Minimize Ripple in Rectifier by Waveform, Polarity, Bridge-Type, Inductor, Trafo - Page 1
Forum section: electronics / general

author: johnywhy
author_rank: Contributor
timestamp: September 15, 2024, 04:47:06 pm
content: In a rectifier and RC filter, which combination of waveform, bi-polarity, inductor/cap, and transformer-type will give the least ripple in the output?My source is100 kHz AC supplying a transformer. I have control over the supply voltage, wave shape, and polarity, over the transformer type, and over the rectifier / filter design. This question is about how to minimize ripple through selection of those parameters.My load wants 5V @ 3A (after the filter).Assume there is no regulator involved. Just AC source, transformer, rectifier, filter.This isn't for safety. My source is already isolated from mains. This is for operational needs.Ie, how is ripple affected by:an AC source that goes negative on the troughs, vs an AC source that only goes positive, never below 0v?sine vs square source?pulse transformer vs non-pulse transformer?full-bridge vs half-bridge?Use an inductor in the filter? Or just a cap?ChatGPT says:To achieve the least ripple in the output of a bridge rectifier and RC filter:Use a bipolar AC source (e.g., a sine wave) rather than a unipolar one, as it results in a higher ripple frequency. [specifically, 2 x f-in]Use a sine wave input rather than a square wave for a smoother, more manageable ripple. [specifically, no harmonics]Use a standard non-pulse transformer designed for power applications rather than a pulse transformer. [i need to understand more]Use a full-bridge rectifier instead of a half-bridge rectifier to take advantage of the higher ripple frequency produced by using both halves of the AC waveform. [specifically, 2 x f-in](also asked on EDA Board, EE Web, All About Electronics, electro-tech-online.com)

author: trobbins
author_rank: Frequent Contributor
timestamp: September 18, 2024, 04:33:57 am
content: 24 phase, active fet rectifier, huge CLC filter, active ripple filler on first C.Or very large RC dropper from say 1kV to suit constant load.All for fun, given your limited details on what you can and can't accept.

author: jonpaul
author_rank: Super Contributor
timestamp: September 18, 2024, 05:19:38 am
content: Chat GPT = GIGO Garbage in>garbage out.I humbly suggest that you NOT rely on forums, internet , videos and ESPECIALLY AI.Please buy and read a text book on power supply design !!You can actually LEARN how to design a power supplyMany fine books are available.It takes time and effort, there are NO shortcuts/Bon chanceHAVE AN ABSOLUTELY FANTASTIC DAYJon

author: Electrodynamic
author_rank: Regular Contributor
timestamp: September 18, 2024, 06:40:06 pm
content: I'm sure many will disagree but I found most RC and RLC filters to be substandard because they are designed for average conditions. I found most filter/buffers I inspected to be substandard and at my place of work we have dirty power, power failures, brown outs and phase loss constantly wiping out our electronics and countless VFD's. Logically, if the filters were actually doing there job none of this damage would have occurred but it did.From my experience the only real filter is an active filter because it has the intelligence to handle abnormal conditions. Normally we have RL in series with C in parallel. R limits voltage changes while L limits current changes and C attempts to buffer any voltage changes with respect to ground.I suspect what you found is that some ripple/transients remain even after an RLC filter. This is mainly because the circuit elements like the capacitor cannot react fast enough to small time period changes in voltage. Normally we add little caps for small fast transients and larger caps for larger slow transients. However I found a HV fast transient will blow through all of this with little resistance.If you want a safe ripple free output I would use an isolation transformer, full bridge rectifier, CLC filter because the resistor is basically useless and an active filter before the output. An active filter is just a threshold device or clipper circuit using a fast acting mosfet to remove any voltage changes above or below our 5v set point.In effect, RLC filters are like a model T and smart active components more like a modern EV. I like smart circuits and all my DC/DC converters and power supplies use inexpensive micro-controllers. Why build a dumb circuit when we could build a smart one which can adapt?. I wouldn't mess around with 1950's technology considering the technology we have today.

author: johnywhy
author_rank: Contributor
timestamp: October 06, 2024, 08:32:10 pm
content: Quote from: Electrodynamic on September 18, 2024, 06:40:06 pmThx for that. I assume your iso trafo is just for safety from mains, and not related to reducing ripple?In what way is the R useless? Aren't RC filters a fundamental electronic design?I thought an "active filter" means a filter designed around an op amp, not a clipping device.Are you using the mosfet as an active diode? Or as an turn-off device?- Cheers