AAA Battery Protection with Wrong Polarity LED Indicator

This simple circuit will protect the AA or AAA battery from the wrong polarity connection to your device. If the battery is connected in the opposite way, D1 will conduct and PTC Fuse will break the circuit. Wrong polarity indicator, LED 1 will be turned on at the same time.

A Basic Transistor Amplifier with self-bias

This circuit will amplify the input signal with self-bias or feedback which can prevent amplitude distortion. However, it has two small drawbacks. It is only partially effective and, therefore, is only used where moderate changes in ambient temperature are expected. It reduces amplification since the signal on the collector also affects the base voltage. This is because the collector and base signals for this particular amplifier configuration are 180 degrees out of phase (opposite in polarity) and the part of the collector signal that is fed back to the base cancels some of the input signal. This process of returning a part of the output back to its input is known as DEGENERATION or NEGATIVE FEEDBACK. Sometimes degeneration is desired to prevent amplitude distortion (an output signal that fails to follow the input exactly) and self-bias may be used for this purpose.

Common Mode and Differential Mode Filters to limit EMI Issues

Noise can propagate in two major ways: Differential Mode (DM) Noise occurs between two conductors carrying opposing currents, such as the positive and negative lines in a DC circuit. Common Mode (CM) Noise appears in the same direction on both conductors relative to ground. Each sort of noise behaves differently, requiring a specific filtering technique.

This EMI filter consists of a common-mode filter and a differential-mode filter. Differential mode filters typically filter noise below 30 MHz, while common mode filters filter noise between 30 MHz and 100 MHz. Both filters affect the entire frequency range where EMI needs to be limited.

Simple Logic Gates using Diodes

Diodes can be used for implementing simple logic gates such as AND or OR combinations. For the AND gate, all inputs must be tied to high, 5V for the output logic high. For OR gate, the output is high if any input(s) are high.

Emergency Phone Charger From 3 x AA Battery with output Protection

Three AA batteries (3 x 1.5V) is used as emergency power sources for mobile devices or phone charging. Output current is limited to 0.5A and protected from out short circuit or high current drawn from the batteries.