Ideal Diode - Page 1
Forum section: electronics / projects

author: Asad
author_rank: Contributor
timestamp: March 26, 2015, 08:50:24 am
content: While browsing LT's (Linear Technology) website, I saw some ideal diode devices which look pretty good on paper. They have whitepapers singing praises of FET based diode circuits.Powerpath controllers and ideal diodes[urlhttp://www.linear.com/parametric/Ideal_Diode_Bridge]Ideal diode bridgeThis led me to wonder what are the down sides of using such a device in reverse voltage protection and full wave bridge rectifier applications over a regular diode with Vf ranging between 0.3-1.1V at rated current. Are there any issues with its use? Will powered/unpowered state of the controller IC have bearing on its function/operation? Is there anything to be wary of with these devices?If you have had the occasion to use these devices, please provide some feedback and any observations.

author: tszaboo
author_rank: Super Contributor
timestamp: March 26, 2015, 09:10:21 am
content: I wrote the ideal diode bridges on my blog.At 10A, you can save possibly something like 14W. If you are building a linear PSU, it is almost pointless, because you will dissipate the voltage on you linear regulator anyway, and off the shelf transformers will be sized for the diode drop. The only reason I can find is to have some extra power for a class A amplifier, or to make the solution smaller, or less heat spread, all of the goals are contradicting all general applications. if you are building a switching PSU, they are too slow, if you are building a linear, they are pointless.The only reason to have them is to replace those really big off PCB bridges and have a better physical construction.

author: Asad
author_rank: Contributor
timestamp: March 26, 2015, 08:02:04 pm
content: I am considering using it for an application where an external DC supply passes through a bridge rectifier. By doing that, the input lines become polarity insensitive; i.e. user can plug in power with any polarity and device will still work. Using an ideal diode type device will save on diode power losses (~5W) and should add to long term reliability with lower operating temperatures albeit with higher component count.I just want to know of any potential pitfalls and gotchas before diving in.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: March 27, 2015, 05:28:53 am
content: I haven't tested them yet, but I'm planning to use them on a bunch of systems designed for sailing-boats to improve efficiency. They should improve efficiency quite a bit, considering that currently normally a bunch of Schottkys are handling the separation of the batteries, while the Diesel-Engine is pumping around 15Amps into each of the three batteries (Figures from the boat of my parents: 80A Alternator fitted to a 18kW Diesel-Engine and connected through Schottky-Diodes to 3 Batteries, resulting in a loss of approximately 60W).The disadvantages I discovered so far:- Speed: These things are SLOW! Especially the LTC4412. It is extremely low power, lower than the self-discharge of a 120Ah Lead-Acid Battery and for an ORing-Diode replacement to separate the batteries, they are ideal. But once you try to rectify some quickly alternating stuff, they will probably be useless.- They need to actively shut down the current-path. Requiring at least 2 of them in Series if reliability is essential, plus some stuff to protect the IC from transients and other nasty things.

author: Jeroen3
author_rank: Super Contributor
timestamp: March 27, 2015, 06:27:02 am
content: You'd typically use them on battery powered applications. Where a voltage drop actually matters.As you'd possible found on the linear website, they're advertised for hot-swap and switch-over applications.However, ideal bridge rectifiers might help you somewhat in other fields. Only problem is their low voltage. You'd still need something converting 200-400 ac-ish to sub-100 ac.And they're more expensive. But you should have seen that already.

author: tszaboo
author_rank: Super Contributor
timestamp: March 27, 2015, 09:27:14 am
content: Quote from: Asad on March 26, 2015, 08:02:04 pmIf you are passing DC current through it, isnt there a better way to drive the FETs? Like using PFETs, connecting them to conduct only if the voltage is in the proper way? I mean these things aren't cheap.

author: calexanian
author_rank: Super Contributor
timestamp: March 27, 2015, 10:55:34 pm
content: I just did a design with some new trench style shottky rectifiers and the drop under a load of about 1.5 amps was only about .15 volts. Under very very small load it was well under .1 volt. Not to shabby for a non active rectifier.

author: dom0
author_rank: Super Contributor
timestamp: March 28, 2015, 12:56:46 am
content: Got to admit that trench rectifiers doesn't sound peaceful at all. They are probably mil-spec only, yes?

author: Asad
author_rank: Contributor
timestamp: March 30, 2015, 09:02:05 am
content: Quote from: SaabFAN on March 27, 2015, 05:28:53 amSince I plan to use it for DC, the frequency factor is not a big concern. What kind of protection for transients do you propose? TVS and the like on input side?

author: Asad
author_rank: Contributor
timestamp: March 30, 2015, 09:13:17 am
content: Quote from: NANDBlog on March 27, 2015, 09:27:14 amApprox. 3A of current at 32V max. passes through depending on usage (minor peaks might cross 4A). As such, reliability is more critical factor for me due to high power voltage source feeding the circuit. I absolutely do NOT want any shorts occurring and blowing safety devices or damaging circuitry. If reliability and dependability is in doubt, I would much rather stick with the SB550 x 4 arrangement which I am currently using.

author: calexanian
author_rank: Super Contributor
timestamp: March 31, 2015, 05:33:38 pm
content: Quote from: dom0 on March 28, 2015, 12:56:46 amTrench refers to the conduction zone in the semiconductor material associated with fets. Nothing evil or secret here. Many of the new fets from the various companies are using this kind of design. Just search Trench Fet. pretty cool stuff. High efficiency.