TWI514709B - Control methods for over voltage protection and relevant power controllers - Google Patents

Description

Overvoltage protection control method and related power controller

The techniques disclosed in this specification are generally related to overvoltage protection of power converters.

Power converters need to be equipped with some protection features to prevent human or environmental damage caused by abnormal events. For example, driving a light emitting diode as a power converter for illumination requires over voltage protection (OVP) to prevent excessive output voltage. Possible impact.

FIG. 1 is a conventional power converter 10. The bridge rectifier 12 provides a full-wave rectification function, taking the AC voltage V _AC from the _mains as an input, and generating a rectified DC voltage V _IN and a ground line. The power converter 10 belongs to a buck converter, and the LED module 14 is used as a load, and is connected in series with the main winding PRM of the transformer, and is connected between the rectified DC voltage V _IN and the ground line. The power controller 17 has a power switch 18. When the power switch 18 is turned on, the LED module 14 emits light, and the main winding PRM can store energy. When the power switch 18 is turned off, the electric energy originally stored in the main winding PRM can be transmitted through the flywheel diode 16 to continue to drive the LED module 14 to emit light. The current detecting resistor 20 can provide a current detecting signal V _CS that the power controller 17 flows through the power switch 18.

When the LED module 14 has an open event, that is, when at least one of the LEDs is not turned on, if there is no OVP mechanism, the driving voltage V _LED will be high. At this time, if one touches the two terminals of the LED module 14, there is a danger of being shocked.

Therefore, the power supply controller 17 in FIG. 1 detects the driving voltage V _LED through the VOP terminal, the voltage divider 22, and the secondary winding SEC of the transformer. When the transformer is released, the voltage across the main winding PRM is approximately equal to the forward voltage of the driving voltage V _LED and the flywheel diode 16 , and the voltage across the secondary winding SEC is proportional to the main winding PRM. Cross pressure. Therefore, when the transformer is released, if the voltage of the VOP terminal exceeds a predetermined standard, it can be said that the driving voltage V _{LED is} already too high, and the power controller 17 continuously turns off the power switch 18 to stop the power conversion of the power converter 10. In this way, the effect of OVP is achieved.

The embodiment discloses an overvoltage protection control method suitable for a power converter including a rectifier for rectifying an AC voltage into a rectified DC voltage. The overvoltage control method includes: determining whether the rectified DC voltage is at a local minimum value; providing a detection voltage representative of the rectified DC voltage; comparing the detection voltage with an overvoltage reference voltage; When the rectified DC power source is at the local minimum value, and the detection voltage is lower than the overvoltage reference voltage, an overvoltage protection signal is provided to stop the power conversion of the power converter.

The embodiment discloses a power supply controller suitable for use in a power converter. The power converter includes a rectifier for rectifying an AC voltage to a rectified DC voltage. The power controller includes a valley detector, an overvoltage comparator, and a logic Circuit. The valley detector is configured to determine whether the rectified DC voltage is at a local minimum. The overvoltage comparator is configured to compare a detected voltage with an overvoltage reference voltage. The detected voltage can represent the rectified DC voltage. When the rectified DC voltage is at the local minimum value, and the detection voltage is higher than the overvoltage reference voltage, the logic circuit is configured to provide an overvoltage protection signal to stop the power conversion of the power converter.

