HF PACKER
AMP
V4R6
Page 46
PSU HFPA 10
drawing. The waveforms shows that the RF
signal may come and go due to keying or speaking but the
PSU is active until a hold time has been exceeded.
U4 Control
U4 is controlled by the digital on/off control labeled
PSU
.
When PSU measures 0V, the PSU is on. When PSU is 5V, the
PSU is off. This control signal switches Q4 connected to pin 1
of U4 (VC) voltage control. You can learn more about U4 at:
http://cds.linear.com/docs/Datasheet/lt1270afc.pdf
Fully Protected High Side Power MOSFET Switch, U5
See
info/datasheets/data/ips511.pdf
power switch and circuit breaker. The IPS511S switch is
controlled by the digital on/off control signal
IPS.
This signal is
switched on (0V) when the PSU is already on and switches off
(5V) before or at the same time that PSU is switched off. The
device also acts as a thermal operated circuit breaker. The
IPS511S is rated up to 5A. Above that, the switch will
purposely heat up and the output will drop to zero volts. It will
recover when it cools down. This part neatly switches voltage
to the AMP drain connections when on. In the event of a short-
circuit the circuit breaker will kick in. Because of the circuit
breaker action you will keep from destroying the DC-DC
converter chip, U4. Without the protection, the DC-DC
converter will deliver the battery current into the short-circuit
until the U4 blows up. How can you know if you have a short-
circuit? The front panel LED will not light. You might hear a
squeal from the amp and U5 will get hot. Don’t worry; it is
doing its job. What is the most likely thing to cause a short-
circuit? The MOSFETs. We will get more into MOSFET failure
in the AMP descriptions to follow.
At this point, you should sufficiently know how the PSU works,
what controls it and what safe guards you have. What to
measure? You can use a volt meter probing R18 on the end
closest to the PSU for the voltage measurements. This voltage
is what lights the LED. It means, when lit, that the MOSFET
has a transmit source voltage on the drain connections. You
can see the control signals on U2 pins 9 and 10. Placing a
jumper on H3 (TEST) will cause both of these control signals
to have 0V outputs.
This concludes the PSU discussions. We will discuss the
timing of the PSU and IPS signals when we talk about the
controller chip, U2.
CONTROL HFPA 10
The next discussion is about signal flow through the AMP from
RF IN to RF-OUT. Follow along by looking at
CONTROL
HFPA 10
Schematic during this description.
Big Picture
RF enters at the case mount BNC connector and is attached
via a cable to J3.
U6
is a RF Module that
provides RF detection for the amp
without impacting the Input SWR. It consists of a dual CMOS
Schmidt trigger device.
K2, K3 and J4
Relays K2 and K3 form the T/R (transmit/receive) function
controlled by the control signal TX. K2 is used to divert the RF
output from the transceiver to the AMP input. (Signal name
Summary of Contents for PackerAmp V4
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