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How To Minimize Ripple In DC Power Supplies

July 14, 2017

AMETEK Programmable Power DC power supplies convert AC power to DC power. While our supplies are very good at doing this, they're not perfect. On the output, there will be some small amount of AC still present. This is called ripple.

Minimizing ripple is important because excessive ripple because it can have adverse effects on the systems or circuits that a supply is powering. It can for example, cause measurement errors when a supply is powering instrumentation circuits or cause distortion when power audio circuits.

To see how ripple occurs, let's take a look at a simple linear power supply. Linear supplies generally use a transformer to convert 120 VAC or 240 VAC mains power to a lower AC voltage. That AC voltage is then rectified to convert the AC to DC. A full wave rectifier will convert the AC voltage to the DC waveform shown as a dashed line in Figure 1.

To smooth that voltage we can put a filter capacitor across the output of the rectifier. It will charge when the rectified voltage is increasing and discharge when the rectified voltage is decreasing, but not discharge to zero. The voltage across the filter capacitor is shown as the orange line in Figure 1. The peak-to-peak value of the AC component of the voltage across the capacitor is the ripple voltage. The addition of a choke and a second capacitor to for a low-pass pi filter will reduce the ripple even more.

Of course, AMETEK Programmable Power supplies use much more sophisticated circuits to filter and regulate the output voltage. Our linear supplies, for example, use semiconductor voltage regulators to nearly eliminate ripple. The Sorensen XT Series, for example, has an output noise and ripple specification of less than 1 mV.

On most AMETEK Programmable Power data sheets, you'll find noise and ripple combined into a single specification. Noise is any added and unwanted electronic interference, and it's difficult to really differentiate how much of the unwanted output variation is due to ripple and how much is added noise. In switching power supplies, the measurement is given as a peak-to-peak voltage, indicating how much the output voltage can deviate from the nominal value.

For more information on power supply ripple, contact AMETEK Programmable Power. You can send an e-mail to sales.ppd@ametek.com or phone 800-733-5427.