My offline smps design has 3 parts making the most heat. A power diode, a mosfet and a bridge rectifier.
I'm interested in any cookbook designs that replaces a bridge rectifier. Any pointers?
My offline smps design has 3 parts making the most heat. A power diode, a mosfet and a bridge rectifier.
I'm interested in any cookbook designs that replaces a bridge rectifier. Any pointers?
-- D from BC British Columbia
An active(synchronous) rectifier? i.e., mosfets.
for 100A, say, your looking at about 70W dissipation per diode verses a
5mOhm resistor of about 50W. It gets much better for smaller currents. For 10A it is 0.5W. Similarly you can parallel the mosfets to reduce the dissipation even further.Obviously it adds to the complexity and cost...
Ancient, but really huge, selenium ones with stacked fins were cool. Four of those in a bridge would take some space but also double as a nice hand-warmer.
Then there is germanium and leaky but lower voltage Schottky.
But what about synchronous rectifiers using MOSFETs? I have to guess they are NOT simple. But in concept they seem as though they should be efficient.
...
Just for giggles, here's a synchronous rotary mechanical one:
It would be a kick to one day open up a stereo amplifier and see one of those inside it!
Jon
Maybe you can cook something up around this chip but I've not tried that yet:
-- Regards, Joerg http://www.analogconsultants.com/
I havent seen any FET's capable of blocking line voltages in the
400-600V range with that low of an Rdson. The few sub 0.1 ohm ones I've seen are expensive. They would also likely need a beefy drive circuit.If you know of a cheap supplier of even 0.05 ohm 400V-600V Fets I'd be intrested.
The rdson doubles at working temperature so even 0.05 ohm would be 0.1 ohms. So you would probably be better off with the diodes both cost and complexity wise and power wise.
The only time I've seen Fets used is after a transformer steps the voltage down.
But I'll be following the thread to see if there are alternatives. I dont think there is though.
Well ...
About $13 in qties.
-- Regards, Joerg http://www.analogconsultants.com/
How many volts, amps, what efficiency?
Tim
-- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
You can buy a massive heatsink for your bridge build an aux supply for a fan and maybe even liquid cool the works for what one of those would cost let alone the other 3.
But IXYS makes nice ones.To rich for my blood though.
The lowest Rdson 500Vds Fet I have is the FQA24N50 and thats 0.2 ohms
90nC gate charge.They were on sale for a buck a piece when I got them.
Sure, diodes screwed onto a large heatsink is the usual way to do this but there are situations where you can't. Like tightly enclosed areas.
Normally those run almost 3 bucks a pop and abs max is 24A at 25C. So it won't be cheaper when you parallel enough of those. Unless there is a buy one get one free deal again :-)
-- Regards, Joerg http://www.analogconsultants.com/
Line voltage here is 120VAC 60Hz. The bridge rectifies 120VAC 60Hz. Diode current is complicated.. Say 2amps to 4amps.
Efficiency: Just wondering how good it gets and/or how complicated it'll get.
-- D from BC British Columbia
OK so can an 'internal drive' system be built into the device to mimic a diode? Just being silly.
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Well, ya know, getting rid of heat isn't free either. Devices that run cool usually last longer. And not everyone is price conscious.
IXYS has used Samsung as a foundry for years, probably decades. There may be equivalent parts from Samsung that are cheaper.
You might look into Silicon Carbide Schottky rectifiers. Here is one from Sensitron that has a 1.75V forward drop at 10 amps and possibly 1.2V at 2-4 amps. Rated at 600V, too!
There is a 1A 600V SiC device in the LTC SwitcherCad library for a MicroSemi UPSC600 but I could not find any data sheet or availability. Also the simulation shows it drops 1.2V at 500 mA.
Diode drop on a 120 VAC rectifier circuit should be negligible in terms of overall efficiency. Just use a bridge rated at a lot more than you need.
Here is a 35A rated bridge that exhibits less than 1 volt per leg drop at
2-4 amps (25C):And for a dual diode rated 200V and 30A with about 0.75V drop at 2-4A:
Your application seems to be for a PSU rated about 300W, so 5W or so in the primary rectifier bridge is not even 2% losses.
Paul
Average or peak? (PFC'd?)
Depending on how you count the current, that's around 2-10W for an average silicon bridge. If schottkies aren't good enough, your only choice is an active FET rectifier.
I think silicon stops at ~100V, but SiC schottkies go higher, although I forget what Vf gets to. Lesse...
Neat, PTC for currents over only 1.8A. Looks resistive for anything over
1A, no wonder the 10ms surge current is so small. It almost acts like a low voltage vacuum tube.If it had better semiconductor characteristics (i.e., still exponential, as in the
I have a little M-G set I got for a few dollars at a Hamfest fleas market. That's another way to generate DC from AC mechanically. It can be done fairly efficiently, but is costly in terms of size, weight, expense, maintenance, mechanical noise, and other factors. And a DC generator has a commutator which essentially acts as a mechanical rectifier.
Paul
It's not silly. I have recently done that on a project. There just wasn't any place where we could have dumped the heat into.
-- Regards, Joerg http://www.analogconsultants.com/
.
That can be very efficient, indeed. It suggests another way to solve the original problem, using a direct switching power supply of (+) polarity in parallel with one of (-) polarity. Just disable each for the half- cycle it can't handle. The motor-generator wins, here, because it includes a flywheel and covers the AC zero crossings without a filter capacitor.
The 'computer power supply' of the 1950s was such a motor/generator with regulation by motorized rheostat controlling the DC field windings.
Real men use IGBTs ;-)
Vceo 1200V, Vce(sat) 2-3 volts at 1000 amps if you really need it.
-- "Electricity is of two kinds, positive and negative. The difference is, I presume, that one comes a little more expensive, but is more
Yep when you start pushing close to 1kW IGBT's are pretty well the best alternative.
I've never built anything requiring anywhere near that power though. I start counting micro amps at the start of anything I do so I can keep the power supply requirements small and inexpensive.
Here in Canada they are going to start charging us a premium for electricity during peak usage hours. They just installed the new meter on my house a couple of weeks ago. So I'm not likely to go anywhere near a kW anytime soon. I think the rate almost doubles during peak hours!! I would imagine the next step is to gouge us for poor PF that will likely be the next cash cow. The US probably pays less for the electricity we generate here and sell to them.
I don't know if the US or anywhere else for that matter charges a premium for electricity during peak hours or if we are the only country?
Plus a 3/4-horse motor to drive the cooling propeller :-)
Oh yeah, probably depends on the political leanings in the area. Here in California we pay roughly $0.15/kWh. But the millisecond you exceed a rather modest baseline qty for the month it shoots up, big time. So people who want to start a business that uses some energy will think twice about it and maybe do it elsewhere.
-- Regards, Joerg http://www.analogconsultants.com/
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