Transformer isolated drive circuit

A transformer isolated drive circuit, for selectively energizing a load switch over a duty cycle of 0-100% in response to a load switch control signal, comprising:

• retriggerable timer means, for providing at least one timed output signal having a preselected time period in response to one of at least first and second trigger signals;
• voltage enable and control means, responsive to a load switch input control signal, and said at least one timed output signal, for providing at least one voltage control signal;
• said load switch input control signal operative as said first trigger signal;
• first and second voltage sources, responsive to said at least one voltage control signal, for providing first and second voltage signals which are of selectable voltage potentials for providing a primary voltage of selectable voltage potential and wherein different combinations of the first and second voltage signals of selectable voltage potentials provide first and second voltage signals at an alternating positive and negative voltage polarity;
• a transformer having a primary side and a secondary side, said primary side including first and second inputs coupled to said first and second voltage signals, and operative for inducing a secondary voltage across first and second outputs of said secondary side, said induced secondary voltage of the same relative voltage polarity as said primary voltage on said primary side, and of a voltage potential proportional to the turns ratio of the primary to the secondary side;
• said first and second voltage sources including first and second current sense means respectively, for sensing current flow in said transformer primary side, and for providing first and second zero current indicator signals respectively, upon the detection of zero current flow in the primary side of said transformer;
• trigger signal generator means, responsive to said first and second zero current indicator signals, said at least one voltage control signal and said at least one timed output signal, for providing said second trigger signal;
• and
• voltage level sense and switch control means, coupled to said first and second outputs of said transformer secondary side, and responsive to said relative voltage potential and polarity induced across said first and second transformer secondary side outputs, for enabling said load switch in response to a first sensed voltage potential and polarity, and for disabling said load switch in response to a second sensed voltage potential and polarity.