The basic selection basis of switching power supply
First, the basic basis for selecting a switching power supply
Voltage and current range, which are the two easiest indicators to determine, as long as the power consumption of the circuit is calculated according to the circuit. Consideration should also be given to testing the high and low supply voltage poles.
Most fixed power supply allows the output voltage ± 10% of the range of changes, if this is not enough to meet the circuit requirements, the output can be adjustable or allow a greater range of changes in the power supply.
If the power supply to the combined device power supply, the device requires the maximum current of 75% to 90% by a power supply, not enough part can be connected to two or more power supply.
Second, the expansion and safety of switching power supply
1), parallel or series operation
When a power supply can not meet the required voltage or current range, two or more power supplies (or different outputs of the same power supply) can be used in parallel or series. In this mode of operation, the connection between the voltage regulator and control circuitry between the power supply modules still exists, except that one power supply is used as the main controller and the other power supply is used as the controlled party.
2),Overload protection
Because a power supply to supply different circuits, the current flow of these circuits may be unknown, in order to avoid damage to the power supply, the need to set the scope of the protection circuit.
Almost all power supplies have the following characteristics: when the output range is exceeded, either the output is maintained at the maximum output value or the power supply turns itself off. Some programmable power supplies, in addition to the programmable output range, can automatically set the type of output that the power supply stabilises. This means that the power supply can automatically change from a constant voltage source to a constant current source or from a current source to a constant voltage source when the voltage or current required by the external circuitry exceeds the set limit.
Adding a protection diode to the power supply prevents damage caused by misconnecting the polarity of the external power supply. Thermal sensors can also be used to prevent the power supply from burning out due to the power supply continuously operating in an overloaded state or ineffective cooling.
Third, the switching power supply potential causes damage to the root cause of internal
1), pulsation and noise
Ideal DC power supply should provide pure DC, however, there are always some interference, such as the superimposed pulsating current and high-frequency oscillations in the output port of the switching power supply. These two types of interference coupled with the power supply itself generated by the spike noise makes the power supply intermittent and random drift.
2) Stability
When the line voltage or load current changes elbow, the output voltage of the DC power supply will also rise and fall. The degree of voltage stabilisation is determined by the parameters of the voltage stabilisation circuit, which are the capacity of the filter capacitors and the rate of energy release.
If a relatively constant power supply is supplied to the power supply, then only basic load voltage stabilisation is required. The magnitude of the degree of stabilisation is generally defined as the percentage of output voltage at no load or full load, or the value of the change in voltage.
3), internal impedance
Relatively large power supply internal resistance to the load in terms of two unfavourable points, the first is not conducive to the work of the load voltage regulator circuit, more unfavourable is any change in the load current will lead to the DC power supply output of the ups and downs of this ups and downs on the test results of the impact of the same impulse with the impact of the noise caused by the results of the test is exactly the same.
4), switching power supply transient response or recovery
The size of the power supply transient response and recovery time indicates that the output load suddenly change, the power supply regulator circuit to restore the normal voltage ability of the size. There are two parameters to calibrate the power supply transient response and recovery: one is when the load suddenly changed when the output of the deviation value; the second is the output recovery to the original value of the time used. For the sake of uniformity, generally in the load change of 10%, the output deviation from the peak voltage with the output of the number of milliamps calibrated output deviation, with the output back to normal value of the number of millivolts used to calibrate the recovery time. Other manufacturers, use a larger change in load current to determine the recovery time. For example, the recovery time to normal value is measured using a 50 per cent to 100 per cent change in output current.
