In electronic circuits, the circuit that converts the input DC voltage into the DC voltage required in the circuit is calledDC-DC power supply circuit。For example, our wireless module is generally 5V to 33v。DC-DC circuits can usually be divided into step-up type, step-down type, and step-up type, which are generally composed of electronic switching devices, inductors, and capacitors. The DC-DC circuit mainly uses the electronic switching device to periodically turn on and off, so as to realize the function of output voltage adjustment and automatic voltage regulation.
Buck type
When Q1 is turned on, the power supply charges the inductor, and the freewheeling diode is in the cut-off state, when Q1 is cut-off, because the inductor current cannot be abruptly changed, the inductor current gradually decreases, and the load and freewheeling diode form a loop. The output voltage vo = vin d (d is the time when the electronic switch is turned on in one cycle). Generally, the inductor between the SW pin and the output is the buck circuit, see the figure below
Step-up type (boost
When the electronic switch Q1 is turned on, the power supply charges the inductor, in this process, the on-resistance of Q1 is very small, so that D1 is short-circuited, and the load is provided by the capacitor C1 to maintain the load work.
When the electronic switch Q1 is cut-off, the energy stored by the inductor and the power supply charge the capacitor and maintain the load through D1 because the current of the inductor cannot be abruptly changed.
Generally, there is no inductance between the SW pin and the output is the boost circuit, see the figure below
Buck-boost type (buckboost
When switch Q1 is closed, the power supply charges the inductor, and in this process the RL is powered by the C1 capacitor itself. When the Q1 switch is disconnected, because the current of the inductor cannot be abruptly changed, the inductor, C1 and D1 freewheeling diodes form a closed loop, and the energy stored by the inductor supplies power to the C1 charge and RL load.
dcDC circuit design considerations
Input and output voltage ranges: Determine the input and output voltage ranges to ensure that the selected DC-DC power supply chip can meet the requirements. Also consider the system's requirements for the output ripple of the DCDC power supply.
Efficiency, power loss: High-efficiency DC-DC converters can reduce power loss and heat. So pay attention to the heat dissipation design.
Output current and load capacity: Ensure that the DC-DC circuit can stably supply the current required by the system, and the output capacity can be adjusted according to the load.
PCB layout: A good PCB layout design needs to reduce electromagnetic interference and noise. Pay attention to the separation of the ground wire from the signal wire to improve electromagnetic compatibility.
Environment and temperature conditions: Considering the operating temperature range and environmental conditions of the DC-DC circuit, select the appropriate heat dissipation design, vias, and heat sinks. Ensure that the DC-DC circuit can operate stably under the temperature and environmental conditions required by the system.
Comply with relevant standards and specifications: Follow safety standards and EMC specifications to ensure that the DC-DC power supply circuit design meets regulatory requirements.
In summary, the design of DC-DC power supply circuits needs to take into account factors such as input and output voltage ranges, efficiency, power consumption, output current and ability to drive loads, ripple and noise, stability and feedback control, input and output protection, PCB layout and electromagnetic compatibility, temperature and environmental conditions, reliability and life.