You're asking about types of Direct Current (DC) other than the "ideal" DC from a battery. Here's a breakdown

Ideal DC (Like from a Battery):
Characteristics

Perfectly constant voltage and current. A flat line on a graph.

Source

Primarily chemical sources like batteries or ideal theoretical sources.

Use

Used as a reference point or in simple circuits. Not really found in any practical implementations.

Real-World DC (Often called "Ripple DC" or "Filtered DC")

This is what you encounter in most electronics. It's DC that has some imperfections. It is still mostly DC, just has some degree of noise (AC components) and fluctuations in its voltage level.

Characteristics

The voltage is generally positive (or negative, depending on the polarity), but it fluctuates slightly over time. This fluctuation is called "ripple". A wobbly line on a graph that is generally on one side of the x-axis.

Source



Rectified AC

Most common. AC power from the wall outlet is converted to DC using diodes (a rectifier). The resulting DC is pulsating, so smoothing capacitors are used to reduce the ripple. Think of it like filling a bucket with a leaky tap. The capacitors act to smooth out the water level between drips.

DC Power Supplies

Regulated supplies attempt to provide a very stable DC output, but even they have some ripple. The degree of ripple may be very small, but it exists.

Solar Cells

Solar cells produce DC, but the output varies based on sunlight intensity.

Causes of Ripple



Imperfect Rectification

Diodes don't convert AC to perfectly smooth DC on their own.

Inadequate Filtering

The filter capacitors have to charge and discharge, creating voltage fluctuations.

Load Variations

Changes in the current drawn by the circuit can affect the output voltage of the power supply, causing variations.

Switching Noise

In switching power supplies (very common), the rapid switching of transistors can generate noise.

Why Ripple Matters



Circuit Performance

Excessive ripple can interfere with the proper operation of sensitive electronic circuits. It can cause: Noise in audio amplifiers. Errors in digital circuits. Instability in control systems.

Component Life

High ripple currents can cause increased heating in components, reducing their lifespan.

Electromagnetic Interference (EMI)

Ripple can radiate as EMI.

How to Reduce Ripple



Larger Capacitors

Using larger filter capacitors in the power supply.

Better Filtering Circuits

Using more complex filter designs (e.g., LC filters, active filters).

Voltage Regulators

These maintain a constant output voltage even when the input voltage or load current changes.*

Shielding

To reduce EMI caused by ripple.

In Summary:

When you talk about "proper DC," you're likely thinking of the idealized, constant voltage source. In reality, almost all DC power sources have some degree of ripple. The amount of ripple and the specific needs of the circuit determine how much filtering and regulation are required to achieve acceptable performance. Flag for review