TWI399910B - Power converter, controller for controlling a transformer and method thereof - Google Patents

Description

Power converter, controller for controlling transformer and method thereof

The present invention relates to a controller, and more particularly to a controller and method for controlling a transformer.

The flyback converter is a switch mode regulated power supply that can be used in applications such as AC/DC adapters or battery chargers. A conventional flyback converter 100 is shown in FIG. The flyback converter 100 controls a transformer using the controller 120. The transformer includes a primary winding 104 coupled to a DC power source V _BB , a secondary winding 106 coupled to the load 112 , and an auxiliary winding 108 . Controller 120 controls switch 118 coupled in series with primary winding 104. When the switch 118 is turned on, current flows through the primary winding 104, and the magnetic core 124 of the transformer stores energy. When the switch 118 is turned off, the diode 110 coupled to the secondary winding is forward biased, and the energy stored in the core 124 is discharged through the secondary winding 106 to the capacitor 122 and the load 112. The error amplifier 114 compares the current flowing through the current monitoring resistor 111 with a reference current and generates a feedback signal FB. The feedback signal FB is transmitted to the controller 120 through the optical coupler 116. The controller 120 controls the switch 118 to adjust the output power of the transformer based on the feedback signal FB. A disadvantage of the conventional flyback converter 100 is that it is relatively large in size.

The invention provides a power converter comprising: a transformer having a primary winding coupled to a power supply and a primary winding coupled to a load And a signal generator for generating a sawtooth signal, wherein the transformer operates in a plurality of switching cycles, and at least one of the plurality of switching cycles includes a charging phase, a discharging phase, and an adjustment phase, wherein During the charging phase, the sawtooth wave signal is raised from a predetermined reference voltage value to a first voltage value, wherein the sawtooth wave signal is decreased from the first voltage value to a second voltage value during the discharging phase. And wherein, in the adjusting phase, the sawtooth wave signal rises from the second voltage value to the preset reference voltage value, wherein in the charging phase, the transformer is powered by the power source and an electric current flowing through the primary winding increases In the discharge phase, the transformer discharges power to the load and a current flowing through the secondary winding decreases, and wherein a length of the discharge phase is one of the charging phase, the discharging phase, and the adjusting phase A ratio of the total length of time is constant.

The invention also provides a controller for controlling a transformer, comprising: a first signal generator, receiving a first feedback signal and generating a first signal, the first feedback signal indicating a primary winding of the transformer An output voltage coupled to the first signal generator, generating a pulse signal according to the first signal, wherein the pulse signal controls power of the transformer, wherein in a charging phase, the first The signal rises from a predetermined reference voltage value to a first voltage value, wherein in a discharging phase, the first signal decreases from the first voltage value to a second voltage value lower than the preset reference voltage value, and In an adjustment phase, the first signal is raised from the second voltage value to the predetermined reference voltage value, wherein a length of the discharge phase and the charging phase, the discharging phase, and a total time of the adjusting phase A ratio of lengths is constant, wherein during the charging phase, a current flowing through a primary winding of the transformer increases, and wherein In this discharge phase, a current flowing through the primary winding of the transformer is reduced.

The invention further provides a method of controlling a transformer, comprising: operating the transformer during a plurality of switching cycles, at least one of the plurality of cycles comprising a charging phase, a discharging phase and an adjusting phase; wherein the transformer is in the charging phase Powering; using the transformer to supply power to a load during the discharging phase; and determining a length of time of the adjusting phase, comprising: generating a sawtooth wave signal; causing the sawtooth wave signal to rise from a predetermined reference voltage value during the charging phase a first voltage value; the sawtooth wave signal is decreased from the first voltage value to a second voltage value during the discharging phase; the sawtooth wave signal is raised from the second voltage value during the adjusting phase; and when The adjustment phase is ended when the sawtooth wave signal rises to the preset reference voltage value, wherein a ratio of the length of the discharge phase to the charge phase, the discharge phase, and a total length of the adjustment phase is constant.

