Datasheet

2 2
AC
FU
AC
FU
Tips & tricks
LEDs and how to use them
Power LEDs dos and don’ts
Open collector outputs
Screw the LED firmly onto an appropriate heat sink
Use a series resistor or a current limiter circuit
Use the LED without a heat sink!
Use the LED beyond maximum operating current
Look directly into the light source
An open collector output can be compared to a switch that switches
to ground when powered.
Example: How to switch an LED by
means of an open collector output
Remember: relay outputs are switches meaning there is no voltage coming out of them.
An external source is required.
So how to connect a load to a relay output:
Relay contacts and how to use them
Common mistake:
LEDs feature a specific voltage drop,
depending on type and colour.
Check the datasheet for exact voltage drop
and rated current!
How to calculate the series resistor:
Example: operate a red LED (1.7V) on a 9Vdc source.
Required LED current for full brightness: 5mA (this can be found in the datasheet of the LED)
Never connect LEDs in parallel!
LEDs in series:
closest value:
use a 1k5 resistor
a standard ¼ W
resistor will do the job
Supply voltage (V) - LED voltage (V)
required current (A)
= series resistance (Ohm)
= 1460 Ohm
9V - 1.7V
0.005A

Required resistor power handling =
voltage over resistor x current passed trough resistor
(9V-1.7V) x 0.005A = 0.036W

Example:
• 3 x red LED (1.7V) on 9V battery
• Required LED current for full brightness:
5mA (this can be found in the datasheet of
the LED)
use an
820 Ohm resistor
= series resistance (Ohm)
Supply voltage (V) - (number of LEDs x LED voltage (V))
required current (A)
= 780 Ohm
9V - (3 x 1.7V )
0.005A
