# The advantages and disadvantages of various topological circuits of communication switching power supply

Everything has a way, and the switching power supply is a variety of topologies. Knowing these topologies, you can see the essence of switching power supplies. In order to characterize the quality of various voltage or current waveforms, generally the amplitude, average value, effective value, first harmonic and other parameters of the voltage or current are compared with each other.

Among broadcast communication switching power supplies, the amplitude and average value of voltage or current are the most intuitive. Therefore, we use the ratio of the amplitude of voltage or current to its average value, which is called the pulsation coefficient S; some people use the effective value of voltage or current. The ratio of the value to its average value is called the form factor K.

Therefore, the pulsation coefficients Sv and Si of voltage and current and the waveform coefficients Kv and Ki are separately marked as:

Sv=Up/Ua—Voltage ripple coefficient

Si=Im/Ia—current ripple coefficient

Kv=Ud/Ua—voltage waveform coefficient

Ki=Id/Ia—current waveform coefficient

In the above 4 formulas, Sv, Si, Kv, Ki separately indicate: the pulsation coefficient S of voltage and current, and the waveform coefficient K of voltage and current,

Generally speaking, only capital S or K is written when it can be clearly distinguished. The pulsation coefficient S and the waveform coefficient K are both targets that characterize the quality of voltage or current. Obviously, the smaller the value of S and K, the better. The smaller the value of S and K, the more stable the output voltage and current.

The ripple of voltage and current is also smaller.

1. Advantages and disadvantages of flyback switching power supply   Everything has a way, and the switching power supply is a variety of topologies. Knowing these topologies, you can see the essence of switching power supplies. In order to characterize the quality of various voltage or current waveforms, generally the amplitude, average value, effective value, first harmonic and other parameters of the voltage or current are compared with each other.

Among broadcast communication switching power supplies, the amplitude and average value of voltage or current are the most intuitive. Therefore, we use the ratio of the amplitude of voltage or current to its average value, which is called the pulsation coefficient S; some people use the effective value of voltage or current. The ratio of the value to its average value is called the form factor

Therefore, the pulsation coefficients Sv and Si of voltage and current and the waveform coefficients Kv and Ki are separately marked a

Sv=Up/Ua—Voltage ripple coefficie

Si=Im/Ia—current ripple coefficie

Kv=Ud/Ua—voltage waveform coefficie

Ki=Id/Ia—current waveform coefficie

In the above 4 formulas, Sv, Si, Kv, Ki separately indicate: the pulsation coefficient S of voltage and current, and the waveform coefficient K of voltage and curren

Generally speaking, only capital S or K is written when it can be clearly distinguished. The pulsation coefficient S and the waveform coefficient K are both targets that characterize the quality of voltage or current. Obviously, the smaller the value of S and K, the better. The smaller the value of S and K, the more stable the output voltage and curren

The ripple of voltage and current is also smalle

1. The voltage and current output characteristics of the flyback switching power supply are worse than those of the forward switching power supp

The flyback switching power supply does not supply power output to the load when the control switch is turned on, and only converts the stored energy into back electromotive force to supply output to the load when the control switch is turned off. But when the duty cycle of the control switch is 0.5, the average value of the voltage output by the transformer secondary coil is approximately equal to one-half of the maximum voltage, and the current flowing through the load is exactly equal to a quarter of the maximum current of the transformer secondary coil One. That is, the voltage ripple coefficient is equal to 2, and the current ripple coefficient is equal to

The voltage ripple coefficient of the flyback switching power supply is basically the same as that of the forward switching power supply, but the current ripple coefficient is twice that of the forward switching power supply. It can be seen that the voltage and current output characteristics of the flyback switching power supply are worse than those of the forward switching power supply. Especially when the flyback switching power supply is used, in order to avoid the overvoltage of the power switch, the duty cycle is generally less than 0.5. At this time, the current flowing through the secondary coil of the transformer will appear intermittent, and the pulsation coefficient of voltage and current Will add, its voltage and current output characteristics will become wors

