Need advice for designing a circuit that gives 5V and 3.3V as outputs - Page 1
Forum section: electronics / beginners

author: milothepuli
author_rank: Newbie
timestamp: July 05, 2023, 01:55:32 pm
content: Hi!Not sure where to ask this, I'm a new user in this website, so I hope my question is relevant.I'm a junior electrical engineering student and we've given a small task, where we have to design a circuit that takes 12 V DC as input and gives 5 V DC and 3.3 V DC as outputs, with a current value of 2 A for each output. Then we have to draw our circuits in LTSpice. I've searched about how should I draw this circuit for some time but couldn't really figure out what to do. I'm thinking of a dual voltage supply circuit, or maybe using mosfets, though not every mosfet is found in LTSpice. Any advice would be appreciated, thanks!

author: CountChocula
author_rank: Unknown
timestamp: July 05, 2023, 02:32:24 pm
content: What parameters did your teacher give you? There are a surprising number of different answers to your question, depending on what the circuit needs to do. Assuming you are supposed to design the circuit out of discrete components, try searching for “linear voltage regulator” either on the forum or on google, and you will find what you're looking for.

author: ArdWar
author_rank: Frequent Contributor
timestamp: July 05, 2023, 02:46:43 pm
content: 3.3V at 2A from 12V supply...This is one of those "all answers are valid but your rationale and explanation for picking certain solution is where you're actually going to be graded" surely

author: CountChocula
author_rank: Unknown
timestamp: July 05, 2023, 02:49:30 pm
content: Quote from: ArdWar on July 05, 2023, 02:46:43 pmAll answersarevalid… as long as you use a sufficiently large heatsink 😬

author: RAPo
author_rank: Super Contributor
timestamp: July 05, 2023, 02:58:28 pm
content: There is an existing solution. SeeTikstation.

author: dferyance
author_rank: Regular Contributor
timestamp: July 05, 2023, 04:15:47 pm
content: Unlikely to be the answer being looked for, but a technically correct answer for exactly 12V DC and exactly 2A could be a simple (and very beefy) resistor to get your voltage drop. You'd need at least a 17.4 watt power resistor. Such a solution would never work for electronics, but I have an old radio controlled car that uses power resistors switched in and out by relays as a speed controller.I'd look at a switch mode regulator.

author: gnuarm
author_rank: Super Contributor
timestamp: July 06, 2023, 01:48:40 am
content: Quote from: milothepuli on July 05, 2023, 01:55:32 pmIf you need to simulate it in LTspice, I would go to the LT website... I mean the Analog Devices web site and pick a switching regulator that accepts 12V input and produces both 5V and 3.3V output. I'm sure there is more than one. If it was an LT part, it will be in LTspice nearly 100% for sure. In any event, pick one that has a simulation model in LTspice and use the recommended circuit from the data sheet.It's hard to go wrong if you do that. LT parts usually have an excellent description aka "theory of operation", which can be very educational in general.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: July 06, 2023, 04:20:56 am
content: This page shows how to use Zener diodes to achieve this:https://www.electronics-tutorials.ws/diode/diode_7.htmlNext would be a pair of linear regulators. Go from 12 to 5 then go from 5 to 3.3.The more complicated approach but not too hard: Use something like this:https://www.analog.com/media/en/technical-documentation/data-sheets/3510fe.pdf

author: gnuarm
author_rank: Super Contributor
timestamp: July 06, 2023, 05:19:28 am
content: Quote from: JustMeHere on July 06, 2023, 04:20:56 amZener diodes and linear regulators will dissipate a lot of heat. The Zener diode dissipates more heat when the load is light, the linear regulator dissipates more heat when the load is heavy.Switchers burn less power, sometimes a lot less power, but they are more complex and more expensive. They also make noise, which can be hard to filter.

author: milothepuli
author_rank: Newbie
timestamp: July 06, 2023, 09:46:31 am
content: The ones I mentioned in my question are the only information that we have. Our teacher said that there are more than one correct answer(a lot of people asked about this). After reading the replies, I decided to work on a circuit that includes a regulator, and it's almost finished. Thanks for your advice

author: milothepuli
author_rank: Newbie
timestamp: July 06, 2023, 10:01:22 am
content: Quote from: gnuarm on July 06, 2023, 01:48:40 amWow, how did I miss this? Thanks for the advice!I checked the Analog Devices website and indeed found a regulator that's suitable for my needs. The LTM4622A regulator (you can check it from here:https://www.analog.com/en/products/ltm4622a.html#product-overview) gives 5V and 3.3V as outputs respectively, which is what our teacher expected from us.I've completed my assignment, thanks for your answers everyone!

author: liaifat85
author_rank: Regular Contributor
timestamp: July 06, 2023, 03:18:52 pm
content: You can follow the updated version of this circuit:https://embedded-lab.com/blog/multi-purpose-dual-power-supply-5-0v-and-3-3v-regulator-board/The updated version of this circuit supports 12V input. Is is based on AMS1117.

author: gnuarm
author_rank: Super Contributor
timestamp: July 06, 2023, 03:45:47 pm
content: Quote from: liaifat85 on July 06, 2023, 03:18:52 pmI don't think this will handle 2 amps on each output without overheating, no?