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  MOST FREQUENTLY ASKED QUESTIONS
FQ 1001 What does the Compliance Voltage specification in laser diode drivers mean?
FQ 1002 Why is my PLD laser diode driver current limit disabling the output even when the output is below the limit current level?
FQ 1007 What limits the temperature control range of a temperature controller?
FQ 1009 Why won't my temperature controller settle my load to temperature?
FQ 1010 Why does it take so long to settle to the setpoint temperature?
FQ 1011 Why won't my load stabilize to your temperature controller specification?
FQ 1012 Why is my load heating when it should be cooling?
FQ 1013 Why is there electrical noise on the device I'm trying to temperature control?
FQ 1014 What DC power supplies do you recommend to achieve the stability specifications listed in your manuals?
FQ 1015 Should I use a switching power supply for my application?
FQ 1016 How do I view and print your manuals on-line?
FQ 1019 Which address do I use to remit payment or a purchase order?
FQ 1020 Can I buy from you or do I need to go through a distributor in my area?
FQ 1021 Do you take Credit Cards?
FQ 1022 Where do I send my unit for repair or calibration?
FQ 1040 What is the latest firmware version of the LFI3751?
FQ 1041 How do I tell what version of firmware my LFI3751 has in it?
FQ 1042 Where can I get the BenchLink software for the LFI3751?
FQ 1043 How often does the sensor circuitry update on the analog LFI3751?
FQ 1044 How often does the control circuitry update on the analog LFI3751?
FQ 1045 What is the accuracy of the thermistor bias current as a function of the supply voltage to which the bias resistor is connected?For example, what is the percentage change in bias current for, say, 1% and 5% changes in the supply voltage?
FQ 1047 I would like to know if my laser diode is of type B and I want to use it in constant current mode. The anode of the LD is internally connected to the case. Now I would like the case to be grounded, how should I connect it with the WLD3343 LD Driver? Ground the anode and then connect the cathode to pin 11? Can pin 11 supply a negative voltage so that the LD can be lit up?
FQ 1048 How do I know whether or not I need a heat sink or a fan on my WTC3243 thermoelectric temperature controller?
FQ 1049 How do I know whether or not I need a heat sink or a fan on my WLD3343 laser diode driver?
FQ 1050 I use the WLD3343 in collaboration with the WHY5640 and a Peltier element to keep the laser diode temperature constant. After I set the LD current to 40mA and start changing the temperature from about 16C to 50C the LD current starts to rise to 60mA.

