Detecting overcurrents in a switching regulator using a voltage dependent reference
View Patent ↗A switching regulator provides energy to an inductor-capacitor combination that supply a DC voltage as an output. The presence of a current that can be significantly lower than the typical load current is detected using a pulse signal that provides a measure of the current supplied by the regulator to the inductor. A comparator compares this signal to a reference voltage that is related to the current level to be detected. This reference voltage is adjustable based on the voltage applied by the regulator and the voltage being ultimately supplied as the DC output voltage. The comparator and a capacitor perform an integration function that results in a voltage that ramps upward if the current threshold is being exceeded. When this ramping voltage passes a predetermined level, a signal is provided to indicate that the threshold has been exceeded.
1. An active circuit for being coupled to a reactive circuit that provides an output voltage, comprising:
a control regulator circuit having an output for providing pulses;
a first switch that has an input coupled to the output of the control regulator curcuit, a power supply input coupled to a power supply terminal, and an output that is an output of the active circuit;
a pulse shaper having an input coupled to the control regulator circuit and an output;
a reference voltage generator for providing a reference voltage that changes in response to changes in a voltage at the power supply terminal; and
an integrator having a first input coupled to the output of the pulse shaper, a second input for receiving the reference voltage, and an output for providing a signal indicative of a current level supplied at the output voltage, wherein:
the reference voltage generator is responsive to a first programming signal in addition to being responsive to the voltage at the power supply terminal;
the first programming signal is representative of the output voltage; and
the first programming signal is the output voltage.
2. The active circuit of claim 1 further comprising a crowbar switch coupled to the control regulator circuit and a crowbar comparator coupled to the crowbar switch.
3. The active circuit of claim 1 , wherein the pulse shaper comprises:
a first transistor having a control electrode coupled to the output of the control regulator circuit, a first current electrode coupled to the output of the first switch, and a second current electrode; and
a first resistor having a first terminal coupled to the second current electrode of the first transistor and a second terminal coupled to the power supply terminal.
4. The active circuit of claim 1 , wherein the integrator comprises:
a voltage-to-current converter having a first input coupled to the output of the pulse shaper, a second input to the output of the reference voltage generator, and an output; and
a capacitor coupled to the output of the voltage-to-current converter.
5. The active circuit of claim 1 , wherein the first switch comprises an N channel transistor.
6. An active circuit, comprising:
pulse means for generating current pulses from a supply voltage for use in providing a DC output voltage;
replication means, coupled to the pulse means, for generating pulses representative of the current pulses;
reference means for providing a reference voltage based on information as to the DC output voltage and the supply voltage;
comparator means, coupled to the replication means and the reference means, for generating current pulses, wherein each pulse has an amount of charge related to the reference voltage; and
a capacitor for receiving the current pulses;
wherein the information as to the DC output voltage is the DC output voltage.
7. The active circuit of claim 6 further comprising a crowbar switch coupled to the pulse means and a crowbar comparator coupled to the crowbar switch.
8. The active circuit of claim 6 , wherein the replication means comprises:
a transistor coupled to the pulse means; and
resistor means for being coupled between the transistor and the supply voltage.
9. The active circuit of claim 6 , wherein the reference means comprises three current sources and a resistor.
10. The active circuit of claim 6 , further comprising a Schmitt Trigger coupled to the capacitor.
11. The active circuit of claim 6 , wherein;
the information as to the DC output voltage is a first programming signal; and
the reference means is responsive to a second programming signal.