KR20010060202A - 2 level switching power transform apparatus - Google Patents

Abstract

PURPOSE: A switching power converter of two levels is provided to stabilize an output voltage level of the secondary side of a transformer by fixing a duty rate of a semiconductor switch connected with the primary side of the transformer and controlling a level of a direct current voltage applied to the first side. CONSTITUTION: A voltage level control portion(210) is used for controlling a power factor by switching an input voltage(V1) and controlling a size of the input voltage(V1). A switching portion(220) is used for converting the output voltage(V2) to a square wave voltage by switching the output voltage(V2) of the voltage level control portion(210). The first control portion(230) generates a switching pulse and controls a switching operation of the switching portion(220). A transformer(240) is used for inducing the square wave voltage to the secondary side by transforming the square wave voltage of the primary side. An output portion(250) is used for rectifying the voltage of the second side. The first feedback portion(260) is used for detecting current of the first side and feeding back the detected current. The second voltage level control portion(270) is used for detecting an output voltage the voltage level control portion(210).

Description

2-stage switching power converter {2 LEVEL SWITCHING POWER TRANSFORM APPARATUS}

The present invention relates to a two-stage switching power conversion device, and more particularly, the duty ratio of the semiconductor switch connected to the primary side of the transformer is fixed, and stable by adjusting the level of the DC voltage applied to the primary side. It relates to a two-stage switching power converter for implementing the output voltage of the vehicle side.

In general, a switching power converter includes a switching unit 110 for switching an input voltage Vi to a square wave voltage as shown in FIG. 1; A transformer 120 for converting the square wave voltage according to a turns ratio and inducing it from the primary side to the secondary side; An output unit 130 for rectifying and outputting the voltage on the secondary side; A feedback circuit unit 140 for detecting and feeding back the output voltage Vo of the output unit 130; And a pulse width modulator (PWM) 150 for controlling the rate of application of the switching unit 110 based on the feedback signal.

In the conventional switching power converter as shown in FIG. 1, the semiconductor switch Q of the switching unit 110 is alternately turned on according to a control signal of the pulse width modulator 150 with an applied DC input voltage Vi. -Off control to make a high frequency high frequency square wave voltage, and the generated square wave voltage is transformed through the transformer 120 having an arbitrary turns ratio and output to the secondary side, and then rectified and smoothed through the output unit 130 to be desired. It is made of DC output voltage (Vo). At this time, the secondary output voltage Vo of the transformer 120 is detected and feedback through the feedback circuit unit 140 so that the output voltage Vo is always kept constant even when the load is changed. The pulse width modulator 150 adjusts the application rate of the switch Q of the switching unit 110 based on the variation of the output voltage. If the secondary output voltage is higher than the reference value, the application rate is lowered. When lowered, increase the application rate.

However, such a conventional power converter has a risk of low frequency oscillation or parasitic oscillation when not only designed and manufactured by the delay characteristic of the insulation circuit included in the feedback circuit unit 140, but also a lot of time is required to solve this problem. Effort is required, and if the ratio of the semiconductor switch for the generation of the square wave voltage on the primary side is not constant and the characteristics of the switch are not good, the generation of heat on the on-off increases and the efficiency of the circuit decreases. Since the current is a square pie rather than a sinusoidal wave, the current slope per unit time is high, which causes a lot of spike noise and harmonics. Therefore, there is a disadvantage in that an effort and a cost for suppressing noise such as EMI / RFI are additionally required.

The present invention has been made to solve the above-mentioned conventional problems, and an object thereof is to fix a frequency and a ratio of square wave voltages produced in a primary side switching circuit of a transformer so that the DC voltage input to the switching circuit is fixed. It is an object of the present invention to provide a two-stage switching power converter configured to realize a stable secondary output voltage by adjusting a level.

1 is a circuit diagram of a conventional switching power converter.

2 is a circuit diagram of a two-stage switching power converter according to an embodiment of the present invention.

3 is a signal waveform diagram of the main part of FIG. 2;

5 is a circuit diagram of a two-stage switching power converter according to another embodiment of the present invention.

