Introduction to the Main Technical Specifications of Regulated Power Supplies
1. Good Stability
When the input voltage Uin (the output voltage of rectification and filtering) varies within the specified range, the change in the output voltage Uout shall be very small, which is the general requirement.
The degree to which the output voltage changes due to variations in the input voltage is called the stability index, usually expressed by the voltage regulation coefficient S:
The value of S reflects the ability of a regulated power supply to resist input voltage fluctuations. Under the same input voltage variation, the smaller S is, the smaller the output voltage change and the higher the power supply stability. Typically, S is approximately within a certain range.
2. Low Output Resistance
The output voltage Uout should remain essentially constant when the load changes (from no-load to full-load). This performance of a regulated power supply can be characterized by the output resistance.
The output resistance (also known as equivalent internal resistance), denoted as ro, is equal to the ratio of the output voltage variation to the load current variation.
ro reflects the ability to maintain a constant output voltage under load changes. The smaller ro is, the smaller the output voltage variation when the load current IL changes. For high-performance regulated power supplies, the output resistance can be as low as 1 ohm, or even 0.01 ohm.
3. Small Voltage Temperature Coefficient
Variations in ambient temperature will cause drift in the output voltage. A high-quality regulated power supply shall effectively suppress output voltage drift and maintain stable output voltage against ambient temperature changes. The output voltage drift is expressed by the temperature coefficient KT:
4. Low Output Voltage Ripple
Ripple voltage refers to the AC component of 50 Hz or 100 Hz in the output voltage, usually expressed by its effective value or peak value. Voltage regulation can greatly reduce the ripple voltage after rectification and filtering, and the reduction factor is inversely proportional to the voltage regulation coefficient S.
The series regulator circuit introduced in the previous section, as a simple regulated power supply, can meet the needs of general radio enthusiasts. However, this type of power supply has many inherent drawbacks. To improve its performance, further improvements are required. By optimizing its performance in the following four aspects, a practical regulated power supply can be developed:
Add an amplification stage to improve stability and realize adjustable output voltage;
Use a composite transistor as the pass transistor to increase the output current;
Add a protection circuit to ensure reliable operation of the power supply.
