BIAS POWER REGULATOR CIRCUIT FOR ISOLATED CONVERTERS WITH A WIDE OUTPUT VOLTAGE RANGE

1 . A circuit comprising:

a transistor having a first current terminal, a second current terminal, and a control terminal;

a current sense circuit coupled to the second current terminal;

modulation circuitry coupled to the control terminal and to the current sense circuit; and

a mode controller coupled to the modulation circuitry.

2 . The circuit of claim 1 , further comprising:

an inductor having a first inductor terminal and a second inductor terminal, the first inductor terminal coupled to the first current terminal and the second inductor terminal coupled to the modulation circuitry;

a diode having an anode and a cathode, the anode coupled to the first inductor terminal and the cathode coupled to the modulation circuitry and to the modulation circuitry; and

a capacitor having a first capacitor terminal and a second capacitor terminal, the first capacitor terminal coupled to the diode.

3 . The circuit of claim 1 , wherein the first current terminal, the modulation circuitry, and the mode controller are adapted to be coupled to a controller.

4 . The circuit of claim 1 , wherein the mode controller comprises:

a comparator having a first comparator input, a second comparator input, and a comparator output, the first comparator input coupled to the modulation circuitry; and

a logic gate having a first logic input, a second logic input, and a logic output, the first logic input coupled to the comparator output and the logic output coupled to the modulation circuitry.

5 . The circuit of claim 1 , wherein the modulation circuitry comprises:

a constant peak-current modulation circuit coupled to the current sense circuit;

a constant off-time modulation circuit coupled to the mode controller; and

a latch having a first latch input, a second latch input, and a latch output, the first latch input coupled to the constant peak-current modulation circuit, the second latch input coupled to the constant off-time modulation circuit, and the latch output coupled to the control terminal.

6 . The circuit of claim 5 , further comprising a logic gate having a first logic input, a second logic input, and a logic output, the first logic input coupled to the constant peak-current modulation circuit, the second logic input coupled to the constant off-time modulation circuit, and the logic output coupled to the second latch input.

7 . The circuit of claim 6 , wherein the logic gate is a first logic gate and the logic output is a first logic output, the constant peak-current modulation circuit comprising:

a comparator having a first comparator input, a second comparator input, and a comparator output, the first comparator input coupled to the current sense circuit;

a second logic gate having a third logic input, a fourth logic input, and a second logic output, the third logic input coupled to the comparator output, and the second logic output coupled to the first latch input;

a feedback circuit having a feedback output; and

a voltage controlled oscillator (VCO) having a VCO input and a VCO output, the VCO input coupled to the feedback output and the VCO output coupled to the second logic input.

8 . The circuit of claim 5 , wherein the constant off-time modulation circuit comprises:

an inverter having an inverter input and an inverter output, the invertor output coupled to the latch output;

a delay circuit having a delay input and a delay output, the delay input coupled to the invertor output; and

a logic gate having a first logic input, a second logic input, and a logic output, the first logic input coupled to the delay output, the second logic input coupled to the mode controller, and the logic output coupled to the second latch input.

9 . The circuit of claim 5 , wherein the modulation circuitry further comprises:

a modulation controller;

a logic gate having a first logic input, a second logic input, and a logic output, the first logic input coupled to the modulation controller and the second logic input coupled to the latch output; and

a driver having a driver input and a driver output, the driver input coupled to the logic output and the driver output coupled to the control terminal.

10 . The circuit of claim 5 , further comprising a switch coupled to the current sense circuit and to the modulation circuitry, wherein the modulation circuitry is configured to provide a plurality of modulation modes to modulate a switching frequency of the switch and the mode controller is configured to select one of the plurality of modulation modes.

11 . A circuit comprising:

a controller;

a transistor having a first current terminal, a second current terminal, and a control terminal, the first current terminal coupled to the controller;

a current sense circuit coupled to the second current terminal; and

a control circuit coupled to the control terminal, to the current sense circuit, and to the controller.

12 . The circuit of claim 11 , wherein the control circuit comprises:

modulation circuitry coupled to the controller, to the current sense circuit, and to the control terminal; and

a mode controller coupled to the modulation circuitry and to the controller.

13 . The circuit of claim 12 , wherein the mode controller is configured to:

receive a light load signal from the controller; and

send pulse requests to the controller while the light load signal is asserted.

14 . The circuit of claim 12 , wherein the modulation circuitry comprises:

constant peak-current modulation circuitry coupled to the current sense circuit, to the control terminal, and to the first current terminal; and

constant off-time modulation circuitry coupled to the mode controller and to the control terminal; and

wherein the mode controller is configured to select the constant off-time modulation circuitry responsive to receiving a load signal from the controller and a voltage level from the current sense circuit; and

wherein the mode controller is configured to select the constant peak-current modulation circuitry responsive to receiving the load signal from the controller and the voltage level from the current sense circuit.

15 . The circuit of claim 12 , further comprising:

an inductor having a first inductor terminal and a second inductor terminal, the first inductor terminal coupled to the first current terminal and the second inductor terminal coupled to the modulation circuitry;

a diode coupled to the first current terminal and to the controller; and

a capacitor coupled to the diode.

16 . A circuit, comprising:

a power transformer having a primary winding, a secondary winding, and an auxiliary winding;

a first switch having a first current terminal, a second current terminal, and a first control terminal, the first current terminal coupled to the primary winding;

a controller coupled to the first control terminal of the first switch;

a second switch having a third current terminal, a fourth current terminal, and a second control terminal, the third current terminal coupled to the controller and to the auxiliary winding; and

a control circuit coupled to the controller and to the third current terminal.

17 . The circuit of claim 16 , wherein the control circuit comprises:

modulation circuitry coupled to the second control terminal, and to the auxiliary winding; and

a mode controller coupled to the controller and to the control circuit.

18 . The circuit of claim 17 , further comprising a current sense circuit coupled to the fourth current terminal and to the modulation circuitry.

19 . The circuit of claim 18 , wherein the modulation circuitry comprises:

constant peak-current modulation circuitry coupled to the current sense circuit, to the second control terminal, and to the first current terminal; and

constant off-time modulation circuitry coupled to the mode controller and to the second control terminal; and

wherein the mode controller is configured to select the constant off-time modulation circuitry responsive to receiving a load signal from the controller and a voltage level from the current sense circuit; and

wherein the mode controller is configured to select the constant peak-current modulation circuitry responsive to receiving the load signal from the controller and the voltage level from the current sense circuit.

20 . The circuit of claim 16 , wherein the secondary winding is adapted to be coupled to a universal serial bus (USB) power delivery adapter.