KR20010083999A - Soft switching method of asymmetrical flyback circuit - Google Patents

Abstract

PURPOSE: A soft switching method is provided to achieve a zero voltage control by soft switching the transistor and diode without adding circuit or changing configuration. CONSTITUTION: An asymmetric fly back circuit comprises a PWM controller for generating a pulse width modulation signal; a switch gate driver for driving high side and low side switch gates in accordance with the pulse width modulation signal output from the PWM controller; a high side switch and a low side switch operating in accordance with the output signal from the switch gate driver; a transformer for organizing the first side voltage into the second side voltage in accordance with the switching operation of the high side switch and the low side switch; a synchronous rectifier for rectifying the second side output voltage of the transformer; an insulation transformer for driving the gate of the synchronous rectifier in accordance with the low side switch gate driving signal output from the switch gate driver; a resonance type capacitor arranged at the common contact between the high side switch and the low side switch and the first side voltage input terminal of the transformer; and a diode arranged between the second side voltage output terminal of the transformer and the synchronous rectifier. A method is characterized in that the current flowing through the diode increases/decreases in accordance with the change amount of the first side current of the transformer, and such increase/decrease is performed in a horizontal direction.

Description

Soft switching method of asymmetric flyback circuit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an asymmetrical flyback circuit applied to an AC adapter, and in particular, minimizes the loss incurred during conduction of parasitic diodes of a MOS transistor, the secondary switch of the synchronous rectifier, when the synchronous rectifier is turned on. The present invention relates to a soft switching method of an asymmetrical flyback circuit for soft switching to a transistor and a diode, which is a passive switch, away from the conventional transistor soft switching scheme in order to prevent a double delay in an off state.

In recent years, notebook PCs are becoming smaller and lighter in the world, while at the same time pursuing high performance, it is inevitably required to increase system specifications such as multimedia system construction, CPU speed, and memory.

In addition, as the capacity of each system specification increases, the AC adapter for notebook PCs currently uses 45 to 50 watts (W), but gradually increases to 60 watts, 75 watts and 80 watts. The demand for high capacity, ultra-slip slip and high efficiency is increasing.

In addition, the reason why the AC adapter should be made higher is that the higher the efficiency, the smaller the internal power loss, which means that the internal heat generation is smaller, so that the miniaturization is possible.

However, the most typical method used as an AC adapter at present is a flyback circuit method and a resonant type method. Among them, a flyback circuit method is a turn-off of a MOSFET, a semiconductor device. ) There is a disadvantage in that the power loss is large because the hard switching of the voltage (Vds) and the turn-on current (Ids) is large, and the resonance type reduces the switching loss. However, it is an effective method for weight reduction, but has poor controllability because the voltage and current are made into a sinusoidal shape, and has a disadvantage of high voltage and current stress in the switching element.

Therefore, in recent years, due to the high efficiency, the synchronous rectification method using the synchronous rectifier (SR) is attracting attention. The synchronous rectifier uses a MOSFET instead of an output diode and the R _{ds (on)} loss when the synchronous rectifier conducts. I _F ² * R _{ds (on)} ) occurs, but R _{ds (on)} is very small, such as 0.020 ~ 0.025Ω, so the loss is small, which greatly increases the efficiency.

The configuration of the conventional AC adapter to which the synchronous rectification method as described above is shown in FIG.

Referring to the configuration of FIG. 1, the noise mixed in the commercial AC power input is removed and transmitted to the device provided at the rear end, and the power noise generated at the device side at the rear end is transmitted to the commercial AC power input end side. EMI filter 10 for preventing the bridge, the bridge rectifier 20 for rectifying the AC power input through the EMI filter 10 to convert to DC power, and the DC power rectified through the bridge rectifier 20 An asymmetrical voltage doubler 30 that maintains a DC power state at a constant 220V AC input state and a zero voltage switching operation for power flowing through the voltage doubler 30 according to an input switching control signal. The flyback converter 40 and the asymmetrical flyback converter 40 with respect to the variation of the voltage of the zero voltage switching operation is carried out through the transformer (T1) The synchronous rectification unit 50 rectifies the power by a specific synchronous signal, and the feedback unit 100 for detecting the state of the final output voltage through the synchronous rectification unit 50 to transfer information on the voltage state to the front end and The protection circuit 110 prevents damage to the devices located at the rear end of the feedback unit 100 and the synchronous rectification unit 50, and the output of the synchronous rectification unit 50 transmitted through the feedback unit 100. PWM controller 70 for modulating the control signal PWM signal in accordance with the voltage state, and a drive signal for controlling the zero voltage switching operation of the asymmetric flyback converter 40 in accordance with the control signal output from the PWM controller 70 To drive the low-side switch in the asymmetric flyback converter 40 of the switch gate driver 80, and a drive signal output from the switch gate driver 80 for generating a; SR drive driver 90 for controlling the synchronous state of the synchronous rectification unit 50 by the drive signal (L).

