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

Inputs

Input Voltage

Output Voltage

Output Current

Output Voltage Ripple Factor

mv (pp)

Operating Frequency

kHz

Output

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):

$$VOUT = VIN × D/(1-D)$$

Application

Switching power supplies are more efficient than linear power supplies.