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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PP8xx LED Controller - User Manual
Sending the
AN
command to the controller reports the internal
temperature measurement.
If the thermal guidance isn’t followed the controller may over heat. There is
a safety cut out, which will turn the output channels off when the internal
temperature indicated by the
AN
command command exceeds 70°C.
6.3
Minimising thermal dissipation
There are several ways to reduce the heat output from the PP8xx:
Use pulse mode. If the output is only on when you need it then you can
dramatically reduce the heat output. Feed the camera trigger into the
PP8xx and pulse the lights.
Turn the light off when not needed. If you don't have precise timing of
when the camera will trigger, you can use switched mode to switch the
output off or on depending on the trigger input (or use remote commands
to turn the output on and off).
Reduce the output current if possible.
Reduce the supply voltage. Most PSUs have some adjustment in their
output voltage.
Connect lights in series instead of parallel. If you have an array of lights or
LEDs in parallel then changing the arrangement to serial will increase the
voltage across them but reduce the overall current.
Use two PP8xx's and use less channels from each. For high power
applications this may be the easiest solution.
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