Vigitek QBU Series Pockels Cell Driver User Manual

Vigitek QBU Series Pockels Cell Driver

Important Information

Warning! This equipment produces high voltages that can be very dangerous. Please read user manual before starting operations.

Important note : please measure the output with symmetrical (differential) high voltage probe only. Measurement made with inappropriate equipment is a common cause of driver’s failure.

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Overview

QBU series Pockels cell drivers produce high voltage pulses with high repetition rates, fast rise times and fall times, adjustable voltage amplitude and pulse width. Two control types are available: manual and automatic.

Pulse Parameters

Module produces bipolar output. It means that 4kV pulse is physically formed by applying +2kV to positive output wire and –2kV to negative|
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Attention! Further description of HV output will be given in terms of voltage differences. Please keep it in mind!

Typical pulse shape|
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Risetime / Fall time| <15ns (about 10ns typ.) 1, 2
Pulse width| from 200 ns to DC
HV pulse amplitude| from HVMIN to HVMAX 3
Repetition rates| from single shot to ~50kHz (continuously) 2, 4, to ~100kHz (short-term) 2, 4
Internal timing 5| ~100us

1. At 10-90% level
2. Depends on HV pulse amplitude and load capacitance
3. HVMIN and HVMAX values see in How to order? section
4. Depends on working mode and cooling conditions
5. See description below

Internal Timing

Without Q-switch signal is switched driver maintains its state. Internal timer continuously refreshes driver condition every ~100us. It is cause of:

1. HV output levels have small ripple with period ~100us
2. It’s prohibited to trigger HV output level as internal timing is occurring.
   Therefore triggering of HV output is sometimes (very rarely) a little delayed.

Cooling

At middle and high operation frequencies (more than 5-10kHz) forced air cooling is required. The driver has internal protection from overheating – it automatically shuts down at ~70C.

Connections, Signals, Signal Descriptions

There are three connectors at Pockels cell “driver” board. Hereafter is description of corresponded female connectors (supplied with the board)

INTERFACE

(Molex 39-30-1060):

INTERFACE

is maintained correspondingly at 0V or HV level.
Sequences of triggering pulses with period less than approx. 1us are ignored by driver
2 (violet)| Temp Monitor|

This pin returns output voltage showing the internal temperature of the driver. Approximate U(T) dependence is given below.

3 (red)| +15 V| Provides +15V DC level
4 (blue)| Enable| The high voltage output is enabled by PIN4 (“1” – enable, “0” – disable)
5, 6 (black)| Interface Return| PIN5 and PIN6 are connected to the circuit ground of all internal circuits
7 (yellow)| HV Monitor| The voltage at PIN7 is a monitor signal proportional to the measured value of high voltage output.
HVMAX corresponds to 10V at PIN7, HVMIN corresponds to approx. 4V at PIN7.
8 (green)| HV Program| Positive DC voltage applied to PIN8 sets up high voltage value HV.
HVMAX corresponds to 10V at PIN8, HVMIN corresponds to approx. 4V at PIN8.

“0” means logical 0 low level (0V), “1” means logical 1 high level (5V)

INTERFACE CIRCUITS

Q-Switch|
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Enable|
HV Program and HV Monitor|
Temp Monitor|

+24V (Molex 39-30-1040):

+24V

cell driver
3, 4 (black)| RETURN| Return from power supply producing +24VDC

HV OUTPUT (Molex 39-30-1060):

HV Output

“ENABLE” JUMPER:

Use “ENABLE” JUMPER instead of “ENABLE” PIN4 of INTERFACE.
Don’t use “ENABLE” JUMPER and “ENABLE” PIN at the same time.

“HV PROGRAM” JUMPER AND “HV PROGRAM” TRIMPOT:

Use “HV PROGRAM” JUMPER instead of “HV PROGRAM” PIN8 of INTERFACE. If jumper is on it sets output voltage according to “HV PROGRAM” TRIMPOT state.
Don’t use “HV PROGRAM” JUMPER and “HV PROGRAM” PIN at the same time.

