SLVUBB4B November 2017 – February 2023

5 AC/DC Bulk Capacitor Calculator

AC/DC power supplies typically require a bulk capacitor behind the input rectifier that provides a quasi-constant input voltage for the converter stage (see #SLVUBB45377). Power Stage Designer can calculate the minimum capacitance based on the desired minimum bulk voltage V_bulk,min, the maximum acceptable voltage ripple ∆V in percent, the input power P_in and the minimum line frequency f_line,min (see #SLVUBB41731).

Figure 5-1 Bulk Capacitor Calculator for AC/DC Power Supplies Window

V_{A C, m i n} = \frac{V_{b u l k, m i n}}{(1 - ∆ V) \times \sqrt{2}}

t_{d i s c h a r g e} = \frac{1}{4 \times f_{l i n e, m i n}} + \frac{1}{2 \times π \times f_{l i n e, m i n}} \times \sin^{- 1} (1 - ∆ V)

t_{c h a r g e} = \frac{1}{4 \times f_{l i n e, m i n}} - \frac{1}{2 \times π \times f_{l i n e, m i n}} \times \sin^{- 1} (1 - ∆ V)

C_{b u l k} = \frac{2 \times P_{i n} \times t_{d i s c h a r g e}}{{V_{b u l k, m i n}}^{2} \times ({(\frac{1}{1 - ∆ V})}^{2} - 1)}

Equation 13.

I_{b u l k, r m s} = \sqrt{{(\frac{C_{b u l k} \times V_{b u l k, m i n} \times (\frac{1}{1 - ∆ V} - 1)}{t_{c h a r g e} \times \sqrt{3}})}^{2} + {(\frac{P_{i n}}{V_{b u l k, m i n}})}^{2}}