Output Noise; Stability; Series 657Xa Network - Agilent Technologies 654 A Series Operating Manual

Output Noise

Any noise picked up on the sense leads also appears at the output of the power supply and may adversely affect the load
voltage regulation. Be sure to twist the sense leads to minimize external noise pickup and route them parallel and close to
the load leads. In noisy environments, it may be necessary to shield the sense leads. Ground the shield only at the power
supply. Do not use the shield as one of the sense conductors
Note
Agilent 657xA Series - The signal ground binding post on the rear panel is a convenient place to ground
the sense shield.

Stability

Using remote sensing under unusual combinations of load-lead lengths and large load capacitances may cause your
application to form a low-pass filter that becomes part of the voltage feedback loop. The extra phase shift created by this
filter can degrade the supply's stability and result in poor transient response. In severe cases, this may cause output
oscillations. To minimize this possibility, keep the load leads as short as possible and tie wrap them together.
In most cases, following the above guidelines will prevent problems associated with load lead inductance. This leaves load
load-lead resistance and load capacitance as the major source of reduced stability. Further improvement to the stability of
the supply may be obtained by keeping the load capacitance as small as possible and by decreasing the load-lead resistance
by using larger diameter wires. However, if heavy gauge wire (≥AWG 10) is used, conditions may arise where the load-lead
inductance and load capacitance can form an undamped filter. This can actually reduce the damping in the system and create
a destabilizing phase response.
Note
If you need help in solving a stability problem with any Series 654xA, 655xA, or 657xA supply, contact
an Agilent Service Engineer through your local Agilent Sales and Support office.

Series 657xA Network

If a large bypass capacitor is required at the load and the load-lead length cannot be reduced, then a sense-lead bypass
network may be needed to ensure stability (see Figure 4-5). The voltage rating of the 33 µF capacitors should be about 50%
greater than the anticipated load-lead drop. Addition of the 20-Ω resistors will cause a slight voltage rise at the remote
sensing points. For utmost voltage programming accuracy, the supply should be recalibrated with the DVM at the remote
sensing points (see Appendix A).
46 User Connections and Considerations
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Figure 4-5. Series 657xA Sense Lead Bypass Network