JP2008035691A - Half-bridge type switching regulator, and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a half-bridge type switching regulator which properly controls the off-timing of a synchronous switching element by a simple circuit, and effectively reduces switching noise and a switching loss. <P>SOLUTION: The switching regulator is constituted by including an output voltage adjustment switching element Q1 to adjust an output voltage, the synchronous switching element Q2, a voltage detecting portion 10, and a soft switch control portion 20. The synchronous switching element is connected in series with the output voltage adjustment switching element Q1, and turned on complementarily when the output voltage adjustment switching element Q1 is turned off. The voltage detecting portion detects a voltage of a joint of both the switching elements when the synchronous switching element Q2 is turned off. The soft switch control portion adjusts timing to turn off the synchronous switching element Q2, based on voltage fluctuation detected by the voltage detecting portion 10. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention comprises an output voltage adjustment switch element that adjusts an output voltage, and a synchronous switch element that is connected in series with the output voltage adjustment switch element and that is complementarily turned on when the output voltage adjustment switch element is turned off. The present invention relates to a half-bridge type switching regulator.

  In this type of switching regulator, an output voltage adjustment switch element that adjusts an output voltage and a synchronous switch element that complementarily turns on when the output voltage adjustment switch element is turned off are connected between input voltage terminals (in the case of a step-down regulator) or A soft switching method is adopted that is connected in series between the output voltage terminals (in the case of a boost regulator), and the switching control unit complementarily turns on and off the synchronous switch element and output voltage adjustment switch element to reduce switching loss and noise. Has been.

  Patent Document 1 discloses a half-bridge inverter configured to include two switching elements as a soft switching inverter control method capable of reducing switching noise and switching loss and controlling an output voltage with a constant switching frequency. On the other hand, a control method has been proposed in which when switching on / off of each switching element, a dead time is provided for these switching elements to perform zero voltage switching and zero current pressure switching.

  For example, as shown in FIG. 1A, a step-up type comprising an output voltage adjustment switch element Q1 for adjusting an output voltage and a synchronous switch element Q2 connected in series with the output voltage adjustment switch element Q1. In the switching regulator, in order to appropriately adjust such dead time, the off timing of the synchronous switch element Q2 is determined by a map calculation value set in advance based on the input / output voltage value.

  Details will be described below. The step-up switching regulator is connected in series with an output voltage adjustment switch element Q1 that adjusts the output voltage Vout at the output voltage terminal OUT, and the output voltage adjustment switch element Q1, and is complementary when the output voltage adjustment switch element Q1 is off. Synchronous switching element Q2 that is turned on automatically, a resonant circuit that is composed of a booster coil L1 that performs LC resonance for the purpose of reducing the voltage Vds between both switching elements described later and a capacitor C1, and a bypass capacitor for stabilizing the output voltage And C2.

  The output voltage adjustment switch element Q1 and the synchronous switch element Q2 are composed of n-channel MOS-FETs, and each switch is controlled by controlling the gate voltage of each of the output voltage adjustment switch element Q1 and the synchronous switch element Q2. A switch control unit for switching on and off the element is provided.

  The switch control unit controls the switching regulator according to the timing chart shown in FIG. The switch control unit determines a timing (TA1) for switching the output voltage adjustment switch element Q1 from on to off based on the output voltage Vout. When the output voltage adjustment switch element Q1 is turned off, the voltage Vds between the switch elements rises, and at the timing (TA2) when the voltage Vds between the switch elements becomes equal to the output voltage Vout, the synchronous switch element Q2 is turned off. Switch on.

  The switch control unit calculates a timing at which the coil current IL flowing through the booster coil L1 that decreases by turning on the synchronous switch element Q2 becomes zero by a map operation described below, and the calculated coil current IL is zero. At the timing (TA3), the synchronous switch element Q2 is switched from on to off.

  Then, the output voltage adjustment switch element Q1 is switched from OFF to ON at the timing (TA4) when the voltage Vds between the switch elements becomes zero. The switch control unit controls the output voltage to be constant by repeating the above basic operation.

  In the basic operation described above, the timing for switching the synchronous switch element Q2 from on to off, that is, the on-time t2 of the synchronous switch element in FIG. 1B can be obtained according to [Equation 1].

  The maximum current Imax flowing through the booster coil L1 in [Equation 1] can be obtained according to [Equation 2] based on the input voltage Vin at the input voltage terminal IN and the time t0 determined by the off timing of the output voltage adjustment switch element Q1. it can.

