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

[Paul Andrews]

Just to close this up:

The problem with the ESP32 resetting was caused by the quite ridiculous 
voltage drop across several jumpers.

In the end I am using a small 5V module I can wire into the mains side of 
the circuit. My design has changed and the 6.3V secondary I was going to 
tap for the 5V supply will now be biased high.

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

[martin martin]

Sir Nixie Bunny
I have one of your 10 year old Burroughs Nixie clocks.  Is there any chance 
you would upgrade the FW to include the "slot machine" affect?  I only 
replaced one tube in about 9 years

I'll pay of course!


martin

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

[Paul Andrews]

@gregebert: Yes, I ordered a switching regulator. The 6.3V AC just happens 
to be available on the transformer I am using for other purposes.

@jfeng: I am tending to agree that an isolated 5V power adapter is the way 
to go, particularly as I will want the logic circuits to stay functioning 
even if I disconnect the mains transformer. However, as an exercise, this 
is turning out to be more interesting than I thought, so I will pursue it 
for a while longer. Not sure if I'm up for building my own buck/boost 
converter. Yet.

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 
> 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?
>

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

['jf...@my-deja.com' via neonixie-l]

If all you want is to get 5Vdc rom the mains, a USB charger seems like a 
very attractive option.  They are usually less than US$5 and occupy about 
1cu in (plus the power plug).  My initial concern would be safety 
isolation, but some of these will surely be UL listed or CE qualified.

However, if you are doing an engineering laboratory exercise requiring 
using a 6.3vac source then this is almost interesting.  It should be 
possible to build a buck-boost regulator that will tolerate a very wide 
range of unregulated inputs.

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

[gregebert]

I tend to use higher voltage transformers, in the 8-12VAC range, full-wave 
rectifiers + filter-cap, then use switching-regulators that are 
pin-compatible replacements for the popular LDO regulators. They are 90%+ 
efficient, and therefore generate almost no measurable heat. 

If the current is really low, say 50mA or less, I'll use an LDO.

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

[johnk]

And I’d ask about mains stability.

Was half-wave ruled out?

 

John K

 

 

From: neonixie-l@googlegroups.com [mailto:neonixie-l@googlegroups.com] On 
Behalf Of petehand
Sent: Monday, 25 March 2019 18:43
To: neonixie-l
Subject: [neonixie-l] Re: Q: Active full-wave rectifiers

 

I would use four discrete schottky diodes in a bridge, and a low dropout 
regulator like an LM1117. The 5V version of the LM1117 regulates down to 6.2V 
input and delivers 800mA.

 

 

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

[petehand]

I would use four discrete schottky diodes in a bridge, and a low dropout 
regulator like an LM1117. The 5V version of the LM1117 regulates down to 
6.2V input and delivers 800mA.


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

[Paul Andrews]

@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 
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 
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 
> 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?
>

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

[David Forbes]

I'm surprised that you can't just use the Schottky diode bridge, a rather
large filter capacitor and an LDO regulator chip. What components are you
using, and what's the lowest voltage you see at the input to the regulator?


On Sun, Mar 24, 2019, 10:27 AM Dekatron42  wrote:

> In the circuit with the FDMQ8205 that you refer to they are connected in a
> POE circuit (Power Over Ethernet) where they make use of DC-voltages for
> the power and AC-voltages via the transformers for the data-transmissions -
> so the FDMQ8205 actually only work as polarity protection in that circuit
> and not as full-wave rectifiers.
>
> There is an old Elektor circuit here:
> http://projectcircuit4u.blogspot.com/2010/04/power-mosfet-active-bridge-rectifier.html
> that you might be able to use in some combination with the FDMQ8205.
>
> /Martin
>
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[neonixie-l] Re: Q: Active full-wave rectifiers

[Dekatron42]

In the circuit with the FDMQ8205 that you refer to they are connected in a 
POE circuit (Power Over Ethernet) where they make use of DC-voltages for 
the power and AC-voltages via the transformers for the data-transmissions - 
so the FDMQ8205 actually only work as polarity protection in that circuit 
and not as full-wave rectifiers.

There is an old Elektor circuit here: 
http://projectcircuit4u.blogspot.com/2010/04/power-mosfet-active-bridge-rectifier.html
 
that you might be able to use in some combination with the FDMQ8205.

/Martin

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

['jf...@my-deja.com' via neonixie-l]

If I had to use the 6V transformer, I would make a voltage doubler.  

Then I would use the switching mode regulator in a USB car charger adapter 
to produce the regulated 5V.   My Dollar Tree carries them.  Sometimes, 
Fry's has these for under US$1.  Or you can probably find one at your 
favorite truck stop for US$9.95.  I would physically hack iawy the case to 
get at the electronic innards. 

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