Power supply is not a simple small box, it is equivalent to the heart of active devices, providing energy to components continuously. The quality of power supply directly affects the performance of components.
The design, manufacturing, quality management and other tests of the power supply require sophisticated electronic instruments and equipment to simulate the characteristics (i.e. specifications) of the power supply during actual operation, and can be put into use only after being verified.
The engineer shall consider the following elements when designing or evaluating the power supply:
I Describe several index forms of input voltage influencing output voltage
1. Constant voltage coefficient
A. Voltage stabilizing coefficient: it refers to the ratio of the output DC change △ U0 of the voltage stabilizing power supply to the change △ Ui of the input power grid when the load is unchanged. That is, K=△ U0/△ Ui.
B. Relative voltage stabilizing coefficient: it refers to the ratio of the relative change of the output DC voltage △ Uo of the voltage regulator to the relative change of the output grid Ui when the load is unchanged. That is, S=△ Uo/Uo/△ Ui/Ui.
2. Grid adjustment rate
It refers to the relative change of the output voltage of the stabilized voltage supply when the input grid voltage changes ± 10% from the rated value, sometimes expressed as.
3. Voltage stability
The load current is kept at any value within the rated range, and the relative change △ Uo/Uo percentage value of the output voltage caused by the change of the input voltage within the specified range is called the voltage stability of the voltage regulator.
II Several index forms of load influence on output voltage
1. Load regulation (also called current regulation)
Under the rated grid voltage, when the load current changes from zero to zero, the relative change of output voltage is usually expressed as a percentage, sometimes also expressed as a change.
2. Output resistance (also called equivalent internal resistance or internal resistance)
Under rated grid voltage, the output voltage changes △ Uo due to load current change △ IL, then the output resistance is Ro=| △ Uo/△ IL | Ω.
III Several Index Forms of Ripple Voltage
1. Ripple voltage
Under rated output voltage and load current, the ripple (including noise) of output voltage is usually expressed in terms of peak to peak value or RMS.
2. Ripple coefficient Y (%)
Under rated load current, the ratio of effective value of output ripple voltage Urms to output DC voltage Uo, i.e. y=Umrs/Uo x 100%
3. Ripple voltage rejection ratio
Under the specified ripple frequency (such as 50Hz), the ratio of ripple voltage Ui~in the output voltage to ripple voltage Uo~in the output voltage, namely: ripple voltage rejection ratio=Ui~/Uo~.
Here's a statement: Noise is different from ripple. Ripple is a component that appears between output terminals and is synchronous with input frequency and switching frequency. It is expressed by peak to peak value, generally below 0.5% of output voltage; Noise is a high-frequency component that appears outside the ripple between output terminals, and is also expressed by peak to peak value, which is generally about 1% of the output voltage. Ripple noise is a combination of the two, expressed in peak to peak value, which is generally below 2% of the output voltage.
IV Impulse current
Impulse current refers to the instantaneous current passed before the input current reaches a stable state when the input voltage is turned on or off at a specified time interval.
Generally 20A - 30A.
V Overcurrent protection
Overcurrent protection is a power load protection function to avoid damage to power supply and load caused by overload output current, including short circuit on output terminal.
The set value of overcurrent is generally 110% - 130% of the rated current.
VI Overvoltage protection
Overvoltage protection is a load protection function for excessive voltage between terminals.
It is generally specified as 130% - 150% of the output voltage.
VII Output undervoltage protection
When the output voltage is below the standard value, detect the output voltage drop or stop the power supply to protect the load and prevent misoperation and send an alarm signal,
Most of them are about 80% - 30% of the output voltage.
VIII Overheating protection
Stop the power supply and send an alarm signal in case of any abnormality in the power supply or excessive temperature rise of the power supply due to improper use.
IX Temperature drift and temperature coefficient
Temperature drift: the change of ambient temperature affects the change of component parameters, thus causing the change of voltage regulator output. The commonly used temperature coefficient indicates the size of temperature drift.
Temperature coefficient: the change of output voltage △ UoT caused by temperature change of 1 ℃, in V/℃ or millivolt per ℃.
Relative temperature coefficient: relative change of output voltage △ UoT/Uo caused by temperature change of 1 ℃, unit: V/℃.
X drift
When the input voltage, load current and ambient temperature of the voltage regulator are kept constant, the stability of component parameters will also cause changes in the output voltage. Slow changes are called drift, fast changes are called noise, and the intermediate changes are called fluctuation.
There are two ways to express drift:
The change △ Uot of the output voltage value within the specified time.
The relative change △ Uot/Uo of the output voltage within the specified time.
The time for investigating drift can be 1 minute, 10 minutes, 1 hour, 8 hours or more. Temperature coefficient and temperature drift are two indicators only in regulators with high accuracy.