A detailed description of embodiments of the invention will be provided below. While the invention will be described in conjunction with the embodiments, it should be understood that On the contrary, the invention is intended to cover various modifications, modifications and equivalents

In addition, in the following detailed description, numerous specific details are It will be understood by those of ordinary skill in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail. In order to highlight the gist of the present invention.

In accordance with an embodiment of the present invention, a circuit and method are provided for controlling a power converter that can be used to power various loads. The power converter includes a transformer and a controller that controls the transformer. The controller controls a switch coupled in series with the primary winding of the transformer. Advantageously, by controlling the on/off time of the switch, the transformer can provide a substantially constant current in the secondary winding. By using the power converter of the present invention and the method of controlling the power converter, components such as an optical coupler and an error amplifier included in the conventional power converter shown in FIG. 1 can be omitted, and the power converter can be reduced. Size and increase efficiency.

2 is an illustrative block diagram of a power converter 200 in accordance with an embodiment of the present invention. 4 is an illustrative waveform diagram of signals received or generated by power converter 200. Figure 2 will be described in conjunction with Figure 4.

In the example of FIG. 2, power converter 200 includes a controller 220 for controlling transformer 202. In an embodiment, transformer 202 includes a primary winding 204, a secondary winding 206, and an auxiliary winding 208. One end of primary winding 204 is coupled to DC input voltage V _BB and the other end is coupled to ground through switch 218 and resistor 230. Secondary winding 206 is coupled to load 212 through diode 210. In an embodiment, the auxiliary winding 208 is located on the side of the primary winding 204 of the transformer 202. One end of the auxiliary winding 208 is coupled to ground through a resistor 214 and a resistor 216, and the other end is coupled to ground.

Controller 220 controls transformer 202 by controlling a switch 218 coupled in series with primary winding 204. In an embodiment, controller 220 is powered by voltage _VDD generated by auxiliary winding 208. Resistor 230 provides a feedback signal FB1 indicating the current I _PR flowing through primary winding 204. The auxiliary winding 208 provides a feedback signal FB2 indicating the output voltage of the auxiliary winding 208 and further indicating the output voltage of the secondary winding 206. Therefore, the feedback signal FB2 can reflect whether the current I _SE flowing through the secondary winding 206 drops to a preset current value, such as zero. In an embodiment, the feedback signal FB2 is generated at a node between the resistor 214 and the resistor 216.

Power converter 200 also includes a signal generator 226 (such as oscillator 226) and a clamp circuit 228. When the switch 218 is turned on, the clamp circuit 228 clamps the voltage of the feedback signal FB2. In an embodiment, the controller 220 receives the reference signal PEAK and the reference signal SET. The reference signal PEAK determines the maximum current value I _PEAK of the current I _PR flowing through the primary winding 204. The reference signal SET has a reference voltage value V _SET . In another embodiment, the reference signal PEAK and the reference signal SET are generated by the controller 220.

The controller 220 receives the feedback signal FB1 and the feedback signal FB2, and generates a pulse signal (such as the pulse width modulation signal PWM1) according to the feedback signal FB1 and the feedback signal FB2 to control the switch 218. Controller 220 operates transformer 202 for a plurality of switching cycles by controlling switch 218 coupled in series with primary winding 204. In one embodiment, one switching cycle includes a charging phase T _ON , a discharging phase T _{DIS ,} and an adjustment phase T _ADJ , as shown in FIG. 4 . During the charging phase T _ON , the transformer 202 is powered by the input voltage V _BB and the current I _PR flowing through the primary winding 204 is increased. During the discharge phase T _DIS , the transformer 202 discharges power to the load 212 and the current I _SE flowing through the secondary winding 206 decreases.

More specifically, during the charging phase T _ON , the controller 220 turns on the switch 218 such that the transformer 202 receives the input voltage V _BB . When switch 218 is turned on, diode 210 coupled to secondary winding 206 is reverse biased and no current flows through secondary winding 206. Current I _PR flows through primary winding 204, switch 218, and resistor 230 to ground. The current I _PR increases linearly. Thus, during the charging phase T _ON , the core 224 of the transformer 202 stores energy. The clamp circuit 228 clamps the voltage of the feedback signal FB2 during the charging phase T _ON such that the voltage of the feedback signal FB2 is substantially zero.