  Accordingly, the on-time t2 of the synchronous switch element is determined by the input voltage Vin and the output voltage Vout based on [Equation 3] derived from [Equation 1] and [Equation 2].

  The switch control unit includes map data of the output voltage Vout with respect to various input voltages Vin prepared in advance, and is based on a map calculation that applies the input voltage Vin and the output voltage Vout obtained from the map data to [Expression 3]. Thus, the synchronous switch element on-time t2 is calculated.

JP 07-46853 A

  However, when controlling the OFF timing of the synchronous switch element based on the result of the map calculation described above, it is necessary to construct a complicated circuit to detect the input / output voltage and perform the map calculation. Since it was not employed, there was a problem that the off-timing of the synchronous switch element could not be controlled so accurately.

  Furthermore, in order to ensure the safety of the circuit, it is necessary to set the map data so that the synchronous switch element is turned off before the current flows backward from the output side to the power supply side. There was a problem that it was not possible to reduce it.

  In view of the above problems, an object of the present invention is to provide a half-bridge type switching regulator capable of appropriately controlling the off-timing of a synchronous switch element with a simple circuit and effectively reducing switching noise and switching loss. It is in.

  In order to achieve the above-described object, a characteristic configuration of a half-bridge type switching regulator according to the present invention includes an output voltage adjustment switch element for adjusting an output voltage, and the output voltage adjustment switch element connected in series, and the output voltage adjustment switch A synchronous switch element that complementarily turns on when the element is off, a voltage detector that detects a voltage at a connection point of both switch elements when the synchronous switch element is turned off, and a voltage variation detected by the voltage detector On the basis of this, a soft switch control unit for adjusting the turn-off timing of the synchronous switch element is provided.

  According to the above configuration, based on the voltage at the connection point of both switch elements detected by the voltage detection unit, the soft switch control unit feedback-controls the off timing of the synchronous switch element at an appropriate timing. Switching noise and switching loss can be effectively reduced.

  In addition, such a half-bridge type switching regulator has a large-capacity memory that stores a large number of input voltage values and output voltage values that are conventionally required as map data, and for calculating the off timing of a synchronous switch element. There is no need to provide a complicated circuit, and it is only necessary to provide a circuit for detecting the voltage at the connection point of both switch elements.

  As described above, according to the present invention, it is possible to provide a half-bridge type switching regulator that can appropriately control the off-timing of the synchronous switch element with a simple circuit and can effectively reduce switching noise and switching loss. It became so.

  The half-bridge type switching regulator according to the present invention will be described below.

  As shown in FIG. 2, the step-up half-bridge switching regulator is connected in series with an output voltage adjustment switch element Q1 that adjusts an output voltage Vout at an output voltage terminal OUT, and the output voltage adjustment switch element Q1. For the purpose of adjusting LC voltage for the purpose of adjusting the voltage at the connection point of the synchronous switch element Q2 that complementarily turns on when the output voltage adjustment switch element Q1 is off and the switch elements Q1 and Q2, that is, the voltage Vds between the switch elements. The step-up coil L1 and the capacitor C1, the smoothing capacitor C2 for stabilizing the output voltage, the voltage detection unit 10 for detecting the inter-switch element voltage Vds when the synchronous switch element Q2 is turned off, and the voltage detection unit 10 Based on the voltage fluctuation detected by the synchronous switch element Q2 It is constituted by a soft switch control unit 20 for adjusting the timing of turn-off.

  The output voltage adjusting switch element Q1 and the synchronous switch element Q2 are composed of n-channel MOS-FETs.

  The drain terminal of the output voltage adjustment switch element Q1 is connected to the input voltage terminal IN with the booster coil L1 interposed therebetween, and the source terminal is grounded.

  Further, the drain terminal of the synchronous switch element Q2 is connected to the output voltage terminal OUT, and the source terminal is connected to the input voltage terminal IN with the booster coil L1 interposed therebetween.

  Furthermore, each of the gate terminals of the output voltage adjustment switch element Q1 and the synchronous switch element Q2 is connected to the soft switch control unit 20, and the respective gate terminal voltages are controlled by the soft switch control unit 20, Each switch element Q1, Q2 is switched on and off.

  Parasitic diodes D1 and D2 formed between the drain and source of the output voltage adjustment switch Q1 and the synchronous switch element Q2 formed of MOS-FETs function as flywheel diodes.

