Output Resistance Index of Regulated Power Supplies
The output voltage Uo of the voltage regulator circuit is affected by three factors: input voltage UI, load current Io, and ambient temperature T
Uo=f(UI,Io,T)
So, the general expression for the change in output voltage of a regulated power supply can be expressed as Uo=f (UI, Io, T)
It can be seen that the four main indicators reflecting the quality of DC stabilized power supply are Su, Ro, ST, and Ur. The following are respectively explained:
(1) Input adjustment citation and voltage stabilization coefficient
We refer to the ratio of the change in input voltage after rectification and filtering to the change in output voltage caused by it as the input voltage regulation factor. In fact, the voltage regulation performance of a power supply is often characterized by the ratio of the relative change between the output voltage and the input voltage, which is called the voltage regulation coefficient. By definition, it can be recorded as
or
(2) Output resistance
The ratio of the change in output voltage to the change in load current under constant input voltage and temperature is defined as the output resistance, denoted as
The negative sign in the equation indicates that Δ Uo and Δ Io change in opposite directions.
(3) Temperature coefficient
When the input voltage and load circuit remain constant, the output voltage change caused by a unit temperature change is the temperature coefficient or temperature drift of the regulated power supply, denoted as
(4) Ripple voltage
At the rated operating current, the AC component value in the output voltage becomes the ripple voltage. The sign of the effective value of ripple voltage is Ur, and UIr can be regarded as the change in input voltage. Obviously, the voltage regulator circuit itself will suppress this variation. So Ur ≈ SuUIr
Sometimes the ripple suppression ratio is also commonly used to indicate the magnitude of the ripple voltage, written as 20lg (UIr/Ur) (dB). Obviously, the larger the ripple suppression ratio, the better.
For a high-performance voltage regulator circuit, the smaller the four indicators mentioned above, the better.
