Chapter 5: Functional Circuit Description
Type 150/150G/400/400G Course Computers Service Manual 83156-1
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Type 150/400 Course Computers
5.2. Main functional parts of circuit
Power Supply
The Type 150 Course Computer is a nominal 12 Volt only product where as the Type 400
can run from a nominal 12 or 24 Volt supply.
The incoming power is protected by fuse FS1 and is protected against reverse polarity
connection by the components controlling relay RLY1. The Type 150 Course Computer is
further protected against connection to supplies in excess of 18V by the circuit connected
to Zener diode ZD16.
The heavy-duty power supply can be forced into an off state by shorting the TB2 terminals.
This generates a logic zero signal /KILL to signal this has happened.
The incoming supply is fed directly into the H-Bridge circuit.
VIN+12V is a rail that is nominally 12 Volts greater than the incoming power supply that is
required to control high side FETs TR18, TR34, TR8 and TR56. This rail is produced
using a charge pump circuit formed by FETs TR14 and TR15 and capacitors C31 and C32.
Link LK2 is fitted on the Type 150 Course Computers only, and connects the incoming
supply directly to rail V12.
The following switch mode regulator components are not fitted on Type 150 Course
Computers:
•
Inductors L43 and L1
•
Diodes D7 and D9
•
Switch Mode Regulator IC3
•
Capacitors C121, C122, C123, C13, C18 and C21
•
FET TR8.
On Type 400 Course Computers, the feed to V12 is switched via FET TR8 from either the
incoming supply or the output of the nominal 12 Volt switching regulator provided by IC3.
Comparator IC5c monitors the incoming supply voltage and switches TR8 depending on
the magnitude of the voltage. When the supply is less than 17 Volts, the supply is
connected directly to V12. When the supply is more than 17 Volts, V12 is fed from the
regulator output.
V12 is further regulated down to provide the other required voltage rails.
Transistor TR81 is configured as a simple series pass linear regulator to provide a voltage
limited rail VREG. This ensures that no more than 15 Volts is ever applied to the gates of
FETs TR24 and TR27.
5V-STABLE is a 5 Volt supply provided by linear regulator IC23 to power critical circuit
elements that must stabilise quickly at power-up.
IC21 is also a linear regulator and provides rail 7.8V, which is used by the microcontroller
during the Flash memory download (re-programming) process.
