OSRAM OPTOTRONIC Constant current LED power supplies with 3DIM - Manual (Page 30)

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3.3.1.6. Application solution 6 – TC620(1) solution
The TC620 and TC621 (from Microchip) are programmable
logic output temperature detectors designed for use in ther-
mal management applications. The TC620 features an on-
board temperature sensor, while the TC621 connects to an
external NTC thermistor for remote sensing applications.
Both devices feature dual thermal interrupt outputs (“high
limit” and “low limit”), each of which is programmed with a
single external resistor. With the TC620, these outputs are
driven active (high) when the measured temperature equals
the user-programmed limits. The CONTROL (hysteresis)
output is driven high when the temperature equals the “high
limit” setting and returns to “low” when the temperature falls
below the “low limit” setting. This output can be used to pro-
vide “on/off” control to a cooling fan or heater. The TC621
provides the same output functions, except that the logical
states are inverted.
Below, an application example using the TC620 is given.
Thanks to the two programmable temperatures, it is possible
to set an intermediate current level before turning the LED
module off completely.
LEDset APPLICATIONS
C
1
= 100 nF 25 V 10 % X7R 0603
Q
1
, Q
2
= NPN signal transistor (i.e. BC847)
R
2
= 330 kΩ 5 % 0603
R
3
= 330 kΩ 5 % 0603
Rset
1
Rset
2
R
HS
R
LS
Figure 22: Thermal derating – TC620 solution.
see example on the right
For more information, please see the general notes on page 33.