Low noise mains operated and battery power supplies for SQUID electronics

Abstract

The magnetic signal from the heart is extremely weak(approximately 10 pT). Its measurement requires the use of highly sensitive superconducting SQUID magnetometers and gradiometer coils. This study concentrates on design and construction of mains driven and battery powered supplies for SQUID control electronics. The supplies provide an output current of 0.5 A and a split supply voltage of +/- 15 V with the following features: The ripple of the mains driven power supply (PSU) is maintained as low as possible by using high quality components. The Battery Operated power Supply for SQUID electronics (BOSS) has no ripple. Magnetic interference produced the mains driven PSU is used, magnetic interference from AC mains connections and transformers is totally avoided.The outputs of both supplies are protected against over currents and short circuits. The BOSS batteries are rechargeable and the charging procedure is automatic. The charging unit of the BOSS incorporates a cut-off circuit which activates when the batteries are fully charged, and also indicates when the batteries need recharging. Measurements of noise and ripple voltages, efficiency, thermal stability and dependence on variations in the load current demonstrated the supplies' suitability for use in situations where a stable low-noise DC supply is required. /Kir10