2. The transient control characteristics of the flyback switching power supply are relatively

Since the flyback switching power supply only supplies energy output to the load during the switch-off period, when the load current changes, the switching power supply cannot immediately respond to the output voltage or current, and when the demand is higher than the next cycle, the output voltage With the function of sampling and widening control circuit, the switching power supply has only begun to respond to the work that has passed, that is, to change the duty cycle. Therefore, the transient control characteristics of the flyback switching power supply are relatively poor. Sometimes, when the frequency and phase of the load current change are consistent with the time delay characteristics of the voltage output by the sampling and widening control circuit, the output voltage of the flyback switching power supply may tremble. This is the case in the TV. The simplest appearance among switching power supplie

3. The leakage inductance of the primary and secondary coils of the flyback switching power supply transformer is relatively large, and the working efficiency of the switching power supply transformer is

The iron core of the flyback switching power supply transformer generally needs to leave a certain air gap. On the one hand, it is to prevent the iron core of the transformer from flowing excessively through the primary coil of the transformer, and simply generate magnetic saturation. On the other hand, because the output power of the transformer is small, it is necessary to adjust the inductance of the primary coil of the transformer by adjusting the air gap of the voltage transformer and the number of turns of the primary coil. Therefore, the leakage inductance of the primary and secondary coils of the flyback switching power supply transformer is relatively large, and then the working efficiency of the switching power supply transformer will be reduced, and the leakage inductance will also generate back electromotive force, which simply breaks down the switching tub

4. The advantage of the flyback switching power supply is that the circuit is relatively simple and the volume is relatively s

The output voltage of the flyback switching power supply is ruggedly modulated by the duty cycle, which is much higher than that of the forward switching power supply. The advantage of the flyback switching power supply is that the circuit is relatively simple. Compared with the forward switching power supply, it uses a large energy storage filter inductor and a freewheeling diode. Therefore, the volume of the flyback switching power supply is smaller than that of the forward switching power supply, and the cost is also lower. In addition, the output voltage of the flyback switching power supply is ruggedly modulated by the duty cycle, which is much higher than that of the forward switching power supply. Therefore, the flyback switching power supply requires a relatively low fault signal for regulating the duty cycle. The gain and dynamic scale of the signal amplifier should also be smaller. Because of these advantages, flyback switching power supplies are still widely used in the field of home appliances. Flyback switching power supplies are mostly used in occasions with small power or multiple output

5. Flyback switching power supply does not need to add a magnetic reset win

In the flyback switching power supply, when the switch tube is turned off, the energy stored in the transformer of the flyback converter is released to the load, and the magnetic core is reset naturally, without the need for a magnetic reset method. In the flyback switching power supply, the voltage transformer not only has the function of energy storage, but also has the function of voltage transformation and isolatio

1. The transient control characteristics of the output voltage of the forward transformer switching power supply are relatively go

The forward transformer switching power supply happens to be when the primary coil of the transformer is excited by the DC voltage, the secondary coil of the transformer supplies power output to the load, and the rugged output voltage is fundamentally stable. At this time, although the output power is constantly changing, the rugged foundation of the output voltage is still the same, which shows that the transient control characteristics of the output voltage of the forward transformer switching power supply are relatively good. As long as the control switch is turned off, the power output is all supplied by both the energy storage inductor and the energy storage capacitor. At this time, although the output voltage is affected by the load current, it is assumed that the capacity of the energy storage capacitor is relatively large. The impact on the output voltage is also very smal

2. The load ability of forward transformer switching power supply is relatively stro

Since the forward transformer switching power supply generally selects the one-week average value of the transformer output voltage, the energy storage inductor supplies current output to the load during the turn-on and turn-off periods of the control switch. Therefore, the load capacity of the forward transformer switching power supply is relatively strong, and the ripple of the output voltage is relatively small. Assuming that the output voltage of the forward transformer switching power supply is required to have a large adjustment rate, under normal load conditions, the duty cycle of the control switch should be selected at about 0.5, or slightly greater than 0.5. At this time, it flows through the energy storage filter inductance. The current is continuous current. When the current flowing through the energy storage filter inductor is a continuous current, the load capacity is relatively strong.ngl.odpplyn.dings.malle. lows.poore.4.lyy一r.t.t,ntntntnts:K.