※ Explanation of code for main part of drawing

210: voltage level adjusting unit 220: switching unit

230: first control unit 240: transformer

250: output unit 260: first feedback unit

270: second feedback unit 280: second control unit

290: the third feedback

In order to achieve the above object, the two-stage switching power converter according to the present invention, the transformer means for transforming the voltage on the primary side in accordance with the winding ratio to the secondary side; Voltage conversion means for switching the input voltage in two stages, converting the level of the voltage, and outputting the voltage to the primary voltage of the transformer means; Output means for rectifying and smoothing the voltage of the secondary side of the transformer means; First feedback means for detecting and feeding back a current flowing into the primary side of the transformer means at a constant ratio; Second feedback means for detecting and returning the output voltage of the voltage conversion means at a constant ratio; And control means for controlling the shear switching operation during the two-stage switching of the voltage conversion means based on the feedback signals of the first and second feedback means to adjust the level of the output voltage. The converting means includes a front switching means for switching the input voltage at a specified rate and controlling the magnitude of the output voltage, and a rear end for switching the output voltage of the front switching means at a fixed rate and applying it to the primary side of the transformer. It consists of a switching means.

According to the present invention configured as described above, instead of adjusting the rate of output voltage of the output means by adjusting the ratio of the primary square wave voltage, the frequency and the ratio of the square wave voltage produced by the rear stage switching means are fixed, By controlling the magnitude of the input DC voltage to correspond to the change of the primary current through the boost type front end switching means, it is possible to obtain a stable secondary output voltage. Therefore, in the configuration of the switching means, it is not necessary to use a high-performance switching element, and since the non-isolated feedback is detected by detecting the current flowing on the primary side, various oscillations frequently generated in the conventional method of insulation feedback of the secondary side voltage are performed. The phenomenon is eliminated, and the ratio of the rear stage switching means is fixed at 50%, whereby the ripple can be reduced to obtain a clean DC voltage. In addition, when AC is input, the boost type shear switching means also performs a power factor correction function to solve the low power factor problem of the condenser input type power converter.

Hereinafter, a power converter according to a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a circuit diagram of a two-stage switching power converter according to an embodiment of the present invention, which comprises a front end switching means for adjusting the magnitude of the input voltage V1 while compensating for the power factor by switching the input voltage V1. A voltage level adjusting unit 210 as a unit; A switching unit 220 as a rear end switching means for switching the voltage V2 regulated and output by the voltage level adjusting unit 210 again to form a square wave voltage; A first control unit 230 for controlling a switching operation of the switching unit 220 by generating a switching ratio of a fixed ratio; A transformer 240 for transforming the square wave voltage on the primary side according to a desired turns ratio to guide the secondary side; An output unit 250 for rectifying and smoothing the voltage on the secondary side; A first feedback part 260 for detecting and returning a primary current flowing between the switching part 220 and the transformer 240; A second feedback unit 270 for detecting and returning an output voltage V2 of the voltage level adjusting unit 210; And a second control unit 280 for adjusting the output voltage level by controlling the switching of the voltage level adjusting unit 210 based on the feedback signals from the first and second feedback units 260 and 270. have.

The voltage level adjusting unit 210 may include a coil L1 and a diode D1 connected in series with each other, and a field effect transistor Q1 having a drain and a source connected between the common contact of the coil L1 and the diode D1 and ground, respectively. And a capacitor C1 connected at both ends between the output terminal of the diode D1 and ground.

The switching unit 220 includes two field effect transistors Q2 and Q3 connected in series between a common contact of the diode D1 and the capacitor C1 and a resistor R5 connected to ground. The controller 230 preferably amplifies and inverts the pulse generator 231 for generating a switching pulse having a fixed rate of 50% and the pulse control signal output from the pulse generator 231, respectively, so that the two electric fields are amplified. An amplifier 232 and an inverting amplifier 233 are applied to the gates of the effect transistors Q2 and Q3.

The transformer 240 is composed of a primary winding (L2) and secondary windings (L3, L4) having a mutually arbitrary turns ratio, the primary winding (L2) and the two field effect transistors (Q2, Q3) The capacitor C2 is connected between the common contacts.

