Innovative CircuitsOutput Impedance vs. Frequency
What is Superpower's output performance under load? Amazing! Here is a graph of Zout vs.
frequency, showing a 7mΩ maximum impedance
while delivering 100mA at 40KHz. This is measured on a typical production SPL78 with 5V out.
How do we get such amazing performance? Sorry, that's a secret. But we can tell you how we measured it—we connected a resistor between the regulator output and a sine wave voltage source, then used a spectrum analyzer to measure the variation in regulator output voltage, which ideally is zero. The difference from zero equates to the output impedance of the regulator.
Test conditions
Vout=5V
DC load = 5mA
voltage at load resistor = (5VDC - 5Vpp)
dB measurements relative to 200mV full scale
| Frequency | 50Ω load (100mA pk-pk) |
| 10Hz | -80dB |
| 100Hz | -85dB |
| 1KHz | -83dB |
| 5KHz | -74dB |
| 10KHz | -71dB |
| 20KHz | -67dB |
| 40KHz | -63dB |
We know the current and the voltage so the values above are used to calculate output impedance. Using the spectrum analyzer full
scale value of 0.2Vpp, we see the following values for output impedance vs. frequency:
| Frequency | 50Ω load (100mA pk-pk) |
| 10Hz | 1.0mΩ | 100Hz | 0.56mΩ |
| 1KHz | 0.71mΩ |
| 5KHz | 2.0mΩ |
| 10KHz | 2.82mΩ |
| 20KHz | 4.47mΩ |
| 40KHz | 7.08mΩ |
Superpower Zout is low and flat across the entire audio band. We dare you to find or
build a better regulator! Below is a capture of the 20KHz measurement spectrum. Note that the noise floor
is due to the spectrum analyzer, not the Superpower.
Superpower, 100mApk-pk load at 10KHz
Spectrum of Superpower driving 100mA pk-pk into 50Ω.