ILX Lightwave LDX-3620 User manual

User’s Guide
Ultra Low Noise Current Source
LDX-3620
ILX Lightwave Corporation P. O.Box 6310 Bozeman, MT, U.S.A. 59771 :· · · 1-800-459-9459 · ·
www.ilxlightwave.com
U.S. & Canada International Inquiries: 406-586-1244 Fax [phone]
E-mail: [email protected]
70001802_7/01

Safety and Warranty Information
! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !
S AFETY AND W ARRANTY I NFORMATION
The Safety and Warranty Information section provides details about cautionary symbols used in the
manual, safety markings used on the instrument, and information about the Warranty including
Customer Service contact information.
Safety Information and the Manual
Throughout this manual, you will see the words Caution and Warning indicating potentially
dangerous or hazardous situations which, if not avoided, could result in death, serious or minor
injury, or damage to the product. Specifically:
!
CAUTION
Caution indicates a potentially hazardous situation which can result in minor or
moderate injury or damage to the product or equipment.
WARNING
Warning indicates a potentially dangerous situation which can result in serious injury or
death.
WARNING
Visible and/or invisible laser radiation. Avoid direct exposure to the beam.
General Safety Considerations
If any of the following conditions exist, or are even suspected, do not use the instrument until safe
operation can be verified by trained service personnel:
•Visible damage
•Severe transport stress
•Prolonged storage under adverse conditions
•Failure to perform intended measurements or functions
If necessary, return the instrument to ILX Lightwave, or authorized local ILX Lightwave distributor,
for service or repair to ensure that safety features are maintained.
All instruments returned to ILX Lightwave are required to have a Return Authorization Number
assigned by an official representative of ILX Lightwave Corporation.

Safety and Warranty Information
S AFETY S YMBOLS
This section describes the safety symbols and classifications.
Technical specifications including electrical ratings and weight are included within the manual. See
the Table of Contents to locate the specifications and other product information. The following
classifications are standard across all ILX Lightwave products:
•Indoor use only
•Ordinary Protection: This product is NOT protected against the harmful ingress of moisture.
•Class I Equipment (grounded type)
•Mains supply voltage fluctuations are not to exceed ±10% of the nominal supply voltage.
•Pollution Degree II
•Installation (overvoltage) Category II for transient overvoltages
•Maximum Relative Humidity: <80% RH, non−condensing
•Operating temperature range of 0 °C to 40 °C
•Storage and transportation temperature of ˘40 °C to 70 °C
•Maximum altitude: 3000 m (9843 ft)
•This equipment is suitable for continuous operation.
Safety Marking Symbols
This section provides a description of the safety marking symbols that appear on the instrument.
These symbols provide information about potentially dangerous situations which can result in death,
injury, or damage to the instrument and other components.
Caution,
refer to
manual
Earth
ground
Terminal
Alternating
current
Visible and/or
invisible laser
radiation
Caution, risk
of electric
shock
Protective
Conductor
Terminal
Caution, hot
surface
Frame or
chassis
Terminal
On: In position of a bistable push control. The
slash (I) only denotes that mains are on.
Off: Out position of a bistable push control.
The circle (O) only denotes that mains are off.
or
(I) or
(O)

Safety and Warranty Information
W ARRANTY
ILX LIGHTWAVE CORPORATION warrants this instrument to be free from defects in material and
workmanship for a period of one year from date of shipment. During the warranty period, ILX will
repair or replace the unit, at our option, without charge.
Limitations
This warranty does not apply to fuses, lamps, defects caused by abuse, modifications, or to use of
the product for which it was not intended.
This warranty is in lieu of all other warranties, expressed or implied, including any implied warranty
of merchantability or fitness for any particular purpose. ILX Lightwave Corporation shall not be liable
for any incidental, special, or consequential damages.
If a problem occurs, please contact ILX Lightwave Corporation with the instrument’s serial number,
and thoroughly describe the nature of the problem.
Returning an Instrument
If an instrument is to be shipped to ILX Lightwave for repair or service, be sure to:
1Obtain a Return Authorization number (RA) from ILX Customer Service.
2Attach a tag to the instrument identifying the owner and indicating the required service or
repair. Include the instrument serial number from the rear panel of the instrument.
3Attach the anti−static protective caps that were shipped with the instrument and place the
instrument in a protective anti−static bag.
4Place the instrument in the original packing container with at least 3 inches (7. 5 cm) of
compressible packaging material. Shipping damage is not covered by this warranty.
5Secure the packing box with fiber reinforced strapping tape or metal bands.
6Send the instrument, transportation pre−paid, to ILX Lightwave. Clearly write the return
authorization number on the outside of the box and on the shipping paperwork. ILX
Lightwave recommends you insure the shipment.
If the original shipping container is not available, place your instrument in a container with at least 3
inches (7.5 cm) of compressible packaging material on all sides.
Repairs are made and the instrument returned transportation pre−paid. Repairs are warranted for the
remainder of the original warranty or for 90 days, whichever is greater.
Claims for Shipping Damage
When you receive the instrument, inspect it immediately for any damage or shortages on the
packing list. If the instrument is damaged, file a claim with the carrier. The factory will supply you
with a quotation for estimated costs of repair. You must negotiate and settle with the carrier for the
amount of damage.

