Re: [neonixie-l] Q: Active full-wave rectifiers

[chuckrr]

A typical 7805 regulator drops out at around 7.5 volts at the input.
 You'll need a little more overhead than 6.3 volts.
 That, in my humble observation, is trying to cut it too close.

 -Original Message-
 From: "Paul Andrews" 
 Sent 3/24/2019 7:46:22 AM
 To: "neonixie-l" 
 Subject: [neonixie-l] Q: Active full-wave rectifiers

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 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 neonixie-l+unsubscr...@googlegroups.com.
 To post to this group, send email to neonixie-l@googlegroups.com.
 To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/09f8e9f7-3f34-4f89-811a-e12901b4d631%40googlegroups.com.
 For more options, visit https://groups.google.com/d/optout.

-- 
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 neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/201903241003418.SM2162785%40%5B66.242.162.246%5D.
For more options, visit https://groups.google.com/d/optout.

[neonixie-l] Q: Active full-wave rectifiers

[Paul Andrews]

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 
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 neonixie-l+unsubscr...@googlegroups.com.
To post to this group, send an email to neonixie-l@googlegroups.com.
To view this discussion on the web, visit 
https://groups.google.com/d/msgid/neonixie-l/09f8e9f7-3f34-4f89-811a-e12901b4d631%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.