Introduction to Main Technical Indicators of Regulated Power Supplies
The technical indicators of regulated power supplies fall into two categories. The first category refers to characteristic indicators, including output voltage, output current and voltage adjustment range. The second category is quality indicators which evaluate the overall performance of power supplies, such as stability, equivalent internal resistance (output resistance), ripple voltage and temperature coefficient.
The performance of regulated power supplies is mainly required to meet the following four standards:
1. High Stability
When the input voltage (output voltage after rectification and filtering) fluctuates within the specified range, the variation of output voltage shall be kept to a minimum.
The degree of output voltage fluctuation caused by input voltage change is defined as stability index, which is commonly expressed by voltage stabilization coefficient S.
The value of S reflects the ability of a regulated power supply to resist input voltage fluctuation. Under the same input voltage variation, the smaller the value of S, the slighter the output voltage changes and the higher the power supply stability.
2. Low Output Resistance
The output voltage shall remain basically unchanged when the load changes from no load to full load. This performance is measured by output resistance.
Denoted by \(r_n\), output resistance, also known as equivalent internal resistance, equals the ratio of output voltage variation to load current variation.
It represents the capacity to maintain stable output voltage under varying load conditions. The smaller the output resistance, the more stable the output voltage is against load current changes. High-quality regulated power supplies feature extremely low output resistance, which can reach as low as 1 Ω or even 0.01 Ω.
3. Low Voltage Temperature Coefficient
Ambient temperature change will lead to output voltage drift. A qualified regulated power supply can effectively restrain such drift and maintain stable output voltage, and this characteristic is represented by temperature coefficient \(K_T\).
4. Low Output Voltage Ripple
Ripple voltage refers to the 50Hz or 100Hz AC component contained in output voltage, which is usually expressed by effective value or peak value. Voltage regulation can greatly reduce the ripple voltage after rectification and filtering, and the reduction ratio is inversely proportional to the stabilization coefficient S.
The series voltage regulator circuit mentioned above can be made into a simple regulated power supply suitable for ordinary electronic application scenarios. Nevertheless, it has inherent defects and needs further optimization for higher performance requirements. Practical high-performance regulated power supplies can be developed through four improvements: adding amplifying circuits to enhance stability and realize adjustable output voltage; adopting composite transistors as regulating tubes to increase output current; equipping protection circuits to ensure reliable operation.
