QCL-LAB datasheet(20/24 Pages) WAVELENGTH

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ADDITIONAL TECHNICAL NOTES

This section includes useful technical information on these

topics:

•

Reduce internal temperature or provide compliance

voltage limit

•

Use Passive and Active interlocks

•

Soft-clamp current limit

•

Square wave response

•

Remove the bail and feet from an instrument

•

Update firmware

•

Determine firmware version installed

REDUCE INTERNAL TEMPERATURE

OR PROVIDE COMPLIANCE

VOLTAGE LIMIT

At full current, the Maximum Compliance Voltage available

to the QCL is about 7.5 V below the maximum supply

voltage. This 7.5 V estimate decreases as operating current

decreases. To determine the best internal supply voltage for

your application, follow these steps:

1. Wire your QCL to the instrument and adjust the current

limit on the Limit screen and setpoint on the Control

screen for your application.

2. Press the Enable button to enable the output current. The

actual current displayed should match the setpoint.

3. On the Limit screen, select the blue MAX Supply Voltage

value and, using the Adjustment knob, adjust it down

slowly until the actual current starts to decrease. The QCL

current is now limited by the compliance voltage of the

instrument.

4. Using the Adjustment knob, now increase the MAX

Supply Voltage value until the current is no longer below

the setpoint. This is the optimal maximum supply voltage

for your setup.

5. On the Monitor screen, observe the QCL Voltage. This is

the voltage across the QCL at this operating current and

is the effective voltage limit to the QCL for your setup.

NOTE:

If you reach 18 V on the MAX Supply Voltage

input and the current is still not compliance voltage limited,

the instrument is operating at its lowest voltage and the

voltage limit cannot be reduced further.

USE PASSIVE AND ACTIVE

INTERLOCKS

The passive interlock is designed to trigger if Pins 1 and 2 on

the QCL D-SUB are not shorted. Use this interlock with doors

and enclosures that trigger an open circuit when opened.

The active interlock (ACTIVE LOCK BNC) can be used with

a temperature controller or other active system component to

disable the current output if the QCL exceeds an acceptable

temperature operating range.

SOFT-CLAMP CURRENT LIMIT

The QCL driver employs a soft-clamping current limit that

begins to act at a current lower than the calculated absolute

current limit.

The Limit Current is the absolute current limit, which is the

current that will not be exceeded under any circumstance.

Because of the soft-clamp circuit, the actual current where the

limit circuit begins to act is 20% below the absolute current

limit.

NOTE: When operating at low currents around 100 mA

with the QCL500 LAB, the limit circuit begins to act around

32 mA below the absolute current limit.

If the output current is between this point and the Absolute

Current Limit, the output response to the analog input

setpoint is nonlinear. The result is that the drive current will

asymptotically approach the absolute current limit, and will

never exceed it even if the external modulation setpoint

voltage far exceeds the current limit.

Figure 22 illustrates the behavior of the soft-clamp current

limit. In this case the analog input voltage setpoint signal is

a triangle wave, with the amplitude set so that the driver will

attempt to overdrive the current limit.

Figure 22. Soft Clamping Current Limit Behavior

QCL-LAB Datasheet(PDF) 20 Page - Wavelength Electronics, Inc.

QCL-LAB Datasheet(HTML) 20 Page - Wavelength Electronics, Inc.

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