Looking at the configuration of the portion related to the synchronous rectification method of the conventional AC adapter applying the synchronous rectification method configured as described above, as shown in FIG. 2, the asymmetric flyback converter 40 of FIG. And a simplified circuit configuration of the synchronous rectifier 50 and the SR gate driver 90, and the PWM controller 70 and the switch gate driver 80 are shown.

Referring to the configuration shown in FIG. 2 in the same manner, the high and low side switch gate according to the PWM controller 70 for generating a pulse width modulation signal and the pulse width modulation signal output from the PWM controller 70. A switch gate driver 80 for driving the switch, a high side switch SWH and a low side switch SWL for switching according to an output signal of the switch gate driver 80, the high side switch SWH, and In accordance with the switching operation of the low side switch SWL, a transformer T1 for inducing a primary voltage to a secondary side, a synchronous rectifier SR for rectifying a secondary output voltage of the transformer T1, and the switch gate driver An insulating transformer T2 for driving the gate of the synchronous rectifier SR with the low side switch gate driving signal outputted from 80).

The asymmetric flyback circuit using the conventional synchronous rectifier configured as described above is a pulse width modulated signal output from the pulse width modulator 70 and the gate driver 80 has a high side switch (SWH) inside the asymmetric flyback converter 40. And a gate of the low side switch SWL.

The transformer T1 causes the primary side voltage to be induced to the secondary side according to the switching operation of the high side switch SWH and the low side switch SWL, and the synchronous rectifier SR is the secondary side of the transformer T1. The output voltage is rectified and output. The isolation transformer T2 drives the gate of the synchronous rectifier SR by using the low side switch gate driving signal output from the switch gate driver 80.

That is, the gate driving signal of the synchronous rectifier SR is turned off between the high side switch SWH and the turn-on of the synchronous rectifier SR, and the turn-off of the synchronous rectifier SR and the high side switch SWH. Is supplied with a delay between turns on.

In addition, the energy transferred to the secondary side is consumed until the high side switch SWH is turned on after the low side switch SWL is turned off. The synchronous rectifier SR must be turned off within the turn-off of the switch SWL.

To this end, conventionally, the gate drive signal of the low side switch SWL is transferred through the isolation transformer T2 for the purpose of making the gate signal of the synchronous rectifier SR the same as that of the low side switch SWL. Is applied to the gate.

The waveform a shown in FIG. 3 is the high side switch gate voltage waveform, the waveform b is the low side switch gate voltage waveform, and the waveform c is the gate voltage waveform of the synchronous rectifier.

Referring to the operation of the circuit shown in FIG. 2 with reference to the voltage waveform shown in FIG. 3, since the high side switch SWH is on in the section of waveform a in FIG. 3, energy is applied to the transformer T1. Stored.

Thereafter, when the voltage state of the waveform a is changed to the low state, the high side switch SWH is turned off, and thus the polarity of the transformer T1 is switched so that the voltage is induced to the secondary side so that the current isise Will flow.

At this time, the synchronous rectifier SR is turned on through the SR gate driver 90 using the turn-on operation voltage of the low side switch SWL, that is, the voltage of the waveform b, in order to flow the current isec.

Therefore, the current isec continuously flows while the low side switch SWL is on, and the current isec stops flowing when the low side switch SWL is turned off.

However, in practice, there is a delay time between the high side switch SWH turn-off time and the turn on time of the low side switch SWL, and the secondary side current isc of the transformer T1 is the high side. Since it flows from the turn-off time of the switch SWH, it flows through the parasitic diode inside the synchronous rectifier SR until the synchronous rectifier SR is turned on (see waveform c in FIG. 3).

Therefore, a power loss D _SR is generated due to the voltage drop in the parasitic diode while the current isec flows through the parasitic diode inside the synchronous rectifier SR.

In addition, since the synchronous rectifier SR is operated by a signal via the switch gate driver 80 and the SR gate driver 90 from the output signal of the PWM controller 70, a double time delay occurs. Since the turn-off operation is performed at a time delayed from the turn-off time of the low side switch SWL by time, a problem of malfunction occurs (see waveform d in FIG. 3).

