Negative charge pump doubling output voltage range for step-up LED driver

1. A supply circuit comprising:

a regulated positive supply circuit including:

an inductor arranged to receive input energy from an input circuit node;

a switch circuit coupled to the inductor at a switch circuit node; and

a control circuit coupled to the switch circuit, the control circuit configured to control activation of the switch circuit to regulate a voltage at a regulated circuit node and generate a positive output voltage at a positive output circuit node; and

an unregulated negative supply circuit operatively coupled to the switch circuit node and configured to generate a negative supply voltage at a negative output circuit node.

2. The supply circuit of claim 1 , wherein the regulated positive supply circuit includes a switching power converter circuit and the unregulated negative supply circuit includes a negative charge pump circuit.

3. The supply circuit of claim 2 ,

wherein the switch circuit includes:

a first transistor coupled to the switch circuit node configured to charge the inductor when activated; and

a second transistor coupled to the switch circuit node configured to transfer charge from the inductor to the regulated circuit node when activated; and

wherein the unregulated negative supply circuit includes:

a switching capacitor arranged between the switch circuit node and the negative output node; and

wherein activation of the first transistor provides an unregulated negative voltage to the negative output circuit node.

4. The supply circuit of claim 3 , wherein activation of the second transistor charges the switching capacitor to the voltage of the regulated circuit node, and the activation of the first transistor generates a negative polarity of the voltage of the regulated circuit node at the negative output circuit node.

5. The supply circuit of claim 1 , wherein the regulated positive supply circuit includes a switching power converter circuit and the unregulated negative supply circuit includes a Cúk converter circuit.

6. The supply circuit of claim 5 ,

wherein the switch circuit includes:

a first transistor coupled to the switch circuit node configured to charge the inductor when activated; and

a second transistor coupled to the switch circuit node configured to transfer charge from the inductor to the regulated circuit node when activated; and

wherein the unregulated negative supply circuit includes:

a switching capacitor and a negative supply inductor arranged between the switch circuit node and the negative output node.

7. The supply circuit of claim 1 , wherein the regulated positive supply circuit includes a step-up converter circuit.

8. The supply circuit of claim 7 , including:

an input circuit node;

wherein the switch circuit includes:

a first transistor coupled to the switch circuit node configured to charge the inductor when activated; and

a second transistor coupled to the switch circuit node configured to transfer charge from the inductor to the regulated circuit node when activated; and

wherein a regulated voltage (Vout) between the regulated circuit node to circuit ground is equal to a voltage at the input circuit node (Vin) multiplied by the inverse of one minus the duty cycle (D) of the activation of the first transistor, or Vout=Vin/(1−D), and the voltage between circuit ground and the negative output circuit node is equal to a negative of the regulated voltage (−Vout).

9. The supply circuit of claim 1 , including:

a pulse width modulated (PWM) switch circuit arranged between the regulated circuit node and the positive output circuit node;

wherein the control circuit is configured to modulate activation of the PWM switch circuit to control load current when a load is coupled between the positive output circuit node and the negative output circuit node.

10. A method of operating a supply circuit, the method comprising:

charging an inductor using energy provided at an input circuit node of the supply circuit;

generating a regulated voltage at a regulated circuit node by controlling the charging of the inductor using a switch circuit coupled to a switch circuit node of the supply circuit;

generating a positive output voltage at a positive output circuit node using the regulated voltage; and

generating an unregulated negative supply voltage at a negative output circuit node using the voltage of the switch circuit node.

11. The method of claim 10 , wherein the generating the unregulated negative supply voltage includes generating the unregulated negative supply voltage using a negative charge pump.

12. The method of claim 10 , including:

activating a first transistor coupled to the switch circuit node to charge the inductor;

activating a second transistor coupled to the switch circuit node to transfer charge from the inductor to the regulated circuit node; and

providing a negative unregulated voltage to the negative output circuit node when activating the first transistor.

13. The method of claim 12 , wherein activating the second transistor charges the switching capacitor to the voltage of the regulated circuit node, and the activating the first transistor generates a negative polarity of the voltage of the regulated circuit node at the negative output circuit node.

14. The method of claim 10 , wherein the generating the unregulated negative supply voltage includes generating the unregulated negative supply voltage using a Cúk converter circuit.

15. The method of claim 10 , wherein the generating the regulated voltage includes generating the regulated voltage using a step-up converter circuit.

16. The method of claim 15 , including:

activating a first transistor coupled to the switch circuit node to charge the inductor; and

activating a second transistor coupled to the switch circuit node to transfer charge from the inductor to the regulated circuit node;

wherein the generating the regulated voltage includes generating a regulated voltage (Vout) between the regulated circuit node to circuit ground equal to a voltage at the input circuit node (Vin) multiplied by the inverse of one minus the duty cycle (D) of the activation of the first transistor, or Vout=Vin/(1−D); and

wherein the generating the unregulated negative supply voltage includes generating the unregulated negative supply voltage between circuit ground and the negative output circuit node equal to a negative polarity of the regulated voltage (−Vout).

17. The method of claim 10 , including modulating activation of a PWM switch circuit of the supply circuit to control load current when a load is coupled between the positive output circuit node and the negative output circuit node.

18. A light emitting diode (LED) driver, the LED driver comprising:

a regulated positive supply circuit including:

an inductor arranged to receive input energy from an input circuit node;

a switch circuit coupled to the inductor at a switch circuit node; and

a control circuit coupled to the switch circuit, the control circuit configured to control activation of the switch circuit to regulate a voltage at a regulated circuit node and generate a positive output voltage at a positive output circuit node;

an unregulated negative supply circuit operatively coupled to the switch circuit node and configured to generate a negative supply voltage at a negative output circuit node;

a pulse width modulated (PWM) switch circuit arranged between the regulated circuit node and the positive output circuit node;

a load current sensing circuit element operatively coupled to the PWM switch; and

wherein the control circuit is further configured to modulate activation of the PWM switch circuit to control load current when a load is coupled between the positive output circuit node and the negative output circuit node.

19. The LED driver of claim 18 , wherein the regulated positive supply circuit includes a switching power converter circuit and the unregulated negative supply circuit includes a negative charge pump circuit.

20. The LED driver of claim 18 , wherein the regulated positive supply circuit includes a switching power converter circuit and the unregulated negative supply circuit includes a Cúk converter circuit.