1. The voltage and current output characteristics of the flyback switching power supply are worse than those of the forward switching power supply

The flyback switching power supply does not supply power output to the load when the control switch is turned on, and only converts the stored energy into back electromotive force to supply output to the load when the control switch is turned off. But when the duty cycle of the control switch is 0.5, the average value of the voltage output by the transformer secondary coil is approximately equal to one-half of the maximum voltage, and the current flowing through the load is exactly equal to a quarter of the maximum current of the transformer secondary coil One. That is, the voltage ripple coefficient is equal to 2, and the current ripple coefficient is equal to 4.

The voltage ripple coefficient of the flyback switching power supply is basically the same as that of the forward switching power supply, but the current ripple coefficient is twice that of the forward switching power supply. It can be seen that the voltage and current output characteristics of the flyback switching power supply are worse than those of the forward switching power supply. Especially when the flyback switching power supply is used, in order to avoid the overvoltage of the power switch, the duty cycle is generally less than 0.5. At this time, the current flowing through the secondary coil of the transformer will appear intermittent, and the pulsation coefficient of voltage and current Will add, its voltage and current output characteristics will become worse.

2. The transient control characteristics of the flyback switching power supply are relatively poor

Since the flyback switching power supply only supplies energy output to the load during the switch-off period, when the load current changes, the switching power supply cannot immediately respond to the output voltage or current, and when the demand is higher than the next cycle, the output voltage With the function of sampling and widening control circuit, the switching power supply has only begun to respond to the work that has passed, that is, to change the duty cycle. Therefore, the transient control characteristics of the flyback switching power supply are relatively poor. Sometimes, when the frequency and phase of the load current change are consistent with the time delay characteristics of the voltage output by the sampling and widening control circuit, the output voltage of the flyback switching power supply may tremble. This is the case in the TV. The simplest appearance among switching power supplies.

3. The leakage inductance of the primary and secondary coils of the flyback switching power supply transformer is relatively large, and the working efficiency of the switching power supply transformer is low

The iron core of the flyback switching power supply transformer generally needs to leave a certain air gap. On the one hand, it is to prevent the iron core of the transformer from flowing excessively through the primary coil of the transformer, and simply generate magnetic saturation. On the other hand, because the output power of the transformer is small, it is necessary to adjust the inductance of the primary coil of the transformer by adjusting the air gap of the voltage transformer and the number of turns of the primary coil. Therefore, the leakage inductance of the primary and secondary coils of the flyback switching power supply transformer is relatively large, and then the working efficiency of the switching power supply transformer will be reduced, and the leakage inductance will also generate back electromotive force, which simply breaks down the switching tube.

4. The advantage of the flyback switching power supply is that the circuit is relatively simple and the volume is relatively small

The output voltage of the flyback switching power supply is ruggedly modulated by the duty cycle, which is much higher than that of the forward switching power supply. The advantage of the flyback switching power supply is that the circuit is relatively simple. Compared with the forward switching power supply, it uses a large energy storage filter inductor and a freewheeling diode. Therefore, the volume of the flyback switching power supply is smaller than that of the forward switching power supply, and the cost is also lower. In addition, the output voltage of the flyback switching power supply is ruggedly modulated by the duty cycle, which is much higher than that of the forward switching power supply. Therefore, the flyback switching power supply requires a relatively low fault signal for regulating the duty cycle. The gain and dynamic scale of the signal amplifier should also be smaller. Because of these advantages, flyback switching power supplies are still widely used in the field of home appliances. Flyback switching power supplies are mostly used in occasions with small power or multiple outputs.

5. Flyback switching power supply does not need to add a magnetic reset winding

In the flyback switching power supply, when the switch tube is turned off, the energy stored in the transformer of the flyback converter is released to the load, and the magnetic core is reset naturally, without the need for a magnetic reset method. In the flyback switching power supply, the voltage transformer not only has the function of energy storage, but also has the function of voltage transformation and isolation.