How to classify switching power supplies
All the switching power supplies we have come into contact with operate on the principle that the adjustment tube works in the switching state. The excitation voltage for driving the adjusting tube can be a square wave pulse width modulation voltage, or a sine wave resonance voltage.
Switching power supplies can be divided into self-excited and other-excited according to the way the excitation voltage of the regulator tube is generated.
The self-excited switching power supply uses the regulator tube and the auxiliary winding of the switching transformer to form a forward and flyback loop to realize self-excited oscillation and stable voltage output.
Since the adjustment tube of the self-excited switching power supply also serves as an oscillation tube, there is no need to set up an additional oscillator. Its pulse signal is formed by self-excited oscillation, which is a non-fixed frequency pulse signal that changes with the input voltage and load.
The frequency is high at light load, low at heavy load, and intermittent oscillation occurs at no load.
The self-excited switching power supply itself has a certain self-protection function. Once the load is too heavy, it will inevitably destroy the feedback condition and stop the oscillation, thus protecting the switching power supply.
Due to its high current peak value, large ripple current, especially poor stability when working with high power and high current, it is mostly used in low power applications below 60W.
The adjustment tube of the separately excited switching power supply circuit does not participate in the oscillation process of the excitation pulse, and a special oscillator generates pulses to control the adjustment tube.
For example, integrated controllers such as commonly used integrated circuits UC3842, NCP1200, and TL494 can output PWM pulses with adjustable duty ratios. Today, many integrated controllers can automatically raise or lower the switching frequency according to the output power level, so as to maintain a good power conversion frequency under different load conditions.
Since the integrated controller integrates the protection circuit, control circuit, oscillation circuit and feedback signal detection circuit on the same chip, it has good anti-interference performance, simple circuit and powerful functions, and can complete oscillation, voltage regulation, overcurrent, overvoltage and Protection functions such as undervoltage are unmatched by discrete switching power supplies, so they have been more and more widely used in recent years.
According to the circuit structure of the converter, the switching power supply can be divided into isolated type and non-isolated type.
The non-isolated type mainly includes three types: buck type, boost type and buck-boost type, which are mainly suitable for low-voltage DC power conversion occasions.
