Constant Current Compensation - AE Techron LVC608 Technical Manual

1.4 Constant Current Compensation

The following is a guideline for compensating amplifiers in the controlled current
mode. Constant voltage mode does not require compensation. For this procedure,
use C 104 and R109. Jumper JMP is in the CC position.
a) Calculate the approximate value of the resistor using the following formula:
•
Rc is compensation resistance in ohms.
•
L is load inductance in henries.
•
BW is bandwidth in hertz.
b) Calculate the approximate value of the capacitor using the following formula:
•
Cc is compensation capacitance farads.
•
L is load inductance in henries.
•
R is resistance of load in ohms.
•
Rc is compensation resistance in ohms.
c) Find the optimum values of the resistor and the capacitor by using an RC
decade box:
1. Use a short pair of twisted wires to connect the box to the main board.
2. Dial in the calculated values.
3. Connect load to output at "output" and 'sampled common" terminals.
4. Input square wave at highest frequency used in application with generator
set for minimum amplitude.
5. Connect oscilloscope to current monitor with ground.
6. Enable the amplifier from Standby to Ready and observe oscilloscope.
7. If the system is stable (no oscillations), increase generator amplitude to a
workable level and go to step 11.
8. If the system oscillates, switch to Standby and try different compensation
values.
9. If the system still oscillates, increase the value of the capacitor by factors
of three until stable.
10. After refining further the values of the R and C, find the optimum values
of R109 and C104, by adjusting according to the observed oscilloscope
waveform illustrated on the facing page.
11. After the optimum values have been found, remove the RC decade box
and install components with values shown on the decade box. Slight
adjustment of values may be needed due to use of decade box.
Rc = 20,000 x 3.14 x L x BW
Cc = L/(R x Rc)
Pre-Installation 1-15