  The booster coil L1 and the capacitor C1 are connected in series between the input voltage terminal IN and the ground to constitute an LC resonance circuit. That is, one end of the booster coil L1 is connected to the input voltage terminal IN, the other end is connected to one end of the capacitor C1, and the other end of the capacitor C1 is grounded.

  The smoothing capacitor C2 is connected between the output voltage terminal OUT and the ground at the subsequent stage of the synchronous switch element Q2.

  A variation of the inter-switch element voltage Vds when the switch elements Q1 and Q2 are controlled by the soft switch control unit 20 will be described. As described above with reference to FIG. 1 (b), as shown in FIG. 3 (a), when the output voltage adjustment switch Q1 is turned off, the inter-switch element voltage Vds rises, and the synchronous switch element Q2 When the switch element is turned off after the switch is turned on, the voltage Vds between the switch elements gradually decreases. In FIGS. 3B to 3D, the region where the voltage Vds between the switch elements gradually decreases, which is indicated by a broken-line circle in FIG. 3A, is enlarged and displayed.

  If the coil current IL does not flow through the synchronous switch element Q2 at the moment when the synchronous switch element Q2 is turned off by the soft switch control unit 20, that is, the timing for turning off the synchronous switch element Q2 is ideally zero. When the current switching (Zero Current Switching) is realized, as shown in FIG. 3 (b), the voltage Vds between the switching elements does not fluctuate smoothly before and after the synchronous switching element Q2 is turned off. To drop.

  However, when the synchronous switch element Q2 is turned off, the coil current IL flows from the input voltage terminal IN side to the output voltage terminal OUT side in the synchronous switch element Q2, that is, the synchronous switch element Q2 is turned off. When the timing is early, a current flows through the parasitic diode D2 even after the synchronous switch element Q2 is turned off. Therefore, as shown in FIG. It rises by the potential difference V1 caused by the forward voltage drop of the diode D2. The characteristic indicated by the alternate long and short dash line in FIG. 3C is the characteristic of the inter-switch element voltage Vds shown in FIG.

  On the other hand, when the synchronous switch element Q2 is turned off, when the coil current IL flows from the output voltage terminal OUT side to the input voltage terminal IN side at the moment when the synchronous switch element Q2 is turned off, that is, the synchronous switch element Q2 is turned off. When the timing is late, as shown in FIG. 3D, the inter-switch element voltage Vds is lowered by a voltage drop V2 caused by the on-resistance of the synchronous switch element Q2. In addition, the characteristic shown with the dashed-dotted line in FIG.3 (d) is a characteristic of the voltage Vds between switch elements shown in FIG.3 (b).

  The voltage detection unit 10 is provided to detect the above-described switching element voltage Vds that varies depending on the timing of switching the synchronous switching element Q2 from on to off.

  As shown in FIG. 2, the voltage detection unit 10 includes a comparison circuit 11 that detects a change in the voltage across the synchronous switch element Q2, and a mask circuit that extracts an output from the comparison circuit 11 when the synchronous switch element Q2 is turned off. 12 is provided. The comparison circuit 11 includes a comparator 111 and a constant voltage source 110 that inputs a reference voltage Vth to an inverting input terminal of the comparator 111, and a non-inverting input terminal of the comparator 111 from a connection point of both switch elements Q1 and Q2. A coupling capacitor C3 for cutting off the direct current component is provided in the path to.

  The constant voltage source 110 includes a diode D3 whose cathode is grounded and a constant current source 112 connected in series to the anode side of the diode D3. The anode of the diode D3 serves as the inverting input terminal of the comparison circuit 11. It is connected. The constant current source 112 can be composed of a current mirror circuit or the like.

  The reference voltage Vth is set based on the forward voltage drop characteristic of the diode D3 with respect to the current supplied from the constant current source 112. For example, the reference voltage Vth is a forward drop voltage Vf (about 0.7V) of the parasitic diode D2. It can be set to about 0.35 V, which is a half value.

  According to the configuration described above, since the AC component is removed by the coupling capacitor C3, it is possible to accurately detect the variation of the inter-switch element voltage Vds with respect to the reference voltage Vth with respect to the ground. In addition, since the reference voltage Vth is configured to be set based on the forward voltage drop characteristic of the diode D3, if the inter-switch element voltage Vds fluctuates due to the temperature characteristic of the parasitic diode D2, the fluctuation occurs. Following this, the reference voltage changes in the same manner, and the influence of the temperature characteristic is offset.