Safety

Warning! This equipment produces high voltages that can be very dangerous. Don’t be careless around this equipment.

• To provide safety the QBU-series Pockels cell driver module is designed to be powered with supply voltage +24VDC, which must be galvanically separated from mains.
• It is the user’s responsibility to ensure that personnel are prevented from accidentally contacting the QBU-series Pockels cell driver module, especially the high voltage connector and cable. Casual contact could be fatal. Output cables must have good isolation for output voltage and low capacitance.
• After shut down, do not touch the load until it has been discharged. Use an appropriate measurement device to check for complete discharge.
• Disconnect the QBU-series Pockels cell driver module from DC power supply before changing electrical or mechanical connections.

Operations

(Manual control)

1. Connect +24VDC power supply, pulse generator and Pockels cell
2. Set up “HV PROGRAM” JUMPER
3. Turn on +24VDC power supply
4. Set up “ENABLE” JUMPER
5. Use “HV PROGRAM” TRIMPOT to set up required output voltage
6. Send driving pulses from pulse generator to PIN1 of INTERFACE. Set both pulse length and distance between pulses not less than 1us
7. To power down the driver, turn off +24VDC power supply or remove “ENABLE” JUMPER

(Automatic control)

1. Connect +24V, INTERFACE and HV OUTPUT connectors to the board.

2. Remove “HV PROGRAM” JUMPER, remove “ENABLE” JUMPER

3. DISABLE the high voltage output

4. Apply the correct nominal DC INPUT power to the module

5. Set up the required output voltage by applying a DC voltage to the HV PROGRAM PIN8 of INTERFACE

6. ENABLE the high voltage output

7. Send driving pulses to PIN1 of INTERFACE.
   Too short pulses will be processed as 200ns pulses

8. To power down the driver, remove DC INPUT power or DISABLE high voltage output.

Measure The Output Voltage

Important note : please measure the output with symmetrical (differential) high voltage probe only. Measurement made with inappropriate equipment is a common cause of driver’s failure.

Specification

ELECTRICAL SPECIFICATION

section for the details)
HV basement level| 0V, fixed
Pulse width| From 200ns to DC
Risetime / falltime| ~10ns (10-90% level, warranted at load capacitance 11pF and below)
Jitter| ± 10ns (± 1ns in LJ-modification)
Delay time| 1us (100ns in LJ-modification)
Repetition rate| Up to 100kHz (see Performance section for details)
Cooling:| Forced air cooling at high repetition rates
Environment|
Operation temperature| +10…+40 C
Storage temperature| -20…+60 C
Humidity| 90%, non-condensing

MECHANICAL SPECIFICATION

DRAWINGS

How To Order?

QBU-XXYY-ZZ, where
XX codes the maximum output voltage (VMAX, user selectable up to 6000V), YY codes the minimum output voltage (VMIN, 40% of VMAX).
ZZ codes options:
LJ – low jitter option (mandatory for 6kV modification, optional for others) – jitter is as low as ± 1ns, delay time is as short as 100ns;

Examples (the most popular modifications):

QBU-5020
QBU-5020-LJ| 5000V| 2000V
QBU-4016
QBU-4016-LJ| 4000V| 1600V
QBU-3012
QBU-3012-LJ| 3000V| 1200V
QBU-2008
QBU-2008-LJ| 2000V| 800V
QBU-1004
QBU-1004-LJ| 1000V| 400V

Other modifications are available on request.

Performance

For continuous operation with the appropriate cooling we warrant the performance table as follows:

11 pF load capacitance

Voltage, kV| 2.0| 2.5| 3.0| 3.5| 4.0| 4.5| 5.0| 6.0
Max. rep. rate, kHz| 56| 40| 31| 24| 18| 15| 12| 9

In the burst-mode (= short time operations) performance is increasing approximately twice and may achieve 100 kHz value at low operating voltage and low load capacitance.
Higher load capacitance decreases the performance.

Note : modules with the higher performance are available on request.

Typical Output

• QBU-6024-LJ, Capacitance load 11pF + HV Probe (about 13pF), 6kV pulses
  
  
  

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