Electronics > Projects, Designs, and Technical Stuff
STmicroelectronics ultra-low Vf Schottky
MustardMan:
In case anyone is interested I did some rough-and-ready tests. My instrument was not calibrated so the absolute value of the readings could be off, however, they were all performed within the hour so the relative figures are good. The test was only performed on one device so I would expect some variance.
I don't know why I got a bump on all the reverse readings, but it is consistent amonst all of them (although the reverse characteristics are important, I am more interested in the forward performance).
As expected the reverse leakage of the LSM115 is bad, but not as bad as I had expected and with a forward performance only marginally different from my test FERD... I have two contenders...
BrianHG:
If you are going for full wave bridge rectification, have you considered the LT4320-1 Ideal Diode Bridge Controller?
I mean, if you really need that 0v drop, though, it needs at least 9v to work.
There are also smart Smart Diode Rectifier Controller which emulate the solar cell diodes with the mosfet of your choice. Use one of those with a cheap SOT23 N-Channel 5amp mosfet with those ridiculous small RDS-On figures and only a 2.5v VGs on and you will have a small voltage drop.
MustardMan:
I am working with a really small voltage in this project: +0.6 to -0.6 swing. With the LSM115 (at approx 50mA) I am loosing ~175mV off each peak, giving me a rectified voltage in the order of 850mV.
I will be using a TPS61220 (or similar, 0.8 v input) to step it up to either 3.3 or 5 volts. A couple of manufacturers do very-low voltage switchers, some claiming they work down to 0.65 volts, but deeper reading of the datasheets indicates that once started that is what they will run down to. Usually the start voltage is a bit higher.
I have been giving a lot of thought to syncronised rectification with a FET, but unless I get some voltage to work with first, I can't drive the gate - and once I get enough voltage (eg: the 0.8 volts the TPS61220 needs) then I don't need syncronised rectification. My input will either be zero, or +-0.6
I saw the syncronised FET bridge in my travels, and it is a device I will certainly keep in mind. But it won't work for this particular project. Thanks for the suggestion though!
Cheers, MM.
BrianHG:
If you are not extracting power, you do realize that with an op-amp, you can get a 0v ideal switch with an opamp and normal diode.
Also, if the signal is always oscillating, you and use 1 diode and caps to multiply that voltage with the loss of a single diode drop instead of 2 in full bridge rectification applications, however, you double the current across the diode.
Also, for low power higher frequency apps, a small transformer can multiply your source voltage 10 fold.
MustardMan:
I am using the device to suck power, and the power it vampires is the only power it will have to operate. Once bootstrapped I could use something better (eg: syncronised FET), but once I have power available, then everything is hunky-dory anyway.
I had looked at a half-wave multiplier with more than one stage to boost the voltage to a decent level, but with a half wave doubler (or tripler, or n-er), the ripple becomes very large as soon as I start to vampire power out of the thing - hence my (so far) deciding a full-wave is better.
My input will be close to a square wave. I had not thought about a transformer to boost the voltage, although at 50Hz (my operating frequency) I could run into size problems.
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