Basic theory of Linear supplies

The incoming ac voltage is stepped down to a lower ac voltage. For example, 120Vac is stepped down to 24Vac. The 24Vac is then rectified through a full-wave bridge rectifier, usually with a high-current, low-voltage bridge. A filter capacitor is used to maintain a constant dc level with minimum ripple.

The output voltage is controlled by a power transistor operating in its linear region. It acts as a variable resistor in series with the load. The power transistor receives its control from a circuit that senses output voltage. The control circuit modifies the transistor bias to maintain a constant voltage output, regardless of changes in the load current.

More on Power Supplies:

• Transformers Power Supplies
• Switching Transformers
• Linear Supplies
• Switching Supplies
• Advantages and Disadvantages