The output unit 250 is a capacitor C3 connected between the rectifier diodes D2 and D3 connected to the secondary windings L3 and L4 of the transformer 240 and the output terminal of the rectifier diodes D3 and D4 and ground, respectively. Consists of

The first feedback unit 260 may include a source and a shunt resistor R5 of the field effect transistor Q3 of the switching unit 220 and a source and sample of the field effect transistor Q3 of the switching unit 220. An amplifier 261 having an inverting input terminal connected through a sample and hold circuit R1, a resistor R2 having both ends connected to a non-inverting input terminal and an output terminal of the amplifier 261, and the non-inverting input terminal and the reference; A resistor R3 connected at both ends to a power supply (not shown), and a base are connected to an output terminal of the amplifier 261, and a collector is composed of a PNP transistor Q4 grounded.

The second feedback unit 270 includes two resistors R6 and R7 connected in series between the output terminal of the diode D1 of the voltage level adjusting unit 210 and the ground, and the transistor R2 through the resistor R4. The inverting input terminal is commonly connected to the emitter of Q4) and the common contact of the resistors R6 and R7, and the noninverting input terminal is an amplifier 271 connected to a reference power supply (not shown), and an inversion of the amplifier 271. It consists of a resistor (R8) and a capacitor (C4) connected in series between the stage and the output stage.

The second control unit 280 has an input terminal electrically connected to an output terminal of the amplifier 271 to generate a switching pulse having an adjusted ratio based on feedback signals through the first and second feedback units 260 and 270. A pulse width modulation generator (PWM generator) 281 and a pulse control signal output from the pulse width modulation generator 281 and amplified and applied to the gate of the field effect transistor (Q1) of the voltage level adjusting unit (210) The amplifier 282 is comprised.

Next, the operation of the apparatus of FIG. 2 configured as described above will be described.

First, the input voltage V1 is a direct current voltage, which may be a pulse current converted from an alternating current into a simple rectifier circuit. The DC input voltage V1 is converted into a relatively larger voltage V2 through the voltage level adjusting unit 210 including the coil L1, the switch Q1, and the diode D1. In this case, the voltage V2 is detected by the resistors R6 and R7 of the second feedback unit 270 and fed back to the pulse width modulator 281 via the feedback amplifier 271, and the pulse is supplied. The width modulation generator 281 controls the switching of the field effect transistor Q1 by adjusting the pulse width of the switching pulse based on the feedback signal. When the voltage V2 becomes higher than the reference voltage, the width of the switching pulse The pulse width is made small and, if it is lowered, adjusted high so that the voltage V2 is maintained at a constant value. At this time, the voltage (V2) is usually adjusted to be slightly higher than 380V bar. This value is slightly higher than the highest AC voltage used in the world, and is intended to maximize the use range.

Next, the switching unit 220 is input to the DC voltage (V2) to make a square wave voltage (V3). The square wave voltage V3 is a voltage having a predetermined fixed frequency and a fixed ratio of 50%, and the pulse generator 231 generates a pulse control signal having a ratio of 50%, and the generated pulse control signal is Amplified and inverted through the amplifier 232 and the inverting amplifier 233, respectively, as shown in G1 and G2 of FIG. 3, and then applied to the gates of the pair of field effect transistors Q2 and Q3. The pair of field effect transistors Q2 and Q3 are alternately turned on and off to make the DC voltage V2 into a square wave voltage V3 having a 50% ratio as shown in FIGS. 1 and 2. At this time, the current on the primary side is made almost close to the sine wave as shown in FIG. That is, if the resonance frequency of the primary coil L2 of the transformer 240 and the capacitor C2 connected thereto and the frequency of the pulse control signal of the pulse generator 231 are exactly the same, a perfect sine wave is obtained. Since the two frequencies do not exactly match, they appear as a current waveform very close to the sine wave, and a quasi-resonant circuit is used to reinforce it. As described above, in the present invention, since the ratio of the pair of field effect transistor switches Q2 and Q3 is 50% and the current of the primary side of the transformer 240 becomes a sine wave, the switches Q2 and Q3 When the switch is turned on and off, the current flows to the switches Q2 and Q3 so that switching losses and heat generation are reduced. Conventionally, since the ratio of the switching pulses of the switches Q2 and Q3 is not fixed and changes depending on a signal fed back from the voltage on the secondary side, zero current switching as described above was impossible. In the present invention, in order to maintain the output voltage Vo at a stable constant voltage, while adjusting the magnitude of the input voltage V2, the ratio of the switches Q2 and Q3 is fixed, so that stable switching is always possible. A characteristic operation of the present invention for stabilizing the output voltage Vo by adjusting the size of will be described later.

