# US 2021/0281184 A1 · Auto-Tuned Synchronous Rectifier Controller

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- Number: US 2021/0281184 A1
- Document ID: US20210281184A1
- Status: Published application
- Kind: A1
- Application number: 16/811,827
- Filed: 2020-03-06
- Published: 2021-09-09
- Earliest claimed: 2020-03-06
- Assignees: Silanna Asia Pte Ltd
- Applicants: Silanna Asia Pte Ltd
- Inventors: Aleksandar Radic
- Web page: https://patentgrep.com/patent/US20210281184A1

## CPC

- H02M 3/33592: {having a synchronous rectifier circuit or a synchronous freewheeling circuit at the secondary side of an isolation transformer}
- H02M 1/0058: {by employing soft switching techniques, i.e. commutation of transistors when applied voltage is zero or when current flow is zero (using an auxiliary actively switched resonant commutation circuit connected to an intermediate DC voltage or between two push-pull branches of an inverter bridge H02M7/4811; in resonant inverters H02M7/4815; in inverters operating from a resonant DC source H02M7/4826)}
- H02M 1/083: {for the ignition at the zero crossing of the voltage or the current}
- H02M 3/1588: {comprising at least one synchronous rectifier element (H02M3/1582, H02M3/1584 take precedence)}
- H03K 17/133: {in field-effect transistor switches}
- H03K 17/284: in field effect transistor switches
- H03K 2017/307: {circuits simulating a diode, e.g. threshold zero}
- Y02B 70/10: Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
- H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P)
- H03K: PULSE TECHNIQUE (measuring pulse characteristics G01R; modulating sinusoidal oscillations with pulses H03C; transmission of digital information H04L; discriminator circuits detecting phase difference between two signals by counting or integrating cycles of oscillation H03D3/04; automatic control, starting, synchronisation or stabilisation of generators of electronic oscillations or pulses where the type of generator is irrelevant or unspecified H03L; coding, decoding or code conversion, in general H03M)
- Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS

## Abstract

An apparatus includes a high-pass filter circuit configured to receive a drain-source voltage from a drain node of a synchronous rectifier switch at a secondary-side of a power converter and to generate a filtered drain-source voltage using the received drain-source voltage. A current comparison circuit of the apparatus is configured to receive a current indicative of a current through the synchronous rectifier switch and to generate a current comparison signal using the received current. An auto-tuning controller of the apparatus is configured to turn the synchronous rectifier switch on upon determining a body diode conduction of the synchronous rectifier switch, commence an auto-tuned delay upon determining that the current through the synchronous rectifier switch has changed direction, turn the synchronous rectifier switch off upon expiration of the auto-tuned delay, and update, during a detection window of time, a duration of the auto-tuned delay based on the filtered drain-source voltage.

## Claims

### Claim 1

An apparatus comprising:
a high-pass filter circuit configured to receive a drain-source voltage from a drain node of a synchronous rectifier switch at a secondary-side of a power converter and to generate a filtered drain-source voltage using the received drain-source voltage;
a current comparison circuit configured to receive a current indicative of a current through the synchronous rectifier switch and to generate a current comparison signal using the received current; and
an auto-tuning controller configured to:
turn the synchronous rectifier switch on upon determining, using the current comparison signal, a body diode conduction of the synchronous rectifier switch;
commence an auto-tuned delay upon determining, using the current comparison signal, that the current through the synchronous rectifier switch has changed direction;
turn the synchronous rectifier switch off upon expiration of the auto-tuned delay; and
update, during a detection window of time, a duration of the auto-tuned delay based on the filtered drain-source voltage.

### Claim 2 (depends on 1)

The apparatus of claim 1, wherein:
a voltage at a drain node of a primary-side switch of the power converter is reduced, when the synchronous rectifier switch is on, by an amount corresponding to the duration of the auto-tuned delay.

### Claim 3 (depends on 2)

The apparatus of claim 2, wherein:
a maximum duration of the auto-tuned delay corresponds to a drain-source voltage at the drain node of the primary-side switch that is greater than zero volts.

### Claim 4 (depends on 2)

The apparatus of claim 2, wherein:
the auto-tuning controller is communicatively isolated from a signal representative of the voltage at the drain node of the primary-side switch.

### Claim 5 (depends on 1)

The apparatus of claim 1, wherein the auto-tuning controller is further configured to:
update the duration of the auto-tuned delay by increasing the duration of the auto-tuned delay upon determining that the filtered drain-source voltage surpassed a voltage threshold value during the detection window of time; and
update the duration of the auto-tuned delay by decreasing the duration of the auto-tuned delay upon determining that the filtered drain-source voltage did not surpass the voltage threshold value during the detection window of time.

