In my other thread on sizing a power supply, I had spoken of a transmitter design I didn't like, and as long as I had the drawing at hand, I thought I'd put it up for a bit as I had a question.

Is it possible for the high-voltage DC to "contaminate" or "bleed through" to the low-voltage supplies? When I was trying to take readings in an unit that had this panel in it, I got 'bit' by mains even though I was on the 5V bus.

I don't know if this circuit was inherently unsafe, defective, or if it was the factory mods for that application.

I'll have a thread later on the transceiver circuit I had wanted to use in my project, but right now, I needs me some sleep.

 

well, if you got shocked, something is not wired right. that schematics only shows part of the circuit, likely one board. it is unclear what else is there and what actual construction looks like.

 

The overall schematic is too big for one sheet. I'll see about at least adding in the LV power supply and the chassis schematics a bit later on.

 

Well, here is the more or less combined schematics of the amp, power, and chassis drawings.

After I cleaned out some circuitry that isn't populated in this arrangement and started melding the three separate pages together, I finally noticed two very sketchy connections that I'm 99% sure was why!

The whole idea of that bank of diodes was so that vehicle +12V could be used to power the unit when doing on-site testing. I still don't like it.

 

The short answer about "high voltage bleeding over" is that YES, leakage can cross the surface of a contaminated PCB . USUALLY, however, a layout with inadequate spacing is involved, and often the "grounding" connections are inadequate or not soldered at all. And a MISSING return side (ground) connection can cause a whole lot of problems, including nasty shocks and and damaged components, especially expensive IC devices.

 

Certainly, with there not being and power return connection to that bipolar output section, there can be a tendency for leakage to other portions of the system.

 

A picture of the board in question - I bought a few of these units recently... logic and mains intermingled on the same board, what could go wrong?...

Small wonder the next generation of this unit used a different circuit that only requires 28 volts!

J2 carries the +5 for the T1 primary circuit and +12 for the transmit / receive relay, and the four larger holes carries mains (filtered AC, Line 1, Line 2, and neutral).