How do you design an isolated converter for high voltage and high power applications?

1 Principles of isolation

Isolation is the process of separating two or more circuits or systems that have different voltage levels, ground references, or noise characteristics. It prevents the flow of unwanted current, voltage, or power between them, thus avoiding hazards, interference, and damage. Isolation can be achieved by using physical barriers, such as air gaps, insulation, or transformers, or by using devices that convert electrical signals into other forms of energy, such as optical, magnetic, or capacitive couplers.

2 Components of isolated converters

An isolated converter consists of four main components: an input stage, an isolation stage, an output stage, and a feedback loop. The input stage converts the input voltage and current into a suitable form for the isolation stage, such as alternating current (AC), pulse width modulation (PWM), or high frequency (HF). The isolation stage transfers the energy from the input stage to the output stage without direct electrical connection, using one or more of the methods mentioned above. The output stage converts the energy from the isolation stage into the desired output voltage and current, such as direct current (DC), AC, or PWM. The feedback loop regulates the output voltage and current by sensing and adjusting the input stage parameters, such as duty cycle, frequency, or phase.

3 Types of isolated converters

There are various types of isolated converters, depending on the input and output voltage and current characteristics, the isolation method, and the topology. For example, flyback converters use a transformer with a single winding on the primary side and one or more windings on the secondary side. The primary winding is switched on and off by a transistor, creating a magnetic flux that induces a voltage on the secondary winding. Similarly, forward converters use two windings on the primary side and one or more windings on the secondary side. Push-pull converters also use two windings on the primary side and one or more windings on the secondary side, but with two transistors that switch in an alternating manner. Half-bridge converters have two windings on the primary side connected to a half-bridge circuit that switches between two voltage levels, while full-bridge converters have two windings connected to a full-bridge circuit that switches between four voltage levels. In each case, the output voltage and current are controlled by the duty cycle and number of turns of the secondary winding.

4 Tips and tricks for isolated converters

Designing an isolated converter for high voltage and high power applications requires careful consideration of several factors, such as efficiency, size, cost, and reliability. Efficiency is the ratio of the output power to the input power, and it is affected by losses in the components. To improve efficiency, you can choose low-loss components, optimize the switching frequency and duty cycle, minimize the parasitic elements, and use soft-switching techniques. Size is the physical dimension of the converter and is determined by the power density. To reduce size, you can increase the power density by using high-frequency switching, high-voltage components, and compact transformers. Cost is the total expense of the converter and is influenced by the number and type of components, complexity of the circuit, and manufacturing process. To lower cost, you can reduce the number and type of components by using integrated circuits, standard transformers, and simple topologies. Reliability is the ability of the converter to operate without failure or degradation over time and depends on stress and aging of components, thermal management, and fault tolerance. To enhance reliability, you can select high-quality components, provide adequate cooling and ventilation, and implement protection and redundancy features.

5 Examples of isolated converters

To demonstrate how isolated converters can be designed for high voltage and high power applications, here are several examples from different domains. Electric vehicles require isolated converters to charge the battery from the grid, to drive the motor from the battery, and to provide auxiliary power for the lights, radio, and other devices. Additionally, renewable energy systems use isolated converters to connect renewable sources, such as solar panels, wind turbines, or fuel cells, to the grid or to the load. Finally, industrial drives rely on isolated converters to control the speed and torque of electric motors that drive pumps, fans, compressors, or conveyors. All of these converters must be efficient, flexible, reliable, precise, and durable while handling high voltages (up to 800 V) and high currents (up to 300 A) or delivering high power (up to several megawatts) and high voltage (up to several kilovolts).

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?