Does that have to do with the characteristic's of the LD? I know that some things vary depending on the temperature but then I would expect the WLD3343 to adjust the current. It does keep the current constant very well if the temperature stays constant.
FQ 1051 With the WLD3343, I discovered a normal delay between the SHD signal and power to the Laser Diode (slow start). I need to produce pulses of zero to set power (which is set in VSET), and 100 to 1000ms width. I thought to use SHD control, but the delay is a problem. Which is the best way to put the LD on and totally off with no (or little) delay? Or, how much is this delay, in msec, in order to modify the control software? Eventually, I can use constant power or constant current mode.
FQ 1052 I want to drive a 1550nm laser diode, 5mW output, <150mA of current, at a modulation frequency of 1-2MHz. The WLD3343 will do this fine, right? At 1 or 2MHz mod, what modulation depth do you typically see with the WLD? The next step will be to go to a 10MHz modulation frequency, will the WLD be OK? We want the best modulation depth we can get. Will we see 100% depth at 1MHz, and do you have a feeling for the modulation depth we would get at 10MHz?
FQ 1054 Can you give me some hints for minimizing current noise when using the WLD3343?
FQ 1055 I'm using the WTC3243 to drive a TEC using a 10kΩ thermistor. How do I get a measurement of the actual temperature (or something proportional to it)?
FQ 1056 What is the display accuracy of the LFI3751?
FQ 1057 I am planning on using the WHY5640 with the WEV302 heatsink/fan assembly. How is the WXC304 fan terminated (i.e. what type of connector, if any, is on it)?
FQ 1058 What are the pressure vs. air flow characteristics for the WXC303 fan?
FQ 1060 My question has to do with the EXT VSET connector on the WTC3243. How is the voltage I apply to the EXT VSET related to the temperature setting? What is the relationship between this applied voltage and the temperature that will result as the set value? I can not find a transfer function in the manual.
FQ 1061 My question has to do with the EXT VSET connector on the WLD3343. How is the applied EXT VSET voltage related to the current supplied to the LD in CCmode? Is it a 1:1 ratio? Also, in CP mode, how is the applied voltage on EXT VSET related to the photodiode current?
FQ 1062 What is the compliance voltage for the WTC3243-B?
FQ 1063 I have a 4.5V TEC that can draw (up to) 2.85A. Based on your WTC3243 datasheet I believe I would require a supply voltage of 6.06V. I will limit the current applied to 2.3A via the current-limit resistors. Based on the info in your datasheet I will be running in zone 2 (middle shade of blue) of your "Safe Operating Area" plot. This indicates to me that my design will require a heatsink plus a 3.5CFM fan. Am I more or less correct here?
FQ 1064 I have a WTC set up so the current limiting is set to 1.2A (3.12 Kohms) on the cooling side (LIMA) and 0A (1.5 Kohms) on the heating side (LIMB). Why is the WTC3243 able to put out as much as 1.8A when the set point called for more cooling current than the LIMA setting was supposed to allow? Just how 'hard' is the current limiting---brick wall cutoff or really soft, or somewhere in between?
FQ 1065 What is the heatspreader temperature rise with the heatsink and fan attached?
FQ 1066 I am using the WTC3243 and I would like to know if I could use a single power supply for both VDD and VS?
FQ 1067 Using the WTC3243 for controlling the temperature of an aluminum block, at 1A with a 12V power supply, what is the power generated?
FQ 1068 I am developing a new design with the WTC3243 and WLD3343. Is it necessary to feed both circuits with a regulated power supply? Is a rectified voltage with a "smoothing" capacitor sufficient?
FQ 1069 What is the difference between the WTC3243 Rev A and Rev B?
FQ 1071 Would any overheating issues arise from placing the WLD3343 and WTC3243 in a closed area ~ 7"x5"x3"? If so, would the associated thermal solution kits help to relieve this problem?
FQ 1072 How can I master/slave WLD3343's to be used in constant current mode?
FQ 1073 We have a requirement for the WLD3343 laser diode driver for +5V or +12VDC operation. Can it be used for driving a 4W CW laser diode whose threshold current is 1.5A? The diode is to be operated in common cathode configuration.
FQ 1074 I am designing a laser driver circuit using the WLD3343. On page 8 of the data sheet there is a discussion about choosing R(LIM). Apparently, R(SENSE) sets the allowable current range of the laser driver, and R(LIM) then limits the actual current limit to something less than what R(SENSE) allows. The first paragraph says "Divide the maximum laser diode current (determined in Section 1) into the desired maximum operating current for your laser diode." Following the interpretation above, that means dividing a larger number into a smaller number, which is greater than 1. Following example 1, I believe that I want the reciprocal of that number. Are these correct interpretations?
FQ 1075 I'd like to use the WLD3343 Driver and WLD3393 Demo Board to modulate a laser in constant power mode. Do I need any additional or external circuitry?
FQ 1076 We would like to use the WLD3343 and WTC3243 to control a fiber-coupled laser diode which has laser diode anode ground. This ground is connected via the case to the thermistor ground. We are not using the photodiode, we scan through a range of currents to wavelength-tune the laser. When I look at your specification for the WLD3343, the picture on page 13 shows the laser diode anode connected to pin 14 i.e. 5V. None of the other circuits show a grounded laser anode. Is the WLD3343 in fact compatible with an anode ground system? I'm worried because I can't see how it can be, if its supply is 0 and 5V, yet I need to connect the cathode to something less than 0V.
FQ 1077 I am using a WLD3343 (with heat sink and fan) with a laser diode (2W, photodiode and LD isolated, B type). It needs approximately 2.5A to deliver the 2W. The problem is that I get less than about 1.7A from the WLD3343. It is connected using constant power mode, Rsense: 0.5Ohm and 1K preset for Rlimit. Vmod is 0 to 2V (to adjust power). When Vmod=2V, I adjust Rlimit and the current goes up until 1.7A and stops there. I am using a 5V supply and the LD drops 2V, so I think that the compliance is OK, but eventually I can use more voltage (6V, still in the safe operation area).
FQ 1078 We're working with the WLD3343 in constant current mode, and we think we observe a non linearity between VSET and ILD. Is the non-linearity normal? Should we use external feedback between IMON and VSET?

