Communication through the flyback power transformer by the usage of the zero voltage switching pulse
The disclosure describes techniques to send digital information from the secondary side to the primary side of a power converter, such as a flyback power converter. By modulating the amount of time between zero voltage switching (ZVS) pulses initiated by a synchronous rectification (SR) transistor on the secondary side, a power converter circuit of this disclosure may communicate digital information to the primary side from the secondary side. The power converter circuit of this disclosure may include stable, accurate and reliable ZVS pulse detection techniques on the primary side to determine slight changes in the period between ZVS pulses from the secondary side. A controller circuit on the secondary side may encode digital information by modulating the ZVS period, e.g. increased period, decreased period or no change to the period.
1. A system comprising:
an isolated power converter comprising a power transformer;
a secondary side controller configured to:
control a synchronous rectification (SR) switch of the power converter, wherein the secondary side controller is configured to initiate zero voltage switching (ZVS) by controlling a switching time of the SR switch; and
encode digital information by modulating a period between the switching time of the SR switch;
a primary side controller configured to:
control a primary side switch of the power converter;
detect the switching time of the SR switch; and
decode the digital information based on the modulated period between the switching time of the SR switch.
2. The system of claim 1 , wherein the primary side controller is configured to decode the digital information based on a differential decoding scheme with at least three modulation states, wherein the three modulation states are:
a reduced time period;
an increased time period; and
no modulation.
3. The system of claim 1 ,
wherein the secondary side controller is electrically coupled to a gate of the SR switch; and
wherein the primary side controller is configured to detect the switching time of the SR switch based on a reflected voltage sensed on a primary winding of the power transformer.
4. The system of claim 3 , wherein the primary side controller comprises:
a zero cross detection circuit, wherein the zero cross detection circuit detects when a reflected voltage signal is greater than approximately zero volts; and
a ZVS detection circuit, wherein the ZVS detection circuit detects when the reflected voltage signal is less than a predetermined threshold voltage, wherein the predetermined threshold voltage is greater than zero volts.
5. The system of claim 4 wherein the primary side controller further comprises:
a first timer circuit configured to output an amount of time between each instance when the reflected voltage signal momentarily exceeds the predetermined threshold voltage and when the reflected voltage signal becomes less than approximately zero volts; and
a second timer circuit configured to output an amount of time when both:
the output from the zero cross circuit indicates that the reflected voltage signal is greater than approximately zero volts; and
the output from the ZVS detection circuit indicates that the reflected voltage signal exceeds the predetermined threshold voltage.
6. The system of claim 5 wherein the primary side controller further comprises a subtraction circuit, the subtraction circuit configured to:
subtract the output of the second timer circuit from the output of the first timer circuit and output a subtraction result;
compare the subtraction result to a predetermined subtraction threshold; and
in response to the subtraction result satisfying the predetermined subtraction threshold, detect the switching time of the SR switch.
7. A device comprising:
a zero voltage switching (ZVS) detection circuit configured to detect a ZVS pulse;
a timer circuit operatively coupled to the ZVS circuit, the timer circuit configured to:
determine a first time period between a first ZVS pulse and a second ZVS pulse; and
determine a second time period between a third ZVS pulse and a fourth ZVS pulse; and
a decoder circuit operatively coupled to the timer circuit, the decoder circuit configured to decode digital information based on the first time period and the second time period.
8. The device of claim 7 , wherein the device is further configured to control a primary side switch of a power converter.
9. The device of claim 7 , wherein the decoder circuit is configured to decode the digital information based on differential Manchester decoding.
10. The device of claim 7 , wherein the decoder circuit is configured to decode the digital information based on a differential decoding scheme based on three modulation states, wherein the three modulation states are:
a reduced time period;
an increased time period; and
no modulation.
11. The device of claim 10 , wherein decoder circuit is configured to decode the digital information as:
a first sequence of: no modulation, reduced time period, increased time period, no modulation to indicate a digital zero, and
a second sequence of: no modulation, increased time period, reduced time period, no modulation to indicate a digital one.
12. The device of claim 7 , wherein the ZVS circuit is configured to detect a falling edge of the ZVS pulse.
13. The device of claim 7 , wherein the ZVS circuit comprises
a zero cross detection circuit, wherein the zero cross detection circuit detects when a reflected voltage signal is greater than approximately zero volts; and
a ZVS detection circuit, wherein the ZVS detection circuit detects when the reflected voltage signal is less than a predetermined threshold voltage, wherein the predetermined threshold voltage is greater than zero volts.
14. The device of claim 13 , wherein the timer circuit comprises a first timer circuit, and wherein the ZVS circuit further comprises a second timer circuit configured to output an amount of time between a first rising edge of an output from the ZVS detector circuit and continue to count until a falling edge of an output from the zero cross circuit.
15. The device of claim 14 , wherein the ZVS circuit further comprises a third timer circuit configured to output an amount of time when both:
the output from the zero cross circuit indicates that the reflected voltage signal is greater than approximately zero volts; and
the output from the ZVS detection circuit indicates that the reflected voltage signal exceeds the predetermined threshold voltage.
16. The device of claim 15 , wherein the ZVS circuit further comprises a subtraction circuit, the subtraction circuit configured to:
subtract the output of the third timer circuit from the output of the second timer circuit and output a subtraction result;
compare the subtraction result to a predetermined subtraction threshold; and
in response to the subtraction result satisfying the predetermined subtraction threshold, output an indication of detection of the ZVS pulse.
17. A method comprising:
detecting, by a controller circuit, a plurality of zero voltage switching (ZVS) pulses, wherein the plurality of ZVS pulses comprise a first ZVS pulse, a second ZVS pulse, a third ZVS pulse and a fourth ZVS pulse;
determining, by the controller circuit, a first time period between the first ZVS pulse and the second ZVS pulse;
determining, by the controller circuit, a second time period between the third ZVS pulse and the fourth ZVS pulse; and
decoding, by the controller circuit, digital information based on the first time period and the second time period.
18. The method of claim 17 , wherein the controller circuit is configured to control a primary side switch of a power converter.
19. The method of claim 17 , wherein detecting the plurality of ZVS pulses comprises:
detecting, by the controller circuit, when a reflected voltage signal is greater than approximately zero volts;
detecting, by the controller circuit, when the reflected voltage signal is greater than a predetermined threshold voltage, wherein the predetermined threshold voltage is greater than zero volts;
determining, by the controller circuit, a first amount of time between each instance when the reflected voltage signal momentarily exceeds the predetermined threshold voltage and when the reflected voltage signal becomes less than approximately zero volts; and
determining, by the controller circuit, a second amount of time when both:
the reflected voltage signal is greater than approximately zero volts; and
the reflected voltage signal exceeds the predetermined threshold voltage.
20. The method of claim 19 , further comprising:
subtracting, by the controller circuit, the second amount of time from the first amount of time;
comparing, by the controller circuit, results of the subtraction to a predetermined subtraction threshold; and
in response to the results of the subtraction satisfying the predetermined subtraction threshold, outputting an indication of detection of the ZVS pulse.