During the discharge phase T _DIS , the controller 220 turns off the shutdown 218 and discharges the load 212 through the transformer 202. When the switch 218 is turned off, the diode 210 coupled to the secondary winding 206 is forward biased, and the energy stored in the core 224 is released through the secondary winding 206 to the capacitor 222 and the load 212. During the discharge phase T _DIS , the current I _SE flowing through the secondary winding 206 linearly decreases from a maximum current value I _SE-MAX to a predetermined current value (eg, 0). The maximum current value I _{SE-MAX of the} secondary winding 206 is determined by the maximum current value I _{PEAK of the} primary winding 204 and the turns ratio of the transformer 202.

In the adjustment phase T _ADJ , the switch 218 remains off. In an embodiment, no current flows through the primary winding 204 or the secondary winding 206 during the adjustment phase T _ADJ .

As shown by the waveform of the current I _SE flowing through the secondary winding 206 in FIG. 4, the average current I _OAVG output by the secondary winding 206 in one switching period T _S can be obtained from equation (1).

Where T _S =T _ON +T _DIS +T _ADJ .

In an embodiment, the length of time of the charging phase T _{ON and} the length of time of the discharging phase T _DIS may be determined by the inductance of the primary winding 204 and the secondary winding 206, the input voltage V _{BB ,} and the output voltage V _OUT across the load 212. The controller 220 determines that the adjustment phase T _ADJ has an appropriate length of time such that the ratio of the length of the discharge phase T _{DIS to} the length of the switching period T _S is constant, wherein the length of the switching period T _S is the charging phase T _ON , The total length of time during the discharge phase T _DIS and the adjustment phase T _ADJ . In equation (1), the maximum current value I _{SE-MAX of the} secondary winding 206 is determined by the maximum current value I _{PEAK of the} primary winding 204 and the turns ratio of the transformer 202. In one embodiment, since the maximum current value I _PEAK of the primary winding 204 is a predetermined value and the turns ratio of the transformer 202 is constant, the maximum current value I _SE-MAX of the secondary winding 206 is constant. Therefore, according to equation (1), if the ratio of the length of the discharge phase T _{DIS to} the length of the switching period T _S is constant (ie, T _S =k* T _DIS , k is a constant), the average of the secondary winding 206 The output current I _OAVG is also constant.

Therefore, even if the input voltage V _BB and the output voltage V _OUT may vary, as long as the ratio of the length of the discharge phase T _{DIS to} the length of the switching period T _S is constant, the average output current I _OAVG is also constant. In other words, by utilizing a filter (such as capacitor 222 coupled to load 212), power converter 200 can provide substantially constant output current to load 212. Here, "substantially constant" means that the output current varies only within a range, so current ripple caused by non-ideal conditions of the circuit components is negligible.

FIG. 3 is a schematic diagram showing the architecture of the controller 220 of FIG. 2. Figure 3 will be described in conjunction with Figures 2 and 4. The controller 220 causes the adjustment phase T _{ADJ to} have an appropriate length of time such that the ratio of the length of the discharge phase T _{DIS to} the length of the switching period T _S is constant. Thus power converter 200 can provide a substantially constant output current to load 212.

In one embodiment, controller 220 includes a signal generator (e.g., an oscillator 226), a comparator 314, a comparator 316, and a pulse signal generator 318 (e.g., pulse width modulation signal generator 318). The oscillator 226 generates a sawtooth wave signal SAW based on the feedback signal FB2. The feedback signal FB2 indicates the output voltage of the secondary winding 206. The comparator 314 compares the sawtooth wave signal SAW with the reference signal SET. The reference signal SET has a reference voltage level V _SET . Comparator 316 compares feedback signal FB1 with reference signal PEAK. The feedback signal FB1 indicates the current I _SE flowing through the primary winding 204. The reference signal PEAK determines the maximum current value I _PEAK of the current I _PR flowing through the primary winding 204. The pulse width modulation signal generator 318 is coupled to the comparator 314 and the comparator 316 and generates a pulse width modulation signal PWM1. The sawtooth signal SAW from the oscillator 226 can be used to control the duty cycle of the pulse width modulation signal PWM1. The pulse width modulation signal PWM1 controls the conduction state of the switch 318 to control the power of the transformer 202.

