06 bluetoothBluetooth module. 4. two 12v12V 4-20ma sensors 5. four 5v. leds5V LEDs 6. two transistorsProblem:
Reliability. Currently I drive a ld1117v33LD1117V33 3.3V regulator from a 7805, which I drive from the 12v DC/DC converter. As you might guess the 7805 gets hot even with a heat-sync, sink. I love the boards and would like them to last a long time out in the hot field. So due to the affordability and seeming simplicity of regulators as opposed to DC/DC regulators and the fallout of cascading ripples on my analog circuits, not to mention the questions about shared grounds and isolated grounds etc, I want to add an additional 7809. So that I have 12v -> 9V -> 5V -> 3.3V to share the thermal dissipation load. My problem is how do I go about calculating the input and output capacitors for each of these regulators, especially seeing as the output capacitor of one regulator is the input capacitor of the next regulator. The current 7805 -> LD1117V33 seems to work fine with 1uF input and 100nF output on both. Thanks for reading my question.My problem is how do I go about calculating the input and output capacitors for each of these regulators? Particularly, how to address that the output capacitor of one regulator is the input capacitor of the next regulator? The current 7805 -> LD1117V33 seems to work fine with 1uF input and 100nF output on both.