Digital Kernel; Inverter Inguard Supply; Power Fail Detection - Fluke 2640A Service Manual

Inverter Inguard Supply

The inverter inguard supply provides three outputs: +5.2V dc (Vdd) and -5.2V dc (Vss)
for the inguard analog and digital circuitry, and +5.6V dc (Vddr) for the relays. Diodes
A1CR5 and A1CR6, and capacitor A1C12 create a +6.8V dc source, while diodes
A1CR7 and capacitor A1C13 create a -9.5V dc source.
+5.2V dc (Vdd) The +5.2V dc (Vdd) source is regulated from a +6.8V dc input to
A1U24 with resistors A1R9 and A1R10 setting the output voltage, and A1C4 handling
transient loads. Resistors A1R4, A1R130, A1R128 and A1R13, along with transistor
A1Q1, comprise a current-limiting circuit, which prevents A1U24 from supplying more
than 60 mA of load current.
-5.2V dc (Vss) The -5.2V dc (Vss) source is regulated from a -9.5V dc input to A1U25
with resistors A1R11 and A1R12 setting the output voltage, and A1C5 handling transient
loads. Resistors A1R14, A1R15, A1R129, A1R122, along with transistors A1Q5 and
A1Q6, comprise a current-limiting circuit, which prevents A1U25 from supplying more
than 40 mA of load current. Capacitor A1C9 enables the regulator to start up.
+5.6V dc (Vddr) The +5.6V dc (Vddr) source is regulated from a +6.8V dc input to
A1U6 with resistors A1R131 and A1R132 setting the output voltage, and A1C6 handling
transient loads.

Power Fail Detection

The power fail detection circuit generates a signal to warn the Microprocessor that the
power supply is going down. Microprocessor supervisor A1U10 compares the
divided-down raw supply voltage, via voltage divider A1R19 and A1R20. When the raw
supply voltage falls below approximately 8V dc, A1U10-5 output is low. Resistor
A1R99 is a pull up resistor for the A1U10-7 reset line, and A1C81 provides filtering of
high frequency noise. The reference voltage internal to the A1U10 is nominally 1.3V dc.

Digital Kernel

The Digital Kernel is composed of the following 10 functional circuit blocks:
•
Reset Circuits
•
Microprocessor
•
Address Decoding
•
Flash Memory
•
Static RAM
•
Real-Time Clock
•
FPGA (Field Programmable Gate Array)
•
Serial Communication (Guard Crossing)
•
RS-232 Interface
•
Ethernet Interface
Each of the 10 topics is discussed below.
Theory of Operation
Detailed Circuit Description
2-29.
2-30.
2-31.
2
2-13