We chose RSENSE = 0.35 Ω to get 2 A, trim RLIM not to exceed 2 A, and we adjust R between pins 5 and 6 to get 1 A output with VSET = 1 V.

FQ 1079 We are using the WLD3343 with a C-mount 2W 808nm diode, and questions about how to handle the laser and controller. What handling precautions do you recommend? And what should we be concerned about when were configuring the driver with the laser?

Also, we want to make sure were minimizing current noise to the laser. Do you have any recommendations for noise and transient suppression filters?

FQ 1080 What is the best way to minimize electrical noise in the driver output current when using the WLD3343 Laser Driver?
FQ 1081 Can the WLD3343 laser diode driver be externally modulated with an analog signal, if so what would be the bandwidth?
FQ 1082 What sensor would you recommend to be used with the WTC3243 temp controller: an AD590 temp transducer or a thermistor? Would a larger mass increase the stability?
FQ 1083 Battery power for Laser Drivers and Temperature Controllers - can the laser diode driver and temperature controller be powered by batteries directly?
FQ 1085 Do the temperature controllers always provide full current to the driven element (a TEC or Peltier device, or resistive heater) when the actual temperature does not equal the set point temperature?
FQ 1086 Do you have a chart indicating the relationship between the resistance of the setpoint and the current of the thermoelectric?
FQ 1087 How do you determine where the "load lines" will be and calculate their positions on SOA charts?
FQ 1089 Using the LFI3751, we fail to get any output voltage. On start-up its temperature display is flashing although no other LED is flashing simultaneously (none of the four red error LEDs). While flashing it appears to show the temperature correctly. When we try to enable the output, the instrument gives a long tone, but fails to reset and to output a voltage.
FQ 1090 Can I use an MPT to control a resistive heater?
FQ 1091 Can I use two PLD10000 or PLD10K-CH laser driver modules connected in parallel to feed a single laser diode (or diodes) to achieve up to 20 Amps of drive current?
FQ 1092 What are the dimensions of your thermistors?
FQ 1093 What is the thickness of the plastic on the Wxx products' case (WLD3343 Laser Driver, WTC3243 Temperature Controller or WHY5640 Temperature Controller) and what is the thermal conductivity of the plastic case?
FQ 1094 What is the thickness of the plastic on the WTC3243 case and what is its (the plastic case's) thermal conductivity?
FQ 1095 I have a temperature controller and laser diode driver that have been discontinued. They are designed into a system that we still use but appear to not be functioning correctly. Do you offer repair or calibration services for discontinued items?
FQ 1096 I am looking for a temperature controller so that I can maintain a constant 37°C in a petri dish. This application would require internal immersion heaters.
FQ 1097 We are building a prototype laser cooling system that needs to control the temperature of two thermoelectric coolers (Melcor part: CP1.4-127-10L) connected in series. Each TEC has the following operating specifications:

Qmax = 33.4 Watts

Delta Tmax = 68°C

Imax = 3.9 Amps

Vmax = 15.40 Volts

Module Resistance = 3.44 Ohms

Will the HTC3000, 3.0 Amp product and it's evaluation board be a suitable controller for this application since the TECs won't really be driven too hard (except maybe at start-up)? Would a 24 V power supply be sufficient to drive these TECs if they were connected in series?
FQ 1098 The Wavelength Electronics WLD3343 datasheet specifies the constant current control short term stability (1 hour) and long term stability (24 hours) each at 25°C. I would like to know the dependence of the laser/light regarding the temperature. What happens, when we use the WLD3343 at -50°C or +110°C for example, because the device is specified for -65°C to 150°C.
FQ 1099 Is it possible to have access to the potentiometer of the MPT5000 (temperature setpoint adjust, p-gain adjust) from the outside? We plan to use the MPT5000 for an integration in a laser controller for control with a front panel.
FQ 1100 What is the highest output current temperature controller that Wavelength Electronics currently offers?
FQ 1101 I have a question related to the use of the Analog Input of an MPT10000 temperature controller with an RTD. The sensor we are using is a PT100, with the sensor bias current set for 1 mA.