Safety and Warranty Information
Comments, Suggestions, and Problems
To ensure that you get the most out of your ILX Lightwave product, we ask that you direct any
product operation or service related questions or comments to ILX Lightwave Customer Support.
You may contact us in whatever way is most convenient:
Phone . . . . . . . . . . . . . . . . . . . . . . . . . . . (800) 459−9459 or (406) 586−1244
Fax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (406) 586−9405
Email. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . [e-mail]
Or mail to:
ILX Lightwave Corporation
P. O. Box 6310
Bozeman, Montana, U.S.A 59771
www.ilxlightwave.com
When you contact us, please have the following information:
If ILX Lightwave determines that a return to the factory is necessary, you are issued a Return
Authorization (RA) number. Please mark this number on the outside of the shipping box.
You or your shipping service are responsible for any shipping damage when returning the
instrument to ILX Lightwave; ILX recommends you insure the shipment. If the original shipping
container is not available, place your instrument in a container with at least 3 inches (7.5cm) of
compressible packaging material on all sides.
We look forward to serving you even better in the future!
Model Number:
Serial Number:
End−user Name:
Company:
Phone:
Fax:
Description or sketch of what
is connected to the ILX
Lightwave instrument:
Description of the problem:

i
Table of Contents
CHAPTER 1 - GENERAL INFORMATION................................................................................1
1.1 Introduction...............................................................................................................1
1.2 Product Overview.....................................................................................................1
1.3 Specifications............................................................................................................2
1.4 Options and Accessories........................................................................................3
CHAPTER 2 - OPERATION..........................................................................................................4
2.1 Introduction...............................................................................................................4
2.2 Installation.................................................................................................................4
2.2.1 AC Power Considerations...............................................................................4
2.2.2 Tilt-foot Adjustment........................................................................................4
2.2.3 Rack Mounting.................................................................................................4
2.3 Front Panel Controls and Connectors...................................................................5
2.3.1 DC Power ON/OFF and Range Selection......................................................5
2.3.2 Low Battery Indication....................................................................................5
2.3.3 EXT Modulation...............................................................................................5
2.3.4 Ramp Modulation.............................................................................................6
2.3.5 MODE Selector.................................................................................................6
2.3.6 LIMIT Current Adjustment.............................................................................6
2.3.7 OUTPUT On/Off...............................................................................................6
2.3.8 OUTPUT ADJUST Controls ...........................................................................7
2.3.9 DISPLAY Selector............................................................................................7
2.3.10 Output 4-1/2 Digit LCD Display.....................................................................7
2.3.11 OUTPUT SHORT Indicator.............................................................................7
2.3.12 OUTPUT ERROR Indicator.............................................................................8
2.4 Rear Panel Controls and Connectors...................................................................10
2.4.1 HIGH/LOW BANDWIDTH Selector...........................................................10
2.4.2 OUTPUT Connector (J401)...........................................................................10
2.4.3 PHOTODIODE Feedback Gain Adjustments .............................................10
2.4.4 PHOTODIODE Feedback Input Jack...........................................................10
2.4.5 RAMP TRIGger Output Jack........................................................................11
2.4.6 CHASSIS GROUND Connector....................................................................11
2.4.7 AC POWER/Battery Charge Switch............................................................11
2.4.8 Fuse Holder.....................................................................................................11
2.5 LDX-3620 Operation Procedures..........................................................................13
2.5.1 Outline of Operation.......................................................................................13
2.5.2 Load Considerations......................................................................................14
2.5.3 Safe Settings....................................................................................................15
2.5.4 Safety Interlock Connections.......................................................................15

