Switching voltage regulator with low current trickle mode
View Patent ↗For load currents greater than a threshold current, the voltage regulator operates in a conventional manner by fully turning on and off one or more switching transistors at a duty cycle necessary to maintain the output voltage a regulated voltage. Upon a load current below a threshold being detected, a controller stops the switching of the transistor(s) and applies a reduced drive signal to the high side transistor so as to apply a constant trickle current to the load. Unnecessary components are shut down to save power. When the output voltage falls below a threshold, the normal switching routine is resumed to recharge the regulator's output capacitor to a certain level, and the regulator once again enters the light load current mode. By not completely shutting down the transistors at light load currents, as in done in a conventional intermittent-operation mode, there is lower power loss by less frequent switching of the transistor(s).
1. A voltage regulator for regulating a voltage applied to a load drawing a load current, the regulator comprising:
a switching regulator portion, the switching regulator portion comprising:
a first controller that receives a feedback signal related to an output voltage of the regulator and switches a first transistor at a duty cycle necessary to maintain an output voltage of the regulator at a regulated voltage when load currents exceed a first threshold current,
the first controller intermittently applying a first drive signal to the first transistor for turning on the first transistor during times when load currents exceed the first threshold current, and
a non-switching, non-linear regulator portion comprising:
a second controller that detects when a load current is below the first threshold current and, in response, stops switching the first transistor and applies a constant second drive signal to the first transistor, different from the first drive signal, to cause the first transistor to conduct a trickle current that is below the first threshold current, the constant second drive signal not varying with changes in the output voltage as the first transistor conducts the trickle current.
2. The regulator of claim 1 wherein the first controller comprises a pulse width modulation (PWM) controller.
3. The regulator of claim 1 wherein the first controller comprises an error amplifier that determines a difference between the feedback signal and a reference signal and wherein the first controller controls the duty cycle to approximately match the feedback signal to the reference signal.
4. The regulator of claim 1 wherein the first controller is a voltage mode controller that only uses a voltage feedback signal to control the duty cycle.
5. The regulator of claim 1 wherein the first controller is a current mode controller that uses a voltage feedback signal and a current feedback signal to control the duty cycle.
6. The regulator of claim 1 further comprising a current sensor that senses current through the first transistor.
7. The regulator of claim 6 wherein the first controller senses a signal from the current sensor and prevents the first transistor from shutting off until a minimum peak current through the first transistor has been reached during a switching cycle, whereby when the load current is below the first threshold level, the output voltage will rise.
8. The regulator of claim 1 further comprising a load current detector for detecting when a load current is below the first current threshold.
9. The regulator of claim 8 wherein the load current detector comprises a comparator that compares a signal corresponding to the output voltage of the regulator to a reference voltage to determine if the output voltage has risen above the reference voltage.
10. The regulator of claim 1 wherein the second controller comprises a voltage source that generates the constant second drive signal for the first transistor.
11. The regulator of claim 1 wherein the first transistor has a first conductivity when receiving the first drive signal and a lower second conductivity when receiving the second drive signal.
12. The regulator of claim 1 wherein the first transistor is a PMOS transistor having a gate, and wherein the second drive signal is a gate voltage greater than zero volts such that the PMOS transistor has a first conductivity when receiving the first drive signal and a lower second conductivity when receiving the second drive signal.
13. The regulator of claim 1 wherein the second controller disables the first controller when applying the constant second drive signal to the first transistor.
14. The regulator of claim 1 wherein the second controller comprises a comparator that detects when the output voltage has fallen below a threshold voltage and, in response, enables the first controller to resume switching of the first transistor.
15. The regulator of claim 1 wherein the regulator is a step down regulator.
16. A method performed by a voltage regulator for regulating a voltage applied to a load drawing a load current, the method comprising:
receiving a feedback signal related to an output voltage of the regulator;
switching a first transistor at a duty cycle necessary to maintain an output voltage of the regulator at a regulated voltage when load currents exceed a first threshold current,
switching the first transistor comprising intermittently applying a first drive signal to the first transistor for turning on the first transistor during times when load currents exceed the first threshold current;
detecting when a load current is below the first threshold current; and
in response to detecting when a load current is below the first threshold current, stopping switching the first transistor and applying a constant second drive signal to the first transistor, different from the first drive signal, to cause the first transistor to conduct a trickle current that is below the first threshold current, the constant second drive signal not varying with changes in the output voltage as the first transistor conducts the trickle current.
17. The method of claim 16 wherein switching the first transistor at a duty cycle comprises performing pulse width modulation (PWM).
18. The method of claim 16 wherein switching the first transistor at a duty cycle comprises determining a difference between the feedback signal and a reference signal, using an error amplifier, and controlling the duty cycle to approximately match the feedback signal to the reference signal.
19. The method of claim 16 wherein switching the first transistor at a duty cycle comprises sensing a signal from a current sensor and preventing the first transistor from shutting off until a minimum peak current through the first transistor has been reached during a switching cycle, whereby when the load current is below the first threshold level, the output voltage will rise.
20. The method of claim 16 wherein detecting when a load current is below the first threshold current comprises detecting when the output voltage has risen above a threshold level.
21. The method of claim 16 wherein applying a constant second drive signal to the first transistor comprises applying a voltage source that generates the constant second drive signal to a control terminal of the first transistor.
22. The method of claim 16 wherein the first transistor is a PMOS transistor having a gate, and wherein applying a constant second drive signal comprises applying a gate voltage to the PMOS transistor greater than zero volts.
23. The method of claim 16 wherein the first transistor has a first conductivity when receiving the first drive signal and a lower second conductivity when receiving the second drive signal.
24. The method of claim 16 further comprising disabling components used to switch the first transistor when applying the constant second drive signal to the first transistor.
25. The method of claim 16 further comprising detecting when the output voltage has fallen below a threshold voltage and, in response, resuming switching of the first transistor.
26. The method of claim 16 wherein the regulator is a step down regulator.