## What is a Bi-polar Power Supply? (Basic Knowledge)

The figure above shows an amplifier that can generate a voltage of ±10 kV from ±10 V. In other words, it can amplify the input voltage and output a voltage that is 1000 times greater (high voltage amplification). Basically, an amplifier has a sink function for the output current, and constant voltage operation is possible even with a capacitive load or an inductive load, or a composite load of both. In addition, because it responds at high speed, it is simply an ideal power supply.
Matsusada Precision offers a variety of high voltage amplifiers. Our single polar types have two-quadrant outputs (quadrants I and IV for the P series, II and III for the N series) while our bipolar output types provide full four-quadrant output:quadrants I, II, III, and IV. All of our products use a linear amplifier method and can achieve ultimate high speed response.

### Slew Rate

For the AMP series, AMS series, AMT series, AMJ series, and AS series, responsiveness is specified according to slew rate (SR). Therefore, the step response is as shown in the figure below.

The slew rate is expressed as SR = ΔV / μs, which is the amount of voltage change per unit time. The response time becomes shorter as the output amplitude becomes smaller. The AMP series has a maximum slew rate of 700 V/μs or greater, while the ultra high-speed AMPS series power sources can achieve a slew rate of 1200 V/μs or greater.

### Response Speed

The responsiveness of the AP series is specified according to frequency band. If the output is full swing with a sine wave at the rated resistance load, the amplifier cannot keep up as the input frequency becomes faster, resulting in a decrease in output amplitude. The response speed is defined as the frequency fc at which the output amplitude is 70% (= -3 dB).

If an accurate output waveform is required, use a high voltage amplifier with a frequency band that is sufficiently higher than the operating frequency.
Normally, this requires a frequency band that is 3 to 5 times faster when used with a sine wave and about 10 times faster when used with a square wave. If the frequency band is insufficient, not only does the output amplitude decrease, but the phase difference between input and output increases. Therefore, it is necessary to pay careful attention by monitoring the output waveform.

### Rise Time

Step Response: Responsiveness may be expressed as rise time.
Generally, the rise time of an amplifier with response speed, frequency band, fc (Hz) is found with the equation tr ≒ 0.35/fc.
Fall time tf is the same as tr.

If there is a capacitive load of 100 pF or more, including the stray capacitance of the output wire, output oscillation may occur. In that case, insert high-voltage resistors of between 100 Ω (at 0.1 μF) and 1 kΩ (at 1000 pF) into the output in series. Also, please note that when under capacitive load, the frequency band is restricted based on the equation on the right. In addition, when using corona discharge, etc., the electric current will exceed the rated current and adversely affect the power supply. In this case as well, limit the current by adding an output resistance just as the capacitive load.
* Avoid continuous use at high frequencies where the output amplitude of the high voltage amplifier will decrease. Otherwise, internal loss will increase and result in malfunction.

### Making Full Use of High-speed, High-voltage Amplifiers

High-voltage amplifiers have non-shielded type output wires. If the output wire is grounded and there is a stray capacitance between the line and the ground (or metal parts), there will be excess current as the output becomes a charge/discharge current when the output is an AC waveform or a step waveform.
Since this current flows in parallel with the load, the following phenomena might occur:
1. The slew rate and response speed decrease, 2. The output waveform becomes distorted and deformed.

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