Control device of a switching power supply
A control device controls a switching converter. The converter has an input alternating supply voltage, a regulated direct voltage on the output terminal, and a switch connected to an inductor. The control device controls the closing and opening time period of said switch for each cycle and receives a first input signal representative of the current flowing through one element of the converter. The control device comprises a counter configured to count a time period, a comparator configured to compare said first input signal with a second signal, digital control block configured to control the closing and opening of said switch and to activate said counter to start the counting of said time period when the said first input signal crosses said second signal, with said switch being closed. The digital control block is configured to open the switch when the counter finishes the counting of said time period.
1. A control device for controlling a switching converter that includes a switch coupled to an inductor, said control device comprising:
a counter configured to count a time period;
a comparator configured to compare a first signal, representative of a current flowing through an element of the converter, with a second signal; and
a digital control block configured to control closing and opening of said switch and to activate said counter to start counting said time period when said first signal crosses said second signal with said switch being closed, said digital control block being configured to open the switch when the counter finishes counting said time period.
2. A control device according to claim 1 , comprising:
a digital device configured to set a digital reference value, and
a digital to analog converter configured to convert said digital reference value into said second signal.
3. A control device according to claim 2 , wherein the digital to analog converter is configured to convert said digital reference value into said second signal at a value of zero.
4. A control device according to claim 2 , wherein the digital to analog converter configured to convert said digital reference value into said second signal at a prefixed value different from zero.
5. A control device according to claim 2 , further comprising an analog-to-digital converter to convert to a first digital signal a rectified input voltage, said digital device being configured to set the digital reference value based on the first digital signal.
6. A control device according to claim 2 , further comprising:
a first analog-to-digital converter configured to convert a rectified input voltage to a first digital signal; and
a second analog-to-digital converter configured to convert a signal representative of an output regulated direct current voltage to a second digital signal, said digital device being configured to set the digital reference value based on the first and second digital signals.
7. A control device according to claim 1 , wherein the digital control block includes an input terminal configured to receive a third signal representative of a demagnetization of a core of a transformer that includes the inductor, said digital control block being configured to control the closing of said switch in response to a zero crossing of said third signal.
8. A control device according to claim 1 , comprising:
an analog-to-digital converter configured to convert a signal representative of an output regulated direct current voltage to a digital signal; and
a digital device configured to set the time period based on a difference between said digital signal and a digital reference value.
9. A control device according to claim 1 , wherein the control device is integrated in a semiconductor chip.
10. A switching converter, comprising:
an input terminal configured to receive an alternating supply voltage;
an output terminal configured to provide a regulated direct current voltage;
an inductor;
a switch coupled to the inductor; and
a control device configured to control a closing time period and an opening time period of said switch for each of a plurality of cycles, said control device including:
a counter configured to count the closing time period;
a comparator configured to compare a first signal, representative of a current flowing through an element of the converter, with a second signal; and
a digital control block configured to control closing and opening of said switch and to activate said counter to start counting said closing time period when said first signal crosses said second signal with said switch being closed, said digital control block being configured to open the switch when the counter finishes counting said closing time period.
11. A switching converter according to claim 10 , wherein the control device includes:
a digital device configured to set a digital reference value, and
a digital to analog converter configured to convert said digital reference value into said second signal.
12. A switching converter according to claim 11 , wherein the digital to analog converter is configured to convert said digital reference value into said second signal at a value of zero.
13. A switching converter according to claim 11 , wherein the digital to analog converter configured to convert said digital reference value into said second signal at a prefixed value different from zero.
14. A switching converter according to claim 11 , comprising a rectifier configured to rectify the alternating supply voltage and to output a rectified voltage, wherein the control device includes an analog-to-digital converter to convert the rectified voltage to a first digital signal, and said digital device is configured to set the digital reference value in response to the first digital signal.
15. A switching converter according to claim 10 , comprising a rectifier configured to rectify the alternating supply voltage and to output a rectified voltage, wherein the control device includes:
a first analog-to-digital converter configured to convert the rectified voltage to a first digital signal; and
a second analog-to-digital converter configured to convert a signal representative of the regulated direct current voltage to a second digital signal, said digital device being configured to set the digital reference value based on the first and second digital signals.
16. A switching converter according to claim 10 , wherein the digital control block includes an input terminal configured to receive a third signal representative of a demagnetization of a core of a transformer that includes the inductor, said digital control block being configured to control the closing of said switch in response to a zero crossing of said third signal.
17. A switching converter according to claim 10 , wherein the control device includes:
an analog-to-digital converter configured to convert a signal representative of the regulated direct current voltage to a digital signal; and
a digital device configured to set the time period based on a difference between said digital signal and a digital reference value.
18. A method of controlling a switching converter that includes an input terminal configured to receive an alternating supply voltage, an output terminal configured to provide a regulated direct current voltage, an inductor, and a switch coupled to the inductor, the method comprising:
controlling a closing time period and an opening time period of said switch for each of a plurality of cycles, said controlling including:
counting the closing time period with a counter;
comparing a first signal, representative of a current flowing through an element of the converter, with a second signal;
activating said counter to start counting said closing time period when said first signal crosses said second signal with said switch being closed; and
opening the switch when the counter finishes counting said closing time period.
19. A method according to claim 18 , wherein the controlling includes:
setting a digital reference value, and
converting said digital reference value into said second signal.
20. A method according to claim 19 , wherein:
the converter includes a rectifier configured to rectify the alternating supply voltage and to output a rectified voltage;
the controlling includes converting the rectified voltage to a first digital signal, and
setting the digital reference value includes setting the digital reference value in response to the first digital signal.
21. A method according to claim 18 , wherein:
the converter includes a rectifier configured to rectify the alternating supply voltage and to output a rectified voltage;
the controlling includes converting the rectified voltage to a first digital signal and converting a signal representative of the regulated direct current voltage to a second digital signal; and
setting the digital reference value includes setting the digital reference value based on the first and second digital signals.
22. A method according to claim 18 , wherein the controlling includes:
receiving a third signal representative of a demagnetization of a core of a transformer that includes the inductor; and
closing said switch in response to a zero crossing of said third signal.
23. A method according to claim 18 , wherein the controlling includes:
converting a signal representative of the regulated direct current voltage to a digital signal; and
setting the time period based on a difference between said digital signal and a digital reference value.