Voltage doubler using a switching regulator and voltage limiter

An apparatus comprising:

• a regulator including an input for a variable input voltage and an output of a regulated voltage, the regulator including a switch node that is configured to alternate connection between the input for the variable input voltage and ground;
• a circuit that increases voltage, the circuit being coupled to the output of the regulated voltage of the regulator to charge a first capacitor, the circuit being coupled to the switch node, and the circuit including an output capacitor that receives a charge from the first capacitor, the apparatus producing an output voltage across the output capacitor;
• and
• a limit circuit coupled to the switch node and to the regulated voltage of the regulator, the limit circuit coupled to the first capacitor of the circuit;
• wherein the limit circuit comprises a resistor and a clamp diode arranged such that the resistor is connected between the switch node and a negative terminal of the first capacitor, and an anode of the clamp diode is connected to the resistor connection at the negative terminal of the first capacitor and a cathode of the clamp diode is connected to the regulated voltage of the regulator;
• and
• wherein the limit circuit limits a voltage across the first capacitor from exceeding the regulated voltage.