a 150 watt lamp typically operates at 100 volts i lamp lamp current is 1 5 amps and v r sense voltage across sense resistor 30 is 100 divided by 1 ratio of voltage divider is vd 1 volt vd 1 volt plus i lamp 1 5 totals to 2 5 volts which is set as to equal the internal reference voltage 2 5 volts of ic 16 in other words the voltage divider ratio is selected by the circuit designer so that at proper operation the composite feedback signal to fb equals the reference voltage of ic 16 the lamp is an aged s 56 hps lamp in which the electrodes are worn the v lamp is 150 volts much higher than in example 1 above vc across capacitor 32 is 150 volts v r sense across sense resistor 30 is therefore adjusted by the feedback to be 1 volt i lamp 1 amp so that f b 1 5 1 2 5v the lamp is operated at 150 volts and 1 amp to provide 150 watts of power consumption the lamp is a s 55 lamp which by error replaces a s 56 lamp the s 55 has a nominal 55 volt operating voltage but would likely operate at about 60 volts because.