ii
2.5.5 Laser Diode Connections and Shielding.....................................................16
2.5.6 Photodiode Feedback Connections.............................................................17
2.5.7 RAMP TRIGger Output Connections.........................................................17
2.5.8 Setting the LIMIT Current.............................................................................20
2.5.9 Setting the Output in CONST CURRENT Mode.......................................20
2.5.10 Setting the MODULATION Controls..........................................................20
2.5.11 Using the Internal RAMP Generator...........................................................21
2.5.12 Setting the Photodiode Feedback Gain.......................................................21
2.5.13 Setting the Laser Power in CONST POWER Mode...................................24
CHAPTER 3 - MAINTENANCE..................................................................................................27
4.1 Introduction.............................................................................................................27
4.2 Battery Maintenance..............................................................................................27
4.3 Battery Replacement..............................................................................................28
4.4 AC Line Voltage Selection....................................................................................28
4.5 Fuse Replacement...................................................................................................29
4.6 Calibration................................................................................................................30
4.6.1 Display Calibration.........................................................................................30
4.6.2 MONITOR Current Display Calibration......................................................31
4.6.3 OUTPUT ADJUST Calibration.....................................................................32
4.6.4 LIMIT Current Calibration.............................................................................32
4.6.5 RAMP SPAN Calibration..............................................................................32
4.7 Disassembly ............................................................................................................33
Index.........................................................................................................................................Index-i

1
Chapter 1
GENERAL INFORMATION
1.1- Introduction
This manual contains operation and maintenance information for the LDX-3620 Ultra Low
Noise Current Source and its options. Chapter 2 contains control and connector descriptions
and operation procedures. Chapter 3 has the theory of operation of the LDX-3620. Chapter 4
contains battery and maintenance information.
IMPORTANT
To those in a hurry to turn on and use the LDX-3620 without reading
Chapter 2 of this manual, it is recommended that the IMPORTANT
paragraphs be read since they contain information that may prevent the
destruction of expensive laser diodes (see IMPORTANT in the index). The
most important operating instructions are located in Section 2.5. Output
connector pin-outs are found in Figure 2.3. Recommended cable shielding
schemes are found in Figures 2.4 A through D and discussed in Sections
2.5.5 and 2.5.6. Figure 3.1 is a block diagram of the LDX-3620. Battery
maintenance information is found in Section 4.2.
1.2 The LDX-3620 Ultra Low Noise Current Source
The LDX-3620 Ultra Low Noise Current Source provides laser diode users a power source for
applications requiring current stabilities of better than 10 ppm and noise levels lower than 2
uA in the 5 Hz to 10 MHz band. Its features include:
* Low noise, battery based design
* Built-in battery charger
* High output stability
* Current limit protection
* Two output current ranges: 200 mA and 500 mA
* 4-1/2 digit resolution and display
* Monitor photodiode current display
* Photodiode feedback input for constant optical power operation
* Internal ramp generator with trigger output
* External modulation capability
* Low battery shutdown protection
* High/Low bandwidth switch

2
1.3 Specifications for the LDX-3620
OUTPUT 0-200 mA RANGE 0-500 mA RANGE
Output Current: 0-200 mA 0-500 mA
Compliance Voltage: >5 volts >4 volts
Noise and Ripple:
(5 Hz - 10 MHz bandwidth)
Battery operation <850 nA rms <2 uA rms
AC line operation <3 uA rms <8 uA rms
(5 Hz - 10 KHz bandwidth)
Battery operation <100 nA rms <500 nA rms
AC line operation <2 uA rms <6.5 uA rms
Noise Density:
(Battery Operation)
50/60 Hz 5.2 nA/rt Hz 11.5 nA/rt Hz
1 KHz 815 pA/rt Hz 2.6 nA/rt Hz
25 KHz 315 pA/rt Hz 795 pA/rt Hz
Stability:
10-20 seconds <0.1 ppm
3-5 minutes <1 ppm
10-30 minutes <10 ppm
Temperature Coefficient: <10 ppm/oC
Transients: <10 uA
Ramp Trigger: Ramp start trigger for oscilloscope output;
Optically isolated open collector TTL output
Ramp Flyback Time: 700 uSec, approximately
Output Connector: Shielded 9-pin D-sub on rear panel
CURRENT LIMIT
Range: 10-500 mA
Accuracy: +5 mA
DISPLAY
Type: 4-1/2 digit LCD
0-200 mA RANGE 0-500 mA RANGE
Resolution: 0.01 mA 0.1 mA
Accuracy: +0.05 mA +0.6mA
Reads units: LASER diode current inmA
MONITOR photodiode current inmA

