The Advantages and Disadvantages of Forward Power Supply
1. The transient control characteristics of the output voltage of the forward power supply are relatively good.
In a forward switching power supply, when the primary coil of the transformer is excited by the DC voltage, the secondary coil of the transformer provides power output to the load, and the amplitude of the output voltage is basically stable. At this time, although the output power keeps changing, the amplitude of the output voltage remains basically unchanged, which shows that the transient control characteristics of the output voltage of the forward switching power supply are relatively good. Only when the control switch is off, the power output is provided by both the energy storage inductor and the energy storage capacitor at the same time. Although the output voltage is affected by the load current, if the capacity of the energy storage capacitor is relatively large, the load current The impact on the output voltage is also very small.
2. The forward power supply has relatively strong load capacity.
Forward switching power supplies generally select the one-week average value of the transformer output voltage, and the energy storage inductor provides current output to the load during the turn-on and turn-off periods of the control switch. Therefore, the load capacity of the forward switching power supply is relatively strong and the output voltage ripple is small. If the output voltage of the forward switching power supply is required to have a large adjustment rate, under normal load conditions, the duty cycle of the control switch is best selected to be around 0.5, or slightly greater than 0.5. At this time, the duty cycle flowing through the energy storage filter inductor Current is continuous current. When the current flowing through the energy storage filter inductor is a continuous current, the load capacity is relatively strong.
3. The voltage and current output characteristics of the forward power supply are much better than those of the flyback power supply.
When the duty cycle of the control switch is 0.5, the amplitude of the output voltage uo of the forward switching power supply is exactly equal to twice the average voltage Ua, and the maximum value Im of the current flowing through the filter energy storage inductor is also exactly the average current Io ( twice the output current). Therefore, the pulsation coefficient S of the voltage and current of the forward switching power supply is approximately equal to 2, and compared with the pulsation coefficient S of the voltage and current of the flyback switching power supply, it is almost twice as small, indicating that the forward switching power supply has The voltage and current output characteristics are much better than the flyback switching power supply.
4. The forward power supply uses a large energy storage filter inductor and a freewheeling diode more than the flyback power supply.
The disadvantage of the forward power supply is that the circuit uses a large energy storage filter inductor and a freewheeling diode more than the flyback power supply. The output voltage of the forward power supply is modulated by the duty cycle, which is much lower than that of the flyback power supply. Therefore, the forward power supply requires a relatively high error signal amplitude for regulating the duty cycle, and a relatively large gain and dynamic range of the error signal amplifier.
5. The forward power supply is relatively large.
In order to reduce the excitation current of the transformer and improve the working efficiency of the forward switching power supply, the volt-second capacity of the transformer is generally achieved relatively large (that is, the volt-second capacity is equal to the product of the input pulse voltage amplitude and the pulse width, represented here by US). And in order to prevent the back electromotive force generated by the primary coil of the transformer from breaking down the switching tube, the forward switching power supply transformer has one more back electromotive force absorption winding than the flyback switching power supply transformer. Therefore, the volume of the transformer of the forward switching power supply is larger than that of the flyback switching power supply.
6. The back electromotive force voltage generated by the primary coil of the transformer of the forward power supply is higher than the back electromotive force voltage generated by the flyback power supply.
Another bigger disadvantage of the forward switching power supply is that when the control switch is turned off, the back electromotive force voltage generated by the primary coil of the transformer is higher than the back electromotive force voltage generated by the flyback switching power supply. Because generally when the forward switching power supply is working, the duty cycle of the control switch is set at about 0.5, while the duty cycle of the flyback switching power supply control switch is relatively small.
7. The double-tube forward power supply can be used in situations with higher voltage input and larger power output.
As modern electronic equipment has higher and higher requirements on the size of electronic components, from the previous large switching power supply to the current small power module, the module power supply is required to continue to improve efficiency, power density, and reduce size, so now small power module power supply Basically, it is a flyback switching power supply solution.
