This is how the power circuit is designed

Speaking of circuit design , A particularly important item that can be carried out alone is the power supply design , After all , All electronic devices must be supported by the power supply circuit to work properly .

Let's briefly introduce the power circuit design this time , Let ordinary people have a general understanding of power supply design .

For power supply , At present, there are two main types in the market ： Linear power supply and switching power supply .

So what's the difference between the two power supplies ？

The working principle of linear power supply is to put 220V Or other AC voltage is transformed into low-voltage electricity through transformer （12V Or something smaller AC Alternating current (ac) ）, Then it is corrected and rectified by a series of diodes , And the AC Alternating current becomes pulsating voltage .

After obtaining the pulsating voltage , It is necessary to filter the pulsating voltage , It is usually done by capacitance , Then the filtered low-voltage AC is converted into DC Direct current .

however , At this time, the direct current is not pure enough , There will be some fluctuations （ It's usually called ripple ）, Therefore, voltage stabilizing diode or voltage rectifying circuit is also needed for correction .

Finally, we can get a relatively stable DC Direct current output .

The whole process is the principle of linear power supply .

What about switching power supply ？

Unlike the linear power supply, the process of converting high-voltage AC to low-voltage AC first , The switching power supply is directly connected to 220V The AC input is converted to DC DC, Then under the action of high-frequency oscillation circuit , Switch tube is used to control the on-off of current , Form high-frequency pulse current .

Finally, in the inductance （ High frequency transformer ） With the help of the , Output the required stable low voltage DC .

  For power circuit design , Generally, the first thing to master is the switching power supply circuit , From home AC voltage 220V Obtain the voltage from the , After converting to DC stable voltage , Then supply power to the main board of electronic equipment . And most of the electronic products on the market, such as computers , Mobile phones use switching power supply .

Then there is a simple example of switching power supply （ Reduces the process of AC to DC ）.

As shown in the figure below , This is a simple switching power supply , Use the continuous closing and opening of the switch , The voltage of direct current will change .

For example, according to 0.5s closed 0.5s The law of disconnection , This 12V The voltage can be changed to 6V, The effect of reducing blood pressure is realized .

What is its principle ？

in fact , When the switch just begins to close ,12V DC power supply , At this time, the diode is off , The power supply starts to store energy for inductors and capacitors , Supply power to the load at the same time , But because the inductive current can't change suddenly , So the inductance in order to increase the resistance current , It will sense a voltage opposite to the power supply , This inductance will offset part of the supply voltage , So that the voltage at the load end can not reach 12V, But as time goes on , The effect of inductance cancellation will be weakened , The voltage at the load side will slowly reach 12V.

Then when the switch is off , The inductance counteracts , To prevent sudden changes in current , It will act as a power supply , Power the load . So when the switch is off , The load still has current for a short time .

But over time , The effect of inductance counteraction is gradually weakened , Become a wire , No more power .

therefore , In this continuous process , If the time difference between opening and closing of the switch can be controlled , When the current does not change to zero , Repeated switch , You can get a paragraph in 6V But not particularly stable DC Direct current , The effective value is close to 6V.

So in order to get a stable voltage , The role of capacitance cannot be ignored .

The capacitor mainly plays the role of energy storage and filtering in this circuit , Without it , The waveform will become very sharp .

Finally, the switch in the circuit , In the actual circuit , Generally, crystal triode is used to act as a switch , It's in 1 It can be switched on and off tens of thousands of times in seconds .

Don't underestimate this simple switching power supply , Its efficiency can reach 90% about . Its main loss is inductance , Equivalent resistance of capacitance ; Diode conduction voltage drop ; And the on resistance of the crystal triode .

This is a simple switching power supply design , Of course, in practical application, the design of switching power supply is to meet the requirements of higher precision and more stable performance , The circuit will also be more complex .