3
MODULATION / FEEDBACK INPUTS
Photodiode Feedback
Input Type: Current input from external photodiode
Range: 20 uA to 2 mA for full scale output
Connectors: Rear Panel Isolated BNC Jack or
9-pin Rear Panel D-sub Connector
External Modulation Input
Bandwidth (3 dB point)
AC Coupled: 100 Hz to 1 MHz
DC Coupled: 0 Hz to 1 MHz
0-200 mA RANGE 0-500 mA RANGE
Transfer Function: 100 mA/V 250 mA/V
Connector: Isolated Front Panel BNC Jack
Internal Ramp Generator
Period: Adjustable 50 msec to 100 sec
Span Adjustment: 0-200 mA 0-500 mA
GENERAL
AC Power
Input Voltage Range 100-125 or 210-250 VAC
Line Frequency 50/60 Hz
Battery
+12 volt supply: 4.5 amp-hour sealed lead-acid battery (standard)
-12 volt supply: 1.2 amp-hour sealed lead-acid battery
Temperature Range
Operating: 0 to 40oC
Storage: -40 to 70oC
1.4 Options and Accessories
362038 Long Life Battery Option
The 362038 option is a second, user installable +12 volt battery which doubles the battery
operation time at 500 mA. Instructions for battery installation are included with the 362038
option kit.
132 Rack Mount Kit
The 132 rack mount kit enables installation of the 3620 into a standard 19 inch wide rack. All
hardware and instructions are included with the kit.

4
Chapter 2
OPERATION
2.1 Introduction
This chapter contains the following aspects of operation of the LDX-3620:
* General power and installation considerations
* A description of the front and rear panel controls and connectors
* Step-by-step instructions on the set-up and use of the LDX-3620
2.2 Installation
Sections 2.2.1 through 2.2.3 discuss topics related to the installation of the LDX-3620.
2.2.1 AC Power/ Battery Charge Considerations
The LDX-3620 is normally configured at the factory for your power line voltage. The unit can
be configured for 100-130 VAC or 210-230 VAC operation. Check to be sure that the correct
range is marked on the rear panel. If it is not correct, see Section 4.4 for the procedure to
change the line voltage range.
The AC power cord connects to the rear of the unit. Turning on the AC POWER switch on
the rear panel charges the batteries while permitting full use of the LDX-3620's functions;
however, noise will be increased in this configuration.
2.2.2 Tilt-foot Adjustment
The LDX-3620 can be tilted for easier viewing using the extensions on the front feet of the
unit. These extenders can be rotated 90 degrees until they lock into position. To put the
extenders flat against the bottom of the unit, firmly press them back.
2.2.3 Rack Mounting
The instructions and necessary hardware for mounting the LDX-3620 in a standard 19 inch
wide instrument rack are available in the model 332 Rack Mounting Kit. Contact the factory
for more information.

5
2.3 Front Panel Controls and Connectors
A brief description of the function of the front panel controls and connectors is contained in
the following subsections. Refer to Figure 2.1.
2.3.1 DC POWER Key Switch and Output Range Selection
A three position key switch on the front panel of the LDX-3620 controls the power to the
current source circuits:
* Off........................................................................................center position
* 200 mA ................................................................1/8 turn clockwise (CW)
* 500 mA ...............................................1/8 turn counter-clockwise (CCW)
The front panel power key switch operates independently of the rear panel AC POWER
switch. The rear panel switch controls only AC-line-power/battery-charge operation. With
the rear panel switch turned on, the power LED above the front panel key switch will light up,
indicating that AC power is on and that the batteries are charging.
2.3.2 Low Battery Indication and Shutdown
A "B" indicated on the display of the LDX-3620 means that the batteries should be
recharged. Repeated operation of the unit to the point where the low battery "B" is indicated
greatly reduces the battery life and is not recommended. See Section 4.2 for recommended
battery maintenance.
If the batteries continue to be discharged after the low battery "B" indicator appears,
shutdown circuits may turn off the output of the LDX-3620. Shutdown is indicated on the
display when all of the decimal points are displayed. Use of the instrument will be disabled
until the batteries have been recharged and the DC POWER key switch has been turned off
and then on again.
2.3.3 EXT Modulation
An external voltage wave form can be used to modulate the LDX-3620 output when the
modulation mode selection switch is set to either the EXT AC or EXT DC positions. The
external signal is input through the front panel EXT BNC jack and is AC or DC coupled
according to the mode switch position. The transconductance of the instrument is
determined by the output current range selected by the DC POWER key switch; it is 100
mA/V in the 200 mA output range, or 250 mA/V in the 500 mA output range. Under all modes
of operation, the output is clipped at the level set by the current LIMIT knob.

