High Speed, Unipolar Sine Inverter? - Page 1
Forum section: electronics / general

author: johnywhy
author_rank: Contributor
timestamp: March 21, 2023, 05:05:55 pm
content: Hello,What's a simple, low-parts-count way to do this?I need to convert 120 V, 60 Hz AC USA mains to 5V, 5A, 100Khz varying DC voltage.For convenience, assume we'll use an off-the-shelf isolated mains-to-DC converter for the first stage. You decide your preferred specs of the off-the-shelf mains-to-DC converter for the first stage.Therefor, this question only concerns the design of the second stage, the DC/AC inverter.There are two acceptable outputs. We'd like either one, because we need to test both.It could be the full unipolar sine wave, with peaks are at 0V and 5V. (see attachment)Or it could be a truncated sine pulse (see attachment). I didn't say "half rectified" because that makes an assumption about how the pulse is produced.Voltage regulation should be +/- 1%.Current limiting not needed, but need short-circuit protection.The "0V" mustn't go negative, not even a little.We need sine to improve efficiency of all following circuitry, and reduce various drawbacks of a non-sine PS, eg noise, and because our load wants smooth power. So wave-form-symmetry/distortion is important. I assume it can be a pretty decent but not perfect sine, and still get those benefits. So i assume a very low-res modified sine won't do, but a hi-res MSW may be fine. (see attachment)I'll try to characterize the load. I believe the impedance of the load is: @1kHz AC, 8 mΩI don't know if Ringing, Flyback, and/or, Inductive/Capacitive-Reactive-Load considerations are important. We may have this coupled inductor before the load.https://www.coilcraft.com/en-us/products/power/coupled-inductors/1-1-shielded-coupled/msd_h/msd1260h/msd1260h-472/There won't be any sudden transients.We want voltage regulation, not current regulation. So it's a constant voltage PS. The load will send a control signal back to the PS to regulate voltage as needed.Frequency stability/accuracy isn't important.PWM is fine, but not required. I wonder if we can achieve this with PWM, a sine driver, and a single mosfet, rather than H-bridge.I'd like to accomplish this without a uC, if possible. Unfortunately, the EGS002 is restricted to 60 Hz.I'm fine doing this with all off-the-shelf modules. That's actually preferred in the short-term.Thx

author: uer166
author_rank: Super Contributor
timestamp: March 21, 2023, 05:16:50 pm
content: That output is a 100kHz wave? A switcher likely wouldn't have this kind of voltage regulation bandwidth, you'll need something like a class AB amplifier or similar and do it linearly instead. Kinda like waveform generator amplifiers. Of course you also mention efficiency which makes this a non-starter.. Interested to see what you come up with.

author: johnywhy
author_rank: Contributor
timestamp: March 21, 2023, 05:27:58 pm
content: Quote from: uer166 on March 21, 2023, 05:16:50 pmWhy not a pure sine inverter? Multilevel? PWM? Or drive a Class D amplifier with a sine?

author: Someone
author_rank: Super Contributor
timestamp: March 21, 2023, 10:58:42 pm
content: 25W of 100kHz 1% accurate voltage yet "simple, low-parts-count". Not happening.Quote from: johnywhy on March 21, 2023, 05:27:58 pmThats pretty far away from "simple, low-parts-count".

author: johnywhy
author_rank: Contributor
timestamp: March 22, 2023, 12:04:57 am
content: Quote from: Someone on March 21, 2023, 10:58:42 pmPerhaps. Depends on your definition.Sine DriverThe EGS002 circuit isn't as simple as i'd like, but not too bad. Only 60 Hz, tho'.https://cxem.net/pitanie/files/5-389_EGS002_manual_en.pdfMultilevelThere are some clever multilevel implementations which reduce number of switches.https://core.ac.uk/download/pdf/212980526.pdfClass DI'm not the first person to contemplate using a Class D amplifier as an SMPS. I would simply drive it with a sinewave. 25W Class D amplifier chips and modules are plentiful and cheap."Think of Class D amps as being similar to a switch-mode power supply, but with audio signals modulating the switching action."https://www.extron.com/article/ts122001"A bipolar (positive and negative, not transistor type) output class-D amplifier can make a great output stage for a 4 quadrant power supply""A Class-D amplifier is a switch-mode power supply (SMPS)."https://www.eevblog.com/forum/projects/class-d-amplifier-as-four-quadrant-power-supply-stupid-idea/Single SwitchFor my purpose, a unipolar sine is acceptable, so i think we don't need a full or even half H bridge. Maybe it could be 1 sine driver, 1 pwm generator, and 1 mosfet. Depending on whether an analog or digital sine is needed, the sine driver could be a filtered square wave, a cheap uC, or a sine table with a counter.

author: johnywhy
author_rank: Contributor
timestamp: March 22, 2023, 05:40:48 am
content: I'll have to do some homework before i can give info that makes sense.Thx