6881076C25-E
September 5, 2008
Theory of Operation:
Power Amplifiers
3-61
The power control loop is controlled by the microprocessor U204 on the VOCON board. Through the
SLIC IC U206, the microprocessor enables the RPCIC by pulling TX PA ENABLE (U500 pin 33) low
while the radio synthesizer is locked (U500 pin 35). U520 writes data to a digital-to-analog converter,
U502, to change and control the power-set voltage from pin 10 of U502 to pin 6 of U500. The voltage
on this line, 1.5 to 5 V, will be inversely proportional to the power out of the PA, with 5 V producing
the lowest power output. This voltage may be set with RSS (Radio Service Software) or CPS
(Customer Programming Software).
Figure 3-21. Regulator/Power Control IC Block Diagram
Control Voltage Limiter
R3813 and R3814 form a voltage divider that connects to control voltage drive. The output of this
voltage divider is connected to the control-voltage-limit input (pin 4) of the RPCIC. If the voltage at
this input reaches 3.2 V, then the control voltage will be clamped to a maximum value. For the
25/10-Watt VHF PA, this maximum value is 9.2 V. This voltage-control limit is set by the values of
R3813 and R3814.
Current Limiter
U204, the processor on the VOCON board, sends data to U502, the digital-to-analog converter, to
properly set the voltage on U502, pin 15, which is the TX CURRENT LIMIT control line to the RPCIC
(U500, pin 40). Sixteen different voltages, ranging from 1.5 to 4.5 V, can be programmed from U502.
N.C.
A+
TX P.A. ENABLE
LOCK
CURRENT SENSE +
FROM R9875
CURRENT SENSE
FROM R9875
KEYED 9.4V INPUT
9.6V DRIVE
UNSW 5V REF
9.6V SENSE INPUT
5V DRIVE TO Q502
5V CURRENT SENSE
5V FEEDBACK
TEMPERATURE SENSE
INPUT
TEMPERATURE SENSE
OUTPUT TO 500-2
POWER SET FROM
U502 1.5V 5 VOLTS
FORWARD DET.
VOLTAGE
POWER SET OUT TO
PIN 2 VIA R507
TX CURRENT
LIMIT FROM
U502-15
CONT.
AMP
OUT
REF.
3.2V
5V
CONT.
AMP IN
VOLTAGE
CONTROL
LIMIT
POWER
SET
N.C.
N.C.
N.C.
N.C.
N.C.
N.C.
REGULATOR
GROUND
13.8V
9.6 VOLT
REGULATOR
PA ENABLE
ONE-
SHOT
WIDE-BAND
ENABLE
CONTROL AMP
CURRENT SENSE
AMP
CURRENT
LIMIT SET
BUFFER
POWER CONTROL
GROUND
PACKAGE FLAG
GROUND
POWER SET
BUFFER
DIRECTIONAL
COUPLER BUFFER
THERMISTER
BUFFER
5V REGULATOR
PACKAGE
GROUND
U500
29
30
31
32
33
34
35
36
37
38
39
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
4
3
2
1
44
43
42
40
41
5
+
+
+
Q
+
+
+
+
+
Q538
RPCIC ENABLE
FORWARD BUFFERED
OUT
TO PIN 10
U502 DAIC
R516
100K
R509
68K
R507
47K
R508
68K
RESISTIVE
SUMMING
NETWORK
REGULATOR/POWER CONTROL IC U500
MAEPF-22034-O
Содержание ASTRO Digital Spectra
Страница 1: ...ASTRO Digital Spectra and Digital Spectra Plus UHF VHF 800 MHz Mobile Radios Detailed Service Manual ...
Страница 2: ......
Страница 6: ...September 5 2008 6881076C25 E iv Document History Notes ...
Страница 20: ...xviii List of Tables September 5 2008 6881076C25 E Notes ...
Страница 24: ...September 5 2008 6881076C25 E xxii CommercialWarranty Notes ...
Страница 48: ...September 5 2008 6881076C25 E xlvi Model Numbering Charts and Specifications Notes ...
Страница 142: ...September 5 2008 6881076C25 E 3 82 Theory of Operation Power Amplifiers Notes ...
Страница 218: ...September 5 2008 6881076C25 E 4 76 Troubleshooting Procedures Power Amplifier Procedures Notes ...
Страница 258: ...September 5 2008 6881076C25 E 6 14 Troubleshooting Waveforms ASTRO Digital Spectra Plus VOCON Board Waveforms Notes ...
Страница 434: ...September 5 2008 6881076C25 E Glossary 10 Notes ...
Страница 440: ...Index 6 September 5 2008 6881076C25 E Notes ...
Страница 441: ......