Introduction to the main technical indicators of the regulated power supply
The technical indicators of regulated power supplies can be divided into two categories: one is characteristic indicators, such as output voltage, output electric filter and voltage adjustment range; the other is quality indicators, which reflect the pros and cons of a regulated power supply, including stability , equivalent internal resistance (output resistance), ripple voltage and temperature coefficient, etc. · For the performance of the regulated power supply, there are mainly the following four requirements
1. Good stability
When the input voltage Usr (rectified and filtered output voltage) changes within the specified range, the change of the output voltage Usc should be very small. General requirements.
The degree of output voltage change due to input voltage change is called the stability index, which is often expressed by the voltage stabilization coefficient S:
The size of S reflects the ability of a regulated power supply to overcome changes in input voltage. Under the same input voltage change condition, the smaller S is, the smaller the output voltage change is, and the higher the stability of the power supply is. Usually S is approx.
2. Small output resistance
When the load changes (from no load to full load), the output voltage Usc should basically remain unchanged. The performance of this aspect of a regulated power supply can be characterized by the output resistance.
The output resistance (also known as the equivalent internal resistance) is represented by rn, which is equal to the ratio of the output voltage variation to the load current variation.
rn reflects the ability to maintain a constant output voltage when the load changes. The smaller rn is, the smaller the change in output voltage will be when Ifz changes. A stable voltage power supply with excellent performance, the output resistance can be as small as 1 ohm, or even 0.01 ohm.
3. The voltage temperature coefficient is small
When the ambient temperature changes, it will cause the output voltage to drift. A good regulated power supply should effectively suppress the drift of the output voltage and keep the output voltage stable when the ambient temperature changes. The drift of the output voltage is expressed by the temperature coefficient KT:
4. Small output voltage ripple
The so-called ripple voltage refers to the AC component of 50 Hz or 100 Hz in the output voltage, usually represented by effective value or peak value. After voltage stabilization, the ripple voltage after rectification and filtering can be greatly reduced, and the reduction factor is inversely proportional to the voltage stabilization coefficient S.
The series voltage regulator circuit introduced in the previous section is used as a simple voltage regulator power supply, which can meet the needs of general radio enthusiasts. However, this kind of power supply still has many "inherent" defects, and some improvements must be made to improve the performance requirements. Improve its performance from the following four right sides, and then it can be made into a regulated power supply with practical value. This is: increase the amplification link, improve stability, and make the output voltage adjustable; use a composite tube as an adjustment tube to increase the output current; add a protection circuit to make the power supply work more reliable.
