When it comes to DC-DC, we know these three circuits.
Buck circuits, also known as buck circuits. It is a common non-isolated DC-DC conversion circuit, but it can only be stepped down.
It is mainly composed of switch Q1, freewheeling diode D1, energy storage inductor L1, output filter capacitor C1 and load resistance R1-
When Q1 is high, Q1 is on, D1 is reversed cut-off, and the current flows through the inductor to supply power to the load, and the current gradually rises, but due to the self-inductance potential that the left side of the inductor is positive and the right side is negative, the current is hindered from rising. An inductor converts electrical energy into magnetic energy for storage.
When the pulse of the control circuit is low, Q1 is turned off, because the inductance in L cannot be abruptly changed at this time, so the two ends of the inductor become an induced electromotive force that is negative left and positive on the right, and then hinders the current drop, and D1 is positively biased and conducted.
When the current in L passes through D1, the current value will gradually decrease, and the magnetic energy stored in L will be converted into electrical energy and released to the load R1.
Note that the capacitor here is the filter capacitor (C1), is there any partner who knows what it does?
Next, let's look at the boost circuit, which is also called the boost circuit.
The circuit device is the same as the buck circuit, but it is different, the inductor L1 is on the input side, which is called the boost inductor.
When Q1 is turned on, the input voltage charges the inductor, and the circuit: Vin--- inductor L--- switch tube Q1.
When Q1 is turned off, the input energy and the inductor energy provide energy to the output at the same time, and the circuit is: input Vi→ inductor L→ diode D→ capacitor C→ load RL, at this time, the power supply of the load is equivalent to the input voltage plus the induced electromotive force of the inductor, so the voltage boost is realized.
Buck-Boost电路,也叫作升降压电路。
We can think of it as a series of buck converters and boost converters, but with a combined switch. Its output voltage can be lower or higher than the input voltage, and it is a single-tube DC converter.
When Q1 is turned on, the input current passes through the inductor directly to ground, and the output at the right end is maintained by a capacitor discharge.
When Q1 is turned off, the inductor current flows from ground to the load and capacitor, and then flows through the diode back to the inductor, which is the process of the inductor releasing energy and capacitor charging.
So, is the output voltage buck or boost?
This has a lot to do with the duty cycle of the PWM wave that controls the switch. If the duty cycle is greater than 1/2, it is a boost, and vice versa, it is a buck.
Some of the above pictures and sources come from the Internet