Minimising the impact of source resistance on high-voltage DC/DC converters

Source Resistance (RS) can reduce the efficiency of a DC/DC converter by 10% or more and impact the converter’s reliability. In extremely small converters, such as EMCO’s newest A series ultra-miniature, high-voltage DC/DC converters, engineers need to pay special attention to this design aspect because of the low capacitance values that must be used in the converter to achieve a small footprint. This application note shows system designers how to cope with different RS values using visual measurements from EMCO’s newest A series converters and provides recommendations for highly efficient and reliable operation. It assumes the user is not a power conversion expert, but rather a system expert who has to use power conversion technology as part of his or her design. As a result, it avoids design equations and focuses on empirical analysis. However, the measurements also provide helpful visual guidelines for power system experts regarding how the converter should operate in an application.

EMCO’s A series high-voltage DC/DC converters provide system designers with easy-to-use power conversion in a volume of less than 0.10 cubic inches with a profile of only 0.25". Within this form factor, 0 to 5, 12 or 24V input voltages can be converted to high voltages that range from 100 to 6,000V in both 1 and 1.5W models.

A simple block diagram of EMCO’s transformer-isolated high-voltage DC/DC converter is shown in the figure below. The design has an oscillator, a transformer and a rectifier as well as capacitors on both the input and output. The input capacitor is effectively a decoupling capacitor across the input and ground terminals of the DC/DC converter.

Figure 1 - EMCO’s transformer-isolated DC/DC converter topology includes capacitors for both the input and the output

The A series' small size obviously limits the size of its input capacitor (to less 10μF). For those applications with a source resistance of less than 5Ω, this is not a problem. However, those applications with a higher source resistance need additional design considerations. To determine the correct design values for the maximum source resistance, a series of measurements were made on production A series products.

Download and read the full whitepaper below.