OEM QBU-Mini Pockels Cell Driver User Manual

rev 1.06/2022 07 28

QBU-mini Pockels cell driver

User manual

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-mini-series Pockels cell drivers produce bipolar high voltage pulses with high repetition rate, fast rise time and fall time (typically ~ 10 ns), adjustable voltage amplitude and pulse width (from min. 200 ns to CW).

The module is bipolar. This means that e.g. 4 kV pulse is physically formed by applying +2 kV to the positive output wire and -­2 kV to the negative (see figure).
All mentions of HV output are given in terms of voltage differences. Please, keep this in mind!

The modules require +24 V DC power supply and pulse generator to set an operating frequency and pulse width. An output voltage level can be programmed in working range by user either manually (through onboard configuration trimpot) or remotely (applying a DC voltage to the respective pin).
Triggering by an external low voltage arbitrary TTL signal allows to set any output mode ­ base voltage (zero or HV), user-defined non-periodic pulses.

Interfaces / signals / descriptions

1. HV OUTPUT
2. INTERFACE
3. ENABLE jumper
4. HV PROGRAM jumper
5. HV PROGRAM trimpot
6. 24 V DC

ENABLE jumper:

One can use ENABLE jumper instead of ENABLE signal of INTERFACE to enable the HV output. It’s not recommended to use ENABLE jumper and ENABLE signal at the same time.

HV PROGRAM jumper and HV PROGRAM trimpot:

One can use HV PROGRAM jumper instead of HV PROGRAM signal of INTERFACE. If this jumper is set on, the output voltage is defined with HV PROGRAM trimpot state. It’s not recommended to use HV PROGRAM jumper and HV PROGRAM signal at the same time.

INTERFACE (Molex microfit 2×3):

Interface

maximal current capability is 100mA
2 ( blue)| Enable| Enables / disables HV output
(“1” – enable, “0” – disable)
3 ( yellow)| HV Monitor| The voltage at PIN3 is a monitor signal proportional to the measured value of the high voltage output

HVmax corresponds to 10V at PIN3,
HVmin corresponds to 4V at PIN3

4 ( green)| HV Program| Positive DC voltage applied to PIN4 sets up high voltage level HV

HVmax corresponds to 10V at PIN4,
HVmin corresponds to 4V at PIN4

5 (black)| Interface Return| PIN5 is connected to the driver’s ground circuit
6 ( orange)| Pulse| While “0” or ”1” is applied to PIN6 high voltage output is maintained correspondingly at 0V or HV level

Sequences of incoming pulses with period less than approx. 200ns will be ignored by the driver

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

+24V (Molex microfit 2×2):

+24V

Pockels cell driver
3, 4 (black)| RETURN| Return from +24V DC power supply

HV OUTPUT (Molex microfit 2×3):

Safety

Warning! This equipment produces high voltage that can be very dangerous. Be careful around the device!

• Avoid casual contacts of personnel with output cables and with the load
• Do not connect / disconnect cables while driver is turned on
• Do not operate with disconnected load
• Be very careful setting jumpers on and off and using HV PROGRAM trimpot; accidental contact to the board may be fatal; from the same point of view, it is recommended to control the driver not manually, but remotely via Interface connector
• Be careful with driver’s neighborhood; do not store disordered items close to any side of the driver
• Do not turn the driver on if it was already damaged with water, chemicals, mechanical or electrical shock; do not self-repair the driver

Operations (Manual control)

1. Connect +24 V DC power supply, pulse generator and Pockels cell to the QBU-mini driver

2. Set up HV PROGRAM jumper

3. Turn on +24 V DC power supply

4. Set up ENABLE jumper

5. Use HV PROGRAM trimpot to set up the required output voltage

6. Send driving pulses from pulse generator to PIN6 of INTERFACE.
   A time between switching (driving pulse width and interpulse interval) should be more than 200 ns. Faster logic signal changes will not be proceeded correctly

7. To shut down the driver, turn off +24 V DC power supply or remove ENABLE jumper

Operations (Automatic control)

1. Connect +24 V, 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 PIN4 of INTERFACE

6. ENABLE the high voltage output

7. Send driving pulses to PIN6 of INTERFACE.
   A time between switching (driving pulse width and interpulse interval) should be more than 200 ns. Faster logic signal changes will not be proceeded correctly

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

Technical notes

• Performance of the module greatly depends on load capacitance.
  Full performance is achievable at load capacitance < 11 pF.

Higher load capacitance decreases maximum possible repetition rate

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

Kept cool enough with forced air cooling, at low load capacitance and low operating voltage modules may achieve a performance up to 30 kHz (continuous mode) or 50 kHz (burst-mode). At the full load (3.5 kV, 11 pF) repetition rate is higher than 8 kHz.

• Sometimes output is delayed. If no switching of the output voltage occurs for a long time (about 100 us) the driver needs to refresh its state. During refreshment it’s prohibited to switch the output.

As a result, if pulse width is more than 100 us or if the distance between two sequential pulses is more than 100 us, sometimes switching of the high voltage output may be delayed. The delay time is about 150 ns.

Specifications

ELECTRICAL SPECIFICATION

Input

| +24V DC; 0.5A max
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Output

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Working mode

| repetition of the external TTL signal

HV higher level ¹

| adjustable in HVmin – HVmax range (see How to order? on p.9)

HV lower level ¹

| 0 V, fixed

Pulse width

| 200 ns – ∞

Max. repetition rate

| > 8 kHz at the full load (3.5 kV, 11 pF)

Rise / fall time

| < 15 ns, typ. ~10 ns

Jitter

| ± 2 ns typ.

Delay time

| 150 ns typ.

Protections

| from overheating (approx. 72 °C)

Environment

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Operation temperature

| +10…+40 °C

Storage temperature

| -20…+60 °C

Humidity

| 90%, non-condensing

¹ In terms of bipolar output
² 10-90% level, guaranteed at load capacitance 11 pF and below

We have also a short pulse modification of QBU-mini which is able to provide pulses with 100-2000 ns width, with much lower jitter (< 0.2 ns), small delay time (< 40 ns) and faster rise /fall (< 10 ns, ~7 ns typ.) Please, ask us or find QBU-mini-SP on our web site.

MECHANICAL SPECIFICATION

How to order?

QBU-mini-XXYY, where:
– XX codes the maximum output high voltage level (HVmax)
– YY codes the minimum output high voltage level (HVmin)

Examples (the most popular modifications):

Other modifications are available on request.

Performance

For continuous operation without any additional cooling a performance table is:

11 pF load capacitance

Voltage, kV|

1.0

| 1.5| 2.0| 2.5| 3.0| 3.5|

4.0

Max. rep. rate, kHz|

70

| 35| 23| 15| 10| 7|

5.5

In the burst-mode (= short time operations) if cooled properly, the performance increases 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

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