Current protected integrated transformer driver for isolating a DC-DC convertor
An improved electronic oscillator circuit suitable for use in an isolating DC-to-DC converter circuit, and an improved isolating DC-to-DC converter circuit. In one embodiment, an integrated circuit coupled to a transformer includes an oscillator and an output driver. The integrated circuit is preferably fabricated using a silicon-on-insulator technology. The oscillator outputs an alternating pulse signal defined by electrical characteristics of components other than the transformer. The alternating pulse signal is coupled to the output driver, the alternating output of which is coupled to corresponding legs of the primary winding of the transformer. The secondary winding of the transformer provides an electromagnetically coupled isolated output which may be rectified and filtered to produce a DC output voltage. Additional functionality, such as current protection circuitry for the improved circuits, may be readily added to the integrated circuit at little or no increase in cost.
1. An integrated circuit embodying an electronic oscillator circuit configured for use in an isolating DC-to-DC converter circuit, the integrated circuit including:
(a) an oscillator generating a periodic pulse signal;
(b) a switch, configured to be coupled to the primary winding of a transformer, for providing energy flow in the primary winding of the coupled transformer;
(c) an output driver, coupled to the oscillator, for converting the periodic pulse signal to gate pulses for the switch;
(d) a pulsed control circuit for generating current-limiting gate voltages comprising a current mirror circuit;
(e) an over-current protection circuit, coupled between the output driver and the switch, and coupled to the pulsed control circuit, for selectively coupling the gate pulses to the switch if current through the switch is not greater than a selected value, and for selectively coupling the current-limiting gate voltages from the current mirror to the switch if current through the switch is greater than a selected value.
2. The invention of claim 1 , wherein the over-current protection circuit includes a comparator, coupled to a first voltage derived from a first reference current, and to a second voltage in the switch indicative of the current through the switch, for generating a comparison signal indicating whether the current through the switch is greater or not greater than a selected value.
3. The invention of claim 1 , wherein the over-current protection circuit includes a timing circuit for limiting the amount of time that the current-limiting gate voltages are coupled to the switch.
4. The invention of claim 1 , wherein the over-current protection circuit includes a timing circuit that selectively couples the gate pulses to the switch after a specified time has elapsed since the current-limiting gate voltages were coupled to the switch.
5. A method for over-current protection of a driving circuit for an isolating DC-to-DC converter circuit:
(a) generating a periodic pulse signal in the driving circuit;
(b) providing a switch, configured to be coupled to the primary winding of a transformer, for providing energy flow in the primary winding of the coupled transformer;
(c) converting the periodic pulse signal to gate pulses for the switch;
(d) providing a pulsed control circuit having a current mirror for generating current-limiting gate voltages; and
(e) coupling the gate pulses to the switch if current through the switch is not greater than a selected value, and coupling the current-limiting gate voltages from the current mirror to the switch if current through the switch is greater than a selected value.
6. The method of claim 5 , further including:
(a) comparing a first voltage derived from a first reference current to a second voltage in the switch indicative of the current through the switch; and
(b) generating a comparison signal indicating whether the current through the switch is greater or not greater than a selected value.
7. The method of claim 5 , further including limiting the amount of time that the current-limiting gate voltages are coupled to the switch.
8. The method of claim 5 , further including selectively coupling the gate pulses to the switch after a specified time has elapsed since the current-limiting gate voltages were coupled to the switch.