Load Considerations; Capacitive Loads; Inductive Loads - Agilent Technologies 654 A Series Operating Manual

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
40,000µF 20,000µF 12,000µF
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.
where C = model-dependent internal capacitance (see below); L = inductance of the load; R
of the load; R = model-dependent internal resistance (see below):
int
6541A 6542A
C=
4,200µF 550µF
R =
7 mΩ 30 mΩ
int
6555A 6571A
C=
50µF 44,000µF
R =
250 mΩ 1.8 mΩ
int
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
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6544A 6545A 6551A
7,000µF 3,000µF 100,000µF
1
=
Q
+
R R
int
6543A 6544A 6545A
180µF 68µF 33µF
50 mΩ 125 mΩ 300 mΩ
6572A 6573A 6574A
44,000µF 12,000µF 7,000µF
2.2 mΩ 4 mΩ 14 mΩ
 
 
−
t
 
s i n ω
e t
 
 
2 L
 
 
 
 
R
6552A 6553A
50,000µF 30,000µF
L
C
ext
= equivalent series resistance
ext
6551A 6552A
10,000µF 1,100µF
4 mΩ 20 mΩ
6575A
2,100µF
30 mΩ
2
 
1
−
 
1
 
2 Q
User Connections and Considerations 43
6554A 6555A
18,000µF 8,000µF
6553A 6554A
440µF 120µF
30 mΩ 80 mΩ