10‧‧‧Power Converter

12‧‧‧Bridge rectifier

14‧‧‧LED module

16‧‧‧Flywheel diode

17‧‧‧Power Controller

18‧‧‧Power switch

20‧‧‧ Current Sense Resistor

22‧‧‧Divider

60‧‧‧Power Converter

62‧‧‧Power Controller

64, 66‧‧ ‧ voltage divider resistor

79‧‧‧ Valley Detector

80‧‧‧Valley Comparator

81‧‧‧Delay time generator

82‧‧‧Overvoltage comparator

83‧‧‧Logical circuits

84‧‧‧Ramp signal generator

86‧‧‧ comparator

88‧‧‧Logical Circuit

CS‧‧‧current detection terminal

I _CS ‧‧‧current

I _CS-PEAK ‧‧‧current I _CS peak

L‧‧‧Inductance

PRM‧‧‧ main winding

SEC‧‧‧second winding

S _Protection ‧‧‧Overvoltage protection signal

t _LED-OPEN ‧‧‧Time

t _OVP ‧‧‧Time

T _OVP-DELAY ‧‧‧Preset time

V _AC ‧‧‧AC voltage

V _COMP ‧‧‧compensation signal

V _CS ‧‧‧ current detection signal

V _CS-REF ‧‧‧Preset value

V _IN ‧‧‧Rectified DC voltage

VL ₁ , VL ₂ ‧‧‧ trough

V _LED ‧‧‧ drive voltage

VOP‧‧‧

V _OVP-REF ‧‧‧Overvoltage reference voltage

V _PF ‧‧‧Detection voltage

V _RAMP ‧‧‧Ramp signal

Figure 1 is a conventional power converter.

Figure 2 illustrates a power converter implemented in accordance with the present invention.

Figure 3 illustrates a power controller and some peripheral components.

Figure 4 shows some of the signal waveforms for Figures 2 and 3.

Although the power converter 10 in FIG. 1 can provide an OVP mechanism, the power converter 10 requires a transformer composed of a main winding PRM and a secondary winding SEC. The transformer is relatively large and expensive compared to the general inductance.

In the specification, elements having the same symbols indicate elements having the same or similar functions, and the details and variations thereof may be inferred from the specification by those skilled in the art, and thus are not necessarily described in detail in this specification.

Figure 2 illustrates a power converter 60 implemented in accordance with the present invention having an inductance L in place of the transformer of Figure 1. The power converter 60 can achieve the function of the OVP without a transformer. However, this does not limit the embodiment of the invention and may not have a transformer. For example, in some embodiments, the inductance L can belong to one of a plurality of windings of a transformer.

The voltage dividing resistors 64 and 66 are connected in series between the rectified DC voltage V _IN and the ground line GND to provide a detection voltage V _PF which is approximately proportional to the rectified DC voltage V _IN .

In the embodiment of Figure 2, power controller 62 causes power converter 60 to operate approximately in a critical mode. In general, the inductor L does not store any power at the beginning of each switching cycle. Such an operation mode is called a discontinuous conduction mode (DCM); at the beginning of the switching cycle, the inductor L is also Some power is not released, and such an operation mode is generally called a continuous conduction mode (CCM). The critical mode is between DCM and CCM. Generally speaking, when the inductor L has just discharged the power, it starts the operation mode of the next switching cycle.

When the power switch in the power controller 62 is turned on, the inductor L can start to store energy, and its voltage and current should meet the following formula (I): V _L * T _ON = L _L * I _L

(V _IN -V _LED )* T _ON =L _L * I _CS-PEAK ....(I)

Wherein, V _L and I _L respectively represent the voltage across the inductor L and the current; L _L is the inductance of the inductor L; T _ON is the conduction time of the power switch in the power controller 62; I _CS-PEAK is the current through the current sense The peak value of the current I _CS of the resistor 20 is measured.

From equation (I), it can be found that when the rectified DC voltage V _{IN is} less than or equal to the driving voltage V _LED , the peak value I _{CS-PEAK will be} approximately 0, and the inductor L stops storing energy. At this time, if the absolute value of the AC voltage V _AC is smaller than the rectified DC voltage V _IN , since the inductor L does not consume energy, the rectified DC voltage V _{IN is} stopped at a constant value, which is approximately the driving voltage V _LED . When the absolute value of the AC voltage V _AC is greater than the rectified DC voltage V _IN , the bridge rectifier 12 causes the rectified DC voltage V _{IN to} follow the absolute value of the AC voltage V _AC . In other words, the local minimum of the rectified DC voltage V _IN is approximately equal to the drive voltage V _LED .

Therefore, some embodiments of the present invention detect the minimum value of the rectified DC voltage V _IN to determine whether overvoltage protection should be triggered.

The power supply controller 62 of FIG. 2 may be transmitted through the current detection signal V _CS to the CS terminal of the current detection, to determine the rectified DC voltage V _IN is located at a local minimum value, in other words, after determining whether the rectified DC voltage V _IN Arrived in a trough. For example, when the current detection signal V _{CS is} less than a certain preset value V _CS-REF and continues for a predetermined time, the power controller 62 determines that the rectified DC voltage V _IN is at a local minimum value. At this time, the rectified DC voltage V _IN should be equal to the driving voltage V _LED .

