PD200X4 V2 Manual
10
Modified 13/01/2021
10
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.
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 100V Range 150V Range 200V Range
No Load
470 kHz*
310 kHz*
230 kHz*
10 nF
470 kHz*
270 kHz
130 kHz
30 nF
180 kHz
91 kHz
43 kHz
100 nF
56 kHz
27 kHz
13 kHz
300 nF
18 kHz
9.1 kHz
4.3 kHz
1 uF
5.6 kHz
2.7 kHz
1.3 kHz
3 uF
1.8 kHz
910 Hz
430 Hz
10 uF
560 Hz
270 Hz
130 Hz
Table 4. 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
