Systems and methods for limiting DC voltage

A DC voltage limiting circuit comprising:

• a current supply portion configured to receive a voltage input signal and provide a voltage output signal;
• a protective portion configured to limit or halt, at least temporarily, operation of the current supply portion based on a magnitude of the voltage input signal;
• and
• a voltage level control portion configured to limit the voltage output signal to a predetermined voltage level;
• the DC voltage limiting circuit being provided in a climate control system controller;
• wherein the current supply portion comprises first and second transistors in a Darlington configuration configured to receive the voltage input signal and connected with the voltage output;
• and
• wherein the protective portion comprises a first Zener diode connected between the voltage input and a base of a third transistor, the protective portion configured to limit the operation of one of the transistors in the Darlington configuration.

A method of limiting DC voltage comprising:

• in response to a voltage input signal, supplying current to provide a voltage output signal, the supplying performed by a current supply portion of a DC voltage limiting circuit of a climate control system controller;
• limiting operation of the current supply portion based on a magnitude of the voltage input signal, the limiting performed by a protective portion of the DC voltage limiting circuit;
• and
• limiting the voltage output signal to a predetermined voltage maximum level;
• wherein the current supply portion comprises:
• first and second transistors each having an emitter configured to provide current through a switch to provide the output voltage signal, the second transistor having a base in series with a first Zener diode having a cathode facing away from the base;
• the first transistor configured to supply current through the switch when the voltage input signal has a voltage less than the Zener voltage of the first Zener diode;
• and
• the second transistor configured to supply current through the switch when the voltage input signal exceeds the Zener voltage of the first Zener diode;
• wherein the DC voltage limiting circuit further comprises a second Zener diode connected between a gate of the switch and a source of the switch.

A DC voltage limiting circuit comprising:

• first and second transistors configured to receive a voltage input signal, each having an emitter configured to provide current through a switch to provide an output voltage signal, the second transistor having a base in series with a first Zener diode reverse-biased in relation to the voltage input signal;
• a second Zener diode having a Zener voltage higher than the Zener voltage of the first Zener diode, the second Zener diode connected between a gate of the switch and a source of the switch and reverse-biased in relation to the gate;
• and
• a third transistor having a base connected with the voltage output through a third Zener diode reverse-biased in relation to the voltage output and having a Zener voltage corresponding to a predetermined voltage level.