The power controller 62 can compare the detection voltage V _PF with an overvoltage reference voltage V _OVP-REF . When the rectified DC voltage V _IN is at a local minimum value, if the detection voltage V _PF exceeds the overvoltage reference voltage V _OVP-REF , it means that the driving voltage V _{LED is} already too high. At this time, the power controller 62 can provide an overvoltage protection signal S _Protection to stop the power conversion of the power converter 60.

Figure 3 illustrates a power controller 62 and some peripheral components. The power controller 62 includes a valley detector 79, an overvoltage comparator 82, a ramp signal generator 84, logic circuits 83 and 88, and the like.

The valley detector 79 includes a valley comparator 80 and a delay time generator 81. The valley comparator 80 compares the current detection signal V _CS with a preset value V _CS-REF , and the preset value V _CS-REF is 50 mV in one embodiment. When the valley comparator 80 continues for a preset time T _OVP-DELAY to determine that the current detection signal V _{CS is} less than the preset value V _CS-REF , the delay time generator 81 causes its output to be a logical one as a confirmation. The signal indicates that the rectified DC voltage V _IN is at a local minimum.

When the rectified DC voltage V _IN is at a local minimum value, and the overvoltage comparator 82 determines that the detection voltage V _{PF is} higher than the overvoltage reference voltage V _OVP-REF , the logic circuit 83 provides an overvoltage protection signal S _Protection to enable logic The circuit 88 continuously turns off the power switch 18 to stop the power conversion of the power converter 60 for the purpose of overvoltage protection.

The ramp signal generator 84 provides a ramp signal V _RAMP whose signal slope is determined based on the peak value of the detected voltage V _PF . For example, the peak value of the detection voltage V _PF can be detected and recorded by the power controller 62, which can represent the amplitude of the AC voltage V _AC . In one embodiment, the higher the peak value of the detection voltage V _PF , the greater the slope of the signal of the ramp signal V _RAMP . The ramp signal V _RAMP and the compensation signal V _COMP are supplied to the two inputs of the comparator 86, respectively. For example, when the power switch 18 begins to conduct, the ramp signal V _RAMP rises from 0V. Comparator 86 causes logic circuit 88 to turn off power switch 18 when ramp signal V _RAMP exceeds compensation signal V _COMP . Therefore, the ramp signal generator 84 and the comparator 86 can determine the ON time of the power switch 18.

Figure 4 shows some of the signal waveforms for Figures 2 and 3. The AC voltage V _AC is a sine wave, for example, having an amplitude of 110 V and a frequency of 60 Hz. As shown in Figure 4, the local minimum of the rectified DC voltage V _IN in each valley is approximately equal to the drive voltage V _LED . The detection voltage V _PF is approximately proportional to the rectified DC voltage V _IN .

In Fig. 4, it is assumed that the LED module 14 in Fig. 2 starts to open erroneously from the time t _LED-OPEN . Therefore, as the power switch 18 is turned on and off, the driving voltage V _LED gradually rises.

After the time t _LED-OPEN , the waveform of the rectified DC voltage V _IN appears the first valley VL ₁ . At this time, the overvoltage protection has not been triggered because the detection voltage V _PF is not higher than the overvoltage reference voltage V _OVP-REF .

After the first trough VL ₁ , the waveform of the rectified DC voltage V _IN exhibits a second trough VL ₂ . At this time, the detection voltage V _{PF is} already higher than the overvoltage reference voltage V _OVP-REF . Therefore, the overvoltage protection is triggered when the current detection signal V _CS continues to be approximately equal to 0 (less than the preset value V _CS-REF ) for a time t _OVP after a preset time T _OVP-DELAY . Therefore, after time t _OVP , the current detection signal V _{CS is} always 0 because the power switch 18 is continuously turned off.

Unlike the first figure, a transformer is required. In the second figure, the power converter 60 can be replaced by an inductor, and the same function as overvoltage protection can be achieved. Therefore, the power converter 60 in Fig. 2 can be competitive in terms of product size and cost.

The above are only the preferred embodiments of the present invention, and all changes and modifications made to the scope of the present invention should be within the scope of the present invention.

