The measurement loop is mainly from the constant current source outputting a stable current directly through the windings of the power transformer, without connecting a standard resistance (short-circuit the series resistor with a relay), measuring the charging current, and turning off the relay when the charging current reaches the set value. The resistance is connected in series in the measurement loop. In order to ensure the stability of the single-chip power supply, the relay control power supply is supplied separately.

Due to the existence of winding inductance, residual current will pose a threat to users and test equipment. Therefore, there must be a current discharge circuit. The current discharge circuit is composed of a discharge resistor and a reverse diode. The diode is turned off during charging, and the power supply charges the winding and cuts off The diode is turned on during electricity, and the winding discharges through the diode and the discharge resistor.

At the end of the measurement, the relay K1 is disconnected. Because the transformer winding has a large inductance, the current cannot be immediately reduced to zero, which will generate a large electric potential. Therefore, a discharge circuit must be added. In this discharge circuit, when the relay K1 is off After opening, the diode D1 is turned on, and the current in the winding forms a loop through the discharge resistor R4 and the diode to complete the discharge process. The selection of the discharge resistance should be appropriate to the larger the discharge resistance. The more power consumed by the resistor, the shorter the discharge time, and the higher the voltage across the discharge loop. Therefore, the selection of the discharge resistance must be safe to control the discharge voltage value, but also to make the discharge time as short as possible.