PX200 V2 Manual
7
Rev 1.1, Released, 15-01-2018
7
Power Bandwidth
Launch Online Power Bandwidth Calculator
The online power bandwidth calculator takes into account the current limit, slew-rate,
output impedance, and small-signal bandwidth.
With a capacitive load, the RMS current for a sine-wave is
𝐼
𝑟𝑚𝑠
=
𝑉
𝑝𝑝
𝐶𝜋𝑓
√2
where
𝑉
𝑝𝑝
is the peak-to-peak output voltage,
𝐶
is the load capacitance and
𝑓
is the frequency. Therefore,
the maximum frequency for a given RMS current limit
(𝐼
𝑟𝑚𝑠
),
capacitance, and voltage is
𝑓
𝑚𝑎𝑥
=
𝐼
𝑟𝑚𝑠
√2
𝑉
𝑝𝑝
𝐶𝜋
,
The above equation is also true for any periodic waveform, including triangle waves and square waves. This
property arises since the amplifier detects average current, which not affected by the waveform shape.
The ‘power bandwidth’ is the maximum frequency at full output voltage. When the amplifier output is
open-circuit, the power bandwidth is limited by the slew-rate; however, with a capacitive load, the
maximum frequency is limited by the RMS current and load capacitance. The power bandwidth for a range
of capacitive loads is listed below.
Load Capacitance
50V Range
100V Range
150V Range
200V Range
10 nF
222 kHz
111 kHz
74 kHz
55 kHz
30 nF
222 kHz
111 kHz
74 kHz
55 kHz
100 nF
222 kHz
111 kHz
62 kHz
35 kHz
300 nF
93 kHz
46 kHz
20 kHz
11 kHz
1 uF
28 kHz
14 kHz
6.2 kHz
3.5 kHz
3 uF
9.3 kHz
4.6 kHz
2.0 kHz
1.1 kHz
10 uF
2.8 kHz
1.4 kHz
60 Hz
350 Hz
30 uF
930 Hz
460 Hz
200 Hz
117 Hz
Table 3. Power bandwidth versus load capacitance and output voltage span
In the above table, the frequencies limited by slew-rate are shaded grey. The slew-rate is approximately
35 V/uS which implies a maximum frequency of
𝑓
𝑚𝑎𝑥
=
35 × 10
6
𝜋𝑉
𝑝𝑝
In the following figures, the maximum peak-to-peak voltage is plotted against frequency and capacitance.
