A DC-to-DC voltage regulator circuit comprising: an output node ; a pull-up switch (Q1) having a closed switch state to couple a DC pull-up voltage to the output node and having an open switch state to uncouple the DC pull-up voltage from the output node ; a pull-down switch (Q2) having a closed switch state to couple the output node to a ground voltage and having an open switch state to uncouple the output node from the ground voltage ; a reactive circuit element (L1, C1) coupled to store energy at a voltage level based upon voltage at the output node ; a pull-up setting voltage divider circuit coupled to provide a pull-up setting voltage at a pull-up setting divider node that is a function of a voltage at the output node ; a pull-down setting voltage divider circuit coupled to provide a pull-down setting voltage at a pull-down setting divider node that is a function of the voltage at the output node ; a control circuit configured to produce a control voltage having a value that is a function of an impedance at an end effector of a surgical instrument; the end effector being connected to first and second output terminals of an RF output stage configured to convert a controlled DC voltage (V_REG) of the DC-to-DC voltage regulator circuit to high frequency output energy; a first comparator coupled to cause the pull-up switch (Q1) to transition between open switch state and its closed switch state based upon a comparison of the pull-up setting voltage and the control voltage; and a second comparator coupled to cause the pull-down switch (Q2) to transition between its open switch state and its closed switch state based upon a comparison of the pull-down setting voltage and the control voltage. an output node ; a pull-up switch (Q1) having a closed switch state to couple a DC pull-up voltage to the output node and having an open switch state to uncouple the DC pull-up voltage from the output node ; a pull-down switch (Q2) having a closed switch state to couple the output node to a ground voltage and having an open switch state to uncouple the output node from the ground voltage ; a reactive circuit element (L1, C1) coupled to store energy at a voltage level based upon voltage at the output node ; a pull-up setting voltage divider circuit coupled to provide a pull-up setting voltage at a pull-up setting divider node that is a function of a voltage at the output node ; a pull-down setting voltage divider circuit coupled to provide a pull-down setting voltage at a pull-down setting divider node that is a function of the voltage at the output node ; a control circuit configured to produce a control voltage having a value that is a function of an impedance at an end effector of a surgical instrument; the end effector being connected to first and second output terminals of an RF output stage configured to convert a controlled DC voltage (V_REG) of the DC-to-DC voltage regulator circuit to high frequency output energy; a first comparator coupled to cause the pull-up switch (Q1) to transition between open switch state and its closed switch state based upon a comparison of the pull-up setting voltage and the control voltage; and a second comparator coupled to cause the pull-down switch (Q2) to transition between its open switch state and its closed switch state based upon a comparison of the pull-down setting voltage and the control voltage. <EOS>