  The mask circuit 12 includes a delay circuit 121 that outputs a mask signal obtained by delaying the gate drive signal SQ2 of the synchronous switch element Q2 output from the soft switch control unit 20 by a predetermined time, and the mask signal and the comparison circuit. 11 logic signals 122 to which 11 output signals are inputted.

  The delay circuit 121 can be configured by, for example, a D-type flip-flop 121A in which the gate drive SQ2 is input to the data input terminal D and a clock pulse CK having a predetermined frequency is input to the clock input terminal CK. A high level mask signal SMQ2 obtained by delaying the gate driving signal SQ2 by a predetermined time by the clock pulse CK is output. The delay circuit 121 can also be configured by a known delay circuit using a CR delay circuit using a resistor and a capacitor, a Schmitt trigger circuit, or the like.

  The logic circuit 122 can be composed of, for example, a NAND circuit 122A, and the output signal of the comparison circuit 11 is output to the soft switch control unit 20 while the mask signal is at a high level, and the mask signal is low. A high level signal is always output to the soft switch controller 20 during the level period. That is, a low level signal is output from the logic circuit 122 to the soft switch control unit 20 only when the output signal of the comparison circuit 11 becomes high level during the period when the mask signal is high level.

  The output signal of the comparison circuit 11 is input to the soft switch control unit 20 during a period when the mask signal is at a high level, that is, during a predetermined period before and after the OFF timing of the synchronous switch element Q2.

  As shown in FIG. 4, the inter-switch element voltage Vds immediately after the gate drive signal SQ2 of the synchronous switch element Q2 is switched from OFF to ON decreases by the potential difference V3 due to the forward voltage drop of the parasitic diode D2. To do. When the inter-switch element voltage Vds detected by the comparison circuit 11 at this timing is input to the soft switch control unit 20, a potential difference V3 generated when the synchronous switch element Q2 is switched from off to on is generated. There is a possibility that the potential difference V1 generated when the synchronous switch element Q2 to be detected is switched from on to off is erroneously detected.

  Therefore, the mask circuit 12 generates a mask signal SMQ2 in which the ON period of the synchronous switch element Q2 is delayed by a predetermined time tQ2 in which the potential difference V3 occurs. The soft switch control unit 20 causes the mask signal SMQ2 to be high. The switching element voltage Vds is detected during the level.

  That is, the voltage detection unit 10 detects whether or not the timing for turning off the synchronous switch element Q2 is earlier than the zero current switching.

  As shown in FIG. 3C, when the synchronous switch element Q2 is turned off, a forward voltage drop of the parasitic diode D2 occurs, and the inter-switch element voltage Vds is increased by the potential difference V1 (V1> Vth). A high level signal is output from the comparator 111, and a low level signal is output to the soft switch controller 20.

  Further, as shown in FIG. 3B, the voltage Vds between the switching elements does not fluctuate when the synchronous switching element Q2 is turned off, or as shown in FIG. When the voltage Vds between the switch elements becomes equal to or lower than the reference voltage Vth due to the reverse potential difference V2 at the time of turn-off, a low level signal is output from the comparator 111 and a high level signal is output to the soft switch control unit 20. .

  The soft switch control unit 20 has a current flowing to the output side when the synchronous switch element Q2 is turned off based on the voltage variation detected by the voltage detection unit 10, that is, the off timing of the synchronous switch element Q2. Is determined to be early, the on-time of the synchronous switch element Q2 is extended and corrected.

  Furthermore, the soft switch control unit 20 does not flow current to the output side when the synchronous switch element Q2 is turned off based on the voltage fluctuation detected by the voltage detection unit 10, that is, the synchronous switch element Q2 When the OFF timing is determined to be late, the ON time of the synchronous switch element Q2 is shortened and corrected.

  Specifically, when performing the expansion correction, the soft switch control unit 20 corrects the on-time of the synchronous switch element Q2 to be longer than the current on-time by a predetermined time, When performing the shortening correction, the on-time of the synchronous switch element Q2 is corrected so as to be shorter than the current on-time by a predetermined time.

  The soft switch control unit 20 monitors the voltage at the output terminal Vout, turns off the output voltage adjustment switch element Q1, and turns on the output voltage adjustment switch element Q1 at a timing when the inter-switch element voltage Vds becomes zero. An output voltage adjustment unit 20a formed of a logical operation unit and the synchronous switch Q2 are turned on at a timing when the inter-switch element voltage Vds becomes an output voltage, and the coil current is detected based on the voltage fluctuation detected by the voltage detection unit 10. A zero current control unit 20b is provided which is a logic operation unit that calculates the timing when IL becomes zero and turns off the synchronous switch Q2.