Furthermore, since the low side switch SWL is turned off and the primary side current ipri of the transformer T1 flows through the parasitic diode of the high side switch SWH, the synchronous rectifier SR is turned off. Should be the same as the turn-off time point of the low side switch SWL, but the conventional technology shown in FIG. 2 does not satisfy this requirement.

An object of the present invention for solving the above problems is a loss generated in the parasitic diode conduction of a MOS transistor which is a secondary side switch of the synchronous rectifier in the asymmetric flyback circuit applied to the AC adapter, when the synchronous rectifier is turned on The present invention provides a soft switching method of an asymmetrical flyback circuit for soft switching to a transistor and a diode, which is a passive switch, from the conventional transistor soft switching scheme.

1 is an exemplary block diagram of an AC adapter to which a synchronous rectification method is applied;

2 is a simplified circuit diagram of a part related to the conventional synchronous rectification method;

3 is a waveform diagram illustrating the problem of FIG. 2;

4 is a diagram illustrating a correlation between variation of primary and secondary currents of a transformer and conduction currents of a current conducting diode according to variations in voltages applied to gate and source terminals of a high side switch and a low side switch in a conventional soft switching method. Waveform example showing

5 is a diagram illustrating a variation between a primary side current and a secondary side current of a transformer and a conduction current of a current conducting diode according to a change in voltage across a gate and a source terminal of a high side switch and a low side switch in a soft switching method according to the present invention. Exemplary waveform diagram showing correlation.

Features of the present invention for achieving the above object, a PWM controller for generating a pulse width modulation signal, a switch gate driver for driving the high side and low side switch gate in accordance with the pulse width modulation signal output from the PWM controller; A high side switch and a low side switch performing a switching operation according to an output signal of the switch gate driver, a transformer for inducing a primary side voltage to a secondary side according to a switching operation of the high side switch and the low side switch, and two of the transformers; A synchronous rectifier for rectifying a differential side output voltage, an insulated transformer for driving a gate of the synchronous rectifier with a low side switch gate driving signal output from the switch gate driver, a common contact point for the high side switch and a low side switch, and the transformer In an asymmetrical flyback AC adapter circuit having a resonant capacitor formed at a primary voltage input terminal of a switch and a diode which is a switching element for current conduction formed between the secondary voltage output terminal of the transformer and the synchronous rectifier. In the soft switching method:

When the amount of change in the variation of the primary side current of the transformer increases or decreases, the amount of conduction current of the diode increases or decreases correspondingly, but the change direction of the increase or decrease varies in the horizontal direction.

The above objects and various advantages of the present invention will become more apparent from the preferred embodiments of the invention described below with reference to the accompanying drawings by those skilled in the art.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

First, the present invention does not change the configuration of the circuit shown in FIG. However, if the conventional soft switching method is the soft switching method of the high side switch SWH and the low side switch SWH in FIG. 2, the present invention provides a diode (D2) of FIG. Diode to soft switching.

The diode denoted by the reference numeral "D2" is to perform the function of a passive switch, this scheme is appropriate design of the resonant capacitor (Resonant Capacitor) denoted by reference numeral "C1" of FIG. Can be achieved by

That is, in FIG. 2, variations in the primary and secondary currents of the transformer according to variations in voltages applied to the gate and source terminals of the high side switch SWH and the low side switch SWH, and the reference numeral “D2”. Looking at the correlation between the conduction current of the diode represented by the conventional method as shown in Figure 4 attached.

In this case, as shown in FIG. 4, when the amount of change in the variation ΔI of the primary side current of the transformer T1 increases, the amount of conduction current iD2 of the diode D2 increases correspondingly. As shown in FIG. 4, an intersection region of the corresponding current is generated. That is, zero voltage control is not performed.

Therefore, the conventional method may prevent the double delay at turn-off of the synchronous rectifier, but it is not possible to reduce the loss of the conduction current of the diode. It appears as the secondary voltage, and the variation of current and the amount of conduction current increase accordingly.

The fluctuation of the current and the increase and decrease of the conduction amount are indicated by a double-headed arrow. Since the direction of change of the fluctuation is vertical and vertical, the zero voltage control will be possible if it can be adjusted in the horizontal direction.

Therefore, in the present invention, as shown in the accompanying FIG. 5, the direction of change of the current is adjusted so as to increase and decrease in the horizontal direction.

To this end, a design scheme must be changed, which can be achieved by proper design of a resonant capacitor indicated by reference numeral “C1” of FIG. 2.

The resonant capacitor (C1) design method is to employ a capacitive component that satisfies the following equation (1), the equation (1) is as follows.

In this case, the primary current ipri of the transformer T1 in Equation 1 is defined as Equation 2 below.

