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A closed-loop detection system is established to make optical voltage sensors (OVSs) based on Pockels effect particularly ideal for high-voltage applications. For the closed-loop OVSs, the signal intensity fluctuation due to temperature variation contributes to the gain drift of the forward channel and finally influences the dynamic performance of the OVSs. Meanwhile, the closed-loop error of the OVS is also a weak signal that is hard to be accurately extracted. In this work, we propose a signal detection circuit based on weak signal detection theory to reduce noise levels for improving detection accuracy of OVS. In consideration of the influence of signal intensity fluctuation, we design a control algorithm for the closed-loop detection system to guarantee that the OVS is exponentially stable in order to have a fast dynamic response. The experimental results show that the OVS based on the proposed closed-loop system has accuracy within 0.2%, a fast rise time less than 25.2 μs and a wide bandwidth up to 24.5 kHz.