Driving Capacitive Loads With The HV1000 High Voltage Pulser

Three optional accessories for use with DEI's HV1000 high voltage pulser offers an economical solution to driving capacitive loads. These options facilitate driving capacitive loads without burdening the experimenter with the design and testing of circuitry to connect the load to the pulser. These options are:

• ST1 Series Termination Option, enables a small capacitive load to be pulsed with a fast rise time, low droop, and a slow fall time, with pulse widths to 10 microseconds.
• ST2 Shunt Termination Option, allows the load to be driven with pulse widths to 2 microseconds with fast rise and fall times.
• BT1 Bias Termination Option, applies a bias voltage of -1000V to +1000V to the capacitive load, allowing the HV1000 to pulse the load from this bias voltage.

When used in conjunction with these options, the HV1000 can drive capacitive loads with rise times <7ns, fall times <15ns and pulse widths from <55ns to 10 microseconds. Applications include pulsing extraction grids and deflection plates in time-of-flight (TOF) mass spectrometers and particle accelerators, Pockels cells, acoustic transducers and component testing.

The options are removable modules, therefore the HV1000 can be used without the options if needed. The BT1 option can be used in tandem with either the ST1 or ST2 termination options.

ST1 SERIES TERMINATION OPTION

The ST1 series termination option enables a small capacitive load to be pulsed with a fast rise time, low droop, and a slow fall time, with pulse widths to 10 microseconds. The pulse rise times will typically be as specified in the HV1000 data sheet, and the pulse fall time will be approximately 18-20 microseconds. An example waveform using the ST1 is shown in Figure 1.

The ST1 input connects directly to the output of the HV1000, therefore an interconnect cable between the pulser and the ST1 is not required. The ST1 is used with the HV1000 with the following configuration:

The average power dissipated in the ST1 terminator should be limited to 1W. For most applications operating under 500Hz, this limitation should not be a concern. The average power dissipated in the terminator can be calculated using the formula:

P is power in watts
twft is the output pulse width (flat-top portion)
Vout is the output voltage of the HV1000
f is the pulse recurrence frequency

ST2 SHUNT TERMINATION OPTION

The ST2 shunt termination module is installed at the end of the pulser's output cable, close to the capacitive load, allowing it to be driven with pulse widths to 2 microseconds and fast rise and fall times. The pulse rise and fall times will typically be as specified in the HV1000 data sheet. An example waveform using the ST2 is shown in Figure 3.

The ST2 is used with the HV1000 with the following configuration. The 50 interconnect cable between the ST2 module and the load should be as short as possible, preferably less than 6":

The average power dissipated in the ST2 terminator should be limited to 1W. For most applications operating under 500Hz, this limitation should not be a concern. The average power dissipated in the terminator can be calculated using the formula:

P is power in watts
twft is the output pulse width (flat-top portion)
Vout is the output voltage of the HV1000
f is the pulse recurrence frequency

BT1 BIAS TERMINATION OPTION

The BT1 bias module applies a bias voltage of -1000V to +1000V to the capacitive load, allowing the HV1000 to pulse the load from this bias voltage. Typical waveforms using the BT1 are shown in Figure 5.

The BT1 option must be used in conjunction with either the ST1 or ST2 option, and should be installed immediately after the ST terminator, between the terminator and the load. The 50 Ohm interconnect cable between the ST terminator and the BT1 should be as short as possible, preferably less than 6". The BT1 option requires an external DC bias supply.

When used with either the ST1 or ST2, the output waveform will be comparable to the typical waveforms shown in Figures 1 and 3, and will be offset from ground by the magnitude of the bias voltage, as shown in Figure 5. The BT1 is used with the HV1000 with the following configurations:

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