electrohawk
Newbie level 4
I'm trying to design a flyback based converter. The converter I'm trying to make connects either to the utility (50Hz 220Vac) or to a 12Vdc supply (either ac or 12Vdc but not both) and has 12V, 5V, 4V and 3.3V dc outputs.
- My 12 V has light load (60mA max) and is used to power analog sensors.
- My 5 V drives an opamp that interfaces the sensors to the MCU along with power for my character LCD.
- My 3.3V is used to drive my MCU along with light digital loads.
- My 4 Vdc has heavy load with nominal current at 0.5A and peaks of 2A.
I am really confused of how to realize such a converter. My design is a flyback based power supply based on TI's UCC28911. Initially I was thinking of having 2 output windings on the flyback's transformer. One for my 12Vdc and the other for 5Vdc. My 4Vdc and 3.3Vdc would have been derived by 2 separate LDOs. However (this is my personal reasoning and might be wrong), coming up with such a setting would not permit connecting a 12Vdc source (instead of 220Vac 50Hz) to my supply to generate the rest of the voltage. The only permissible way is to have 1 output winding of 12Vdc and deriving 5, 4 and 3.3Vdc by LDOs (for the 3.3V and 4V) and normal linear regulators (for the 5V). I think in such way it is possible to connect the 12Vdc to power up my system. However in doing so I will not have isolation between my analog sensor ground and the other grounds of my circuitry. Now here comes my questions:
1- What do you think is the best way to solve my problem? Should I have 1 output winding on my flyback transof 12Vdc from my transformer and derive the rest from it?
2- This project brought me up to my 2nd question which is when should we have separate and isolated grounds from each other? I know that galvanic isolation ensures that our circuitry is disconnected from the mains protecting the circuit from failures but what about the isolation of the grounds from each other?
Thank you for your help! I would appreciate your feedback
- My 12 V has light load (60mA max) and is used to power analog sensors.
- My 5 V drives an opamp that interfaces the sensors to the MCU along with power for my character LCD.
- My 3.3V is used to drive my MCU along with light digital loads.
- My 4 Vdc has heavy load with nominal current at 0.5A and peaks of 2A.
I am really confused of how to realize such a converter. My design is a flyback based power supply based on TI's UCC28911. Initially I was thinking of having 2 output windings on the flyback's transformer. One for my 12Vdc and the other for 5Vdc. My 4Vdc and 3.3Vdc would have been derived by 2 separate LDOs. However (this is my personal reasoning and might be wrong), coming up with such a setting would not permit connecting a 12Vdc source (instead of 220Vac 50Hz) to my supply to generate the rest of the voltage. The only permissible way is to have 1 output winding of 12Vdc and deriving 5, 4 and 3.3Vdc by LDOs (for the 3.3V and 4V) and normal linear regulators (for the 5V). I think in such way it is possible to connect the 12Vdc to power up my system. However in doing so I will not have isolation between my analog sensor ground and the other grounds of my circuitry. Now here comes my questions:
1- What do you think is the best way to solve my problem? Should I have 1 output winding on my flyback transof 12Vdc from my transformer and derive the rest from it?
2- This project brought me up to my 2nd question which is when should we have separate and isolated grounds from each other? I know that galvanic isolation ensures that our circuitry is disconnected from the mains protecting the circuit from failures but what about the isolation of the grounds from each other?
Thank you for your help! I would appreciate your feedback