Agilent Technologies 6621A User manual

APPENDIX E
OPTION 750
Operating Instructions for the Multiple
Output, Linear System DC Power Supply
Agilent Models 6621A, 6622A,
6623A, 6624A, 6625A, 6626A,
6627A, 6628A and 6629A
FOR INSTRUMENTS WITH SERIAL NUMBERS
Agilent Model 6621A; Serials US37370101 and above
Agilent Model 6622A; Serials US37360101 and above
Agilent Model 6623A; Serials US37360101 and above
Agilent Model 6624A; Serials US37350101 and above
Agilent Model 6625A; Serials US37380101 and above
Agilent Model 6626A; Serials US37370101 and above
Agilent Model 6627A; Serials US37350101 and above
Agilent Model 6628A; Serials US37380101 and above
Agilent Model 6629A; Serials US37380101 and above
For instruments with higher serial numbers, a change page may be included.
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Agilent Part No. 5957-6372 Printed in USA: 9/2000

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General Information
This document describes the operation of a discrete fault indicator (FLT), a remote inhibit (INH), and relay
controls (RLY), for the power supply. This information is in addition to the standard information provided in
the Operating Manual. The FLT, INH, and RLY circuitry is contained on a separate board (HP P/N 06624-
60025) inside the supply (See Figure 7). U204 and P209; located on the GPIB board, provide a path to transmit
signals between the GPIB board data bus and the Option 750 board.
Table 1. Specifications
FLT Indicator
VOH High-level output voltage: < 17.5V
VOL Low-level output voltage: < 0.5V
IOH High-level output current: < 10µA
IOL Low-level output current: ≤1.25mA
Isolation ≤42V from either terminal to ground
INH Input
VIH High-level input voltage: 2.1 to 5.25V
VIL Low-level input voltage: 0 to 0.7V
IIH High-level input current: < 20µA @ 2.7V
IIL Low-level input current: < 1.25mA @ 0.4V
tw Pulse Width Delay time: 20 mS typ.
RLY Controls
VOH High-level input voltage: ≤36V
VOL Low-level input voltage: ≤2V @ 120mA
VOL Low-level input voltage ≤0.5V @ 2mA
IOH High-level input current: ≤100µA
IOL Low-level input current: ≤120mA
CAUTION:Do not connect capacitive loads greater than 0.01µF maximum to the RLY controls.
FLT Indicator
The fault indicator (FLT) is: a low true, TTL compatible, open collector output, which indicates if any internal
fault register bits have been set. This provides a fault reporting capability that is independent of the GPIB SRQ
function. In other words, you don’t have to rely on your computer to inform you of a fault in the supply. You
can connect the fault indicator to the inhibit input to provide a back-up method of protecting a load. The FLT
signal is accessed through connector J702 on the rear of the supply (See Figure 1). The FLT terminals are
isolated from the chassis by an optoisolator, and may be floated ±42Vdc.
The FLT signal goes true when any unmasked bit in any of the fault registers is true. It goes false when all the
bits in all the fault registers are false (See Figure 2). Because each output has independent status and mask
registers, each output’s status register can be unmasked to generate the FLT signal for different reasons.

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Figure 1. FLT/INH/RLY Connections
Figure 2. Functional Relationship of Status Registers

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INH Input
The inhibit input (INH) is a low true, TTL compatible logic input, which is used to remotely disable all outputs
of the supply. It provides a way to disable the supply that is independent of computer control over the GPIB.
The INH input signal is applied through connector J702 on the rear of the supply (See Figure 1). In addition to
disabling the outputs, the INH input also opens all RLY terminals.
When the supply is disabled by the INH input, all outputs will remain disabled until the supply receives a
RIRST command (explained later). If the INH input is still true when the supply is reset, the outputs will not be
enabled.
The status register of each output contains an additional INH bit, which is available only with Option 750 (See
Figure 2). These INH bits all reflect the state of the single INH input. This allows INH to be unmasked to the
fault register to generate a fault or SRQ. INH is in the ninth position in each status register and has a bit weight
of 256. Note that the addition of a register bit does not require any change in the way that the standard
programming commands are used.
RLY Controls
The relay controls (RLY) are designed to be used with external user-supplied relay circuitry so that the outputs
of the power supply can be physically disconnected from the load (or system). These RLY controls are
available through connector J703 (See Figure 1). Each of the four RLY controls can sink 120mA for controlling
external relays directly from an external power supply. Because they are also open collector, they can also
provide low true, TTL compatible logic levels for connecting to a relay control box.
The RLY controls are programmed with the RELAY and OUT command (explained later). They can also be
operated using the front panel OUTPUT ON/OFF function key. Figure 3 shows how to connect either a relay or
a logic circuit to the RLY controls.
External Connections
As shown in Figure 1, mechanical connections to the FLT, INH, and RLY circuits are made through screw
terminals on the removable 4 and 8 position barrier blocks. These barrier blocks plug into the J702 and J703
connector sockets located on the rear of the power supply.
Loosen the screws on top of the terminal block. Strip your wires back approximately 0.2in. (5mm). Insert wires
fully into the screw terminals to prevent shorted connections. The screw terminals can accommodate wire sizes
from AWG 14 to AWG 28 (Metric 1.5-0.5mm2). Refer to the label above the terminal block to make sure that
you are inserting your wires into the correct opening. Tighten the screws onto the wires.
Note To prevent RFI interference, use shielded or twisted pair wiring for FLT and INH connections.
To prevent ground loops when shielded wire-is used, connect only one end of the shield to
chassis ground. INH low and RLY control low are connected to ground.

