TTI PL Series - Quad Mode Triples; Funcitonal Description - 5 V;7 A Module (PL330 QMT); Circuit Description - 5 V;7 A (Issue 2 PCBs and later)

Quad Mode Triples
Funcitonal Description - 5V/7A Module (PL330 QMT)
The relationship between the major circuit elements is shown in the block diagram.
The transformer incorporates two secondary windings, one which produces the main supply
powering the output, and another which produces an auxiliary supply powering the control and
metering circuits.
The series regulator is placed in the positive output of the main supply, but because of the way in
which the control and metering circuits operate, it is convenient to label the output of the series
regulator as 0 volts, and to regard the negative side of the main supply as being the controlled
output voltage (-V out).
The auxiliary supply provides stabilised symmetrical voltage outputs V+ and V- with the common
point connected to the +ve output.
The series regulator is controlled by the 'voltage control circuit' until the output current flowing
reaches the current limit setting, upon which the 'current control circuit' takes over. The voltage
control buffer amplifies and provides low output impedance from the voltage controls.
The 12 bit A to D measures output voltage with the output switch off and output current with the
output switch on selected by the multiplexer.
The micro-controller reads the output of the A to D and drives the display.
Circuit Description - 5V/7A (Issue 2 PCBs and later)
Power Supply - Mains
This consists of a full wave bridge rectifier feeding the reservoir capacitor C30. The full load
secondary winding voltage is 11V rms giving approximately 15 volts off load and 12V on full load.
Power Supply - Auxiliary
This consists of twin full wave rectified supplies from a 21V centre tapped winding.
IC8 generates +5V for the micro-Controller, display and A to D. Q7 and D10 generate +7.5V for
the analogue section.
D11 generates -5V for the analogue section and A to D.
0V of this supply is connected to the positive output at R62.
Voltage Control
IC7A buffers the voltage control pot and VR7 sets maximum output voltage of the unit. D9 is the
reference which is nominally 2.45V.
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