Supply ripple

Remember our circuit for a smoothed 12V supply ripple dc power supply. We found these waveforms in our supply.

The capacitor acts to store charge when the voltage rises, and releases it when it falls. During the time when the voltage from the transformer is low all the load current is supplied by the capacitor. This means there is an AC current through the capacitor – the “ripple current”. This ripple current causes heating in the capacitor, and over time can be destructive. For high power PSU’s we may need to determine the ripple current.

Here the RMS ripple current is 3. If the internal resistance of the transformer is low the shape of the ripple wave becomes more like a sawtooth. Here the transformer internal resistance is set as 0. However the ripple current also changes. Even though the load has remained the same, the behaviour of current through the capacitor has changed dramatically. The current pulses are shorter and more triangular in shape.

The RMS value of ripple current is now 4. 4A and the initial current pulse has doubled in size. 5A with maximum ripple voltage of 4V peak – peak. Calculating ripple current This is not straightforward. As a guide you can take the capacitor ripple current as being twice the load current. The slope gives the internal resistance.

Here’s how to build your own adjustable power supply based on LM317. The IC LM317 is so versatile that an almost unlimited number of different, small, high grade power supply circuits can be built using it. Let’s try to understand the circuit description of each of the following assorted LM317 circuits. The most fundamental circuit that can be built using an LM317 IC is shown below. The maximum current here is limited up to 1. The set up becomes ideally suitable for all small power supply applications, the IC being featured with complete over voltage, short circuit, over load and thermal run away protections is free from all voltage related hazards and thus becomes a favorite with new electronic enthusiasts.