Newbie: ULN2803, switch positive and negative?

[unbwogable]

Newbie question, haven't got much electronic design experience. I'm redesigning a circuit for a friend, and he's got 52 NPN transistors on this thing .
I'm wondering if I can swap them for several ULN2803 ICs. I know it's feasable, but he's got each transistor switching a positive voltage on and off. All the datasheets I see for the 2803 show it switching the negative side. Is there any other chip that can do this for me, or can I switch the positive and negative pins on the 2803?

Or does anyone have any other suggestions?

Basically, this is what he's got:
**broken link removed**

This is what he wants:
**broken link removed**


Will that last circuit actually work? All the data he's got is saying that the output on the right side of the pins will be a (-) connection

 

[Hero999]

I don't know what you're talking about. Please post a schematic and I might be able to help.

 

[jrz126]

The uln2803 is only capable of sinking current, not sourcing. You'll have to use a different transistor array.

 

[unbwogable]

Can anyone suggest a good replacement for this then?

 

[justDIY]

how much current does the circuit need to handle?

 

[audioguru]

EEK!
Most of the polarities are backwards on your schematics.

EEK!
The LEDs don't have current limiting resistors.

 

[unbwogable]

That was just tossed together to demonstrate what I wanted to do, I always put resistors on my LEDs (except once, and it actually made an audible 'pop')

Circuit only needs to light a LED (25-35ma @ 3.2 volts)

I just don't feel like hand soldering 50+ transistors into place. And plus, it would just look a little cleaner

 

[audioguru]

Use a few ULN2804 ICs. Its outputs sink to ground when turned on and the inputs work well from +12V.

 

[jrz126]

oh, all you have to do is turn the leds around, connect all the anodes to +12V then connect each individual cathode to an output of the uln2803. Putting current limiting resistors in there of course.

 

[unbwogable]

Someone, on another forum, suggested I use the UDN2985, trouble is, can't find a supplier for it. Anybody got any ideas?