### Claim 6 (depends on 5)

The apparatus of claim 5, further comprising:
a voltage comparison circuit configured generate a voltage comparison signal based on a comparison of the filtered drain-source voltage to the voltage threshold value;
wherein the auto-tuning controller is further configured to:
determine, upon receiving a first level of the voltage comparison signal, that the filtered drain-source voltage surpassed the voltage threshold value; and
determine, upon receiving a second level of the voltage comparison signal, that the filtered drain-source voltage did not surpass the voltage threshold value.

### Claim 7 (depends on 1)

The apparatus of claim 1, wherein the current comparison circuit is further configured to:
generate the current comparison signal by comparing the current indicative of the current through the synchronous rectifier switch to a current threshold;
wherein the auto-tuning controller is further configured to:
determine that the body diode conduction of the synchronous rectifier switch has occurred upon receiving a first level of the current comparison signal when the synchronous rectifier switch is in an OFF-state; and
determine that the current through the synchronous rectifier switch has changed direction upon receiving the first level of the current comparison signal when the synchronous rectifier switch is in an ON-state.

### Claim 8 (depends on 7)

The apparatus of claim 7, wherein:
the current threshold corresponds to a current of about zero amps.

### Claim 9 (depends on 1)

The apparatus of claim 1, wherein:
the power converter comprises a transformer having a primary-side winding on a primary side of the power converter and a secondary-side winding on the secondary-side of the power converter; and
the synchronous rectifier switch is configured to be directly electrically connected to the secondary-side winding.

### Claim 10 (depends on 9)

The apparatus of claim 9, wherein:
a primary-side switch is directly electrically connected to the primary-side winding; and
a duration of a forced negative magnetizing inductance current at a drain node of the primary-side switch corresponds to the duration of the auto-tuned delay.

### Claim 11 (depends on 10)

The apparatus of claim 10, wherein:
the auto-tuning controller is communicatively isolated from each of the drain node, a source node, and a gate node of the primary-side switch.

### Claim 12 (depends on 10)

The apparatus of claim 10, wherein:
an increase in the duration of the auto-tuned delay corresponds to an increased discharge amount of a parasitic capacitance of the primary-side switch; and
a decrease in the duration of the auto-tuned delay corresponds to a decreased discharge amount of the parasitic capacitance of the primary-side switch.

### Claim 13 (depends on 12)

The apparatus of claim 12, wherein:
a maximum duration of the auto-tuned delay corresponds to maximum discharge amount of the parasitic capacitance of the primary-side switch; and
the maximum discharge amount of the parasitic capacitance of the primary-side switch is less than a full discharge amount of the parasitic capacitance of the primary-side switch.

### Claim 14

A method comprising:
receiving, at high-pass filter circuit, a drain-source voltage from a drain node of a synchronous rectifier switch at a secondary-side of a power converter;
generating, by the high-pass filter circuit, a filtered drain-source voltage using the received drain-source voltage;
receiving, at a current comparison circuit, a current indicative of a current through the synchronous rectifier switch;
generating, by the current comparison circuit, a current comparison signal using the received current;
turning the synchronous rectifier switch on upon determining by an auto-tuning controller, using the current comparison signal, that a body diode conduction of the synchronous rectifier switch has occurred;
commencing, by the auto-tuning controller, an auto-tuned delay upon determining, using the current comparison signal, that the current through the synchronous rectifier switch has changed direction;
turning the synchronous rectifier switch off upon expiration of the auto-tuned delay; and
updating, by the auto-tuning controller, during a detection window of time, a duration of the auto-tuned delay based on the filtered drain-source voltage.

### Claim 15 (depends on 14)

The method of claim 14, wherein:
a voltage at a drain node of a primary-side switch of the power converter is reduced, when the synchronous rectifier switch is on, by an amount corresponding to the duration of the auto-tuned delay.

### Claim 16 (depends on 15)

The method of claim 15, wherein:
a maximum duration of the auto-tuned delay corresponds to a drain-source voltage at the drain node of the primary-side switch that is greater than zero volts.

### Claim 17 (depends on 15)

The method of claim 15, wherein:
the auto-tuning controller is communicatively isolated from a signal representative of the voltage at the drain node of the primary-side switch.

### Claim 18 (depends on 14)

The method of claim 14, further comprising:
updating the duration of the auto-tuned delay by increasing the duration of the auto-tuned delay upon determining that the filtered drain-source voltage surpassed a voltage threshold value during the detection window of time; and
updating the duration of the auto-tuned delay by decreasing the duration of the auto-tuned delay upon determining that the filtered drain-source voltage did not surpass the voltage threshold value during the detection window of time.

### Claim 19 (depends on 14)

The method of claim 14, wherein:
the duration of the auto-tuned delay corresponds to a duration of a forced negative magnetizing inductance current at a drain node of a primary-side switch of the power converter.

### Claim 20 (depends on 19)

The method of claim 19, wherein:
the auto-tuning controller is communicatively isolated from each of the drain node, a source node, and a gate node of the primary-side switch.