TP620 Service Manual
3.2. Power Section
Figure 3-5 Power Structure Diagram
Battery
SW401
POW
_
DET
POW
_
HOLD
RF PA
AF PA
U404
LDO
U403
LDO
U402
LDO
U401
DC-DC
5C
5R
5T
3.3V
Q401
Q402
U301
STM32F
SAVE
5RC
5TC
This radio applies 7.4V, 2000mAh lithium battery, RF power amplification (Q501, Q502), AF power
amplification (IC101), and direct battery power supply.
The power circuit is composed of power-on/off circuit, 5C, 5R, 5T, and 3.3V DC-DC voltage stabilizing
circuit.
Power-on Circuit: When SW401 is closed, the B level of Q402 becomes high electrical level, and the
switch tube Q401 becomes conductive. The power supplies electricity for every power module through
Q401, when MCU is powered on, POW_HOLD will output high electric level to keep Q401 constantly
conductive so as to turn on the radio.
Power-off Circuit: When SW401 is cut off, POW_DET test pin becomes low electric level, and
POW_HOLD pin of MCU will first stays on high electric level for a while before outputting low electric level.
The Q402 B level thus becomes low electric level, cutting off the switch tube Q401 and the power to turn
off the radio.
5C voltage stabilizing circuit: U404 applies 5V LDO voltage stabilizer and supply 5v power for PLL circuit.
Meanwhile, the 67th pin of U301 outputs high and low electric level to control the enable pin of U404,
making the voltage stabilizer switches between 5V and 0V so as to realize the functions such as energy
saving and Tx/Rx switch.
5R voltage stabilizing circuit: U403 applies 5V LDO voltage stabilizer, and supplies 5V power for Rx circuit.
Meanwhile, the 66th pin of U301 outputs high and low electric level to control the enable pin of U403,
making the voltage stabilizer switches between 5V and 0V so as to realize the functions such as energy
saving and Tx/Rx switch.
5T voltage stabilizing circuit: U402 applies 5V LDO voltage stabilizer, and supplies 5V power for Tx circuit.
Meanwhile, the 34th pin of U301 outputs high and low electric level to control the enable pin of U402,
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