@Chuck: It is 6.3VRMS, so more like 8V after rectification, but yes I think in reality it is a bit fine with load.
@nixiebunny: I haven't tried a Schottky bridge, just simulated one. @jfeng: I hadn't considered a voltage doubler. I tried this <http://www.bristolwatch.com/ele/voltage_doubler.htm>one and with a 6800uF cap on the output it produces a steady output voltage. This leads me to my next observation. I was feeding the output of the 7805 into ESP32 pico, wired up with an SD card reader and MAX98357A class D amplifier driving a small speaker. Even with the voltage doubler solution (and with a nice steady output voltage from that of around 13V), the pico pulled the 5V line down to around 4.7V whenever it tried to read the SD card (or play sound?), which seemed to be enough to cause the PICO to reset. I suspect it is trying to draw more current than the 7805 can supply, but I don't have a way to measure that ATM. A test with a Wemos driving 8 neopixels works fine. Complicating things slightly is the fact that I have this all wired up on breadboards, and there are definitely losses involved with the wiring there. The 6.3V is the output of a heater stage of a transformer I am using. I would like to try to use this if possible, but if not then I could use a 5V SMPS module such as this <https://www.amazon.com/dp/B01F9ZQ2YS/ref=dp_cerb_1>one, but that seems a little defeatist given that I have 6.3V RMS just lying around anyway, and who knows how stable the output of that module is if I get up to around 1A? On Sunday, March 24, 2019 at 10:46:22 AM UTC-4, Paul Andrews wrote: > > I want to create a 5V/1A regulated power supply from a 6.3V RMS input. I > can get a regular diode bridge in a 4 pin DIP package, but it is marginal > and my simulations and actual tests show that the forward voltage drop is > too much under even a light load. My simulations show that a Schottky diode > bridge works OK, and I can get an SMD 4 pin package with a total forward > voltage drop of around 0.8V. However, I have seen designs for active MOSFET > full-wave rectifiers, so I figured I might as well try to go that route. > > I came across two potential ICs to help. One is the LT4320 and the other > is the FDMQ8205. The LT4320 uses external FETs, but the killer seems to be > that the minimum output voltage is 9V. The FDMQ8205 has internal FETs, but > I can't figure out how I would use it in a regular full-wave bridge > rectifier. It has AC inputs and gate drive inputs and I'm not sure what the > gate drive inputs should be. In note 4 in the datasheet > <https://www.onsemi.com/pub/Collateral/FDMQ8205-D.pdf>they show a wiring > diagram that connects the AC input to the gate inputs, but I can't tell if > that is a topology that would provide full wave rectification, or if it is > just something used for testing. > > Does anyone have any experience with active bridges at these voltages, or > with these ICs? Is there an alternative I should be looking at? Should I > just stick with the Schottky diode version? > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/c146e619-54f9-4567-9312-5d6bf5fc6cbb%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