  Hereinafter, the off timing control of the synchronous switch element Q2 by the soft switch control unit 20 will be described based on the flowchart shown in FIG.

  At the start of the control of the soft switch controller 20, the on-time of the synchronous switch element Q2 is set to a predetermined initial value in advance (SA1). In the present embodiment, the predetermined initial value is set to 100 ns (nanoseconds).

  When the voltage switch 10 detects that a current is flowing from the input side to the output side of the synchronous switch element Q2 when the synchronous switch element Q2 is off (SA2), the soft switch control unit 20 is preset. The on-time of the synchronous switch element Q2 is extended and corrected for the fixed correction time (SA3).

  In the present embodiment, when the constant correction time is set to 20 ns and the voltage detection unit 10 detects that current is flowing from the input side to the output side through the synchronous switch element Q2 for the first time, The on-time of the switch element Q2 is extended by 20 ns and corrected to 120 ns. When the voltage detector 10 performs the same detection next time, the on-time is corrected to 140 ns.

  On the other hand, when the synchronous switch element Q2 is turned off and the voltage detection unit 10 detects that no current flows from the input side to the output side of the synchronous switch element Q2 (SA2), the soft switch control unit 20 The on-time of the synchronous switch element Q2 is shortened and corrected for a predetermined correction time (SA4).

  When the voltage detection unit 10 detects that no current flows from the input side to the output side of the synchronous switch element Q2 for the first time, the on-time of the synchronous switch element Q2 is shortened by 20 ns and corrected to 80 ns, When the voltage detection unit 10 performs the same detection next time, the on-time is corrected to 60 ns.

  According to the above-described configuration, the soft switch control unit 20 corrects the on-time of the synchronous switch element Q2 to be expanded or shortened at intervals of 20 ns, so that the on-time is ideally zero current switching (Zero Current Switching). ) Can be brought close to the optimal time, and thereafter, the expansion and shortening are repeated in units of 20 ns, and the almost optimal on-time is guaranteed. In addition, the processing load of the soft switch control unit 20 is small because the processing is only the adjustment for a predetermined time.

  Hereinafter, another embodiment of the correction control by the soft switch control unit 20 will be described. In the above-described embodiment, the configuration in which the soft switch control unit 20 performs the expansion correction or the shortening correction in units of a constant correction time of 20 ns has been described. However, the correction time is not fixed to 20 ns, and a specific circuit is provided. What is necessary is just to set to the optimal fixed value suitably based on a structure. Further, the correction time for extending or shortening the on-time of the synchronous switch element Q2 may be varied based on the past voltage fluctuation history detected by the voltage detection unit 10.

  For example, as shown in FIG. 6, the zero current control unit 20b counts and stores the number of consecutively performed extension corrections and the number of consecutively performed shortening corrections. And a down control 22 that stores and a correction control unit 23 that calculates a correction time based on the values of both counters and controls the synchronous switch Q2, and the correction control unit 23 has a preset initial value. The correction time is multiplied by either a value stored in the up-counter 21 or a correction factor corresponding to the value, and a new correction time is used for the expansion correction. A shortened correction can be performed by using a value stored in the counter 22 or a time multiplied by a correction rate corresponding to the value as a new correction time.

  If the initial value of the correction time is set to a short value and the correction factor is set so that the correction time gradually increases corresponding to the value of each counter indicating the past voltage fluctuation history, ideal zero current switching ( It reaches the optimal time for zero current switching faster, and the fluctuations thereafter can be kept small. The initial value of the correction time is set to a long value, and the correction time gradually decreases according to the value of each counter. If the correction factor is set in this way, the correction time becomes shorter as the optimum time for ideal zero current switching is approached, so that overshoot can be avoided.

  Hereinafter, the off-timing control of the synchronous switch element Q2 by the soft switch control unit 20 when such a configuration is adopted will be described based on the flowchart shown in FIG.

  At the start of control of the soft switch controller 20, the on-time of the synchronous switch element Q2 is set to a predetermined initial value in advance (SB1). In the present embodiment, the predetermined initial value is set to 100 ns, and the initial values of the up counter 21 and the down counter 22 are set to 0.

