97-7796264_09-04-2020
Information subject to change
29
7548/7794/7796/7796HC OPERATOR’S MANUAL – SECTION 5
Once an approximate Rc and Cc have been
computed, these values will need to be evaluated.
To do this, install components with the required
values in the main board at locations R82 and C25
as shown in
Figure 5.10.
Figure 5.10 – Custom Compensation Location
Remember the load you are connecting is a
part of the system and the amplifier should not
be turned on without the load being connected.
After installing the components, check to ensure
that jumper J5 is correctly installed (see
STEP 4
),
then power up the amplifier without signal input.
To begin testing, input a square wave with a fre
-
quency of 100 Hz to 1 kHz, or a squared pulse at a
low level (typically 0.25 to 2.0 volts). A limited-rise-
time, repetitive pulse of low duty cycle is preferred.
Observe the output current through a current
monitor or current probe. Look for clean transition
edges. The presence of ringing or rounding on the
transition edges indicates compensation problems.
(See
Figure 5.11
.)
Figure 5.11 – Compensation Effects on Waveform
STEP 7: Optimizing the Compensation Values.
If a change in compensation is necessary, an ad
-
justment to the resistor component of the Compen-
sation circuit is probably required.
If the output current waveform is ringing, the circuit
is underdamped: You have too much gain and
should lower the resistance (see
Figure 5.12
).
If the output current waveform is rounded, the
circuit is overdamped: You have too little gain and
should increase resistance (see
Figure 5.13
).
Figure 5.12 – Square Wave Showing a
Decrease in R is Required
Figure 5.13 – Square Wave Showing an
Increase in R is Required
Figure 5.14 – Square Wave Showing an
Increase in C is Required
If the output current waveform is neither under-
damped or overdamped, but the top of the square
-
wave is not level, then you should instead increase
the capacitor value (see
Figure 5.14
).
When making adjustments:
Resistor:
Increase or decrease resistance values
in increments of +/- 10%.
Capacitor:
Incrementally increase capacitor val-
ues by a factor of 2 or 3.
Summary of Contents for 7548
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