Electronics Experts: I need a schematic for a simple power amplification circuit.

[dmcowen674]

Originally posted by: PrincessGuard
Just a little side track, but is there any benefit for using the LM393 rather than a driver IC like the ULN2003?

That's more like it espoecially for higher output LEDS available now. You would just have to cut down appropriately the numbers of LEDS you can drive because of the bigger drain of the High Output LEDS.

Have fun, it will work.

 

[Analog]

I'm not sure why you'd want to use a comparitor for this circuit, since all you really need is a current boost. Here are some points you should consider before getting too far into this design:

1. The LM393 can only -SINK- current, 16mA MAX.

2. The LM393 Pd = 0.78 Watts, so be careful.

3. You can better achieve this design with one resistor and one small signal transistor (just about any type), for <$0.50, and you can set it up to either sink or source current. Most plastic small signal transistors have current gains over 150x and can handle about 5x the current of the 393.

HTH

 

[Jeff7]

Originally posted by: yellowfiero
I'm not sure why you'd want to use a comparitor for this circuit, since all you really need is a current boost. Here are some points you should consider before getting too far into this design:

1. The LM393 can only -SINK- current, 16mA MAX.

2. The LM393 Pd = 0.78 Watts, so be careful.

3. You can better achieve this design with one resistor and one small signal transistor (just about any type), for <$0.50, and you can set it up to either sink or source current. Most plastic small signal transistors have current gains over 150x and can handle about 5x the current of the 393.

HTH

Well, whatever; what'd I need for this to work? And wouldn't it need more voltage too? These LED's need at least 3.2V, though I'm hoping for 4.0 - the motherboard gives only ~2.5V, and insufficient amperage.

 

[Demon-Xanth]

Originally posted by: yellowfiero
I'm not sure why you'd want to use a comparitor for this circuit, since all you really need is a current boost. Here are some points you should consider before getting too far into this design:

3. You can better achieve this design with one resistor and one small signal transistor (just about any type), for <$0.50, and you can set it up to either sink or source current. Most plastic small signal transistors have current gains over 150x and can handle about 5x the current of the 393.

HTH

The reason for using a comparator is because you cannot guarentee what the logic levels are coming from the motherboard. It's possible that the MB's header would hold the transistor in an on state.

Edit: What I mean by that, is that the motherboard manufacturer could have chosen a pull down setup, where one pin is +V and the other goes low to turn on the LED, OR they could have a drive up where one pin is ground and the other goes high to turn on the LED. And since most LEDs turn on at about 1.2V, that gives a wide range of voltages that it could be switching between the on and off states. You can't assume that they'll be using TTL or CMOS logic levels. (otherwise I would've suggested a single FET and resistor like you proposed)

 

[Demon-Xanth]

edit: DP