6
2.3.4 RAMP Modulation
The LDX-3620 output can be modulated using the internal ramp generator when the
MODULATION selector switch is set to the RAMP position. The ramp period is variable
between 50 mSec and 100 Sec via the RAMP PERIOD adjustment pot. The ramp peak-to-peak
amplitude is adjusted using the RAMP SPAN front panel pot. A DC offset may be added to
the ramp by using the OUTPUT ADJUST knobs.
Ramp fly-back time is approximately 700 microseconds. The ramp wave form will be clipped,
should it try to exceed the current limit.
2.3.5 MODE Selector
The front panel MODE switch selects the feedback mode of the LDX-3620. In CONST
CURRENT mode, the LDX-3620 is a voltage controlled current source that delivers a current
proportional to the sum of the MODULATION section and OUTPUT ADJUST knob control
signals.
In the CONST POWER mode, the LDX-3620 uses the photodiode feedback signal to
determine how much current should be output to the laser or LED to maintain a constant light
power. The output current increases until the photodiode feedback current equals a value
proportional to the control signal set by the MODULATION and the OUTPUT ADJUST
sections on the front panel. If the control signal is a DC level, then the output optical power
is held constant. If the control signal is modulated, then the output optical power is
modulated, so long as the bandwidth of the modulation is held below 20 Hz. Modulation
frequency components higher than 20 Hz are attenuated, and the modulation becomes a
mixture of optical-power modulation and current modulation.
2.3.6 LIMIT Current Adjustment
The LIMIT knob on the front panel sets the output current limit level. Setting this knob fully
clockwise (CW) limits the LDX-3620 output current to 500 mA. Setting it fully counter-
clockwise (CCW) limits the output to approximately 10 mA. The current limit is active in all
operating modes of the LDX-3620. A more complete description of how to set current limit
may be found in Section 2.5.8.
2.3.7 OUTPUT On/Off
The current output of the LDX-3620 is shorted by a mechanical switch and a JFET when the
front panel OUTPUT push button switch is in the OFF/SHORT position (out). When the
OUTPUT switch is set to the ON position, the short is removed and the JFET is turned off
slowly. This brings the output current up slowly to the level determined by the OUTPUT
ADJUST and MODULATION control signals.
When the output is shorted internally, the OUTPUT SHORT LED on the front panel will light
up.

7
2.3.8 OUTPUT ADJUST Controls
The OUTPUT ADJUST, COARSE, and FINE knobs set the DC output level of the LDX-3620.
The DC bias level is summed with the control signals derived from the MODULATION
section to determine the final output level.
2.3.9 DISPLAY Selector
The display of the LDX-3620 indicates the average output current of the unit when the
DISPLAY push button switch is in the LASER position (out). It displays the average
photodiode feedback current input to the rear panel when the DISPLAY switch is in the
MONITOR position (in).
Note: When in the MONITOR position (in), the display reads the negative value
of the average photodiode current. This reminds the user that the display switch
is in the MONITOR position.
2.3.10 Output 4-1/2 Digit LCD Display
The LDX-3620 output current and monitor photodiode current are displayed on a 4-1/2 digit
liquid crystal display on the front panel of the instrument. When the DISPLAY push button
is in the LASER position (out), the display reads the average current setting determined by
the MODULATION and OUTPUT ADJUST controls. It does so even when the OUTPUT
push button is in the OFF/SHORT position (out) and no current is delivered to the output.
The resolution of the display depends on the range selected by the DC POWER key switch:
0.01 mA in the 200 mA setting and 0.1 mA in the 500 mA setting.
When the DISPLAY switch is in the MONITOR position (in), the display reads the (negative)
average photodiode current input to the rear panel photodiode feedback inputs in
milliamperes. This reading is negative to remind the user that the display is in the MONITOR
position. The resolution of the display in MONITOR mode does not change with the output
range selected by the DC POWER key switch.
The display also announces low battery charge by indicating a "B".
If "low battery shutdown" occurs, the display reads zero current and all of the decimals are
displayed (see Section 2.3.2).