The square wave voltage generated by the switching unit 220 is applied to the primary side of the transformer 240 and appears as an alternating voltage as shown in Figs. 4 and 5 of FIG. 3 on the secondary side according to the turns ratio. The rectifier is rectified by a simple rectifier circuit including the rectifier diodes D2 and D3, and is charged to the capacitor C3 with a current waveform as shown in FIG. 3 and output as a DC output voltage Vo.

At this time, the secondary output voltage (Vo) is the resistance of the internal resistance of the winding of the transformer 240, the diodes (D2, D3), the field effect transistor (Q2, Q3), etc. according to the change of the load (not shown). The voltage fluctuates due to a voltage drop occurring in the component, and the compensation for the fluctuation, that is, the operation of stabilizing the output voltage Vo by adjusting the magnitude of the input voltage V2 is as follows.

First, the primary side current flowing to the primary side of the switching unit 220 and the transformer 240 is detected through the shunt resistor R5. At this time, if the primary side current is detected by using the passive filter, time delay is generated and the response of the entire feedback circuit is delayed. Therefore, the sample and hold circuit R1 is used to approximate a stable DC level without time delay. Since the current converter performs zero current switching, the current detected by the shunt resistor R5 is a half-cycle sinusoidal waveform as shown in Fig. 4 (a), so that the primary current is Tn + α (n = 0,1). Sampling is performed at the center of the period in which the field effect transistor Q3 is turned on for sampling at a point of time (2, 3, ...). In the case of operating the power converter by hard switching, since the current detected by the shunt resistor R5 is a half-wave square wave having an arbitrary slope as shown in Fig. 4B, Tn + β whose primary current is the maximum value. Sampling is performed at the point immediately before the field effect transistor Q3 is turned off to sample at the time point (n = 0, 1, 2, 3...). The sample and hold circuit approximates the primary side current to a direct current value by sampling the current in synchronization with the pulse generator 231 at a time when the switching current is the lowest in the primary side current and maintaining this value until the next sampling period. The feedback signal for the DC component of the primary side current approximated by the sample and hold circuit R1 is controlled by the second control unit 280 via the second feedback unit 260 and the first feedback unit 270. The pulse width modulation generator 281 is provided. The pulse width modulation generator 281 adjusts the pulse width of the pulse control signal based on the feedback signal corresponding to the change in the primary side current, and the adjusted pulse control signal is amplified by the amplifier 282. The field effect transistor Q1 is applied to the gate of the field effect transistor Q1, and thus, the field effect transistor Q1 is switched on and off to adjust the magnitude of the DC voltage V2, thereby stabilizing the output voltage Vo. .

That is, when the load on the secondary side of the transformer 240 is large, a lot of current flows to the secondary side, and thus the primary side current also increases. As such, when the primary current increases, the ON pulse width of the pulse control signal generated from the pulse width modulation generator 281 is increased so that the output voltage V2 of the voltage level adjusting unit 210 increases. It is. As a result, when the voltage V2 increases, the secondary side voltage increases, and when the voltage increases, the output becomes negative feedback in which the current on the primary side no longer increases while the power is constant. The voltage Vo becomes stable.

According to the present invention as shown in FIG. 2, instead of the conventional method of adjusting the pulse widths of the semiconductor switches Q2 and Q3 connected to the primary side of the transformer 240, the output voltage V2 of the voltage level adjusting unit 210 is provided. By adjusting the amplitude of the signal and allowing the feedback to be made directly in the primary, various oscillation problems caused by the feedback delay caused by the conventional method of feeding back from the secondary are eliminated inherently, and the ripple of the output voltage is also eliminated. It is greatly reduced.

In addition, when the load fluctuations on the secondary output are very large or need to be controlled more accurately, the feedback of the secondary side is more effective, and the apparatus of FIG. 5 is applied.

FIG. 5 is a circuit diagram of a two-stage switching power converter according to another embodiment of the present invention. The same parts as in FIG. 2 are denoted by the same reference numerals, and description thereof will be omitted, and only other additional features will be described.

5, the voltage level adjusting unit 210, the switching unit 220, the first control unit 230, the transformer 240, the output unit 250, the first feedback unit 260, and the second feedback unit 270. The configuration of the second control unit 280 is the same as that of FIG. 2, and the configuration of the third feedback unit 290 is added thereto.