In addition, the secondary side current isec corresponding to the primary side current ipri of the transformer T1 defined in Equation 2 is defined as Equation 3 below.

Therefore, when the capacitance component of the resonant capacitor indicated by the reference numeral "C1" in the configuration of the circuit shown in FIG. 2 is satisfied with the conditional expression shown in Equation 1 shown in FIG. A soft switching scheme as can be obtained.

While the invention has been shown and described in connection with specific embodiments thereof, it will be appreciated that various modifications and changes can be made without departing from the spirit and scope of the invention as indicated by the claims. Anyone who owns it can easily find out.

By applying the soft switching method of the asymmetrical flyback circuit according to the present invention as described above, in order to minimize the loss caused during the parasitic diode conduction of the MOSFET which is the secondary side switch of the synchronous rectifier when the synchronous rectifier is turned on, In the transistor soft switching method, it is possible to soft switch the transistor and the diode which is the passive switch without any additional circuit or configuration change in hardware, so that the zero voltage control is achieved.

Claims (3)

A PWM controller for generating a pulse width modulated signal, a switch gate driver for driving a high side and a low side switch gate according to a pulse width modulated signal output from the PWM controller, and a switching operation according to an output signal of the switch gate driver A high side switch and a low side switch, a transformer for inducing a primary side voltage to a secondary side according to a switching operation of the high side switch and the low side switch, a synchronous rectifier for rectifying a secondary output voltage of the transformer, and the switch An insulation transformer for driving the gate of the synchronous rectifier with a low side switch gate driving signal output from a gate driver; a resonance formed at a common contact point of the high side switch and the low side switch and a primary voltage input terminal of the transformer; In the capacitor, and a soft switching method in an asymmetric AC eodeopteo flyback circuit and a switching element of diode current-conduction is formed between the secondary-side voltage output terminal of the transformer and the synchronous rectifier: When the amount of change in the variation of the primary side current of the transformer increases or decreases, the amount of conduction current of the diode increases and decreases, but the fluctuation direction of the increase and decrease of the asymmetrical flyback circuit is characterized in that it changes in the horizontal direction. Switching method. A PWM controller for generating a pulse width modulated signal, a switch gate driver for driving a high side and a low side switch gate according to a pulse width modulated signal output from the PWM controller, and a switching operation according to an output signal of the switch gate driver A high side switch and a low side switch, a transformer for inducing a primary side voltage to a secondary side according to a switching operation of the high side switch and the low side switch, a synchronous rectifier for rectifying a secondary output voltage of the transformer, and the switch An insulation transformer for driving the gate of the synchronous rectifier with a low side switch gate driving signal output from a gate driver; a resonance formed at a common contact point of the high side switch and the low side switch and a primary voltage input terminal of the transformer; In the capacitor, and a soft switching method in an asymmetric AC eodeopteo flyback circuit and a switching element of diode current-conduction is formed between the secondary-side voltage output terminal of the transformer and the synchronous rectifier: The capacitance component of the resonance capacitor, When the change amount of the variation of the primary current (ipri) of the transformer is increased or decreased, the secondary current (isec) of the transformer is changed correspondingly to increase or decrease the conduction current of the diode accordingly. The soft switching method of the asymmetrical flyback circuit, characterized in that the fluctuation direction of the increase and decrease fluctuate in the horizontal direction. A PWM controller for generating a pulse width modulated signal, a switch gate driver for driving a high side and a low side switch gate according to a pulse width modulated signal output from the PWM controller, and a switching operation according to an output signal of the switch gate driver A high side switch and a low side switch, a transformer for inducing a primary side voltage to a secondary side according to a switching operation of the high side switch and the low side switch, a synchronous rectifier for rectifying a secondary output voltage of the transformer, and the switch An insulation transformer for driving the gate of the synchronous rectifier with a low side switch gate driving signal output from a gate driver; a resonance formed at a common contact point of the high side switch and the low side switch and a primary voltage input terminal of the transformer; In the capacitor, and a soft switching method in an asymmetric AC eodeopteo flyback circuit and a switching element of diode current-conduction is formed between the secondary-side voltage output terminal of the transformer and the synchronous rectifier: The capacitance component of the resonant capacitor Under the condition of the primary current of the transformer, Is defined as; The secondary current of the transformer, When the change amount of the variation of the primary current ipri of the transformer is increased or decreased, the secondary current isise of the transformer changes accordingly, and thus the conduction current of the diode is increased or decreased accordingly. Soft switching method of the asymmetrical flyback circuit characterized in that the fluctuation direction of the fluctuations in the horizontal direction.