Extending the voltage operating range of boost regulators
View Patent ↗One embodiment of the invention is a hybrid boost regulator that includes a conventional boost regulator chip that operates when its input voltage is above 2.5 volts and a pre-boost circuit that operates when its input voltage is above 1 volt. A single 1.5 volt battery may be used to power the hybrid boost regulator. The pre-boost circuit is connected to the voltage input terminal of the boost regulator chip. The pre-boost circuit boosts the battery voltage (e.g., 1.5v) at an output terminal of the hybrid boost regulator to approximately the minimum operating voltage (e.g., 2.5v) of the boost regulator chip. Since this pre-boosted voltage is applied to the voltage input terminal of the boost regulator chip, the boost regulator chip will become operational when the ramping output voltage of the hybrid boost regulator exceeds about 2.5 volts. Once the boost regulator chip is operational, the pre-boost circuit is then turned off, and the boost regulator chip runs off the 1.5 volt power supply to ramp up the output voltage to the full regulated voltage.
1. A boost regulator comprising:
a first boost regulator having a voltage input terminal for supplying power to components in the first boost regulator, the first boost regulator for controlling switching of a first transistor to supply a boosted voltage at an output node, the first boost regulator requiring at least a first voltage level at the voltage input terminal to operate properly;
an inductor coupled at one end to a power supply voltage and at a second end to a first node, the first node being coupled to a first terminal of the first transistor, wherein switching of the first transistor charges and discharges the inductor to control a voltage level at the output node;
a pre-boost circuit comprising:
an oscillator powered from the power supply voltage when the power supply voltage is less than the first voltage level required to operate the first boost regulator;
a second transistor connected to the oscillator, the oscillator switching the second transistor when the power supply voltage is less than the first voltage level, the second transistor being coupled to the first node, wherein switching of the second transistor charges and discharges the inductor to ramp up the output voltage at the output node to be greater than the power supply voltage;
a first connection for feeding a boosted voltage at the output node to the voltage input terminal of the first boost regulator, whereby the boosted voltage causes the first boost regulator to be operational after the voltage at the voltage input terminal is at least the first voltage level; and
a detection circuit for disabling the pre-boost circuit after the first boost regulator has become operational and begins switching the first transistor.
2. The regulator of claim 1 wherein the first connection comprises a low dropout (LDO) regulator connected between the voltage input terminal of the first boost regulator and the output node.
3. The regulator of claim 1 further comprising an enable terminal of the first boost regulator, wherein the voltage input terminal is connected to the enable terminal.
4. The regulator of claim 1 wherein the second transistor is a bipolar transistor connected between the first node and ground.
5. The regulator of claim 1 further comprising a filter circuit connected between the first node and the output node.
6. The regular of claim 1 wherein the first transistor and the second transistor are connected between the first node and ground.
7. The regulator of claim 1 further comprising a sense resistor connected to the second transistor for detecting a current flowing through the second transistor.
8. The regulator of claim 1 wherein the first boost regulator is a PWM regulator.
9. The regulator of claim 1 wherein the first boost regulator is a current mode PWM regulator.
10. The regulator of claim 1 wherein the detection circuit comprises a current detector for detecting that a current through the first transistor is above a threshold current and, in response, disabling the pre-boost circuit.
11. The regulator of claim 10 wherein the current detector comprises a comparator that compares a voltage corresponding to a current level to a threshold voltage, wherein tripping of the comparator disables the oscillator.
12. The regulator of claim 1 wherein the pre-boost circuit is operational with a power supply voltage of 1.5 volts, and the first boost regulator requires a voltage greater than 1.5 volts applied to its voltage input terminal to be operational.
13. The regulator of claim 1 wherein the pre-boost circuit is operational with a power supply voltage of 1.5 volts.
14. The regulator of claim 13 wherein the power supply voltage is from a single 1.5 volt battery.
15. The regulator of claim 1 wherein the oscillator comprises:
a shunt regulator connected to the power supply voltage;
an inverter chain;
a capacitor couple to an input of the inverter chain, the shunt regulator controlling voltage to the capacitor and inverter chain;
a switch selectively coupling the power supply voltage to the shunt regulator, the switch uncoupling the power supply voltage from the shunt regulator after the first boost regulator have become operational; and
a driver receiving the power supply voltage, the power supply voltage to the driver not being regulated by the shunt regulator, an output of the driver being coupled to a control terminal of the second transistor.
16. A method performed by a boost regulator comprising:
controlling switching of a first transistor by a first boost regulator to supply a boosted power supply voltage at an output node when the first boost regulator has at least a first voltage level applied to its voltage input terminal, the first boost regulator being non-operational when a voltage of less than the first voltage level is applied to its voltage input terminal;
wherein switching of the first transistor charges and discharges an inductor connected at one end to a power supply voltage and at a second end to a first node, the first node being coupled to a first terminal of the first transistor;
switching a second transistor in a pre-boost circuit by an oscillator powered from the power supply voltage when the power supply voltage is less than the first voltage level required to operate the first boost regulator, the second transistor being coupled to the first node, wherein switching of the second transistor charges and discharges the inductor to ramp up an output voltage at the output node to be greater than the power supply voltage;
feeding a boosted voltage at the output node to the voltage input terminal of the first boost regulator, whereby the boosted voltage causes the first boost regulator to be operational after the voltage at the voltage input terminal is at least the first voltage level; and
disabling the pre-boost circuit after the first boost regulator has become operational and begins switching the first transistor.
17. The method of claim 16 wherein the feeding the boosted voltage to the voltage input terminal comprises regulating the voltage to the voltage input terminal by a low dropout (LDO) regulator connected between the voltage input terminal of the first boost regulator and the output node.
18. The method of claim 16 wherein the first transistor and the second transistor are connected between the first node and ground.
19. The method of claim 16 further comprising detecting a current flowing through the first transistor by sensing a voltage across a sense resistor connected to the first transistor.
20. The method of claim 16 wherein the first boost regulator is a PWM regulator.
21. The method of claim 16 wherein the first boost regulator is a current mode PWM regulator.
22. The method of claim 16 wherein disabling the pre-boost circuit comprises detecting that a current through the first transistor is above a threshold current and, in response, disabling the pre-boost circuit.
23. The method of claim 16 wherein the pre-boost circuit is operational with a power supply voltage of 1.5 volts, and the first boost regulator requires a voltage greater than 1.5 volts applied to its voltage input terminal to be operational.
24. The method of claim 16 wherein the pre-boost circuit is operational with a power supply voltage of 1.5 volts.