DC-DC Circuit Calculator

An inductor, which stores energy, limits the current slew rate through a power switch. The energy stored in the inductor can be expressed in joules as a function of the current with: E = 1/2 X L X I2

Input Voltage
Output Voltage
Output Current
Output Voltage Ripple Factor
mv (pp)
Operating Frequency

Timing Capacitor (Ct)
Rated Peak Withstand Current (Ipk)
Limited to Flow Resistance (Rsc)
Inductance (Lmin)
Filter Capacitor (Co)
Resistor 1 (R1)
Resistor 2 (R2)

Equations & Topology

Figure 1. Simple boost converter


Figure 2. Buck converter topology


Figure 3. Inverting topology.


Figure 4. Transformer flyback topology.


The average voltage of an inductor over the switching cycle is zero in a steady-state operating condition. With this, when calculating for the boost circuit: 


$$VIN X tON = tOFF X VL$$


And because:

$$VOUT = VIN + VL$$

We can then establish the relationship:

$$VOUT = VIN × (1 + tON/tOFF)$$

Using the relationship for duty cycle (D):

$$tON/(tON + tOFF) = D$$

Then for the boost circuit:

$$VOUT = VIN/(1-D)$$

Similar derivations can be made for the buck circuit:

$$VOUT = VIN × D$$

And for the inverter circuit (flyback):

$$VOUT = VIN × D/(1-D)$$



Switching power supplies are more efficient than linear power supplies. 


Further Reading