Controller 220 also includes a control signal generator 320. The control signal generator 320 generates a control signal CTRL based on the feedback signal FB2. Control signal CTRL is applied to oscillator 226. In an embodiment, if the voltage of the feedback signal FB2 is greater than the preset threshold TH (eg, TH>0V), the control signal CTRL is logic 1, otherwise the control signal CTRL is logic 0. In the example of FIG. 3, oscillator 226 includes current sources 302 and 304, switches 306 and 308, and capacitor 310. The voltage signal generated on the capacitor 310 is the sawtooth signal SAW. Depending on the conduction state of switches 306 and 308, capacitor 310 can be charged by current source 302 or discharged by current source 304.

If the voltage of the capacitor 310 rises to the reference voltage value V _SET , the controller 220 generates a pulse width modulation signal PWM1 having a first level to turn on the switch 218 (eg, PWM1 is a logic 1). Thereby the transformer 202 is operated in the charging phase T _ON . In one embodiment, the clamping circuit 228 forces the voltage of the feedback signal FB2 to be substantially zero, such that the control signal CTRL has a first level (e.g., a logic zero). Control signal CTRL controls switch 308 in oscillator 226. Control signal CTRL is coupled to switch 306 through NOT gate 312. In the example of FIG. 3, when control signal CTRL is logic 0, switch 306 is turned "on" and switch 308 is turned "off". Capacitor 310 is charged by the current of current source 302. Therefore, the voltage of the capacitor 310 (for example, the voltage of the sawtooth wave signal SAW) rises from the reference voltage value V _SET . At the same time, the current I _PR flowing through the primary winding 204 increases. Comparator 316 compares feedback signal FB1 with reference signal PEAK. When the voltage of the feedback signal FB1 reaches the voltage of the reference signal PEAK, the current I _PR flowing through the primary winding 204 is increased to the maximum current value I _PEAK , at which time the controller 220 _turns off the switch 318, thereby ending the charging phase T _{ON .} And start the discharge phase T _DIS . In particular, pulse width modulation signal generator 318 generates a pulse width modulation signal PWM1 having a second level to turn off switch 218 (eg, PWM1 is a logic 0). When the charging phase T _ON ends, the voltage of the capacitor 310 (for example, the voltage of the sawtooth wave signal SAW) rises to the first voltage value V ₁ as shown in FIG. In other words, the voltage of the capacitor 310 (for example, the voltage of the sawtooth wave signal SAW) is turned on from the reference voltage value V _SET to the first voltage value V ₁ .

During the discharge phase T _DIS , the switch 218 is turned off and the current I _SE flowing through the secondary winding 206 is reduced from the maximum current value I _SE-MAX . During the discharge phase T _DIS , the auxiliary winding 208 produces a substantially constant output voltage. This output voltage is divided by resistors 214 and 216. Therefore, in the discharge phase T _DIS , the voltage of the feedback signal FB2 (such as the voltage across the resistor 216) is proportional to the output voltage of the auxiliary winding 208 and thus substantially constant. In one embodiment, the resistance of the resistor 214 and the resistor 216 are properly selected such that during the discharge phase T _DIS , the voltage of the feedback signal FB2 is greater than the preset threshold TH. When the voltage of the feedback signal FB2 is greater than the preset threshold TH, the control signal CTRL is logic 1, turning the switch 306 off and the switch 308 conducting. Capacitor 310 is discharged at the current of current source 304. Therefore, the voltage of the capacitor 310 drops from the first voltage value V ₁ .

