Service manual

DCB, DCFCB and DCFCTB Models
42
Theory of Operation
Connectors
JP1
Current Measurement Pass-Through
1
(+) voltage source
2
0-5 Amp (for gear driven rotators) output to motor, (-)
3
0-15 Amp (for belt driven rotators) output to motor, (-)
JP2
Interface, Power In and Signal Output
1
Ground
2
Window comparator output, open collector, pulls low when current is above
minimum and below maximum current
3
DC supply voltage input (7 VDC to 30 VDC)
4
Analog sensor output. 0 – 5 VDC for 0 - 5 Amp input
0 – 5 VDC for 0 - 15 Amp input
JP3 and JP4
Jumper headers
Shorted to set window comparator
thresholds for belt driven rotators
Circuit Description
Power Supply
Power enters through D1, is regulated down to 5 VDC, +/- 2% by U4 and is
filtered by C2 and C3.
The Current Measurement Path
The current sensor, U1, outputs a fixed DC voltage (2.5 V) plus a variable voltage
representing the current being measured. For the 0 - 5 Amp input a 2 Amp current
draw would = 2.5 VDC + 0.625 VDC or 3.125 VDC.
U3B generates an offset voltage. This voltage is summed through U3A with the
voltage from the current sensor. This subtracts off the 2.5 VDC from the current
sensor leaving only the voltage representing the current being measured. U3A
multiplies this voltage and scales it so that 1 Amp of current being measured = 1
VDC at TP3 (3 Amps = 1 VDC for the 0 - 15 Amp input).
The output of window comparator U2A and U2B goes high if the voltage is
greater than the voltage at U2 pin 6 and less than the voltage at U2 pin 3. This
turns on Q1 which pulls the output at JP2 pin 2 low.