Driver with open output protection

A load driver for driving a load, the load driver comprising:

• an output buffer capacitor;
• two output terminals coupled to the output buffer capacitor for coupling to the load;
• a coupling diode coupled in a forward direction from a first output terminal of the two output terminals to a first terminal of the output buffer capacitor;
• a positive voltage bus coupled to a second output terminal of the two output terminals and to a second terminal of the output buffer capacitor for providing a positive bias voltage to the load;
• and
• a converter circuit configured to output power through said two output terminals, the converter circuit comprising:
• a startup terminal configured to receive a startup current, wherein said startup terminal is coupled to said first output terminal;
• and
• a controllable switching element, wherein said startup terminal is connected to a control terminal of the controllable switching element such that the control terminal of the controllable switching element is in series connection with the two output terminals, and said switching element is turned on by the startup current;
• wherein the startup current is from the second output terminal of the two output terminals, through the load, to the first output terminal, to the startup terminal and into the control terminal of the controllable switching element when the load is coupled to the two output terminals,
• wherein the coupling diode is configured to block current from the positive voltage bus towards the control terminal of the controllable switching element when the load is not coupled to the two output terminals,
• wherein the output buffer capacitor is in parallel with a series connection of the two output terminals and the diode, and the startup terminal connects to a junction between the two output terminals and the diode, and wherein the load driver further comprises
• a load terminal coupled to said first terminal of the output buffer capacitor and to a cathode of the coupling diode,
• wherein the controllable switching element is connected between said load terminal and a ground bus, the controllable switching element being configured to selectively couple the load between the positive voltage bus and the ground bus to form a current loop,
• wherein said startup current turns on said switching element.

A load driver for driving a load, the load driver comprising:

• an output buffer capacitor;
• two output terminals coupled to the output buffer capacitor for coupling to the load;
• a coupling diode coupled in a forward direction from a first output terminal of the two output terminals to a first terminal of the output buffer capacitor;
• a positive voltage bus coupled to a second output terminal of the two output terminals and to a second terminal of the output buffer capacitor for providing a positive bias voltage to the load;
• and
• a converter circuit configured to output power through said two output terminals;
• the converter circuit comprising:
• a startup terminal configured to receive a startup current, wherein said startup terminal is coupled to said first output terminal;
• and
• a controllable switching element, wherein said startup terminal is connected to a control terminal of the controllable switching element such that the control terminal of the controllable switching element is in series connection with the two output terminals, and said switching element is turned on by the startup current;
• wherein the startup current is from the second output terminal of the two output terminals, through the load, to the first output terminal, to the startup terminal and into the control terminal of the controllable switching element when the load is coupled to the two output terminals, and
• wherein the coupling diode is configured to block current from the positive voltage bus towards the control terminal of the controllable switching element when the load is not coupled to the two output terminals,
• wherein the converter circuit further comprises a storage capacitor coupled to the startup terminal, and wherein said startup current is for charging the storage capacitor to provide a startup voltage to the control terminal of the switching element, and
• wherein the converter circuit further comprises a diac coupled between said storage capacitor and said control terminal of the switching element, to fire when the startup voltage of said storage capacitor has reached a threshold voltage.