When the voltage of the feedback signal FB2 representing the output voltage of the secondary winding 206 drops to the threshold value TH, indicating that the current I _SE flowing through the secondary winding 206 is reduced to a preset current value, the controller 220 ends the discharge phase. T _DIS starts the adjustment phase T _ADJ . In an embodiment, when the current I _SE flowing through the secondary winding 206 is reduced to substantially zero, the controller 220 ends the discharge phase T _DIS and initiates the adjustment phase T _ADJ . When the discharge phase T _DIS ends, the voltage of the capacitor 310 (for example, the voltage of the sawtooth wave signal SAW) drops to the second voltage value V ₂ as shown in FIG.

In the adjustment phase T _ADJ , since the voltage of the feedback signal FB2 drops to the threshold TH, the control signal CTRL becomes a logic 0. Switch 306 is turned "on" and switch 308 is turned "off". Capacitor 310 is again charged by the current of current source 302. The voltage of the capacitor 310 rises from the second voltage value V ₂ . During the adjustment phase T _ADJ , the switch 218 remains off and no current flows through the primary winding 204 or the secondary winding 206 . When the voltage of the sawtooth signal SAW rises to the reference voltage value V _SET , the controller 220 ends the adjustment phase T _ADJ and turns on the switch 218 to initiate the charging phase T _ON in the next switching cycle T _S . Specifically, the pulse width modulation signal generator 318 generates a pulse width modulation signal PWM1 having a first level to turn on the switch 218 (eg, PWM1 is a logic 1).

Assume that the capacitance value of the capacitor 310 is C ₁ , the current of the current source 302 is I ₁ , and the current of the current source 304 is I ₂ . At the end of the charging phase T _ON , the voltage of the sawtooth signal SAW (the voltage of the capacitor 310) can be expressed as:

At the end of the discharge phase T _DIS , the voltage of the sawtooth signal SAW can be expressed as:

At the end of the adjustment phase T _ADJ , the voltage of the sawtooth signal SAW can be expressed as:

Therefore, the length of the adjustment phase T _ADJ can be derived from equations (2)-(4), namely:

From equation (5), the relationship between the length of the adjustment phase T _{ADJ and} the length of the switching period T _S can be expressed as:

According to equation (6) can be obtained, the ratio of the length of time the total length of the discharge time period T _DIS the charging phase T _ON, and the discharging period T _DIS adjust the period T _{ADJ 1,} I ₂ determined by the current I. If the magnitudes of the currents I ₁ , I ₂ from the current sources 302, 304, respectively, are constant, the length of time of the discharge phase T _DIS is proportional to the length of time of the switching period T _S . Therefore, referring to equation (1), the average output current I _{OAVG of the} secondary winding 206 is substantially constant.

FIG. 5 shows a flowchart 500 of an exemplary method of controlling a transformer in accordance with an embodiment of the present invention. FIG. 5 will be described in conjunction with FIGS. 2, 3, and 4.

In step 502, transformer 202 operates for a plurality of switching cycles. One switching cycle includes a charging phase T _ON , a discharging phase T _{DIS ,} and an adjustment phase T _ADJ .

In step 504, the transformer 202 is powered with an input power source during the charging phase T _ON . In the charging phase T _ON , the switch 218 coupled in series with the primary winding 204 of the transformer 202 is turned on. In one embodiment, the length of time of the charging phase T _ON is controlled by monitoring the current flowing through the primary winding 204. Specifically, when the current flowing through the primary winding 204 increases to a preset maximum current value, the charging phase T _{ON is} ended (turning off the switch 218) and the discharging phase T _{DIS is} started.

At step 506, the load is supplied to the load using transformer 202 during the discharge phase T _DIS . In one embodiment, the length of time of the discharge phase T _DIS is controlled by monitoring the output voltage of the transformer 202 auxiliary winding 208. The output voltage of the auxiliary winding 208 can indicate whether the current flowing through the secondary winding 206 of the transformer 202 drops to a predetermined current value. Specifically, when the current flowing through the secondary winding 206 is reduced to a preset current value (eg, 0), the discharge phase T _{DIS is} ended and the adjustment phase T _{ADJ is} initiated. In an embodiment. When the output voltage of the auxiliary winding 208 is reduced to a predetermined voltage value, the current flowing through the secondary winding 206 is reduced to the preset current value.

