Communication-concepts AN762 Application Note Bedienungsanleitung PDF herunterladen (Seite 6)

HIVE INF

RMATI

PRODUCT TRANSFERRED TO M/A–COM

AN762

6 RF Application Reports

Loops can be provided for current probe measurements.

L3L4

C6C6

C10

C11

R12

R10

C12

MC1723G

R11

C8 C9

C3 C2

B C E

Board Stand Off’s

Terminal Pins and Feedthroughs

Feedthrough Eyelets

OUTP GND

NEG POS

Figure 4. Component Layout of tthe Basic Amplifier

The thermal design (determining the size and type of a

heat sink required) can be accomplished with information

in the device data sheet and formulas presented in

references 5 and 6. As an example, with the 180 W unit using

MRF421’s, the Junction-to-Ambient Temperature (R

) is

calculated first as

– T

where:

= Maximum Allowed Junction Temperature

(150°C).

= Ambient Temperature (40°C).

P = Dissipated Power (180/η) x (100 – η)

η = Collector Efficiency (%).

If the worst case efficiency at 180 W CW is 55%, then

P = 148 W, and

= 1.49°C/W (for one device).

(148/2)

150 – 40

The Heat Sink-to-Ambient Thermal Resistance, R

– (R

+ R

) where: R

= Device Junction-to-

Case Thermal Resistance, 0.60°C/W* (from data sheet).

= Thermal Resistance, Case-to-Heat Sink, 0.1°C/W

(from table in reference 5). Then:

= 0.395°C/W

1.49 – (0.60 + 0.1)

* The R

figure of 0.85°C/W given for the MRF421 is in error, and

will be corrected in the future prints of the data sheet.

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