Output Isolation; Load Considerations; Capacitive Loads; Inductive Loads - HP 654 A Series Operating Manual

Output Isolation
The output of the power supply is isolated from earth ground. Either output terminal may be
grounded, or an external voiatage source may be connected between either output and ground.
However, both output terminals must be kept within ±240 Vdc of ground. An earth ground
terminal is provided on the rear panel for convenience, such as grounding wire shields.
Warning
The earth ground terminal on the rear panel is a low-noise signal ground for
convenience only. It Is not designed to function as a safety ground.
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 HP 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
40,000 mF 20,00 mF 12,000 7,000 ^F 3,000 mF 100,000 mF 50,000 30,000 hF 18,000 iiF 8,000
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 =
Rint + Rt
where: C s model-dependent internal capacitance (see below);
L
as inductance of the load;
fUxx
resistance of the load; Rjni
=
model-dependent internal resistance (see below)
S=
equivaiant series
6541A 6542A
6S43A e544A
6545A 6551A 6553A
6553A 6SS4A
65S5A
c=
4,200 *»F 550
180 mF 68 mF
33 ^F
10,000 mF 1100 nF
440 tiF 120 nF
50 >iF
Rint
—
7 mf)
SOmfl SOmO 125 mO
300 mil
4 mfl
20 mn 30 mn
80 mn 250 mn
6571A 6572A
6573A 6574A
6575A
C= 44,000 nF
44,00 mF 12,000 fiF
7,000 mF
2,100 fiF
Rint
=
1.8 mfl 2.2 mf) 4
mO 14 mO 30 mn
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 sma;t
2
Load Considerations
User Connections and Considerations 4-5