Re: Diode reverse protection and current limiting.

On Sat, 25 Nov 2006 22:14:00 +0000, Chris Jones <lugnut808@xxxxxxxxxxxxxxxx> wrote:
Ignoramus31174 wrote:

On Sat, 25 Nov 2006 05:53:03 GMT, Homer J Simpson <nobody@xxxxxxxxxxx>
wrote:

"Ignoramus7040" <ignoramus7040@xxxxxxxxxxxxxxxxxxx> wrote in message
news:g57pj.ral.17.1@xxxxxxxxxxxxxxx

Do you mean something as pictured in Figure 6? What would be the
point, to turn current on and off like that? Or are you suggesting
high frequency switching? I would rather regulate it, that is my
first, unstudied thought, than switch on and off? I apologize if
my comment is off base.

The point is to handle large currents without large heat losses. SCRs
were used for such tasks before large transistors or FETs were common.
One use was as a speed control for a battery golf cart. Basically you
fire the first SCR to turn the current on. At a certain point you fire
another SCR across it with a capacitor in series. This shunts the first
SCR which turns off and the capacitor then charges and turns the second
SCR off. Then repeat.

A more modern design might have transistors cycling on and off to control
the current with lower heat losses than remaining on. Basically this is a
form of switch mode power supply, perhaps without the transformer and
Schottky diodes.

As I say, it depends on how much current you want to use for electro
plating. 50 A at 12 V drop (say) is mighty hot.

OK, I see now. 50 A at 12V is not that much -- it is just 500
watts. Nothing that a 10 inch long heatsink could not handle. I have a
heatsink with 2 transistors assembly, would be nice to try to make it
into a variable voltage limited and current limited supply using them.

i


If you are thinking of any kind of switching regulator, and given that you
have low voltage DC already, I would definitely avoid SCRs since they
always drop quite a lot of voltage and are difficult to turn off. I would
either use MOSFETs in a switching constant current source, or get a big
heatsink with a fan, and build a linear regulator with either NPN bipolar
transistors or MOSFETs. The switching regulator would be more intersting
and more efficient, and an inductor to handle 50A DC could probably be
scavenged / built up from some computer power supply parts.


Chris, you know me. I am basically looking to see what would it entail
to make the cheapest/easiest solution to making a more versatile power
supply out of this PP-1104B/G. If the power converter is lossy, I
think that in the end it is not a huge consideration.

Is it true that a linear transistor based regulator is basically an
extremely simple solution?

i
.

Relevant Pages

  • Re: CLARIFICATION
    ... do you have an idea as to what the price would be? ... > directly rectify the input and feed it to your chopper stage. ... > day and age (hint look up SCR). ... >> supply (switching)? ...
    (sci.electronics.design)
  • Re: Diode reverse protection and current limiting.
    ... another SCR across it with a capacitor in series. ... A more modern design might have transistors cycling on and off to control ... If you are thinking of any kind of switching regulator, ...
    (sci.electronics.design)
  • Re: Motion Sensor always on?
    ... Some of these motion sensors use a relay to switch the attached load on and ... You might check to see if the relay was perhaps undersized to the work ... There are some that are completely silent when switching. ... might use something like an SCR or triac to do the switching...but I don't ...
    (sci.electronics.repair)
  • Re: What is the state of Robotics Currently.
    ... estimate the amount of computing power to duplicate human intelligence ... We don't need to simulate transistors to create a computer, ... with neurons switching at 1000 times per second and 100 ... Large parts of the brain is filled with interconnects (white ...
    (comp.robotics.misc)
  • Re: Whats in a "wall wart" so-called "transformer"?
    ... that use switching regulator technology to make the transfoprmer so small ... that it's hard to tell from the outside that there's even a transformer in ... supply DC to a switching regulator running at 20-50khz. ...
    (rec.radio.amateur.homebrew)
Quantcast