VOLTAGE CONTROL CIRCUITRY FOR CHARGING OUTPUT CAPACITOR

摘要

Voltage control circuitry (30) driven by a battery (32) for producing a supply for charging an output capacitor (18), which is periodically discharged to supply a current pulse to an impedance load (ZL), e.g., body tissue. The voltage control circuitry (30) converts the battery voltage VBAT to a charging voltage VUPC based upon programmed parameters and the value of the voltage VCOMPL measured at one terminal (15) output capacitor. The circuitry includes a voltage converter (30) for multiplying VBAT by a multiplication factor to produce VUPC. The voltage VCOMPL is sampled to determine its final "droop" at the end of an output current pulse. If the final droop value is lower than a certain threshold, then the voltage converter switches to increase the charging voltage VUPC. If the final droop value is above a certain threshold, then the voltage converter switches to reduce the value of the voltage VUPC. This feedback action maintains the output voltage within an acceptable operating range to provide sufficient energy to produce an efficacious output current pulse for stimulation without causing unproductive energy loss, e.g., heat. In order to avoid premature depletion of battery energy, the charging voltage VUPC is compared with the output voltage VCOMPL to determine the optimum clock rate to be used to convert VBAT to VUPC.