Automatic frequency oscillator for pulse-regulated switch-mode power supply

1. A switch-mode power supply circuit, comprising:

a pulse generation circuit comprising an oscillator, the oscillator configured to generate first pulses using a fixed frequency regulation for a first load condition that exceeds a predefined threshold and configured to generate second pulses using a variable frequency regulation for a second load condition that does not exceed the predefined threshold;

a power converter coupled to the pulse generation circuit and configured to convert a first voltage to a regulated voltage using either one of the first or second pulses generated by the pulse generation circuit; and

an output filter coupled to the power converter and configured to produce a second voltage from the regulated voltage; and

wherein the oscillator includes:

a first transistor and a resistor configured to convert a third voltage to a current, wherein a control terminal of the first transistor is configured to receive the third voltage and the current is a function of the third voltage;

a current mirror coupled to at least one terminal of the first transistor and configured to provide a second current to charge a capacitor, the second current proportional to the current; and

wherein the capacitor is configured to provide a fourth voltage to a buffer having a fixed threshold voltage, the buffer is configured to supply a second clock signal in response to the fourth voltage exceeding the fixed threshold voltage of the buffer.

2. The switch-mode power supply circuit of claim 1 , wherein the oscillator comprises a second transistor, wherein a control terminal of the second transistor is configured to be driven by a first clock signal and a non-control terminal of the second transistor is configured to provide the first clock signal to the buffer, wherein an output of the buffer is configured to provide the second clock signal that is a function of the charging rate of the capacitor.

3. The switch-mode power supply circuit of claim 2 , wherein the oscillator further comprises a current source configured to provide a third current to a non-control terminal of the first transistor.

4. The switch-mode power supply circuit of claim 2 , wherein the oscillator further comprises a comparator configured to control the first transistor.

5. A switch-mode power supply circuit, comprising:

a pulse generation circuit comprising an oscillator, the oscillator configured to generate first pulses using a fixed frequency regulation for a first load condition that exceeds a predefined threshold and configured to generate second pulses using a variable frequency regulation for a second load condition that does not exceed the predefined threshold;

a power converter coupled to the pulse generation circuit and configured to convert a first voltage to a regulated voltage using either one of the first or second pulses generated by the pulse generation circuit;

an output filter coupled to the power converter and configured to produce a second voltage from the regulated voltage; and

wherein the pulse generation circuit further comprises:

a first transistor and a second transistor configured to clamp a third voltage received at a first control terminal of the first transistor, wherein the voltage is based on a comparison of a reference voltage to a feedback voltage based on the second voltage;

a current source configured to provide a current to a non-control terminal of the first transistor; and

wherein a voltage at a control terminal of the second transistor is not less than a threshold voltage of the first transistor and is an input to the oscillator.