Designing an LLC Converter

In this post, I will share one of my electronic projects: designing an open-loop 15 Watts LLC converter circuit. This post will cover the design step, LTSpice circuit simulation, PCB design, and testing of the LLC converter hardware.

1. Design Parameters

First, we will specify the parameters of the LLC circuit, as shown in the table below.

Output voltage	24 V
Input voltage	12 V
Output power	15 W
Resonant frequency	80 kHz

1.1 Once we specify the parameters, we will start by calculating the winding ratio, n, of the inductor. The constant value 2 is used for Half-Bridge configuration; if Full-Bridge changes it into 1

$n = \frac{V_{in}}{2V_o}$

$n = \frac{24V}{2 \times 12V} = 1$

1.2 Next, we will calculate the minimum gain we want for the LCC resonant tank. We will assume the minimum output voltage with the maximum input for this. The constant value 2 is used for Half-Bridge configuration; if Full-Bridge changes it into 1

$M_{min} = \frac{n \times V_{o\underline min}}{V_{in\underline max}/ 2}$

$M_{min} = \frac{1 \times 10V}{26V⁄2} = 0,76$

1.3 Next, we will calculate the maximum gain we want for the LCC resonant tank. We will assume the maximum output voltage with the minimum input for this.

$M_{max} = \frac{n \times V_{o\underline max}}{V_{in\underline min}/ 2}$