User Connections and Considerations
43
Load Considerations
Capacitive Loads
In most cases, the power supply will continue to be stable with additional external load capacitors (see the following table
for Series 654xA/665xA recommendations). However, large load capacitors may cause ringing in the supply's transient
response. It is possible that certain combinations of load capacitance, equivalent series resistance, and load lead inductance
will result in instability. If you need help in solving a stability problem, contact an Agilent service engineer through your
local Sales and Support office (see end of this manual).
Series 654xA/655xA Power Supplies, Maximum External Capacitance
6541A 6542A 6543A 6544A 6545A 6551A 6552A 6553A 6554A 6555A
40,000µF 20,000µF 12,000µF 7,000µF 3,000µF 100,000µF 50,000µF 30,000µF 18,000µF 8,000µF
If the power supply output is rapidly programmed into capacitive loads, the supply may momentarily cross into CC mode.
This extends the CV programming time and limits the maximum slew rate to the programmed current divided by the total
internal (see “Inductive Loads”) and external capacitance. These momentary crossovers into CC mode will not damage the
supply.
Inductive Loads
Inductive loads provide no loop stability problems in CV mode. However, in CC mode inductive loads will form a parallel
resonance network with the power supply's output capacitor. Generally, this will not affect the stability of the supply, but it
may cause ringing of the current in the load. Ringing will not occur if the Q (quality factor) of the parallel resonant network
is ≤ 0.5. Use the following formula to determine the Q of your output.
Q
R
L
C
=
+
1
R extint
where C = model-dependent internal capacitance (see below); L = inductance of the load; R
ext
= equivalent series resistance
of the load; R
int
= model-dependent internal resistance (see below):
6541A 6542A 6543A 6544A 6545A 6551A 6552A 6553A 6554A
C=
4,200µF 550µF 180µF 68µF 33µF 10,000µF 1,100µF 440µF 120µF
R
int
=
7 mΩ 30 mΩ 50 mΩ 125 mΩ 300 mΩ 4 mΩ 20 mΩ 30 mΩ 80 mΩ
6555A 6571A 6572A 6573A 6574A 6575A
C=
50µF 44,000µF 44,000µF 12,000µF 7,000µF 2,100µF
R
int
=
250 mΩ 1.8 mΩ 2.2 mΩ 4 mΩ 14 mΩ 30 mΩ
Note for Series 657xA Supplies: If Q >0.5, inductive loads will ring with the output capacitance and be damped according
to the following equation
e
t
L
R
t
Q
−
−
2
1
1
2
2
sin ω
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