The third feedback unit 290 detects the output voltage Vo and feeds it back to the second control unit 280. The third feedback unit 290 is connected between the output terminal of the output unit 250 and the ground to divide the output voltage. Two resistors R9 and R10 connected in series; A comparator 291 for comparing the divided voltage with a reference voltage (not shown); An NPN transistor Q5 driving on / off according to a comparison result of the comparator 291; A photodiode (PD) connected between an output terminal of the output unit 250 and a collector of the transistor via a resistor R11 to operate according to on / off driving of the transistor Q5; And a collector is commonly connected to the emitter of the transistor Q4 via the resistor R4, the divided point by the resistors R6 and R7, and the inverting input terminal of the feedback amplifier 271, and the emitter is And a phototransistor PT connected to the photodiode PD. The pulse width modulation generator 281 of the second control unit 280 may be configured to further configure the third feedback unit 290. By adjusting the pulse width of the pulse control signal for controlling the field effect transistor Q1 on / off based on the feedback signals of the first, second and third feedback units 260, 270 and 290, the output voltage Vo According to the variation, the magnitude of the output voltage V2 of the voltage level adjusting unit 210 is controlled. In this case, the possibility of oscillation according to the delay characteristic of the feedback circuit may be the same as before, but as in the apparatus of FIG. 2, since the switching ratio of the semiconductor switches Q2 and Q3 is fixed at 50%, zero current switching is realized. Of course, the characteristics of the switches Q1 and Q2 do not have to be good.

As described in detail above, according to the two-stage switching power converter according to the present invention, eliminating the oscillation problem caused by the feedback delay, lowering the requirements of the switch required for AC voltage generation, and improve the current waveform of the transformer to improve EMI / By minimizing noise, such as RFI, it is possible to simplify the design of the power converter and lower the price, and furthermore, it is possible to integrate ICs used in the power converter.

Claims (10)

In the switching power converter, Transformer means for transforming the voltage on the primary side in accordance with the winding ratio to guide the secondary side; Voltage conversion means for switching the input voltage in two stages, converting the level of the voltage, and outputting the voltage to the primary voltage of the transformer means; Output means for rectifying and smoothing the voltage of the secondary side of the transformer means; First feedback means for detecting a current flowing into the primary side of the transformer means at a constant ratio and approximating the current to a DC value using a sample and hold circuit; Second feedback means for detecting and returning the output voltage of the voltage conversion means at a constant ratio; And And a control means for controlling the shear switching operation during the two-stage switching of the voltage conversion means based on the feedback signals of the first and second feedback means to adjust the output voltage level. Switching power converter. The method of claim 1, And controlling the front end switching operation by the control means by a pulse width modulation method. The method of claim 2, And said control means increases the turn-on pulse width of said front end switching in proportion to the direct current value of the current fed back from said first feedback means. The method of claim 1, And a third feedback means for detecting the output voltage of the output means at a constant rate and returning it to the control means, wherein the control means converts the voltage based on the feedback signals of the first to third feedback means. A two stage switching power converter, characterized by adjusting the level of the output voltage of the means. The method of claim 1, The second stage switching of the voltage converting means is performed by alternately turning on / off two switching elements connected in series between the output terminal of the voltage converting means and the ground by pulses having a fixed ratio. Power converter. The method of claim 5, The fixed rate of conversion is a two-stage switching power converter, characterized in that 50%. The method of claim 1, And the voltage converting means boosts the input voltage above a predetermined voltage to compensate for the power factor of the input voltage. The method of claim 1, And sampling of the sample and hold circuit is performed at a time point at which the current flowing from the primary side has a maximum value. Transformer means for transforming the voltage on the primary side in accordance with the winding ratio to guide the secondary side; Front end switching means for switching the input voltage to a predetermined rate and regulating the magnitude of the output voltage; Rear stage switching means for switching the output voltage of said front end switching means at a fixed rate and applying it to the primary side of said transformer means; Output means for rectifying and smoothing the voltage of the secondary side of the transformer means; Detection means for detecting an amount of electricity flowing into the primary side of the transformer means; And And control means for varying a designated switching ratio of the front end switching means in accordance with the magnitude of the detected electrical quantity. The method of claim 9, And said electrical quantity is a current.