Question about diode bridges/rectifiers

[Tenorikuma]

I'm a total electronics newbie and I'm trying to rig something up for buildings.

 

The idea is to have a 9-12V bus, and then in each building, have a standard circuit consisting of:

 

diode bridge » 20 mA current regulator » LEDs (in series)

 

The reason for the diode bridge is that I won't have to worry about matching up the polarity. However, I have no idea what part to get or how to read the datasheets. Would anyone know if this would do?

 

http://jp.mouser.com/ProductDetail/Central-Semiconductor/CBRHDSH2-100-TR13/?qs=sGAEpiMZZMu5uoOCJ4OfqqzZegZvOUof

 

Or how about this?

 

http://catalog.chtechnology.com/item/bridge-rectifiers/single-phase-diode-bridge-rectifiers/26mb05a?

 

(But how do you solder that kind of thing to a circuit board?)

 

Or maybe this one:

 

http://jp.mouser.com/ProductDetail/Vishay-Semiconductors/KBU4A-E4-51/?qs=sGAEpiMZZMtcLAek5QF0iwu6i7RElklMqNve1OjwR%252bk%3d

[CaptOblivious]

Tenorikuma,

 

The first one has about the right specs, but would be tricky for a novice to solder. The second one is very much overkill, and as you point out, is also not going to be easy to solder but for entirely different reasons.

 

The third one you listed is about right, though! The pin spacing is a bit non-standard however. If you are soldering to generic perfboard, you should try to find a rectifier with pin spacing to match your board. Standard is 0.1" (2.54mm).

 

You might also consider just a single diode. If you apply power backwards, it would simply prevent the circuit from energizing, but it might be easier to work with in terms of soldering and circuit design.

[KenS]

Well, doing it in every building may be overkill, but I'd been thinking of adding a protection circuit on an area-by-area basis, just in case I ever hooked up my power supply backwards.  A simple diode in one wire would probably be sufficient, if all you care about is blocking a reverse polarity that could damage the LEDs.  A rectifier will let you use an AC supply, or hook up DC either way.

 

The characteristics that matter are the maximum reverse voltage (V-sub-R for DC, V-sub-R(RMS) for AC) you want it to block before failing, which just needs to be higher than the maximum possible voltage that might be involved, and the maximum current that will pass through it in normal operation (average forward current, I-sub-O on the first data sheet, and often just cited as "amps").  

 

Even the smallest rectifier you list (the first) has Vr(rms) = 70 volts, which seems to be more than enough, and a forward current of 2 amps, which is quite a lot for LEDs (the brightest LEDs are under a tenth of an amp, and most are around 30mA or less, so you could drive about 66 LEDs with it).

 

That first one looks like a good choice for a small area or single building.  The second one is a high-power unit that's probably far beyond your needs.  The third one is about twice the amperage of the first, but it's a lot bulkier.  It would be okay for an "under the table" mount (and probably easier to solder wires to), but it's a bit large to put in a building.

 

The current limiting and rectifier are separate functions, and can be done independently (or together).  Think of this in the form of a raw power bus (two wires from the power supply, which can be AC or DC with several amps at your chosen voltage), a subordinate DC bus (+ and - wires from the output of the rectifier, which have a maximum allowed current based on the rectifier) and the LED circuit(s) which starts at your chosen voltage (e.g., 12 volts) and provides no more than "X" to each LED, using resistors and chains of LEDs.  You can hook up one or more LED circuits in parallel to each subordinate bus, and as many subordinate buses (also in parallel) to the raw bus as the power supply will handle (based on its amperage or power rating).

 

Current limiting is a more complex area.  I just use resistors and worry about the voltage (current will adjust itself based on the voltage in a complex manner, but will be "safe" as long as you don't exceed the LEDs voltage).  Then add up the maximum current per LED to estimate load on the power supply (or use a current meter, to be more accurate). There was a discussion of new current-limiting diodes (different from current-limiting ICs, which have been around for years) that could take the place of the resistor in another thread (which I can't seem to find now) and limit current more precisely, but that's not something I have any experience with.

 

Update: fixed a typo.

[cteno4]

ken,

 

that discussion on the CRDs is in this thread

 

http://www.jnsforum.com/index.php/topic,4307.0.html

 

cheers

 

jeff

[Tenorikuma]

The third one you listed is about right, though! The pin spacing is a bit non-standard however. If you are soldering to generic perfboard, you should try to find a rectifier with pin spacing to match your board. Standard is 0.1" (2.54mm).

 

You might also consider just a single diode. If you apply power backwards, it would simply prevent the circuit from energizing, but it might be easier to work with in terms of soldering and circuit design.

 

Well, I'm hoping to use metal tape to make electrical contacts on the bottom of buildings, like I saw in another thread here. Since there's a good chance (me being me) that I'll screw up the polarity on the base contacts sometimes, I want things to "just work" regardless of polarity.

 

Okay, spec and pin-spacing-wise, how are these rectifiers?

http://jp.mouser.com/ProductDetail/Vishay-Semiconductors/GBPC6005-E4-51/?qs=sGAEpiMZZMtcLAek5QF0iwu6i7RElklMpG6EjpLc4lc%3d

http://jp.mouser.com/ProductDetail/Vishay-Semiconductors/2KBP005M-E4-51/?qs=sGAEpiMZZMtcLAek5QF0i50HOmaG79qIsYAQS24p6t0%3d

 

Ken, for limiting the current, I'm just using a "CL2" limiter. See http://www.supertex.com/pdf/datasheets/CL2.pdf . It seems dead simple and limits current to 20 mA no matter how many LEDs you have hooked up. No resistor calculations means one less place for me to err.