In step 508, it determines the length of the time period T _ADJ adjusted such that the length of the discharge time period T _DIS with the charging phase T _ON, the ratio between the total duration of the discharge period T _DIS and adjusting period T _ADJ is constant. In one embodiment, the length of the adjustment phase T _ADJ is determined by an oscillator 226. The oscillator 226 generates a sawtooth wave signal SAW. During the charging phase T _ON , the voltage of the sawtooth signal SAW rises from the preset reference voltage value V _SET to the first voltage value V ₁ . In the discharge phase T _DIS , the voltage of the sawtooth wave signal SAW drops from the first voltage value V ₁ to the second voltage value V ₂ . In the adjustment phase T _ADJ , the voltage of the sawtooth signal SAW rises from the second voltage value V ₂ to a preset reference voltage value V _SET . When the voltage of the sawtooth signal SAW rises to the preset reference voltage value V _SET , the adjustment phase T _{ADJ is} ended and a new switching period T _{S is} initiated.

Accordingly, the present invention provides a circuit and method for controlling a power converter that can be used to power various loads. The power converter includes a transformer that operates over multiple switching cycles. At least one switching cycle includes a charging phase T _ON , a discharging phase T _{DIS ,} and an adjustment phase T _ADJ . The power converter can have the adjustment phase T _ADJ have a suitable length of time such that the ratio of the length of the discharge phase T _{DIS to} the length of the switching period T _S is constant. The length of the switching period T _{S is} the total length of time in the charging phase T _ON , the discharging phase T _DIS and the tuning phase T _ADJ . Therefore, the average current output per switching cycle is substantially constant.

The power converter provided by the present invention can be applied to various occasions. In an embodiment, the power converter can provide a substantially constant current output to drive a light source such as a light emitting diode string. In another embodiment, the power converter can provide a substantially constant current to charge the battery.

The power converter provided by the present invention is relatively small in size compared to conventional flyback converters including optocouplers and error amplifiers.

In addition, even if the change of the input voltage and the output voltage of the power converter may cause a change in the length of the charging phase T _ON and the discharging phase T _DIS , the power converter can automatically determine the length of the adjustment phase T _ADJ to maintain the discharging phase T The ratio of the length of the _{DIS to} the length of the switching period T _S is constant. Therefore, the power converter can automatically adjust to output a current having a constant average value. Moreover, it can be seen from equation (1) that the average value of the output current of the power converter is not affected by the inductance value of the transformer winding, so that the output current can be controlled more accurately.

The above detailed implementation modes and drawings are merely common embodiments of the present invention. It is apparent that various additions, modifications and substitutions are possible without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood by those of ordinary skill in the art that the present invention can be applied in the form of the form, the structure, the arrangement, the ratio, the materials, the elements, the components, and the like in the actual application and the specific requirements. Changed. Therefore, the embodiments disclosed herein are intended to be illustrative and not restrictive, and the scope of the invention is defined by the scope of the appended claims and their legal equivalents.