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Figure 3. Relay and Logic Circuits Connections
Additional and Changed Commands
The following power supply programming commands and queries have been added to the standard commands
(See Tables 5-1 and 5-2 of Operating Manual) to permit programming the supply with Option 750.
RELAY < ch >, < on/off > Opens (on/off = 0), or closes (on/off = 1) the RLY control for the specified
output channel (ch). All four RLY controls are available regardless of the
number of outputs in the power supply.
RELAY? < ch > Queries whether the RLY control for the specified output channel (ch) is open
or closed. The response is either 0 (open), or 1 (closed).
DC < ch >, < on/off > Turns the output off (on/off = 0), or turns the output on (on/off = 1) for the
specified output channel (ch) without affecting the state of the RLY controls.
DC? <ch> Queries whether the output for the specified channel (ch) is turned on or off.
The response is either 0 (off), or 1 (on).
DCPON < on/off > Sets the state of the output and RLY controls at power-on. For on/off = 0, the
outputs will be off and the RLY controls will be open. For on/off = 1, the
outputs will be on and the RLY controls will be closed. A CLR command will
put the outputs and RLY controls in the power-on state.
DCPON? Queries the power-on state of the outputs and RLY controls. The response is
either 0 (outputs off; RLY controls open), or 1 (outputs on; RLY controls
closed).

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RIRST Resets a remote inhibit (INH). The external remote inhibit signal opens all
RLY controls and turns off all outputs. RIRST returns the outputs and RLY
controls to their previously programmed state. If the remote inhibit signal is
still true when the RIRST command is programmed, the outputs remain off
and the RLY controls remain open.
The meaning of the following standard power supply programming command has been changed to permit
programming the supply with Option 750.
OUT < ch > < on/off > Programs both the output and RLY control for the specified output channel
(ch). For on/off = 1, the RLY control is first closed and then the output is
turned on after a 20ms delay. For on/off = 0, the output is turned off and the
RLY control is opened after a 20ms delay. Having the output off when the
RLY control changes state extends the life of the external relay.
Note This change to the OUT command also applies to the operation of the front panel OUTPUT
ON/OFF function key.
Operating Examples
The FLT/INH/RLY circuits can be used in a variety of applications as shown by the following examples.
INH Example
As shown in Figure 4, an external, normally open switch (S1) is connected to the INH input. This switch could
be attached to a hinged protection hood, which covers the power supply output terminals. When the hood is
lifted and the switch closes, the following action is taken by the supply:
1. The power supply outputs turn off and the RLY controls open.
2. The INH bit in the status and accumulated status registers is set true.
3. If the INH bit in the mask register has been unmasked, the INH bit in the fault register as well as the FAU
bit in the serial poll register will also be set true.
In this example, the computer would be made aware that a fault exists during a serial poll via the FAU bit in the
serial poll register. Merely closing the hood does not re-enable the supply. To re-enable the supply, first read
the fault register to reset the FLT line and INH bit. Then either send RIRST to restore the output of the supply
to the programmed values that were in effect before the supply was disabled, or send CLR to initialize the
supply to its power-on state (See Table 5-3 in Operating Manual). Note that the on/off state of the outputs and
RLY controls is determined by the DCPON command.

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Figure 4. INH Example
FLT/INH/RLY Example with Multiple Supplies
The setup in Figure 5 chains the FLT output of one supply to the INH input of the next supply. A fault
condition in any of the supplies causes all of the supplies to be disabled without computer involvement or
external circuitry. With four external relays connected to the RLY controls, the fault opens all externally
connected relays in addition to disabling the outputs.
The computer can be made aware of a fault via a service request (SRQ). Sending FAULT? and then RIRST,
restores the output of the supplies to their programmed values before the FLT circuit was tripped. Sending CLR
initializes the supplies to their power-on state (See Table 5-3 in Operating Manual). Note that the on/off state of
the outputs and RLY controls is determined by the DCPON command.
Figure 5. FLT/INH/RLY Example