18‧‧‧Power switch

62‧‧‧Power Controller

64, 66‧‧ ‧ voltage divider resistor

79‧‧‧ Valley Detector

80‧‧‧Valley Comparator

81‧‧‧Delay time generator

82‧‧‧Overvoltage comparator

83‧‧‧Logical circuits

84‧‧‧Ramp signal generator

86‧‧‧ comparator

88‧‧‧Logical Circuit

S _Protection ‧‧‧Overvoltage protection signal

V _COMP ‧‧‧compensation signal

V _CS ‧‧‧ current detection signal

V _CS-REF ‧‧‧Preset value

V _IN ‧‧‧Rectified DC voltage

V _OVP-REF ‧‧‧Overvoltage reference voltage

V _PF ‧‧‧Detection voltage

V _RAMP ‧‧‧Ramp signal

Claims (12)

An overvoltage protection control method is applicable to a power converter, comprising a rectifier for rectifying an AC voltage into a rectified DC voltage, the overvoltage control method comprising: determining whether the rectified DC voltage is located a local minimum; providing a detection voltage representative of the rectified DC voltage; comparing the detection voltage to an overvoltage reference voltage; and when the rectified DC power source is at the local minimum value, and When the detection voltage is higher than the overvoltage reference voltage, an overvoltage protection signal is provided to stop the power conversion of the power converter. The overvoltage protection control method of claim 1, wherein the power converter comprises a series inductance, a light source load, and a power switch, and the determining step comprises: providing a current detection signal, It may represent a current flowing through the power switch; compare the current detection signal with a preset value; and when the current detection signal is lower than the preset value, determine that the rectified DC voltage is at the local minimum value . The overvoltage protection control method as claimed in claim 2 includes: determining that the rectified DC voltage is at the local minimum value after the current detection signal continues to be lower than the preset value for a predetermined time. The overvoltage protection control method of claim 1, wherein the power converter comprises a series inductance, a light source load, and a power switch, the power converter The utility model further comprises a flywheel diode having two ends electrically coupled to the rectified DC voltage and the power switch. The overvoltage protection control method as claimed in claim 1 further includes: providing a ramp signal; detecting and recording a peak value of the detected voltage; and determining a signal slope of the ramp signal according to the peak value. The overvoltage protection control method of claim 5, further comprising: determining an opening time of a power switch according to the ramp signal and a compensation signal. A power controller is provided for a power converter, the power converter includes a rectifier for rectifying an AC voltage to a rectified DC voltage, the power controller includes; a valley detector, To determine whether the rectified DC voltage is at a local minimum value; an overvoltage comparator for comparing a detection voltage and an overvoltage reference voltage, wherein the detection voltage can represent the rectified DC voltage; and The logic circuit is configured to provide an overvoltage protection signal to stop the power conversion of the power converter when the rectified DC voltage is at the local minimum value and the detection voltage is higher than the overvoltage reference voltage. The power controller of claim 7, wherein the power converter comprises a buck converter comprising a power switch and an inductor, the valley detector comprising: a valley comparator for Comparing a current detection signal with a predetermined value; wherein the current detection signal can represent a current flowing through the power switch. The power controller of claim 8 is as claimed in claim 8 , wherein the valley detector further comprises And a delay time generator connected to the comparator, when the current detection signal continues to be lower than the preset value for a predetermined time, to provide an acknowledgment signal, indicating that the rectified DC voltage is at the local minimum value. A power converter includes: a rectifier for rectifying an AC voltage to a rectified DC voltage and a ground line; and a power controller including: a valley detector for determining Whether the rectified DC voltage is at a local minimum value; and an overvoltage comparator for comparing a detection voltage and an overvoltage reference voltage, wherein the detection voltage can represent the rectified DC voltage; wherein, when The rectified DC voltage is at the local minimum value, and when the detection voltage is higher than the overvoltage reference voltage, the power controller stops the power conversion of the power converter. The power converter of claim 10, comprising: a buck converter comprising a power switch and an inductor connected in series between the rectified DC voltage and the ground line; wherein the valley The detector includes a valley comparator for comparing a current detection signal with a predetermined value; and the current detection signal can represent a current flowing through the power switch. The power converter of claim 10, wherein the valley detector comprises a delay time generator connected to the comparator, and when the current detection signal continues to be lower than the After the preset value is a preset time, the delay time generator provides an acknowledgment signal to determine that the rectified DC voltage is at the local minimum value.