NQB-N Datasheet, PDF (22/30 Pages) CUI INC – FULLY REGULATED ADVANCED BUS CONVERTERS

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CUI Inc │ SERIES: NQB-N │ DESCRIPTION: FULLY REGULATED ADVANCED BUS CONVERTERS
date 11/07/2014 │ page 22 of 30
Definition of product operating temperature
The product operating temperature is used to monitor the
temperature of the product, and proper thermal conditions
can be verified by measuring the temperature at positions
P1, P2, P3 and P4. The temperature at these positions (T_P1,
T_P2, T_P3, T_P4) should not exceed the maximum temperatures
in the table below. The number of measurement points
may vary with different thermal design and topology.
Temperatures above maximum T_P1, measured at the
reference point P1 (T_P3 / _P3 for base plate versions) are not
allowed and may cause permanent damage.
Position
P1
P2
P3
P4
Description
Max temperature
PWB (reference point, open
frame)
T_P1=125º C
Opto-coupler
T_P2=105º C
PWB (reference point for
base-plate version)
T_P3=125º C
Primary MOSFET
T_P4=125º C
Resistance graph found in the Output section for
each model. Note that the thermal resistance can be
significantly reduced if a heat sink is mounted on the top
of the base plate.
Calculate the temperature increase (ΔT).
ΔT = R_th x P_d
3. Max allowed ambient temperature is:
Max T_P1 - ΔT.
E.g. NQB-468 at 2m/s:
1. ((1/0.95) - 1) × 468 W = 24.6 W
2. 19.5 W × 2.8°C/W = 69.0°C}
3. 125 °C - 69.0°C = max ambient temperature is 56°C
The actual temperature will be dependent on several
factors such as the PWB size, number of layers and
direction of airflow.
Connections (Top view)
Top view
Pin
1
2
3
4
5
16
Bottom view
(Best air flow direction is from positive to negative pins.)
Ambient Temperature Calculation
For products with base plate the maximum allowed
ambient temperature can be calculated by using the
thermal resistance.
1. The power loss is calculated by using the formula
((1/η) - 1) × output power = power losses (P_d).
η = efficiency of product. E.g. 95 % = 0.95
2. Find the thermal resistance (R_th) in the Thermal
cui.com
Designation
+In
RC
Case
-In
-Out
+Out
Function
Positive Input
Remote Control
Case to GND (optional)
Negative Input
Negative Output
Positive Output