Pulse frequency modulated voltage regulator with linear regulator control
View Patent ↗A PFM-type voltage regulator circuit converts an unregulated input voltage into a regulated output voltage using a first transistor controlled by a pulse control circuit and a second transistor controlled by a linear regulator circuit. The linear regulator circuit controls the second transistor when the regulated output voltage falls to a predetermined minimum target voltage level, thereby maintaining the regulated output voltage at the minimum target voltage level. The pulse control circuit detects the current passing through the second transistor, and in response generates a pulse signal having a predetermined duration that fully turns on the first transistor. The voltage through the first transistor is converted to an increasing inductor current that refreshes the regulated output voltage to a maximum target voltage level. When the pulse signal ends, the regulated output voltage again begins to fall toward the predetermined minimum target voltage level, and the cycle is repeated.
1. A voltage regulator circuit for converting an unregulated input voltage received at an input node into a regulated output voltage provided at an output node, the voltage regulator comprising:
a first transistor having a first terminal coupled to the input node;
an inductor coupled between a second terminal of the first transistor and the output node;
a linear regulator circuit coupled in parallel with the first transistor and the inductor between the input node and the output node, wherein the linear regulator circuit includes means for passing a first current from the input node to the output node when the regulated output voltage provided at the output node drops below a predetermined minimum target voltage level such that the first current maintains the output node at the minimum target voltage level; and
a pulse control circuit including means for detecting the first current through the linear regulator circuit, and means for transmitting a pulse signal having a predetermined duration to a gate terminal of the first transistor in response to said detected first current.
2. The voltage regulator circuit of claim 1 , wherein the linear regulator comprises:
a second transistor having a first terminal connected to the input node, a second terminal connected to the output node, and a gate terminal; and
a linear control circuit including means for comparing a linear reference voltage and a feedback signal, and for generating a linear control signal having a voltage level that is proportional to a difference between the linear reference voltage and the feedback signal,
wherein the linear control signal is applied to the gate terminal of the second transistor, whereby a conductance of the second transistor is controlled in response to the linear signal such that said first current passed by the second transistor is proportional to the linear control signal.
3. The voltage regulator circuit of claim 2 , wherein the second transistor comprises a PMOS transistor sized such that the second transistor operates in a saturated operating state in response to the linear signal.
4. The voltage regulator circuit of claim 1 , wherein the pulse control circuit comprises:
a current sensing circuit for asserting a pulse control signal when the first current passing through the linear regulator exceeds a predetermined minimum current; and
a pulse generating circuit for generating the pulse signal in response to the pulse control signal.
5. The voltage regulator circuit of claim 4 , wherein the current sensing circuit comprises:
a sensor for generating a current detection signal in response to the first current passing through the linear regulator; and
a comparator for comparing the current detection signal with a predetermined reference signal, and for generating the pulse control signal when the current detection signal is greater than the predetermined reference signal.
6. The voltage regulator circuit of claim 5 , wherein the current sensing circuit further comprises a third transistor having a first terminal connected to the input node, a second terminal connected to the output node, and a gate terminal connected to the linear regulator circuit, wherein the sensor is coupled to the first terminal of the third transistor.
7. The voltage regulator circuit of claim 5 , wherein the pulse generating circuit comprises a one-shot circuit.
8. The voltage regulator circuit of claim 1 , wherein the first transistor comprises a field-effect transistor and the pulse control circuit comprises means for generating the pulse signal at a sufficient level such that the first transistor is switched in response to the pulse signal during the predetermined duration.
9. The voltage regulator circuit of claim 8 , wherein the field-effect transistor comprises a PMOS transistor.
10. The voltage regulator circuit of claim 1 , further comprising a diode connected between the output node and a ground terminal.
11. The voltage regulator circuit of claim 1 , further comprising a capacitor connected between the output node and a ground terminal.
12. The voltage regulator circuit of claim 1 , further comprising means for generating a pulse-width modulated control signal, and means for selectively applying one of the PWM control signal and the pulse signal to the gate terminal of the first transistor in response to an applied load condition.
13. A voltage regulator circuit for converting an unregulated input voltage received at an input node into a regulated output voltage provided at an output node such that the regulated output voltage is maintained at a predetermined minimum target voltage level, the voltage regulator comprising:
a first transistor having a first terminal coupled to the input node;
an inductor connected between a second terminal of the first transistor and the output node;
a second transistor having a first terminal coupled to the input node, and a second terminal connected to the output node;
linear control means for controlling the second transistor such that the second transistor conducts a first current between the input and output nodes when the regulated output voltage is equal to or less than the predetermined minimum target voltage level such that the first current maintains the output node at the minimum target voltage level; and
pulse control means for controlling the first transistor to conduct a second current between the input node and the inductor when the linear control means causes the second transistor to conduct said first current such that the regulated output voltage provided at the output node is raised above the minimum target voltage level by the second current.
14. The voltage regulator circuit of claim 13 , wherein the pulse control means comprises:
current sensing means for asserting a pulse control signal when the first current through the second transistor exceeds a predetermined minimum current; and
pulse generating means for generating a pulse signal in response to the pulse control signal,
wherein the pulse generating means is coupled to the gate terminal of the first transistor.
15. The voltage regulator circuit of claim 14 , wherein the current sensing means comprises:
a sensor for generating a current detection signal in response to the first current through the second transistor; and
means generating the pulse control signal when the current detection signal is greater than a predetermined reference signal.
16. The voltage regulator circuit of claim 15 , wherein the current sensing means further comprises a third transistor having a first terminal connected to the input node, a second terminal connected to the output node, and a gate terminal connected to the gate terminal of the second transistor, wherein the sensor is coupled to the first terminal of the third transistor.
17. The voltage regulator circuit of claim 16 , wherein the first, second and third transistors comprise PMOS transistors.
18. The voltage regulator circuit of claim 14 , further comprising means for generating a pulse-width modulated control signal, and means for selectively applying one of the PWM control signal and the pulse signal to the gate terminal of the first transistor in response to an applied load condition.
19. The voltage regulator circuit of claim 13 , further comprising a capacitor connected between the output node and a ground terminal.
20. A voltage regulator circuit for converting an unregulated input voltage received at an input node into a regulated output voltage provided at an output node such that the regulated output voltage is maintained at a predetermined minimum target voltage level, voltage regulator comprising:
an inductor coupled between the input node and the output node;
linear regulator means arranged in parallel with the inductor for selectively generating a first current between the input node and the output node only when the regulated output voltage is equal to or less than the predetermined minimum target voltage level such that the first current maintains the output node at the minimum target voltage level; and
means for generating a second current between the input node and the inductor for a predetermined duration when the linear regulator means generates the first current such that the regulated output voltage provided at the output node is raised above the minimum target voltage level by the second current.