Oscillator design to convert 12–21 VDC into AC for a 15–20 W transformer (100 kH - Page 1
Forum section: electronics / projects

author: SKYVsebasC20
author_rank: Newbie
timestamp: September 29, 2025, 07:37:36 pm
content: Hi everyone,I’m working on designing an oscillator to convert a DC supply (12–21 V) into an AC signal to drive a transformer (15–20 W). Here are the requirements and doubts:RequirementsFixed frequency between 100 kHz and 2 MHz (the higher the better, but I’m open to recommendations).Transformer secondary power: 15–20 W.I want the transformer to be as small as possible, which is why I’m considering high-frequency operation (ferrite or planar cores).Any suggestions and contributions are very welcome and would be of great help.

author: moffy
author_rank: Super Contributor
timestamp: September 29, 2025, 11:02:52 pm
content: The SN6507 might well do the trick:https://www.ti.com/product/SN6507

author: Someone
author_rank: Super Contributor
timestamp: September 30, 2025, 12:44:39 am
content: Quote from: SKYVsebasC20 on September 29, 2025, 07:37:36 pmWhy AC but you don't really care about the frequency? What is the AC being used for?

author: David Hess
author_rank: Super Contributor
timestamp: September 30, 2025, 01:04:10 am
content: There is nothing special about doing it. Many dual output switching regulator controllers can be configured to their maximum duty cycle to produce non-overlapping drive to a pair of transistors to drive a transformer primary. Some of them include voltage and/or current slew rating limiting for lower noise.Operating up to 2 MHz will be more difficult because existing solutions tend to be limited to lower frequencies, but of course it could be done.AC flux balancing may be required depending on the transformer design.Royer based designs are also suitable but again, usually at lower frequencies. Royer resonance based designs are suitable for low noise.Quote from: moffy on September 29, 2025, 11:02:52 pmI forgot about those but a higher output current will be required.

author: Analog Kid
author_rank: Super Contributor
timestamp: September 30, 2025, 02:27:44 am
content: Was I dreaming, or did the OP omit to tell us what output voltage they want?

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 30, 2025, 03:26:49 am
content: There are lots of flyback controller chips that will work nicely for a small isolated supply.

author: langwadt
author_rank: Super Contributor
timestamp: September 30, 2025, 09:19:42 am
content: https://xyproblem.info/

author: David Hess
author_rank: Super Contributor
timestamp: September 30, 2025, 10:02:16 am
content: Quote from: Analog Kid on September 30, 2025, 02:27:44 amI took the context to mean that they want an inverter and not a regulator.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: September 30, 2025, 10:58:45 pm
content: Quote from: SKYVsebasC20 on September 29, 2025, 07:37:36 pmNo mention of minimum load or inrush or regulation specs or protection against over load ?There are simple transformer driver IC's for isolated power from Nexperia, TI etc but usually target single-digit wattsFor a bit more power, you could look at gate drivers like the 21531 series.https://www.lcsc.com/search?q=21531&s_z=n_21531Those have an inbuilt RC oscillator and are designed to give nominal 50% drive.They also have apull the cap lowprotection path, so you can add current sense externally.Or you could use a current-sensing gate driver and drive that from an external oscillator.Addit: TI's DRV8161 gate driver looks very flexible, you can adjust gate drive to trade off Slew/RFI and adjust VDS levels, for current protection.It needs an external PWM drive, which can be a SOT363 package.

author: Seekonk
author_rank: Super Contributor
timestamp: October 01, 2025, 05:01:23 pm
content: I use the IR2153 in a design and surprised to see the IR21531 which appears to be identical, haven't looked that close in the data sheet which makes no mention of the 2153. Did notice the diagrams are reversed, D version has the internal bootstrap diode. They used to sell "300W inverter board" from China which was cheap except push pull. Not hard to convert to half bridge. You never know what you get when ordering. Often a board is pictured with 2153 and they ship SG3525. There are a lot of fake 2153 which do not have shutdown mode.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: October 01, 2025, 08:22:08 pm
content: Quote from: Seekonk on October 01, 2025, 05:01:23 pmI think the only change is the 2153'1' drops the dead time from 1.1us to 600ns