Switching converter and AC adapter using the same
View Patent ↗Disclosed herein is a switching converter capable of preventing a period in which a switch SW of a primary side is turned on and a period in which a synchronous rectifying switch SR SW of a secondary side is turned on from being overlapped with each other. The switching converter includes: a transformer T inducing primary energy to secondary side; a switch SW connected to a primary coil of the transformer T to switch a primary voltage; a synchronous rectifier SR connected to a secondary coil of the transformer T to rectify a secondary voltage; and a delay locked loop connected between the secondary coil and the synchronous rectifier SR, wherein the delay locked loop generates a signal synchronized with a turn-on control signal of the switch SW and outputs the generated signal to the synchronous rectifier SR to control a turn-off operation of the synchronous rectifier SR.
1. A switching converter comprising:
a transformer T inducing primary energy to secondary side;
a switch SW connected to a primary coil of the transformer T to switch a primary voltage;
a synchronous rectifier SR connected to a secondary coil of the transformer T to rectify a secondary voltage; and
a delay locked loop connected between the secondary coil and the synchronous rectifier SR,
wherein the delay locked loop comprises an edge detector detecting a rising edge in a voltage (SR Sensing Voltage) having a same waveform as that of a control signal of the switch SW to generate a signal (Rising Edge Signal): and
wherein the delay locked loop generates a generated signal synchronized with a turn-on control signal of the switch SW and outputs the generated signal to the synchronous rectifier SR to control a turn-off operation of the synchronous rectifier SR.
2. The switching converter according to claim 1 , wherein the delay locked loop includes:
a voltage controlled oscillator outputting a signal (SR GATE Off Signal) of which a phase is adjusted according to an input voltage level to the synchronous rectifier SR;
a delay compensator delaying the signal input from the voltage controlled oscillator by a predetermined time so that the voltage controlled oscillator outputs a signal synchronized with the signal (Rising Edge Signal);
a phase detector receiving an output signal (Rising Edge Signal) of the edge detector and an output signal (DLL Locking Signal) of the delay compensator, comparing these two signals with each other, and generating a pulse signal corresponding to a difference there between; and
a pulse to voltage converter converting the pulse signal input from said phase detector into a specific voltage level and outputting the specific voltage level to the voltage controlled oscillator.
3. The switching converter according to claim 2 , wherein the pulse to voltage converter includes a charge pump and a loop filter.
4. The switching converter according to claim 1 , wherein the synchronous rectifier SR includes a synchronous rectifying switch SR SW turning on or off a conduction path of a current flowing to the secondary coil and a diode DSR having a cathode terminal and an anode terminal connected to a drain terminal and a source terminal of the synchronous rectifying switch SR SW, respectively.
5. The switching converter according to claim 4 , wherein an input terminal of the delay locked loop is connected to a node N between one end of the secondary coil and the cathode terminal of the diode DSR through an input line, and an output terminal thereof is connected to a gate terminal of the synchronous rectifying switch SR SW through an output line.
6. An alternating current (AC) adaptor comprising:
a bridge rectifier rectifying an input AC voltage to convert the input AC voltage into direct current (DC) power;
a switching converter inducing the DC power applied to a first coil of a transformer T to a secondary coil of the transformer T through a switch SW connected to the primary coil and rectifying the induced power by a synchronous rectifier (SR) connected to a secondary coil;
a feedback unit sensing a state of a voltage finally output by the switching converter and transferring information on the sensed state of the voltage to a pulse width modulation (PWM) adjuster; and
the PWM adjuster outputting a control signal of which a pulse width is modulated according to a signal fed back from the feedback unit to the switch SW,
wherein the switching converter includes a delay locked loop comprising an edge detector detecting a rising edge in a SR Sensing Voltage having a same waveform as that of a control signal of the switch SW to generate a Rising Edge Signal and is connected between the secondary coil and the synchronous rectifier SR, the delay locked loop generating the Rising Edge Signal synchronized with the control signal of the switch SW and outputting the Rising Edge Signal to the synchronous rectifier SR to control a turn-off operation of the synchronous rectifier SR.