Experimenting With Bridge Rectifers For AC To DC Power Conversion

The folks over at Toymaker Television have put together another episode. This time they’re looking at bridge rectifiers and how they’re used in AC to DC converters.

This is a simple concept which is worth taking the time to study for those unfamiliar with it. Since Alternating Current is made up of cycles of positive and negative signals it must be converted before use in Direct Current circuits; a process called rectification. This is done using a series of 1-way gates (diodes) in a layout called a bridge rectifier. That’s the diamond shape seen in the diagram above.

This episode, which is embedded after the break, takes a good long look at the concept. One of the things we like best about the presentation is that the hosts of the show talk about actual electron flow. This is always a quagmire with those new to electronics, as schematics portray flow from positive to negative, but electron theory suggests that actual electron flow is the exact opposite.[youtube=http://www.youtube.com/watch?v=ixthQcMcguo&w=470]

28 thoughts on “Experimenting With Bridge Rectifers For AC To DC Power Conversion

  1. Yeah, I fully admit that the flow of electrons confuses me.

    I’ve heard that it actually goes from – to + when looking at a circuit BUT I’ve also heard that it’s a misinterpretation of what’s really going on.

    That is, electrons really are flowing from + to -, but the actual value of the charge is – and not + as originally assumed.

    So if you count + to – as flow from A to B then yes it is correct but what’s flowing is negatively charged.

    Or is that completely wrong?

    1. Electrons are negative in charge, so they really flow out of the negative terminal of the battery and return to the positive terminal.

      The direction of the current from positive to negative is technically wrong, but it doesn’t really matter whether you count the electrons, or the positive “holes” that travel down the wire in the opposite direction.

      A lot of stuff just makes more sense if you look at it from the perspective of the positive flow.

      1. I think it’s “fine” to look at conventional flow when looking at circuits from a bird’s-eye view so to speak. But when I was learning about how diodes work, it was conventional flow vs electron flow that confused the heck out of me.

        These two posts represent a dark day in my learning. When I realized that there were actually TWO different conventions -_-:

        And ever since, I’ve used electron flow and decided that the diode arrow is the dumbest schematic symbol we have. Though one of the watchers suggested that the arrow was going into a wall – hence not able to go in that direction.

    2. Yes, electrons flow from – to + … however, the gaps between said electrons can be considered to be virtual particles flow in the opposite direction (+ to – … think of moving the beads on an abacus one at a time – beads go one way, the “hole” goes the other).

      Both electrons and holes have important roles to play in semiconductor physics. Neither are relevant to circuit design. If you’re a glutton for punishment, however, this textbook should satisfy all your cravings.

  2. Back when I was teaching electronics to kids I found it extremely useful to build full-wave bridge rectifiers using LED’s as the rectification diodes, and then drive them with 1 Hertz sine waves. It made the operation visually much more obvious.

  3. Minus is DEFINED as a surplus of electrons, and plus is DEFINED as a shortage of electrons. Electrons of like charge repel each other, and electrons of opposite charge attract each other (similar to North and South poles on magnets).

    So, by definition, electrons in a circuit will travel FROM the surplus (- MINUS) TO the shortage (+ PLUS).

    1. And just to make it more confusing, the flow is really slow… at 3A into a 1mm copper wire the electrons flow at 0.3mm/s (about 1 metre per hour)!

      Adding that into the mix really confuses things until you use the “tap on the end of a long hose” analogy – it is the transfer of pressure, rather than the water itself that does the work.

    2. …Electrons of like charge repel each other, and electrons of opposite charge attract each other…

      No. Electrons always have a negative charge and always repel other electrons. Always.

      1. “Like” charges repel, “unlike” charges attract. Antimatter is an exception. Gluons “glue” the protons together in the nucleus, otherwise they’d be repelling each other as well, and our coffee wouldn’t taste right.

        For a cool explanation of the parts of an atom, search youtube.com for “WKRP, Venus Flytrap explains the atom”.

  4. @ Rob. That is the most insanely simple explanation I have ever heard. My physics teacher confused the hell out of me on this topic! It is like water it flows from high to low. The led bridge rectifier sounds like a cool way to demonstrate this to kids.

  5. “This is always a quagmire with those new to electronics, as schematics portray flow from positive to negative, but electron theory suggests that actual electron flow is the exact opposite.”

    It’s really not so much a quagmire as it should be mostly ignored when teaching circuits. It only becomes important when talking about the actual semiconductor physics or how vacuum tubes work.

    Just keep your currents consistent and all your calculations will work out just fine. It’s not about where the electrons are going, it’s about the rules they play by!

    1. In the US military they teach electronics with “holes”. Holes are an electron void or “missing” electron and these virtual particles travel from the positive to negative. The holes framework isn’t wrong in terms of the physical chemistry and holes as charge carriers flow in the same direction as our convention for current. Problem solved.

      The Army teaches high school drop-outs how to repair radios this way or at least they did before everything went solid state.

      Ben Franklin did a lot of great science but he guessed on which charge type was mobile and he guessed wrong.

    2. exactly! when u read about (picture) tubes, u say “electrons strike the… causing the…” meaning you need to know which end they are coming from, tube guys get it burneed into their heads which is which -/+ by means of mistaking polarity on a 400v circuit! ouch!

      PS: if u dont understand why u could get schocked by thinking both wires are +400 when one is -400 then you shouldnt be working on 400v WHILE LIVE!

  6. A good demonstration video, thing is only technical schools have enough equipment for a number of students to do these kind of experiments hands on. Persons attempting to make these kind of videos need to get a hold of the large bread boards that where used in tech school when I attended. Large with plenty of real estate to stretch out a circuit, possibly making for better camera shots. But what we pay for this, it good enough. DIY bridge rectifier :) Even When single component bridge rectifiers where available, manufacturers where designing boards to build them from discrete components. A glut of cheap diodes I suppose.

  7. Did anybody else catch the problem with the opening graphic?

    The generator is connected to the wrong poles of the bridge rectifier?

    The point where the two anodes are connected will be the negative side of the pulsed DC out. and the point where the two cathodes are connected will be the positive (+) pulsed DC out.

    Also the arrows on the AC generator side should be pointing both directions (sigh!)

    The alternating current source needs to be connected to the points where it can “see” either an anode or cathode.

      1. I prefer electron flow myself as well. And aren’t those who make circuits the actual “powers that be”? Why can’t we start changing to being conscious of electron flow rather than saying “Oh well, we know it’s wrong, but that’s how they’ve done it all of this time.”

        It’s silliness!

  8. Get em from old PSU’s! I make my own high-ish power power-supplies all the time with a bridge rectifier pulled out of an old PC PSU, they’re easy to find, black rectangle with 4 big fat leads.

    Get a 120v-12v transformer, add bridge rectifier and a big cap (for the DC side) that can handle the voltage and power and you’re good to go. If you really want to get wild you can tack a buck converter onto the DC side for super smooth power.

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