8
2.3.11 OUTPUT SHORT Indicator
The green OUTPUT SHORT lamp lights up when the output is shorted by setting the
OUTPUT on/off switch to the OFF/SHORT position (out). It is unlit when the OUTPUT is
ON.
2.3.12 OUTPUT ERROR Indicator
The red OUTPUT ERROR indicator lights up when:
*The output has reached the current LIMIT level, set by the LIMIT adjustment.
*The output circuit is open.
*The maximum compliance voltage of the LDX-3620 is insufficient to drive the load.
Table 2.1 lists the possible conditions leading to a lighted OUTPUT ERROR LED:
OUTPUT ERROR CONDITIONS
Condition Indicated By
Current Limit * OUTPUT ERROR LED is lit
* Display reads value of
LIMIT current
Open Circuit * OUTPUT ERROR LED is lit
* Display reads zero
Compliance Voltage * OUTPUT ERROR LED is lit
Exceeded * Display reads a non-zero value
less than the LIMIT current
Table 2.1 OUTPUT ERROR Conditions

9
Figure 2.1 LDX-3620 Front Panel
2.4 Rear Panel Controls and Connectors
The following sections contain brief descriptions of the functions of the rear panel controls
and connectors. Refer to Figure 2.2.
2.4.1 HIGH/LOW BANDWIDTH Selector
The BANDWIDTH selector switches a 0.1 uF capacitor in and out of the output circuit. This
capacitor is connected directly across the output current posts. The capacitor is connected
when the LOW bandwidth position is selected, and it is disconnected when the HIGH
bandwidth position is selected.
In the HIGH position the modulated output bandwidth of the LDX-3620 is 1 MHz. With the
switch in the LOW position the bandwidth across a 100 ohm load is cut to about 20 kHz. The
LOW setting decreases noise and prevents oscillation of the LDX-3620 when it is connected
to an inductive load, such as a bias "tee" circuit. This allows external modulation of the laser
diode using the LDX-3620 as a bias current supply.
2.4.2 OUTPUT Connector (J401)
The rear panel 9-pin D-sub connector (J401) pin-outs are shown in Figure 2.3. The LDX-3620
output current is sourced (+) from pins 8 and 9 and the current returned (-) to pins 4 and 5.
The monitor photodiode feedback current is input to pin 7 (+) and returned from pin 6 (-). The
feedback leads should be shielded with an earth-ground shield available on pin 3. Sections
2.5.5 and 2.5.6 contain more detailed information on connections and grounding.
Pins 1 and 2 of the rear panel OUTPUT can be connected to an external safety interlock

10
switch to disable the LDX-3620 current output when the switch is opened. See Section 2.5.4
for instructions on the connection of an interlock switch.
2.4.3 PHOTODIODE Feedback Gain Adjustments
The photodiode feedback circuit gain is adjustable on the rear panel to accept full-scale
feedback currents from 20 uA to 1 mA. An eight position switch provides COARSE gain
adjustment, while a four-turntrimpot provides FINE adjustment. The adjustment procedure is
described in Section 2.5.12.
2.4.4 PHOTODIODE Feedback Input Jack
The photodiode feedback current may optionally be input through a rear panel BNC jack.
This jack is connected in parallel with pins 6 and 7 of the rear panel 9-pin D-subminiature
connector.

11
2.4.5 RAMP TRIGger Output Jack
Optically isolated RAMP TRIGGER signals are output through two BNC jacks on the rear
panel. The OSCILLOSCOPE output delivers a 200 mV square pulse with rising and falling
edges of the pulse synchronized to the end and start of the output current ramp. This output
remains high during the rampflyback time of approximately 700 microseconds.
The OPEN COLLECTOR output is capable of driving a TTL load, but requires an external
supply and pull-up resistor. See Section 2.5.7 for connection information.
2.4.6 CHASSIS GROUND Connector
Chassis ground is available on the rear of the unit through a banana jack connected to the
LDX-3620 cabinet. When a three-wire line cord with earth-ground is used, the cabinet of the
LDX-3620 is connected to the ground lead of the power cord.
2.4.7 AC POWER/Battery Charge Switch
AC line power operation and battery recharge is accomplished by connecting the AC line
cord and turning on the AC Power switch on the rear panel. With this switch turned off, the
LDX-3620 draws power from its internal battery supply. For lowest noise operation, the AC
POWER switch should be OFF and the AC power cord disconnected.
2.4.8 Fuse Holder
The AC line fuse holder is on the rear panel. See Section 4.5 for fuse replacement information.