[cteno4]

Ken, for limiting the current, I'm just using a "CL2" limiter. See http://www.supertex.com/pdf/datasheets/CL2.pdf . It seems dead simple and limits current to 20 mA no matter how many LEDs you have hooked up. No resistor calculations means one less place for me to err.

 

yes but wont your V input total have to equal or better the V led total then? so with 12v bus you could do 4 3v led in series?

 

seemed like the cl2 would work best in the car lighting situation where you had a variable voltage input you wanted to limit the current but not worry as much about the variable track voltage.

 

jeff

[CaptOblivious]

Ken, for limiting the current, I'm just using a "CL2" limiter. See http://www.supertex.com/pdf/datasheets/CL2.pdf . It seems dead simple and limits current to 20 mA no matter how many LEDs you have hooked up. No resistor calculations means one less place for me to err.

 

yes but wont your V input total have to equal or better the V led total then? so with 12v bus you could do 4 3v led in series?

 

For each string of LEDs wired in serial, yes. But he could have multiple strings of LEDs with one CL2 at the beginning of the string, wired up to the power supply, providing quite a few LEDs total!

 

 

Tenorikuma:

Spec wise, those are fine. Overkill, but fine. Physically, the second one is more problematic. The packages that are flat, with 4 pins in a row, typically have pins too large to fit in perfboard, and the spacing is pretty off. The other one, with the four pins arranged as a square, is a better fit, I think.

[CaptOblivious]

Tenorikuma:

 

These are the ones you want:

 

http://jp.mouser.com/Semiconductors/Diodes-Rectifiers/Bridge-Rectifiers/_/N-2xpqk?P=1z0xs5h&Keyword=W02+bridge+rectifier&FS=True

 

Pick one, any will do. They will fit in breadboards and in perfboard, and are nicely small, but plenty within spec for your purposes.

[Tenorikuma]

Tenorikuma:

 

These are the ones you want:

 

http://jp.mouser.com/Semiconductors/Diodes-Rectifiers/Bridge-Rectifiers/_/N-2xpqk?P=1z0xs5h&Keyword=W02+bridge+rectifier&FS=True

 

Pick one, any will do. They will fit in breadboards and in perfboard, and are nicely small, but plenty within spec for your purposes.

 

Brilliant, captain. Thanks a ton for the recommendation! I'll go ahead and order a bunch.

 

Jeff: Yes, as Captain Oblivious surmised my intention is to equip each building with the rectifier, limiter, and one to four LEDs. Then, it should be possible to treat each building as a "black box" and hook it up to anything from 5 to 50 volts (although I'll standardize on either 9 or 12 volts).

[cteno4]

 

Jeff: Yes, as Captain Oblivious surmised my intention is to equip each building with the rectifier, limiter, and one to four LEDs. Then, it should be possible to treat each building as a "black box" and hook it up to anything from 5 to 50 volts (although I'll standardize on either 9 or 12 volts).

 

yes but you will need at least 12v or maybe more for white leds as they usually draw around 3.2v each and in series youll need some more voltage i think.

 

had anyone disected the xmas tree light sets to see how they are set up? figured there must be some sort of rectifier then a current limiter with a long string of leds in serial. figuring they last so long not that much worry about blowing one out and loosing them all.

 

captian,

with the current properly limited how much over voltage can an led take with one of these clds?

 

cheers

 

jeff

[Tenorikuma]

yes but you will need at least 12v or maybe more for white leds as they usually draw around 3.2v each and in series youll need some more voltage i think.

 

had anyone disected the xmas tree light sets to see how they are set up? figured there must be some sort of rectifier then a current limiter with a long string of leds in serial. figuring they last so long not that much worry about blowing one out and loosing them all.

 

captian,

with the current properly limited how much over voltage can an led take with one of these clds?

 

I'll double-check the LEDs I use and use parallel circuits as needed then.

 

The CL2 current regulator supposedly takes up to 90 volts. Or did I misunderstand the question? I'm not quite sure what over-voltage is.

 

I was originally thinking 9 volts would work well for portable dioramas (using 9-volt batteries) and 12 would work well when using the auxiliary power from a power pack, but maybe I should go with 18 volts and power portable displays with two 9-volts in series.

[KenS]

I don't have any experience with current-limiter ICs, and I didn't know you could use them like this, but I trust Don's (Capt. O's) experience, and the data sheet seems unambiguous.

 

As Jeff noted, your voltage supply needs to be greater than the sum of the voltage drops across the LEDs in a string, and it probably needs a bit of padding for the CL2 (but the data sheet doesn't say what, if any, voltage drop it imposes). Per wikipedia, white LEDs are around 3.5volts, so I wouldn't put more than three on a string with a 12v source.  But with the CL2, it appears you could use a much higher-voltage source as you say, which would allow more LEDs per string.

[CaptOblivious]

 

captian,

with the current properly limited how much over voltage can an led take with one of these clds?

 

 

As I understand it, this is a non-issue. The CLD "absorbs" whatever excess voltage there is, and dissipates it (times the current) as heat.

[cteno4]

interesting so it also limits the voltage then as well.

 

sounds perfect for the application of led lighting in the cars with regular dc operation.

 

sorry my electronics and physics education is like almost 30 years old now... actually thinking of taking an electronics course to catch up some... things have changed some in whats available!

 

thanks

 

jeff