100‧‧‧Reverse converter

104‧‧‧Primary winding

106‧‧‧Secondary winding

108‧‧‧Auxiliary winding

110‧‧‧ diode

112‧‧‧load

114‧‧‧Error amplifier

116‧‧‧Optocoupler

111‧‧‧current monitoring resistor

118‧‧‧ switch

120‧‧‧ Controller

122‧‧‧ Capacitance

124‧‧‧ magnetic core

200‧‧‧Power Converter

202‧‧‧Transformer

204‧‧‧Primary winding

206‧‧‧Secondary winding

208‧‧‧Auxiliary winding

210‧‧‧ diode

212‧‧‧load

214, 216‧‧‧ resistance

218‧‧‧ switch

220‧‧‧ Controller

222‧‧‧ Capacitance

224‧‧‧ magnetic core

226‧‧‧Signal Generator/Oscillator

228‧‧‧Clamp circuit

230‧‧‧resistance

302, 304‧‧‧ Current source

306, 308‧‧ ‧ switch

310‧‧‧ Capacitance

312‧‧‧NOT gate

314, 316‧‧‧ comparator

318‧‧‧Pulse signal generator / pulse width modulation signal generator

320‧‧‧Control signal generator

500‧‧‧flow chart

502, 504, 506, 508‧ ‧ steps

The objects, specific architectural features and advantages of the present invention will become more apparent from the description of the embodiments of the invention.

Figure 1 is a block diagram of a conventional flyback converter.

2 is an illustrative block diagram of a power converter in accordance with an embodiment of the present invention.

FIG. 3 is a schematic diagram showing the architecture of the controller in FIG. 2.

4 is an illustrative waveform diagram of signals received or generated by a power converter in accordance with an embodiment of the present invention.

FIG. 5 is a flow chart showing an exemplary method of controlling a transformer in accordance with an embodiment of the present invention.

200‧‧‧Power Converter

202‧‧‧Transformer

204‧‧‧Primary winding

206‧‧‧Secondary winding

208‧‧‧Auxiliary winding

210‧‧‧ diode

212‧‧‧load

214‧‧‧resistance

216‧‧‧resistance

218‧‧‧ switch

220‧‧‧ Controller

222‧‧‧ Capacitance

224‧‧‧ magnetic core

226‧‧‧Signal Generator/Oscillator

228‧‧‧Clamp circuit

230‧‧‧resistance

Claims (19)

