Driving transistor from HC273

on the

Makes me wonder if there are LEDs with different voltages (colors), since with that many it might pay off dissipation-wise to use separate switching supplies for each color/voltage.

Here's one possible arrangement that would provide about 60mA with a Vcc of 5V.

: Vcc Vcc : | | : | | : \\ | : / Rca_N | : \\ 47k | : / | : Rcb_N | |

Slight change, for somewhat better clarity:

: Vcc Vcc : | | : | | : \\ | : / Rca_N | : \\ 47k | : / | : Rcb_N | |

And that should be Rcc_N, not Rcc_3.

Jon

will

60ma or

stupid

900-1800 of

(Vcc-0.6)/6mA.

drive it

R. If the

it's not

saving on the

It's nearly 10% of the power going up in needless heat for heavens sake !

I very much doubt he *wants* to use 2N2222s at all. Probably he just found them in a text book and hasn't looked at sensible modern alternatives.

Jeez ! 2N2222 is in TO-18 ( un required ) and costs a fortune too ! A very bad choice. Around 10x what you need to pay.

Graham

The led supply *could* be lower voltage since the transistors are open collector to save some dissipation. 2V5 for example.

Graham

But they *aren't* dirt cheap John.

Hermetic TO-18 encapsuation costs an arm and a leg.

He only needs epoxy encapsulation so a more logical choice would be the 'near generic' 2N3904 or BC548

Some textbooks sem to be suck in a time warp with regard to their examples of suitable devices. Things have moved on ! Having a larger beta is very useful and makes design less cricitical.

Graham

Aren't they in epoxy though ? Not 2N2222s at all !

Graham

message

I was referring only to the power dissipated by the LEDs themselves. Worst case with all 1800 on and drawing an average of 6mA (60mA @

10%duty) comes out to 10.8A. As you say, the OP should really consider using as low voltage supply as possible so that he/she isn't burning up another 10-15A in current limiting resistors. I'm guessing, but I figure this device will not be battery operated. ;-)

yeah. Eternally damned TO-92's. I think all BJTs should be at least in a nice TO-5. Maybe a TO-18, if the manufacturers beg forgiveness while offering them. TO-92s can't be decently labeled. But then, I'm a hobbyist.

Jon

choice.

Ah, you can still get them in TO-18 for less than 5 cents each. About

5X, not 10X. ;)

And you can actually _read_ their number, then, because it's nicely visible; hold them in your hands without fearing losing them in the rug; and know that you've got some real metal there -- the feeling of substance! Not to mention that the leads exit the package in the sensible triangular arrangement with the emitter nicely tagged, and not the disgusting linear layout that can confuse you because there are some BJT layouts that differ from each other in that packaging and none of it, sensibly.

It's a veritable crime that their R(theta_JC) is no better than for those little TO-92's, though. :)

Jon

It will

60ma or

stupid

900-1800 of

(Vcc-0.6)/6mA.

drive it

R. If the

matter, it's not

saving on the

in a text

--
You have no clue about why he wants to use them. Perhaps he has a
few thousand of them on hand and can use them to good advantage on
this project.

I'm going to use the ULN2803. More expensive, but better in the long run.

Take a look at these schematics and try to find something wrong. I know of a few things I need to do, like put a pull down resistor on OE (not /OE). This is my first high current design. I don't want any bugs since I'll need 30 boards. :)

There are 19,008 LEDs in the array. The whole LED display will consume

138 amps MAX, and of that at least 276 watts MAX will be heat.

I have a 150A 5v supply. ;)

So, I got the part number wrong. N2222 type. The data sheets I've found list it up to 500ma collector current, have I been reading them wrong?

I chose that transistor because like other people said, through surplus places they are under a penny a piece (in quantities of 2000). I've decided to use the ULN2803, so its over. ;) But I would love to get comments on the above schematics. Tear them apart just as much as this transistor debate. ;)

64x297?

Jon

192x99

8x11 is a good character font 24x9 character display, or bitmap graphics.

I've built a single character as well as a 26x22 array. For the bigger array I have around 10,000LEDs soldered so far. Only 9000 to go. :)

--
But, you have no information as to what color LEDs the OP wants to
run...

99x192 33x576 32x594 man there's a bunch of combinations for such an odd number.

--
But, as I indicated earlier, we all know that he\'s talking about the
chip, not the package.

Yup, but quickest to just ask with one example. I was curious.

Jon