PD200 V6 Manual
7
Rev 1.2, Released, 05-02-2018
8
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
No Load
520 kHz**
470 kHz*
310 kHz*
230 kHz*
10 nF
520 kHz**
470 kHz*
270 kHz
130 kHz
30 nF
370 kHz
180 kHz
91 kHz
43 kHz
100 nF
110 kHz
56 kHz
27 kHz
13 kHz
300 nF
37 kHz
18 kHz
9.1 kHz
4.3 kHz
1 uF
11 KHz
5.6 kHz
2.7 kHz
1.3 kHz
3 uF
3.7 kHz
1.8 kHz
910 Hz
430 Hz
10 uF
1.1 kHz
560 Hz
270 Hz
130 Hz
Table 3. Power bandwidth versus load capacitance and output voltage span
In the above table, the frequencies limited by slew-rate are marked with an asterisk, and the frequencies
limited by small-signal bandwidth are marked with a double asterisk. The slew-rate is approximately
150 V/uS which implies a maximum frequency of
𝑓
𝑚𝑎𝑥
=
150 × 10
6
𝜋𝑉
𝑝𝑝
In the following figures, the maximum peak-to-peak voltage is plotted against frequency and capacitance.
