Simple flyback power supply - Page 1
Forum section: electronics / beginners

author: miler74
author_rank: Newbie
timestamp: March 24, 2025, 09:23:54 am
content: Hi everyone,I'm an electrical engineering student from Poland.For one of my classes, I've been assigned to design a simple flyback power supply with the following parameters, and then run a simulation of it in LTspice.Unfortunately, I'm not very experienced in this area of power electronics, and I'm struggling a bit.Would anyone be willing to help or guide me through the process? I'd really appreciate any support!Specs:Input voltage: AC 230V ±20%Output voltage: DC 24VOutput power: 50WThanks in advance!

author: Picuino
author_rank: Super Contributor
timestamp: March 24, 2025, 09:34:37 am
content: You can start by making a schematic of the power supply and we will correct or help you with the details.EDIT:Start with an input voltage rectifier and a capacitor.Then you will need to choose a transistor (best a mosfet) and a PWM controller (such as the UC3844).https://www.ti.com/lit/an/slua143/slua143.pdfhttps://www.ti.com/lit/ds/symlink/uc3844.pdfOn the transformer secondary (start with a 2:1 transformer ratio to begin with) a diode and a capacitor, followed by an optocoupler and a TL431 to control the output voltage. The optocoupler transistor must feed back into the PWM circuit.You can also control the output of the secondary to feed the PWM controller circuit (this is less precise, but easier).

author: Picuino
author_rank: Super Contributor
timestamp: March 24, 2025, 09:55:00 am
content: An example flyback converter can be found in the datasheet or in the application notes of the PWM controller circuit.Transformer:Primary: 48 turns5V secondary: 4 turns12V secondary: 9 turns

author: Picuino
author_rank: Super Contributor
timestamp: March 24, 2025, 12:00:07 pm
content: Flyback example design fromhttps://www.ti.com/lit/ds/symlink/uc3844.pdf

author: BILLPOD
author_rank: Frequent Contributor
timestamp: March 24, 2025, 12:18:46 pm
content: Dzien dobry Miler, Witamy

author: miler74
author_rank: Newbie
timestamp: March 24, 2025, 04:29:56 pm
content: Thanks for the quick reply, Picuino — it really helped clarify things for me.I spoke with the professor who teaches the subject, and he instructed me to first design a real (non-ideal) transformer, then simulate it in LTspice. Based on the results of that simulation, I’m supposed to select the rest of the components. Unfortunately, I have to follow his guidelines strictly — otherwise, I won’t pass the subject.Cześć BILPOD

author: Picuino
author_rank: Super Contributor
timestamp: March 25, 2025, 08:29:28 am
content: A real transformer is modeled with an ideal transformer with some added elements (resistors and uncoupled inductances in the primary and secondary).You can also add resistors to model the core losses.https://en.wikipedia.org/wiki/Transformer#Equivalent_circuitDid the professor give you some guidance on this?

author: miler74
author_rank: Newbie
timestamp: March 25, 2025, 05:27:56 pm
content: Today I got some links from my professor that might come in handy:http://schmidt-walter-schaltnetzteile.de/smps_e/spw_smps_e.htmlhttp://schmidt-walter-schaltnetzteile.de/snt/snt_eng/snteng6a.pdf

author: Picuino
author_rank: Super Contributor
timestamp: March 26, 2025, 07:12:31 pm
content: A simulation with a real transformer, in continuous conduction mode.https://www.picuino.com/circuits/?ctz=CQAgjCBMCmC0AcIDMAGAdGJA2e37xzAE4ssQBWFCkAFiQrjDACgA3EeKpcyDqmxFX5dI5EEPFpyzAO59kPcDRoLeKNkpXdeYZVHzioUFCapixQjDWZhyRY4kiQVkFIm2H0EMKd+nZmvqIxLyQBupyulqKru6K6gAqDuBhUADsOqkq6CZqUiCwYGhIaSXYWGlpmLjwaTRwaVBoWGCQ3EgdrihEdWBk6ETwAbHgRKFuUM7iwxMh4FhUc+oAJvOLY2spjiDL0ABmAIYArgA2AC7MAMabrcELtILgaH4vvmANUDRpGLgoNG1MSo+ehgNLqABO4FaDyhmUeXRMAT6-GC0IE00iaMQnBhEVhWxuqTxI1uyXRxIm6ORuOGGVGvA6ZCWzFWkDpJGQ2BAHN4u0Opwu10Z3LIwqWkl8RCl0plsvszmKRCQ+BoJngY1ajWctLh6V4HIhtD6IqNTI2i0gATFGxoxuZcmFHNtZANOs2bJ05pmdyoJK9AHsoBAsNkQAAPeA+TDgSzw6iwUpB5CSMQJpDMQONJAM8ORlDRkNcNA6cCltPMIA