Tech Tips

High Voltage Amplifier

High voltage amplifier converts input voltage to high voltage waveform as it is as shown in fig. 1. These days the demand of HV amplifier is growing more and more, and now becoming an indispensable tool for research and development, experiments and integrating to a system for such fields as electronics, physics, biochemical and medical industries. With high voltage technologies Matsusada Precision Inc. manufactures various High Voltage amplifiers to meet all requirements from customers.

* We have amplifiers developed specially for electrostatic chuck or PZT. Please ask for details to our sales staff.

This is the image of circuit to amplify input signal.
(fig. 1)

Four-quadrant Output Range

High Voltage amplifier is generally equipped with the "sink" function for output currents that provides constant voltage operation without regard to the type of load whether it is capacitive or conductive. (Fig.2) As it gives fast response, it is an ideal power supply for applications which require AC output.

Matsusada High Voltage amplifiers are all bipolar type and can be operated in full four-quadrant area. (I, II, III, and IV area)

  • Vomax: Rated output voltage
  • Iomax: Rated output current
A graph of DC and AC Operating range.
A graph of DC and AC Operating range.
(fig. 2) Voltage and Current operation range

Slew Rate

The responsibility of our high speed amplifier is determined with slew rate (SR). The step responsibility of our amplifier is as shown in fig. 3.

SR = ΔV/μS

In case of output amplitude is smaller the response time become shorter. AMP series reach to greater than SR = 700 V/µS at maximum.

This graph explains slew rate. It is defined as the amount of voltage change per unit time for an input signal.
(fig. 3)

Rise Time (step response)

Step response can be indicated with rise time. (fig.4) Usually the rise time of amplifier of response (= bandwidth) fc (Hz) is given by a formula below.

tr ≒ 0.35/fc.

The fall time tf is equals to tr.

This image explains rise time.
(fig. 4)

Frequency Response

Response of Matsusada amplifiers are described as "frequency bandwidth". When swing the output with sinusoidal waveform with rated resistive load, output swing (amplitude) is reduced as input frequency become faster. Frequency response in the specification is the frequency fc is where output swing is 70% (-3 dB). (fig. 5)
In case clear output waveform is required, please select a High Voltage amplifier which has high enough frequency bandwidth against required frequency. In general, three to five times more frequency bandwidth for sinusoidal waveform, and about 10 times more for rectangular waveform, is required. In case of insufficient frequency bandwidth the output swing shall be reduced, and also the phase difference be large, so some solutions, such as monitoring output waveform, shall be required.

This graph explains response speed which is defined in the frequency band.
(fig. 5) Declination of output swing by frequency

* Please avoid continuous inputting of high frequency signal which reduces output frequency of an amplifier. An amplifier will be broken because of increase of internal loss.

Capacitive Load

When a capacitive load of 100 pF or more (including stray capacitance of the output wire) is connected to power supplies, the output voltage may oscillate. In that case, install 100-ohm (@0.1 μF) to 1000-ohm (@1000 pF) of high voltage resistance in the output in series. Please note that the frequency band will be limited as the formula written in the right figure when an amplifier is used with a capacitive load.

Moreover, when an amplifier is used for the use such as a corona discharge, the current which is higher than rating will flow and it will affect the amplifier badly. In this case, as well as the time to use an amplifier with a capacitive load, please install the output resistance and limit the current.

This image explains frequency band when a capacitive load is connected.

* Please avoid continuous inputting of high frequency signal which reduces output frequency of an amplifier. An amplifier will be broken because of increase of internal loss.

Important note to utilize the full performance of high speed High Voltage amplifier

Output cable of High Voltage amplifiers is not shielded. If the output cable has some stray capacity against ground (earth ground or metal objects), output voltage will be sinusoidal or stop waveform and extra current will be drawn. As this current draw parallel to load, the following appearance might be happened.

  1. Slew rate or response frequency drop
  2. The waveform is distorted or changed
A conceptual diagram of leak current of High Voltage amplifier.

When there is output stray capacitance C the leak current by C will be as below.

formula
Solution

Make sure to have proper connection to make stray capasitance of High Voltage cable as low as possible.

  1. Keep the length of output cable as short as possible.
  2. Keep the output cable away from floor, desks, or metal objects.
  3. Have no shielding on the output cable.