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Power LEDs through a Parallel cable?

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mikediamond45

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Would powering a bunch of LEDs be too much for a standard parallel cable?

The LED energy requirements are:

LED Vf = 3.4 V
LED If = 80 mA
 

You'd need a series resistor for every single LED. E.g. 5V supply via a 20Ω resistor (or 4V via 7.5Ω).
 

yes, but i was wondering if a parallel cable could allow that much power running through it?
 

Depends on the cross-section of the cable and the number of LEDs.
 

ok, we are getting nowhere with these responses.

Let's try this.

Can each of the 25 individual wires in a Sub25 standard parallel cable conduct the following: 3.4 Volts at 0.8 amps


or is that too much power?
 

The questions is: can port driver priovide that much current? In least severe sace it will shut down because of some thermal or short-circuit protection. In more severe case smoke can be involved :D
 

I think he just wants to connect the leds to the power supply not the PC port.
The ribbon cable wires are very thin and the current high so I don't think it is the proper wire for the job.

Alex
 

Powering devices from PC parallel port

Data lines

In ordinary parallel port implementations the data outputs are 74LS374 IC totem-pole TTL outputs
which can source 2.6 mA and sink 24 mA Usually the output of the chis is followed by 22 ohm resistors
and 2.2-10 nF capacitor, but some implementations don't use that RC circuit.
The outputs are resigned so that they give at least 2.4V at 2.6 mA load.
This 2.6 mA figure is for ordinary LS-TLL circuits used, the LSI implementations used in many computers
can gvie more or les,. For example quite popular (few years ago) UM82C11-C parallel port chip can only source 2 mA.

Control outputs

You can also use the Control Out pins. They can't source much of anything (about 1 mA through the 4.7K
resistors to +5), and can only sink about 7mA. (The LS TTL gate actually sinks 8 mA, but one is taken up
by the 4.7 K resistor to +5).

Again, check on clones with different electrical specs.
For example very popular (few years ago) UM82C11-C chip implements the control outputs as standard TTL outputs
with lower (1.5 mA) current capacity instead of traditional open collector circuit with pull-up resistors.
82C11 os quite popular IC for implementing parallel ports few years ago, but it was very sensitive to
ESD and CMOS latchup effects. After facing problems with this the manufacturer started to use other solutions
(nowadays the whole I/O card is usually integrated to one chip).

Comparision of different parallel port types

....................................Normal...... UM82C11-C..... IEEE 1284 level II
Data output (>2.4V)...... 2.6 mA........ 2 mA............. 14 mA
Data line sink (<0.4V) .... 24 mA....... 24 mA............. 14 mA
Control output (>2.4 V) .. 0.5 mA*... 1.5 mA.............. ?
Signal lines (short circuit) ...1 mA ...... ?.................... ?
Control line sink (<0.4V).... 7 mA........ 7 mA.............. 14 mA

* This value is caluculated from the known data available from port.

text from..............
Power from parallel port
 
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