The switching power supply more than twenty indicators(1)

Power supply is not a simple small box, it is equivalent to the heart of the active device, the source of energy to the components. The power supply is good or bad, directly affecting the performance of components. Power supply design, manufacturing and quality control testing requires sophisticated electronic equipment to simulate the actual operation of the power supply characteristics (i.e., the specifications), and to verify that they can be put into use.

Engineers should consider the following factors when designing or evaluating power supplies:

（1）Describe the input voltage affects the output voltage several indicators for

  1. Absolute voltage regulation coefficient

     ▅ Absolute voltage regulation coefficient: indicates that when the load is unchanged, the regulated power supply output DC variation △ U0 and input grid variation △ Ui ratio. That is: K = △ U0 / △ Ui.

     ▅ Relative voltage stabilization coefficient: When the load is unchanged, the ratio of the relative change of output DC voltage △Uo of the voltage st abilizer △Uo to the relative change of output grid Ui. That is: S = △Uo/Uo /△Ui/Ui. 

 2. Grid adjustment rate 

     ▆ It indicates that the input grid voltage changes ± 10% from the rated value, the relative change in the output voltage of the regulated power supply, sometimes also expressed in absolute terms.

3. Voltage Stability 

    ▆ Load current is maintained as any value within the rated range, the input voltage changes within the specified range caused by the relative change in output voltage △ Uo / Uo percent), known as the voltage stability of the regulator.

（2） Load on the output voltage impact of several indicators form

1. Load adjustment rate (also known as current adjustment rate)

▆ In the rated grid voltage, the load current from zero to the maximum change, the maximum relative change in output voltage, commonly used as a percentage, and sometimes also expressed as an absolute change.

2. Output resistance (also called equivalent internal resistance or internal resistance) 

▆ In the rated grid voltage, due to the load current change △ IL caused by the output voltage change △ Uo, then the output resistance is Ro = | △ Uo / △ IL | ohm.

（3） Several indicators of ripple voltage

 1. Maximum ripple voltage 

   ▆ In the rated output voltage and load current, the size of the absolute value of the output voltage ripple (including noise), usually expressed in peak-to-peak or RMS. 

 2. Ripple coefficient Y (%)

   ▆ In the rated load current, the output ripple voltage of the effective value of Urms and the output DC voltage Uo ratio, that is, y = Umrs / Uo x100%.

 3. Ripple voltage suppression ratio 

  ▆ Under the specified ripple frequency (e.g. 50Hz), the ratio of the ripple voltage Ui~ in the output voltage to the ripple voltage Uo~ in the output voltage, i.e.: Ripple Voltage Rejection Ratio = Ui~/Uo~ .

  　To be clear: noise is not the same as ripple. Ripple is a component synchronized with the input frequency and switching frequency appearing between the output terminals, expressed as peak-to-peak (peak to peak) value, generally below 0.5% of the output voltage; noise is a high-frequency component other than the ripple appearing between the output terminals, also expressed as peak-to-peak (peak to peak) value, generally around 1% of the output voltage. Ripple noise is the synthesis of the two, with peak-to-peak (peak to peak) value, generally below 2% of the output voltage.

（4） Inrush current

 Inrush current refers to the input voltage according to the specified time interval on or off, the input current to reach a steady state before the maximum instantaneous current. Generally 20A - 30A.

（5） Overcurrent protection Overcurrent protection

Overcurrent protection is a power load protection function to avoid the occurrence of overload output current including short circuit on the output terminals of the power supply and load damage. The given value of overcurrent is generally 110% - 130% of the rated current.

（6） Overvoltage protection

Overvoltage protection is a function of load protection against excessive voltage between terminals. General provisions for the output voltage of 130% - 150%.

（7） Output undervoltage protection

When the output voltage is below the standard value, the detection of the output voltage drop or to protect the load and prevent misuse and stop the power supply and send an alarm signal, more for the output voltage of 80% - 30% or so.

（8） Overheating protection

In the power supply internal abnormalities or due to improper use of the power supply temperature rise exceeds the standard when the power supply to stop the work and send an alarm signal.

（9） Temperature drift and temperature coefficient

Temperature drift: changes in ambient temperature affect the component parameters of the change, thus causing the regulator output voltage changes. Commonly used temperature coefficient indicates the size of the temperature drift.

Absolute temperature coefficient: temperature change of 1 degree Celsius caused by the output voltage value change △ UoT, the unit is V / ℃ or millivolts per degree Celsius.

Relative temperature coefficient: temperature change of 1 degree Celsius caused by the relative change in output voltage △ UoT / Uo, the unit is V / ℃.

（10） Drift

Voltage regulator in the input voltage, load current and ambient temperature to maintain a certain situation, the stability of the component parameters will also cause changes in the output voltage, slow changes called drift, fast changes called noise, between the two is called undulation.

There are two ways to represent drift:

1. the change in output voltage value within a specified time △ Uot.

2. the relative change in output voltage within a specified time △Uot/Uo.

The time for examining the drift can be set at 1 minute, 10 minutes, 1 hour, 8 hours or longer. Temperature coefficient and temperature drift are available only in higher precision regulators.