PicoLAS LDP-V 75-200 Variable Pulses User Manual
- June 3, 2024
- PicoLAS
Table of Contents
PicoLAS LDP-V 75-200 Variable Pulses
How to use the Manual
Notice: Depending on the final application and operation regime this unit
must be assembled onto a heat sink or may stay non-cooled. Improper cooling
may cause damage to the electronic components. Please refer to section “Power
Dissipation” for more details on the thermal power losses during operation.
Before powering on your driver unit read this manual thoroughly and make sure
you have understood everything.
Caution: High voltages up to 200 V are present at several PCB components. Do not touch during operation.
Please pay attention to all safety warnings.
If you have any doubts or suggestions, please do not hesitate to contact us!
Dos and Don’ts
Never ground any output connector.
Never use any grounded probes at the output.
Do not connect your oscilloscope to the output!
This will immediately destroy the driver and the probe!
Do not connect voltages in reverse polarity to the device as there is no
built-in protection circuit.
Do use power-up sequencing: Allow the +5 V supply voltage to fully ramp
up before applying any other voltages (HV; Trigger Input).
Do not use mechanical force on the PCB components as they are fragile.
Resulting damages are not covered by warranty.
Beware: Some lab power supplies cause excessive ringing during powering
on and off. These may damage the unit!
Do keep connecting cables between power supply and driver as short as
possible.
How to get started
| Step | What to do | Check |
|---|---|---|
| 1 | Unpack your device. | |
| 2 | Attach the laser diode to the driver. | Please see section “Connection of |
the Laser Diode” for further details.
3| Assemble the driver onto an appropriate heat sink. This step may only be
omitted if the stress to the driver is kept very low.| See section “Power
Dissipation” for further information on thermal dissipation.
4| Connect GND, +20 V and HV+ to the 6 pin MOLEX 430450606 connector. Keep the
power supply off.| Please see section “How to connect the
Driver” for further details.
5| Connect the pulse generator to the SMA trigger input jack.| Ensure that no
pulse is fed before powering up the unit.
6| Carry out the power-up sequence as follows:
- Fully ramp up the +20 V rail
- Enable the HV+ supply Then feed a pulse signal to the input terminal. For example 5 V amplitude, 10 ns pulse width and 1 kHz repetition rate.
| Security advice : Do not touch the PCB components near the laser diode since they may carry high voltages up to 200 V.
Note : Observe the drivers limits as in section “Power Dissipation” to avoid overloading the driver.
7| Check the optical output of your laser diode.|
8| Turn off sequence: Disable the pulse generator and then turn off all power
sources (+20 V and HV+).|
Connection of the Laser Diode
Figure 1: Dimensions of bonding pads for the laser diode Figure 2: Close up of the LD pads; dimensions in milimeter
The LD- and LD+ pads are located in the upper edge of the driver. For the standard dimensions please refer to the dimensions in Figure 1. Both pads are also marked with + /- to indicate the correct polarity.
Many elements and parasitic “stray” components may affect the performance of the driver unit. The stray inductance of the load connected to the driver is very important. The term “load” not only includes the diode itself but also the packaging (bond wires!) and the connection between the driver and the diode. However, PicoLAS has no influence on these parts.
Refer to the PicoLAS Application Notes “Impedance of Diodes” and “LD- Connections” for more information on parasitic elements and their effect on the pulse shape. If you need a different pad sizes for your laser diode, please do not hesitate to contact us. Customized pad layouts are possible for adapting the dimensions of your load.
How to connect the Driver
Figure 3: Picture of the PCB layout
Signals of the 6 pin Micro-Match header:
| Pin | Name | Description |
|---|---|---|
| 1 | nc | nc |
| 2 | NTC | Internal 10 kOhms NTC versus GND for temperature monitoring, PT1000 |
B-value: 3850 ppm / K
3| GND| Ground return
4| GND| Ground return
5| HV+| External high voltage supply input (0 .. 190 V)
6| +20 .. 25 V| +20 .. 25 V supply voltage, connect to a stabilized power
supply
Trigger Input (7):
The trigger input requires a signal of 5 V and is terminated with 50 Ohms. The
input signal pulse width is in the range from 4 .. 100 ns. For more details
see the next section.
