Diode Bridge Power Supply Protection

[Ohioisonfire]

Typing this for the second time because I accidentally deleted my first draft, my apologies if the clarity of the post suffers as a result.
      
I am looking for a power section that can be very flexible and reliable, so I was very interested to discover the Diode Bridge method of polarity protection. I have spent a lot of time researching this topic and read countless posts and replies from a few of the well regarded members of our community. After studying the circuit and drawing it out several times I think I have a good idea of how it works, and what the drawbacks are (diode drop on power supply voltage and ground offset issues). For my application:

• The diode drop on supply voltage is acceptable since I will be boosting it downstream anyway.
• The power section will need isolation if the ground offset issue needs to be solved.

      
I have done some research on potential solutions/implementations for a design like this and am turning to the community for any input/experience:

• Isolated DC-DC Converter brick (ex: Traco Power TBA 1-0523). This is an enticing option as it solves a lot of the issues discussed out of the box, but introduces some other issues. Isolated. 5VDC in, +/- 15VDC out. Relatively compact. Poorly regulated. Low output current.
• Find a way to provide my own isolation (isolation transformer?) and use a DC-DC booster IC (ex: LT3467, which I have used successfully in the past for a dual supply/booster).
• Design a switching supply in the pedal that is isolating (isolating flyback convertor?). This option would obviously require the most design effort.
• Ignore the ground offset. I am familiar with at least a couple modern boutique pedals and one older unit that appear to use the diode bridge with no isolation. I can't find any reports/complaints about those pedals.

[Kevin Mitchell]

Hello.
A bridge rectifier is not ideal for polarity protection - not sure why you've steered into into that notion.
Put a schottky in-line and call it a day.

[Ohioisonfire]

Hello.
A bridge rectifier is not ideal for polarity protection - not sure why you've steered into into that notion.
Put a schottky in-line and call it a day.

As I understand it, regardless of which polarity you plug into the bridge, you get the same polarity out. This means reverse polarity will not damage the circuit, and the circuit will still function as designed with either polarity powering it.

[Kevin Mitchell]

As I understand it, regardless of which polarity you plug into the bridge, you get the same polarity out. This means reverse polarity will not damage the circuit, and the circuit will still function as designed with either polarity powering it.

I get it, but you're going to burn up quite a bit of current doing it this way - not just a volt or two.
So, I suppose it all depends on what you're powering. A DC-DC converter isn't going to make up amperage.
Consider using AC for the bridge, no more polarity woes and you'll get adequate DC out.

[R.G.]

[...] Ignore the ground offset. I am familiar with at least a couple modern boutique pedals and one older unit that appear to use the diode bridge with no isolation. I can't find any reports/complaints about those pedals.

Ignoring the ground offset may be more easily said than done when pedals and amps are plugged together in all possible combinations. Certain scenarios could cause switching pops or even circulating ground currents. I'm curious - can you give me a pointer to the pedals you mention with FWB isolation on their power supplies?

Something over a decade ago I was taken with the idea that FWBs were the answer to polarity protection. Sadly, I never got it to work, largely on the lines of ground offsets and switching noise.  I did come up with MOSFET and bipolar protection schemes that amounted to nearly-zero voltage diodes, even less voltage loss than a Schottky. If that's an option for you, the articles are on geofex.com.

I'm also curious. You say you're going to be boosting the voltage after the polarity protection. Wouldn't it be simpler to use a power supply that's what you need instead of coping with the design issues and noise of a (presumably switching) voltage booster?

[Ohioisonfire]

Ignoring the ground offset may be more easily said than done when pedals and amps are plugged together in all possible combinations. Certain scenarios could cause switching pops or even circulating ground currents. I'm curious - can you give me a pointer to the pedals you mention with FWB isolation on their power supplies?

I included "ignore the ground offset" mostly as a joke. The idea here is to create something that would play well with any system (power supply, pedal connection, pedal board, etc.) so introducing an issue to a system in the form of a ground offset should definitely be avoided. Regarding the pedals I believe are utilizing a FWB, I think I would be breaking forum rules to post it, but I would be happy to IM you.

Something over a decade ago I was taken with the idea that FWBs were the answer to polarity protection. Sadly, I never got it to work, largely on the lines of ground offsets and switching noise.  I did come up with MOSFET and bipolar protection schemes that amounted to nearly-zero voltage diodes, even less voltage loss than a Schottky. If that's an option for you, the articles are on geofex.com.

I have read your many posts on the topic here on the forum, and learned a lot doing so. I have also read through GEOFEX extensively and cannot thank you enough for what you have contributed to the community. If/when I give up on the FWB idea, I will likely default back to MOSFET protection.

I'm also curious. You say you're going to be boosting the voltage after the polarity protection. Wouldn't it be simpler to use a power supply that's what you need instead of coping with the design issues and noise of a (presumably switching) voltage booster?

I think I need to clarify my goals here. Pretty much everything about this could be simpler, but simplicity isn't what I'm looking for. At least initially this is an exercise in "how do I make a power supply that can accept almost any input (within reason), but always output the same thing." If it ends up too complex, too expensive, too unreliable, etc. to want to move forward with than so be it. At least I learned something along the way.

[MikeA]

...I'm curious - can you give me a pointer to the pedals you mention with FWB isolation on their power supplies?

Lehle pedals specify variable DC input, and used to spec variable AC and DC.  Here's an extract from the manual for their (discontinued) Parallel L.  The difference between battery current draw (37 mA) and external power supply current draw (80 mA) could be a diode bridge and a 9V regulator.

 

[Ohioisonfire]

Lehle pedals specify variable DC input, and used to spec variable AC and DC.  Here's an extract from the manual for their (discontinued) Parallel L.  The difference between battery current draw (37 mA) and external power supply current draw (80 mA) could be a diode bridge and a 9V regulator.

Hadn't seen this one, and a deeper look at their manual recommends using an individual or isolated power supply, interesting.. Thanks for the tip!