Importance

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Abstract

A simmer circuit 18 comprises a power supply unit 54 for the supply of a simmer current I.sub.s to an excitation lamp 22 and a control unit 56 for the control of the current value of the simmer current I.sub.s. In the control unit 56, a current detection signal V.sub.s from a current sensor, e.g., a Hall CT 70 attached to the power supply unit 54 is fed via a buffer amplifier 72 for impedance conversion to a non-inversion input terminal of an operational amplifier 82 for signal amplification. The amplification factor .mu. of the operational amplifier 82 differs depending on which one is selected from three switches 84, 86 and 88. A CPU 38 selects the switch 84 when switching the simmer current I.sub.s to 0.3 A for 'low speed zone', selects the switch 86 when switching to 2 A for 'medium speed zone' and switches 88 when switching to 5 A for 'high speed zone'. A current control circuit 100 provides an on/off control of the simmer current I.sub.s on the basis of a control signal from the CPU 38, and, during on period, compares a current detection signal .mu. V.sub.s from the operational amplifier 82 with a reference current value KI from a reference current value setting unit 102 to provide a simmer current control so as to nullify the comparison error.

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First Claim