Security Advice:
Do not touch any leads of the output or the output capacitors as they can
carry high voltages of up to 200 V.
Pulse Input
The trigger generator must be capable of delivering 5 V into 50 Ohms and at
least 4 ns up to 100 ns pulse width.
Note: It is recommended to keep the trigger pulse width within the range of 4 .. 100 ns since longer pulses will increase the power loss.
Given a valid trigger signal the output pulse form depends only on the high voltage supply level and the laser diode’s characteristics.
Power Supply Requirements
The driver requires a stabilized +20 V supply (used by control logic).
Caution: The +20 V rail must be completely ramped-up within 2 ms to guarantee a proper start-up of the gate driver.
Adhere to the power-up sequence as follows:
- Fully ramp up the +20 V rail
- Enable the HV+ supply
- Apply trigger signal
Should you aim to connect a large number of driver units to a single power supply the high start-up current spikes can be taken care of by using an additional capacitor bank and hard power switching at its output. Failure to meet this requirement may cause the gate driver circuitry to stay in a faulty state.
Note: The HV+ laser diode supply can be interrupted at any time e.g. for safety reasons by the customer.
Current Consumption
Quiescent currents
| Supply input | Conditions | Min. | Max. | Unit |
|---|---|---|---|---|
| +20 V | 20 V .. 25 V | / | / | mA |
Trigger signal present
| Supply input | Conditions | Typ. | Max. | Unit |
|---|---|---|---|---|
| +5 V | 4.8 V .. 5.2 V | 0.3 | 1 | mA |
Cooling
The driver is base plate cooled only. Please assemble the entire unit to a
heat sink which is capable to take out the heat.
The heat sink is suitable if the system temperature does not exceed the
maximum operating limits.
Current Monitor
The trigger generator must be capable of delivering 5 V into 50 Ohms and at
least 4 ns in pulse width.
Given a valid trigger signal the output pulse form depends only on the high
voltage supply level and the laser diode’s characteristics. To illustrate the
driver’s behavior the following scope screenshot shows the current monitor
signal while the LD output is shorted.
The scaling of the current monitor Imon is 0.05 V/A or 20 A/V
Recommended Operating Conditions
| Supply voltages | Min. | Typ. | Max. | Unit |
|---|---|---|---|---|
| HV+ | – | – | +190 | V |
| +20 V | +20 | +24 | +25 | V |
| Trigger input | Min. | Typ. | Max. | Unit |
|---|
HIGH level input voltage
@ Zin=50 Ω
| 2.8| 5| +5.2| V
LOW level input voltage
@ Zin=50 Ω
| 0| 0| +0.8| V
Pulse width| 4| –| 100| ns
Repetition rate| –| –| 250| kHz
Absolute maximum Ratings (destroying limits)
| Supply voltages | Min. | Max. | Unit |
|---|---|---|---|
| HV+ | 0 | +190 | V |
| +20 V | 0 | +25 | V |
| Trigger input | Min. | Max. | Unit |
|---|---|---|---|
| Trigger signal voltage, unterminated | 0 | +5.2 | V |
Trigger Signal:
Note that the maximum ratings for both pulse width and repetition rate depend
on the actual high voltage supply (HV+). See section “Power Dissipation” for
guidance. Since the internal gate driver’s pulse width is limited to 20 ns
minimum, shorter pulses than 20 ns will not give any performance benefit.
However, longer pulse widths than 20 ns will add to the power loss (see
section “Recommended Operating Conditions” above).
The driving signal to the pulse input should be kept low while the +5 V supply voltage is down.
Dimension of Heat Sink and PCB
Figure
4: Dimension of heat sink and PCB
Position of Connectors and Mounting Holes
Figure 5:
Position of connectors and mounting holes