High Current AC Voltage Divider? - Page 1
Forum section: electronics / general

author: johnywhy
author_rank: Contributor
timestamp: October 05, 2024, 05:40:06 am
content: Is a resistor divider suitable for a low-voltage, high-current AC voltage divider?I have an 8V p-p AC sine wave, powering a load that's drawing 1.5A. I need to divide that AC voltage down by half, without distortion, with good precision, so the load will draw 3A @ 4V p-p. And i need it to stay cool.Is there a simple passive way to do it?I assume i could use a step-down trafo, but that's bulkier than i would like.How about a capacitive divider?Or, a capacitive/resistive divider?Inductive divider?

author: geggi1
author_rank: Frequent Contributor
timestamp: October 05, 2024, 06:38:13 am
content: What you are describing is a transformer.With a voltage divider you will never get a higher current out of the circuit than in. the loss will also be at least as high as the load.Voltage dividers is normally only used in low current designs to match impedanze or reduse the voltage for mesuring or similars.

author: johnywhy
author_rank: Contributor
timestamp: October 05, 2024, 07:00:21 am
content: Isn't a capacitive power supply designed to deliver high current?Quote

author: Gyro
author_rank: Super Contributor
timestamp: October 05, 2024, 08:41:48 am
content: Quote from: johnywhy on October 05, 2024, 07:00:21 amThat power supply delivers a mere 10mA and uses a single series capacitor, not a capacitive divider.. It also offers no safety isolation from the mains, so isn't suitable for anything that can be touched.A capacitive divider (two capacitors) is no more suitable for providing any significant current than a resistive voltage divider. They are used (often in combination with a resistive divider) for measurement purposes only.It sounds as if a proper wall wart PSU is what you need Edit: or bite the bullet and use that transformer - it's the only way you're going to achieve any current multiplication in any case].

author: Andy Chee
author_rank: Super Contributor
timestamp: October 05, 2024, 10:40:03 am
content: Quote from: johnywhy on October 05, 2024, 05:40:06 amWhat frequency is your sine wave? If it is >20kHz the transformer can be a relatively compact ferrite transformer.Otherwise, no, there is no passive way to do it.Your distortion and precision specification suggests some unusual application. Care to enlighten us? Showing us a bigger picture may allow us to proffer alternate solutions.

author: johnywhy
author_rank: Contributor
timestamp: October 05, 2024, 11:29:42 pm
content: Quote from: Gyro on October 05, 2024, 08:41:48 amI'm not working with mains. I want to step down a 1.5A, 10V, 400 kHz AC signal.Quote from: Andy Chee on October 05, 2024, 10:40:03 amWhat i can share is that i need to convert a bipolar 3A, 5V p-p, 400 kHz AC signal to a unipolar, positive-only 3A, 5V p-p, 400 kHz signal.My first plan was to use a Villard doubler to convert the biplar wave to unipolar. The video:https://youtu.be/ep3D_LC2UzUMy concern was that the V doubler will halve the current and double the voltage, from 3A, 5V p-p to 1.5A, 10V p-p. That's why i posted this question looking for a divider to restore the original.But i think now this was a misconception. It looks like the p-p doesn't change, the input and output of the Villard will be the same current, same V p-p. In which case i don't need this divider.

author: Andy Chee
author_rank: Super Contributor
timestamp: October 06, 2024, 03:19:24 am
content: Quote from: johnywhy on October 05, 2024, 11:29:42 pmAt 400kHz, a transformer can be made using this core:https://www.digikey.com.au/en/products/detail/epcos-tdk-electronics/B65803P0000Y038/3914034Is that transformer still too "bulky" for your application?

author: johnywhy
author_rank: Contributor
timestamp: October 06, 2024, 02:27:41 pm
content: Quote from: Andy Chee on October 06, 2024, 03:19:24 amNot to bulky! Thx for that. Why did you select RM type?But, as explained in my last comment, i might not need to step down after all.

author: Andy Chee
author_rank: Super Contributor
timestamp: October 06, 2024, 09:38:45 pm
content: No reason for RM core, any core with the same volume (or more, within reason) should work at 400kHz @ your current.

author: johnywhy
author_rank: Contributor
timestamp: October 08, 2024, 08:28:30 pm
content: Quote from: Andy Chee on October 06, 2024, 09:38:45 pmThx! Why did you choose T38 material?

author: Andy Chee
author_rank: Super Contributor
timestamp: October 08, 2024, 10:51:47 pm
content: Quote from: johnywhy on October 08, 2024, 08:28:30 pmActually now that you mention it, that material may not be appropriate.In general, high frequency AC calls for ferrite material.However your application of a unipolar output, may potentially impose a net DC through the secondary winding. If this is the case, you will need something like a powdered iron material instead or larger core size or both.Need your schematic to make an informed decision on that. If you use a full wave diode bridge on the output, then ferrite remains viable. If you've got anything else hanging off it, then perhaps not.