Hysteretic voltage converter with offset voltage correction
A hysteretic power converter wherein an additional adjustment circuit, implemented as an offset correction loop, adds an offset to the comparator detection function to reduce the difference between the average output voltage and the regulation set point voltage. The adjustment circuit lies outside the main hysteretic regulation loop and therefore does not substantially impact the response time of the hysteretic loop, and is slow acting responsive to a low pass filter.
1. A hysteretic power converter comprising:
a reference input signal;
a switched mode power supply comprising an inductor and an electronically controlled switch, wherein the output of the switched mode power supply increases responsive to a first state of the electronically controlled switch and decreases responsive to a second state of the electronically controlled switch, said second state opposing said first state;
a comparator coupled to a feedback signal and a threshold value signal and arranged to compare the feedback signal with the threshold value signal and to change the state of the electronically controlled switch of said switched mode power supply to the first state responsive to the feedback signal falling below the threshold value signal, wherein the feedback signal is responsive to the instantaneous output voltage of said switched mode power supply and the threshold value signal is responsive to said reference input signal;
a reset circuit arranged to change the state of the electronically controlled switch of said switched mode power supply to the second state responsive to a predetermined condition; and
an adjustment circuit comprising a low pass filter and arranged to output one of the threshold value signal and the feedback signal, said adjustment circuit arranged to adjust the output one of the threshold value signal and the feedback signal so as to reduce the difference between the reference input signal and the average output voltage of said switched mode power supply responsive to the low pass filter.
2. The hysteretic power converter according to claim 1 , wherein said adjustment circuit is arranged to output the threshold value signal, and wherein said adjustment circuit comprises:
a differential amplifier, a first input of said differential amplifier coupled to the reference input signal and a second input of said differential amplifier coupled to the output of said switched mode power supply, said differential amplifier arranged to output an amplified difference; and
a summation circuit coupled to the output of said differential amplifier and arranged to subtract the output of said differential amplifier from said reference input signal, the output of said summation circuit coupled to provide the output threshold value signal to said comparator,
wherein said low pass filter is coupled to one of the second input of said differential amplifier, the output of said differential amplifier and the output of said summation circuit.
3. The hysteretic power converter according to claim 2 , further comprising a limit circuit serially connected within said adjustment circuit so as to limit the range of adjustment of the threshold value signal to not exceed predetermined limits.
4. The hysteretic power converter according to claim 1 , wherein said adjustment circuit is arranged to output the feedback signal, and wherein said adjustment circuit comprises:
a differential amplifier, a first input of said differential amplifier coupled to the reference input signal and a second input of said differential amplifier coupled to the output of said switched mode power supply, said differential amplifier arranged to output an amplified difference; and
a summation circuit coupled to the output of said differential amplifier and arranged to add the instantaneous output voltage of said switched mode power supply to the output of said differential amplifier, the output of said summation circuit coupled to provide the output feedback signal to said comparator,
wherein said low pass filter is coupled to one of the second input of said differential amplifier, the output of said differential amplifier and the output of said summation circuit.
5. The hysteretic power converter according to claim 4 , further comprising a limit circuit serially connected within said adjustment circuit so as to limit the range of adjustment of the feedback signal to not exceed predetermined limits.
6. A method of controlling a hysteretic converter so that the average output voltage approaches the value of an input reference value, the method comprising:
providing a switched mode power supply comprising an inductor and an electronically controlled switch, wherein the output of the switched mode power supply increases responsive to a first state of the electronically controlled switch and decreases responsive to a second state of the electronically controlled switch, said second state opposing said first state;
comparing a feedback signal with a threshold value signal and changing the state of the electronically controlled switch of said switched mode power supply to the first state responsive to the feedback signal falling below the threshold value signal, wherein the feedback signal is responsive to the instantaneous output voltage of said provided switched mode power supply and wherein the threshold value signal is responsive to an input reference signal;
changing the state of the electronically controlled switch of said switched mode power supply to the second state responsive to a predetermined condition; and
adjusting one of the threshold value signal and the feedback signal so as to reduce the difference between the input reference value and the average output voltage, wherein said adjusting is responsive to a low pass filter.
7. The method according to claim 6 , wherein said adjusting is of the threshold value signal, and wherein said adjusting comprises:
amplifying a difference between the input reference value and the output voltage of said provided switched mode power supply to output an amplified difference;
subtracting the amplified difference from the input reference value to output the adjusted threshold value signal; and
applying the low pass filter to one of the output voltage prior to said amplifying the difference between the input reference value and the output voltage, the output amplified difference and the output adjusted threshold value signal.
8. The method according to claim 7 , further comprising limiting the range of adjustment of the threshold value signal to not exceed predetermined limits.
9. The method according to claim 6 , wherein said adjusting is of the feedback signal, and wherein said adjusting comprises:
amplifying a difference between the reference input signal and the output voltage of said provided switched mode power supply to output an amplified difference;
summing the output voltage of said provided switched mode power supply with the amplified difference to output the adjusted feedback signal; and
applying the low pass filter to one of the output voltage prior to said amplifying the difference between the input reference value and the output voltage, the output amplified difference and the output adjusted feedback signal.
10. The method according to claim 9 , further comprising limiting the range of adjustment of the feedback signal to not exceed predetermined limits.
11. A hysteretic power converter, comprising:
a switched mode power supply comprising an inductor and an electronically controlled switch, wherein the output of the switched mode power supply increases responsive to a first state of the electronically controlled switch and decreases responsive to a second state of the electronically controlled switch, said second state opposing said first state;
a feedback circuit;
a comparator coupled to said feedback circuit, said feedback circuit arranged to feedback to a first input of the comparator a representation of the output of said switched mode power supply, said comparator arranged to compare the voltage on the first input to a reference signal coupled to the second input of the comparator and to output a control signal to said electronically controlled switch responsive to the comparison of the voltage on the first input to the reference signal, said feedback circuit, comparator and electronically controlled switch comprising a hysteretic loop; and
an adjustment circuit arranged to add an offset to one of the first input and the second input of the comparator so as to reduce the difference between the average output voltage and a regulation set point voltage, said adjustment circuit comprising a low pass filter and arranged so as not to substantially impact the speed of response of said hysteretic loop.