Normally closed solid state relay using normally open components

A door lock control system comprising:

• a solid-state relay comprising:
• a semiconductor switch having a control input operable to cause the semiconductor switch to shift from an open, non-conducting, position to a closed, conducting, position, in response to applying a voltage to the control input, wherein the closed position is associated with a parasitic resistance of the semiconductor switch;
• and
• a voltage boost block including a boost converter and a ground connector,
• wherein a voltage output of the semiconductor switch is electrically connected to a voltage input of the boost converter, and a voltage output of the boost converter is electrically connected to the control input, wherein the ground connector of the boost converter is electrically connected to a voltage input of the semiconductor switch,
• wherein parameters of the semiconductor switch and the boost converter, including one or more of:
• the parasitic resistance, a threshold voltage at the control input of the semiconductor switch, and a voltage step-up ratio of the boost converter, are selected such that, when the semiconductor switch is in the closed position, a voltage at the voltage output of the semiconductor switch results in a voltage at the voltage output of the boost converter sufficient for application to the control input at the semiconductor switch, to cause the semiconductor switch to be maintained in a closed position in the absence of another control signal;
• a control side, accessible to user input, and
• a door lock side, operably connected to a lock;
• wherein:
• the solid-state relay is arranged between the control side and the door lock side to operatively connect the control side with the door lock side, and
• the control side is operable to transmit a control signal to the boost converter, resulting in the semiconductor switch engaging in the open position,
• the door-lock side comprises an electrical actuator for controlling a door lock and a power source, wherein the power source has a supply voltage that is connected to a voltage input of the solid-state relay and to the electrical actuator, and wherein a voltage output of solid-state relay is connected to the electrical actuator so that the solid-state relay and electrical actuator are connected in series,
• such that when the semiconductor switch is in the open position, no current flows through the electrical actuator and the supply voltage is present between voltage input and voltage output of the solid-state relay, and between a voltage input and a ground connector of an inactive boost converter, and when the semiconductor switch is in the closed position, the current flowing through the electrical actuator and semiconductor switch causes a voltage drop on the parasitic resistance of the semiconductor switch such that the voltage reaching the boost converter input is sufficiently increased by the boost converter to result in a voltage at the control input of the semiconductor switch sufficient to cause the semiconductor switch to be maintained in the closed position.