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Principles of Operation
This section describes the operation of the FLT/INH/RLY circuits as shown in the schematic diagram
(Figure 7). The 662x supply automatically recognizes the presence of Option 750 via the ID line (J701/7)
(U214/8 is pulled high with Option 750 installed).
FLT CIRCUIT
The FLT circuit is shown at the top of Figure 7. U701 is driven by the PON line which momentarily holds U701
off when the supply is first turned on. This allows internal nodes within the supply to settle, and prevents false
triggering of any external FLT circuitry. After about one second, the PON line goes high and enables U701.
When the FLT line from the GPIB board goes high (indicating a fault), it causes the output of comparator U702
to go low. This causes current to flow through the diode of opto-isolator U701, which then triggers any external
circuitry connected to the FLT output on the rear of the supply. VR701 protects the FLT circuit by clamping
voltages at U701 to approximately 20Vdc.
INH Circuit
The INH circuit consists of R703 and VR702 (See Figure 7). It is activated by pulling the positive INH input to
ground. VR702 protects the INH circuit by limiting voltages at the INH input to approximately 6Vdc. Note that
correct polarity must be observed when connecting external circuitry to the INH input.
RLY Circuit
As shown in Figure 7, identical circuitry is used in all four RLY controls. The basic RLY circuit consists of a
Shottky diode, a MOSFET, and a 2.15 ohm resistor. These components are connected in series across the
connector terminals. The FET simply acts as switch to open or dose the circuit. It closes when the relay (RLY)
line goes high and positive gate voltage is applied to the FET gate. The zener diode across the FET and resistor
protects the circuit by limiting voltages at the connector terminals to approximately 47Vdc.
In addition to the basic circuit just described, there is additional circuitry consisting primarily of a voltage
comparator and a one-shot that protects the FET and resistor from damage due to excessive current (>140mA).
The voltage comparator compares the voltage drop across the 2.15 ohm resistor to a reference voltage. When
excessive current causes this voltage drop to exceed a predetermined limit, the output of the voltage comparator
goes low. This turns off the FET by removing its positive gate voltage. At the same time, the oneshot applies a
positive pulse to the negative input of the voltage comparator. This keeps the FET off for approximately 1.5ms.
At the end of 1.5ms, the FET is allowed to turn on again. If there is still excessive current flowing through the
RLY circuit, the previously described action is repeated.
Maintenance
The following tests can be performed to ensure that OPTION 750 is functioning properly. The FLT and INH
tests can be performed using either of two methods.
1. Using an external power supply (Agilent 6214B or equivalent), a 3K resistor (Agilent PN 0686-3025 or
equivalent), and an LED (Agilent PN 1990-0486 or equivalent).
2. Using an ohmmeter (Agilent 3456A, Agilent 3478A or equivalent).

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Fault Indicator (FLT) Circuit Testing
Using Method 1:
a. Connect the LED, resistor, and external 5V power supply to pins 1 and 2 of J702 as shown in Figure 6a,
and turn on the 662x power supply. The LED should be off.
b. Unmask the CV bit (bit 1) in the fault register by sending ’’UNMASK <ch>,1’’.
c. Check to see that the front panel display indicates the supply is in CV mode.
d. The LED should be on.
e. Reset the 662x supply by sending ’’CLR".
f. The LED should be off.
g. Turn off the 662x supply. This concludes testing of the FLT circuit.
Figure 6a. FLT Test Setup
Using Method 2:
a. Connect an ohmmeter* to pins 1 and 2 of J702 and turn on the 662x supply. The ohmmeter should indicate
a high** resistance.
b. Unmask the CV bit (bit 1) in the fault register by sending "UNMASK < ch > ,1".
c. Check to see that the front panel display indicates the supply is in the CV mode.
d. The ohmmeter should now indicate a low** resistance.
e. Reset the 662x supply by sending a ’’CLR’’.
f. The ohmmeter should now indicate a high** resistance.
g. Turn off the 662x supply. This concludes testing of the FLT circuit
* Note the polarity of your DMM’s ohmmeter output. Using an Agilent 3456A in two-wire, auto-range, the
polarity of the internal voltage is reversed (current flows from the - jack to the + jack) so the + jack of the
ohmmeter must be connected to the - pin of the FLT/INH circuit, or to the ground pin of the relay (RLY) circuit
under test. Using an Agilent 3478A the polarity of the ohmmeter is as shown on the front panel of the meter
(current flows from the + jack to the - jack).
** Depending on range and model number, low is generally less than 2K ohms and high is an open (overload).

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Remote Inhibit (INH) Circuit Testing
a. Turn on the 662x supply.
b. Momentarily short pins 3 and 4 of J702.
c. The front panel annunciator should indicate "RMT INHIBIT’’.
d. Turn off the 662x supply. This concludes testing of the INH circuit
Relay (RLY) Circuits Testing.
Using Method 1:
a. Connect the LED, resistor, and external 5Vpower supply to one set of relay output (RLY) pins on J703
(Refer to Table 2 and Figure 6b), and turn on the 662x power supply.
b. Send "RELAY <ch>, 0" to turn off the relay output under test.
c. The LED should be off.
d. Send "RELAY <ch>,1" to turn on the relay output (ch) under test.
e. The LED should be on.
f. Repeat steps a through e for each relay output < ch > .
Figure 6b. RLY Test Setup
Table 2. Relay Output Pins
Relay output J703 pins
<ch> +-
112
234
356
478