PCX-7401 Pulsed Current Source

1. Description

The PCX-7401 is a precision pulsed current source for driving laser diodes, bars, and arrays. It delivers current pulses variable from 0.000 A to 3.000 A, with a bias current from 0.000 A to 0.550 A. An internal trigger provides pulse repetition frequencies from 5 Hz to 1.000 MHz and duty cycles of 1.00% to 99.00%. The internal single-shot pulse is adjustable in width from 200 ns to 1.000000000 second.

The system is fully adjustable from the color touch screen or a computer interface. Adjustments include the main output current amplitude, bias current amplitude, main pulse width, trigger source, trigger frequency, duty cycle, and single-shot pulse width. The bias feature delivers the current pulse in two steps: the bias DC turns on before the trigger time and sets the laser diode just below its trigger point (minimizing response time to the main pulse), and the main pulse adds to the bias current and triggers the diode at the intended time. The total output pulse is always the sum of the bias and main pulse currents.

The PCX-7401 can be triggered internally or externally and readily synchronized with other devices via a rear-panel Sync output. The external-trigger input termination is selectable for 50 Ω or 10000 Ω. The Sync amplitude varies between 0 and +5.0 V, its rising edge corresponds to the rising edge of the main output current pulse, and the delay between Sync and the main output pulse is ~100 ns. The unit can store four unique user settings.

2. Safety

Do not open the cover of the PCX-7401; there are no user-serviceable parts inside and opening the cover exposes you to shock and voids the warranty. Do not install, handle, or remove the output cables or laser diode while the unit is operating, and allow at least 10 minutes after power-down before handling the output cable or laser diode. Do not use the device in a manner not specified by the manufacturer. Allow sufficient space for air circulation (cooling air enters the front and exits the back). Do not use where liquids are present or in corrosive environments; clean by wiping with a dry or damp cloth.

3. Quick Start Guide

Before starting, make sure the PCX-7401 is connected with the proper cables and termination impedance, powered up, has all faults cleared, and has the rear enable and keyswitch enabled (the corresponding icons turn green when enabled).

Controlling from the front panel

Press the front-panel Enable button to disable the output (the green light goes out). Press Output on the touch screen, press the encoder knob to set the resolution, turn it to set the output current from 0.000 A to 3.000 A, and press Done. Press Bias and set the bias current from 0.000 A to 0.550 A the same way. Press Trigger and select Internal, External, or Single Shot. Set the internal frequency with the Frequency icon and the Duty Cycle icon as needed. Finally, press Enable — the button lights green.

Controlling from a computer

Send OUTPUT:DISABLE to disable, then set the trigger with TRIG:INTERNAL, TRIG:EXTERNAL, or TRIG:SINGLESHOT. Set frequency with TRIG:INT:FREQ n (n = 5 to 1,000,000 Hz), duty cycle with TRIG:INT:MAIN:DUTYCYCLE n (n = 1.00 to 99.00 %), output current with MAIN:CURRENT:SETPOINT n (n = 0 to 3000 mA), and bias with BIAS:CURRENT:SETPOINT n (n = 0 to 550 mA). Send OUTPUT:ENABLE to enable.

4. Front Panel Features

5. Rear Panel Features

6. Accessories & Output Cable

Included accessories: AC power cord (NEMA C14 to NEMA 5-15R); current/voltage monitor cable (PCA-9550) connecting the laser output PCBA to a monitoring instrument such as an oscilloscope; shorting BNC plug (PCA-9410) for the Rear Enable connector; keyswitch keys; and the laser output PCBA, which provides a connection to the laser and lets you monitor output current and voltage (current monitor J1 = 125 mV/A with a 50 Ω termination).

The output strip-line cable provides output current pulses via a DB-37 connector. The male DB-37 (to the instrument) has pins 1–16 as positive (+) output, pins 20–35 as negative (−) output, pins 17/36/37 no connection, and pins 18 and 19 connected together to satisfy the interlock. The female DB-37 (to the customer’s laser-diode board) has pins 1–16 positive (to anode), pins 20–35 negative (to cathode), and pins 17/18/19/36/37 no connection.

7. Operation

Setup. Make sure the unit has been off for at least ten minutes and the diode connection is the correct polarity (review the output-cable polarity specifications if needed). Make other connections as required (External Trigger, External Bias, Sync, Rear Enable, or the computer connection), then connect the power cable. Any change to a command adjustment typically needs <200 ms to complete.

Power up. Turn on the power switch; the instrument powers up in about 3 seconds, plays a tune, displays BNC information, and then shows the Home screen. The Home screen shows output current, bias current, frequency, trigger source, duty cycle, keyswitch, rear enable, output-connector, and internal-temperature status.

Set output and bias current. Press Output (command MAIN:CURRENT:SETPOINT) or Bias (command BIAS:CURRENT:SETPOINT), press the encoder knob to select a resolution (×0.001, ×0.010, ×0.100, ×1.000), turn it to set the value (0.000–3.000 A output; 0.000–0.550 A bias), and press Done.

Trigger, frequency, and duty cycle. Press the Trigger icon to select Internal or External (the unit defaults to Internal at power-up); for External, set the termination (50 Ω or 10 kΩ). Set the internal frequency with the Set Frequency icon (5 Hz to 1,000,000 Hz; resolution 5 Hz below 1 kHz, 100 Hz from 1.0–49.9 kHz, 1000 Hz from 50 kHz to 1 MHz) and the Duty Cycle icon (1.00%–99.00%).

Single shot. From the Trigger screen press Single Shot. Set the pulse width with the Pulsewidth icon (200 ns to 1.0000000 s; 100 ns resolution from 200–5,000 ns, 1 µs resolution from 6 µs–1,000 ms). Press Enable to produce a pulse of the programmed width. In single-shot mode the bias is a fixed pulse width before and after the main pulse.

Settings, save, recall, and power down. The Tools icon opens the Settings menu, where you can view unit information (*IDN?), configure communication ports (RS232 baud rate, USB, or Ethernet DHCP/Static), and save or recall up to five stored configurations (*SAVE n, *RECALL n). To power down, press Enable to disable, turn the keyswitch OFF, and switch the unit off at the rear.

8. Command Set

The PCX-7401 is controlled remotely via USB, Ethernet, or RS-232. Commands and queries must be in all capital letters; commands that require data (n) need a space between the command and the data. The end-of-line character is \n, and the unit returns a response for every command — wait for it before sending the next command. Any change typically needs <200 ms.

9. Warranty & Service

Berkeley Nucleonics Corporation (BNC) warrants equipment it manufactures to be free from defects in materials and factory workmanship under conditions of normal use, and agrees to repair or replace any standard product that fails to perform as specified within one year after the date of shipment to the original owner. OEM, modified, and custom products are warranted for ninety (90) days from date of shipment. The warranty does not apply to any product repaired or altered by unauthorized persons, subjected to misuse, neglect, or accident, or used other than in accordance with BNC instructions. Returns must be preauthorized and accompanied by a BNC return-authorization number.

Factory service and support. Berkeley Nucleonics Corporation, 2955 Kerner Blvd., San Rafael, CA 94901. Phone: (415) 453-9955 / (800) 234-7858. Email: info@berkeleynucleonics.com. Web: www.berkeleynucleonics.com. Document version 7650-0005 Rev D1.