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PP8xx LED Controller - User Manual
6
Heat dissipation and thermal guidance
The PP8xx has a linear circuit to produce the constant current output. This
means that it generates heat which needs to be dissipated.
For more information on this and a spreadsheet to calculate the heat
output, see application note APP941 at
www.gardasoft.com
.
6.1
Heat output per channel
For a continuous output current, the heat dissipation is given by:
D
H
=
I
O
x
(V
S
-
V
L
)
Where:
D
H
Heat dissipation in watts
I
O
Output current in amps
V
S
Supply voltage in volts
V
L
Voltage across the lighting in volts
This is usually easy to calculate as the voltage across the lighting is
normally the voltage rating of the light given in its specification, or as
measured using a voltmeter.
For a pulsed output, the heat dissipation is given by:
D
H
=
I
O
x
Duty Cycle
x
(V
S
-
V
L
)
Where:
Duty Cycle
=
Pulse width
(s) x
Trigger Frequency
(Hz)
When overdriving, the voltage across the lighting is more difficult to
determine. In most cases it is reasonable to use the voltage rating of the
light.
6.2
Total heat dissipation and heat sinking
The total heat dissipation for the PP8xx is given by adding together the
heat output for all channels, as calculated above.
To maintain normal operation, please adhere to the following thermal
guidance:
If the ambient temperature is below 40°C the maximum heat dissipation
may be 8W without any heat sinking.
If the ambient temperature is less than 25°C, the total heat dissipation
may be 16W without any heat sinking required.
If the controller is thermally bonded to a heat sink, then up to 24 watts may
be dissipated. The heat sink must be of sufficient size to maintain a steady
state internal temperature measurement of 60°C.
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