Classical DC current transformer, based on a linear amplifier as a compensating amplifier, is well known as a power inefficient device. If the linear amplifier is replaced with switching counterpart, significant power saving can be achieved. A natural choice for replacement can be found in a half-bridge class-D amplifier. However, the half-bridge class-D amplifier is prone to bus-pumping effect, and direct replacement cannot be performed in a straightforward manner. This study presents an analysis of power consumption issues and irregular behaviour for a DC current transformer, caused by the bus-pumping effect. For the case of DC current measurement, the main issues are explained, giving better insight into power consumption, and possible hazards to transformer circuitry. Presented analytical results are experimentally verified.