We want to change the set point temperature using an external voltage applied to the Analog Input (Pin 6 on the MPT Series Temperature Controllers). We would like to set the set point to 20C, and apply an analog input that will change the set point up to 40C or down to 0C.
FQ 1103 Is it possible to apply a negative voltage to the Analog Input (pin 5) on the MPT Series Controllers?
FQ 1104 On the MPT, is the analog ground (Pin 5) internally connected to the power supply ground (pins 14 & 15)?
FQ 1105 We operate a WLD3343 and a WTC3243 together from one power supply and want to build this in series and need to specify the power supply:
1) What stability of the power supply is necessary, what ripple is allowed?
2) Do you have any kind of overload protection?
3) Would it do any harm to have a capacitor (i.e. 470pF) in parallel to the laser diode?
FQ 1106 I have a MPT10000 and am wondering about the proportional gain: the potentiometer turns endlessly, there is no left or right stop, I want to know how to obtain a value of the set gain, is there a way of getting a 0-5 V readout?
FQ 1108 What is the shelf life of the thermal paste?
FQ 1109 When using a PTC Temperature Controller, if I set the temperature set point below approximately 0.3 V, the set point always reverts to approximately 1.0 V. What is happening and how can I implement a set point voltage below 0.3 V?
FQ 1110 What are the differences between the PTC Series Temperature Controllers and the MPT Series Temperature Controllers?
FQ 1111 I'm unable to measure any voltage on the photodiode (PD) monitor output of my WLD3343, even when I increase the drive current to the limit. Do you have ideas for trouble-shooting?
FQ 1112 I'm using the WLD3343 and the WLD3393 evaluation board, but my laser does not have a photodiode. How do I wire my laser to the WLD?
FQ 1113 I need to drive approximately 4 A to my laser diode. Should I use the MPL7500 or the PLD5000?
FQ 1115 I would like to run the Benchlink software on a 64-bit Windows OS, but it won't install
FQ 1116 When I open a datasheet or other download in PDF, there are corrupted characters in the file. This is particularly noticeable when I print the document from the PDF. What's wrong?
FQ 1117 The temperature of my Resistive Heater is slow to stabilize and is not within specification.
FQ 1118 How do I determine whether to operate in Constant Current (CC) or Constant Power (CP) mode?
FQ 1119 How do Product Variations work?
FQ 1120 What does the Compliance Voltage specification in temperature controllers mean?
FQ 1121 How do I install a remote Enable/Disable Switching Circuit?
FQ 1123 How do I wire a Nortel Laser with the anode externally grounded to the LDD Series driver and the HTC Series temperature controller?
FQ 1124 What is the difference between the QCL OEM and the QCL OEM(+)?
FQ 1125 How do I wire my Quantum Cascade Laser (QCL)?
FQ 1126 What power supply should I use with the QCL OEM Driver?
FQ 1127 The PLD current does not match my external setpoint. What can I do to fix it?
FQ 1128 What is the best way to wire a resistive heater to my temperature controller to gain compliance voltage?
FQ 1129 How do I modify the default remote SET T voltage in the PTCxx-CH?
FQ 1145 The Status Byte Reporting Structure images in the Command Set document are missing lines when I print out the PDF.
FQ 1146 How do I upgrade my QCL LAB firmware to use the TMC Command Set and Labview Virtual Instrument?
FQ 1147 My QCL LAB isn't working with the Quick Connect Application (QCA). Why?
FQ 1148 My QCL LAB isn't working with the LabView Virtual Instrument or the Command Set. Why?
FQ 1149 How do I upgrade the firmware on my TC LAB instrument?
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