A Buck converter is a DC to DC converter which step down the voltage from the input to the load(i.e greater input voltage and lower output voltage) .The buck converter must contains at least one energy storing device like inductor, capacitor.
WORKING PRINCIPLE OF BUCK CONVERTER
• Recall the basic switching circuit above produces square-wave output.
• The square-wave output voltage contains significant ripple at switching frequency.
• Switching frequency is typically high (10’s to 100’s of kHz), so why not add a low pass LC filter.
Above circuit has a serious problem!
. Switch is on, current flows through inductor.
. switch is off, inductor current refuses to stop creating a high voltage across the switch, destroying the switch.
• Add a freewheeling diode to provide the continuity of inductor current when the switch is off.
Practical Design of Buck converter
• After adding the diode, the circuit is the power stage of a BUCK converter!
• What is still missing is a mechanism to regulate the output voltage– The need to have a feedback control to close the loop which we have integrated in our design.
DESIGN OF 24V TO 3.3V BUCK CONVERTER
First of all we must be clear about the basis requirements of our design
Here we have
Input voltage: 24v
Required Output Voltage: 3.3v
Required Output current : 1 amp
CIRCUIT DIAGRAM OF 24V TO 3.3V BUCK CONVERTER
This is the circuit diagram of 24 volt to 3.3 volt buck converter where there are two input filter capacitor of 10uf , a switching chip tps54331 , a bootstrip capacitor of 100nf, 22uh inductor , voltage divider resistor and three output voltage filter capacitor of 22uf.
The device requires an bulk input decoupling capacitor depending on the application.A ceramic capacitor over 10 μF is recommended for the decoupling capacitor. An additional or 10uf capacitor from VIN to GND is optional to provide additional high frequency filtering.
We have selected this driver chip because due to its easy availability wide input range and has integrated mosfet.
It has 3.5-V to 28-V Wide Input voltage Range.
- BOOT: Connect 100nf capacitor between boot and sw pin.
- EN: Float the EN pin to enable.
- VSENSE: Connect to output voltage with feedback resistor divider.
- SS: It is slow start pin. The external capacitor is connected to this pin set the output rise time.
- GND: Ground pin
- VIN: Input supply pin
The N-ch MOSFET for the high-side switch requires a gate voltage of VIN+ Vth (threshold voltage of the N-ch MOSFET) or higher. A step-up circuit is required because the gate voltage is higher than VIN. This circuit is configured with an internal diode and an external bootstrap capacitor (charge pump type).
The voltages on the SW and BOOT pins in the example of Figure 1 are described as shown in Figure 2, where Vf is the forward direction voltage of the built-in diode.
When the SW voltage is low during the switching operations in Figure 2, the electric charge is stored in the capacitor from VIN, thus resulting in the voltage of VIN-Vf across the capacitor. When the SW voltage is high, the BOOTvoltage increases up to 2 × VIN-Vf, and the built-in diode maintains the voltage at 2 × VIN-Vf. Therefore, the BOOT voltage switches between VIN-Vf and 2 × VIN-Vf
OUTPUT VOLTAGE SET POINT(VOLTAGE DIVIDER)
The output voltage of the TPS54331dr device is externally adjustable using a resistor divider network.I this divider network is comprised of R1 and R2. Use Equation6 and Equation7 to calculate the relationship of the output voltage to the resistor divider.
This PCB is integrated PCB for 24 volt to 3.3 volt and 24 volt to 18 volt buck converter .We have down the voltage from 24 volt to 3.3 volt for providing supply to our esp32.