A power converter comprising: a transformer having a primary winding coupled to a power supply and a primary winding coupled to a load; and a signal generator for generating a sawtooth signal, wherein the transformer operates at a plurality a switching cycle, and at least one of the plurality of switching cycles includes a charging phase, a discharging phase, and an adjusting phase, wherein in the charging phase, the sawtooth wave signal rises from a predetermined reference voltage value to a first a voltage value, wherein the sawtooth wave signal drops from the first voltage value to a second voltage value, and wherein the sawtooth wave signal rises from the second voltage value to the adjustment phase a preset reference voltage value, wherein during the charging phase, the transformer is powered by the power source and a current flowing through the primary winding is increased, wherein during the discharging phase, the transformer discharges power to the load and flows through the secondary a current of the winding is reduced, and wherein a ratio of a length of the discharge phase to the total length of time of the charging phase, the discharging phase, and the adjusting phase It is a constant. The power converter of claim 1, further comprising: a resistor coupled in series with the primary winding, providing a feedback signal indicative of the current flowing through the primary winding. The power converter of claim 1, wherein the transformer further includes an auxiliary winding providing an indication of the flow through the secondary winding Whether the current is reduced to a feedback signal of a predetermined current value. The power converter of claim 3, further comprising: a clamp circuit that clamps a voltage of the feedback signal during the charging phase. The power converter of claim 1, further comprising: a switch coupled in series with the primary winding, wherein the switch is turned on when the sawtooth wave signal rises from the reference voltage value to the first voltage value And wherein the switch is turned off when the current flowing through the primary winding increases to a predetermined maximum current value. The power converter of claim 1, further comprising: a switch coupled in series with the primary winding, wherein the switch is turned on during the charging phase, and wherein the switch is turned off during the discharging phase and the adjusting phase. The power converter of claim 1, further comprising: a switch coupled in series with the primary winding, wherein the sawtooth signal is set to control a duty cycle of a pulse signal, the pulse signal controlling the switch. The power converter of claim 1, wherein the signal generator comprises: a capacitor coupled to the transformer, the capacitor providing the sawtooth signal, wherein the capacitor is first in the charging phase The current is charged and a voltage across the capacitor rises from a predetermined reference voltage value to a first voltage value, wherein during the discharging phase, the capacitor is discharged with a second current and the current The voltage across the capacitor drops from the first voltage value to a second voltage value, and wherein during the adjustment phase, the voltage across the capacitor rises from the second voltage value to the predetermined reference voltage value. The power converter of claim 8, wherein the ratio is determined by the first current and the second current. A power converter as claimed in claim 1 wherein the average of the current flowing through the secondary winding is substantially constant. A controller for controlling a transformer, comprising: a first signal generator, receiving a first feedback signal and generating a first signal, the first feedback signal indicating an output voltage of a primary winding of the transformer a pulse signal generator coupled to the first signal generator, generating a pulse signal according to the first signal, wherein the pulse signal controls power of the transformer, wherein in a charging phase, the first signal is from a pre- Setting the reference voltage value to a first voltage value, wherein in a discharging phase, the first signal decreases from the first voltage value to a second voltage value lower than the preset reference voltage value, and wherein an adjustment a phase, the first signal is raised from the second voltage value to the predetermined reference voltage value, wherein a ratio of a length of the discharge phase to the total duration of the charging phase, the discharging phase, and the adjusting phase Is a constant, wherein in the charging phase, a current flowing through a primary winding of the transformer increases, and wherein in the discharging phase, the voltage is passed through A current of the primary winding of the device is reduced. The controller of claim 11, wherein the pulse signal controller is coupled in series with a primary winding of the transformer, and wherein the switch is turned on during the charging phase, and the discharging phase and the adjusting phase are The switch is turned off. The controller of claim 11, wherein when a current flowing through a primary winding of the transformer increases to a predetermined maximum current value, the controller ends the charging phase and starts the discharging phase, and wherein When a current flowing through the primary winding of the transformer is reduced to a predetermined current value, the controller ends the discharge phase and initiates the adjustment phase. The controller of claim 11, wherein the first signal generator comprises a capacitor coupled to the pulse signal generator, wherein during the charging phase, the capacitor is charged with a first current and the capacitor is a voltage is raised from the predetermined reference voltage value to a first voltage value, wherein in the discharging phase, the capacitor is discharged by a second current and the voltage across the capacitor is decreased from the first voltage value to a second voltage a value, and wherein in the adjustment phase, the voltage across the capacitor rises from the second voltage value to the predetermined reference voltage value. The controller of claim 14, wherein the ratio is determined by the first current and the second current. The controller of claim 11, further comprising: a comparator coupled to the pulse signal generator, comparing a second feedback signal and a preset maximum current value, the second feedback signal indicating the flow A current through the primary winding of the transformer. A method of controlling a transformer, comprising: operating the transformer during a plurality of switching cycles, at least one of the plurality of cycles comprising a charging phase, a discharging phase, and an adjusting phase; supplying power to the transformer during the charging phase; The discharge phase uses the transformer to supply power to a load; and determining a length of time of the adjustment phase includes: generating a sawtooth wave signal; and increasing the sawtooth wave signal from a predetermined reference voltage value to a first voltage during the charging phase a value in which the sawtooth wave signal is decreased from the first voltage value to a second voltage value; the sawtooth wave signal is raised from the second voltage value during the adjustment phase; and when the sawtooth wave signal rises to The adjustment phase is ended when the predetermined reference voltage value is reached, wherein a ratio between the length of the discharge phase and the total duration of the charging phase, the discharging phase, and the adjusting phase is constant. The method of claim 17, further comprising: turning on a switch coupled in series with a primary winding of the transformer during the charging phase; and increasing a current flowing through the primary winding of the transformer to a preset At the maximum current value, the charging phase is ended and the discharging phase is initiated; the switch is turned off at the end of the discharging phase; When a current flowing through the primary winding of the transformer is reduced to a predetermined current value, the discharge phase is terminated and the adjustment phase is initiated; and the switch is turned on at the end of the adjustment phase. The method of claim 17, further comprising: monitoring an output voltage of an auxiliary winding of the transformer, wherein the output voltage indicates whether the current flowing through the secondary winding is reduced to the predetermined current value.