Agilent Technologies 664xA, 665xA, 667xA, 668xA, AGILENT Model 6653A: 3145A-00551, Model 6641A: 3217A-00111, Model 6645A: 3215A-00111, Model 6651A: 3130A-00171, Model 6652A: 3201A-00381, Model 6654A: 3148A-00391, Model 6655A: 3152A-00176, Model 6671A: 3129A-00218, Model 6672A: 3138A-00101, Model 6673A: 3138A-00101, Model 6674A: 3133A-00161, Model 6675A: 3138A-00101, Model 6680A: 3302A-00101, Model 6681A: 3250A-00101, Model 6682A: 3339A-00101, Model 6683A: 3339A-00161, Model 6684A: 3339A-00101

User Connections

Series 664xA/665xA Power Supplies, Maximum OVP External Capacitance (µF)

6641A 6642A 6643A 6644A 6645A 6651A 6652A 6653A 6654A 6655A

700,000 35,000 15,000 7,000 3,000 1.6 (F) 100,000 50,000 18,000 8,000

If a load capacitance approaches the specified limit, it is recommended that you do not make it a normal practice of tripping

the OVP circuit and discharging the load capacitance through that circuit. This could cause long-term fatigue in some circuit

components.

Because of its high output voltage, the Agilent 6555A generates very high currents when discharging

the load capacitor under overvoltage conditions. Excessive currents can damage the supply. The peak

discharge current is limited by the sum of the external capacitor’s ESR (equivalent series resistance)

and the series resistance of the external circuit. For the Agilent 6555A external capacitance limit of

8,000 µF, this total resistance must be not less than 56 milliohms. For smaller values of external

capacitance, this resistance may be derated linearly.

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.

QRR

int ext

where: C = model-dependent internal capacitance (see below); L = inductance of the load; Rext = equivalent series

resistance of the load; Rint = model-dependent internal resistance (see below):

6641A 6642A 6643A 6644A 6645A 6651A 6652A 6653A 6654A 6655A

C = 4,200 µF 550 µF 180 µF 68 µF 33 µF 10,000 µF 1100 µF 440 µF 120 µF 50 µF

Rint = 7 mΩ 30 mΩ 50 mΩ 125 mΩ 300 mΩ 4 mΩ 20 mΩ 30 mΩ 80 mΩ 250 mΩ

Battery Charging

The power supply’s OVP circuit contains a crowbar SCR that effectively shorts the output of the supply whenever OVP

trips. If a battery (or other external voltage source) is connected across the output and the OVP is inadvertently triggered or

the output is programmed below the battery voltage, the power supply will continuously sink a large current from the

battery. This could damage the supply. To avoid this, insert a reverse blocking diode in series with the ⊕ output of the

supply. Connect the diode cathode to the + battery terminal and the diode anode to the supply ⊕ output terminal. The

diode may require a heat sink.

Note that if the OVP trips, you must remove the external current source in order to reset the internal SCR as part of clearing

the OVP circuit (see Clearing the OV Condition in “Chapter 5 - Front Panel Operation”).

Local Voltage Sensing

Your power supply was shipped set up for local sensing. This means that the supply will sense and regulate its output at the

output terminals, not at the load. Since local sensing does not compensate for voltage drops across screw terminals, bus

bars, or load leads, local sensing should only be used in applications that require low output current or where load regulation

is not critical.

Local sensing is obtained by placing the SENSE switch (see Figure 4-3a) in the Local position. The power supply is

shipped with the switch in this position.