  When the synchronous switch element Q2 is turned off and the voltage detection unit 10 detects that a current flows from the input side to the output side of the synchronous switch element Q2 (SB2), the soft switch control unit 20 The up counter 21 is incremented by 1 (SB3), and the on-time of the synchronous switch Q2 is extended and corrected by a value obtained by multiplying a predetermined correction time by a value stored in the up counter 21 (SB4). The value stored in the down counter 22 is reset (SB5).

  When the fixed correction time is set to 20 ns and the voltage detection unit 10 detects for the first time that a current flows from the input side to the output side of the synchronous switch element Q2, the synchronous switch element Q2 is turned on. The time is extended by 20 ns × 1 and corrected to 120 ns (= 100 + 20 × 1) (SB3). When the same detection is performed by the voltage detection unit 10 next time, the value of the up counter 21 is incremented to 2. Therefore, it is expanded by 20 ns × 2 = 40 ns and corrected to 160 ns (= 120 + 20 × 2) (SB4).

  On the other hand, if the voltage detecting unit 10 detects that no current flows from the input side to the output side of the synchronous switch element Q2 when the synchronous switch element Q2 is off (SB2), the down counter 22 is incremented by one. (SB6), the on-time of the synchronous switch Q2 is shortened and corrected by a value obtained by multiplying a preset fixed correction time by the value stored in the down counter 22 (SB7), and stored in the up-counter 21. The set value is reset (SB8).

  When the voltage detection unit 10 detects that no current flows from the input side to the output side of the synchronous switch element Q2 for the first time, the on-time of the synchronous switch element Q2 is shortened by 20 ns × 1 to 80 ns ( = 100−20 × 1) (SB7), and when the voltage detection unit 10 performs the same detection next time, the value of the down counter 22 is counted up to 2 (SB6). It is shortened by × 2 = 40 ns and corrected to 40 ns (= 80−20 × 2) (SB7).

  According to the above configuration, since the expansion correction amount or the shortening correction amount changes based on the voltage fluctuation history, for example, when the soft switch control unit 20 continuously performs the expansion correction or the shortening correction, the correction amount Is gradually increased, and the on-time can be brought closer to the optimum time sooner.

  In the above-described embodiment, the correction time of the expansion correction or the shortening correction is calculated by the soft switch control unit 20 based on the value of the up counter or the down counter that stores the past voltage fluctuation history by a predetermined arithmetic expression. Although the calculation case has been described, the soft switch control unit 20 includes correction amount map data in which an expansion correction time or a shortening correction time is set corresponding to the value of the up counter or the down counter, and the software The switch control unit 20 may be configured to extend or shorten the ON time of the synchronous switch element Q2 based on the correction amount map data.

  An example will be described below. As shown in FIG. 8, in the zero current control unit 20b, a memory in which correction amount map data 25 for determining a correction time for shortening and correcting the on-time of the synchronous switch element Q2 is stored, and correction amount map data 25 is stored. The map down counter 24 for specifying the target correction time from the map, and the shortening correction time corresponding to the value of the map down counter 24 is obtained from the correction amount map data 25 to perform the shortening correction, and a predetermined fixed correction time. The correction control unit 26 for correcting the expansion time can be provided.

  Hereinafter, the off-timing control of the synchronous switch element Q2 by the soft switch control unit 20 when such a configuration is adopted will be described based on the flowchart shown in FIG.

  At the start of the control of the soft switch controller 20, the ON time of the synchronous switch element Q2 is set in advance to a predetermined initial value (SC1). In the present embodiment, the predetermined initial value is set to 100 ns, the initial value of the map down counter 24 is set to 1, and the maximum value is limited to 3. Further, as shown in FIG. 9, the correction amount map data 25 is set so as to become shorter as the value of the map down counter 24 increases.

  When the voltage detecting unit 10 detects that a current is flowing from the input side to the output side of the synchronous switch element Q2 when the synchronous switch element Q2 is off (SC2), the soft switch control unit 20 The on-time of the synchronous switch element Q2 is extended and corrected for a set fixed time (SC3).

  In the present embodiment, when the extension correction time is set to 20 ns and the voltage detection unit 10 detects for the first time that a current flows from the input side to the output side of the synchronous switch element Q2, the synchronous switch element The on-time of Q2 is extended by 20 ns and corrected to 120 ns (= 100 + 20). When the voltage detection unit 10 performs the same detection next time, it is corrected to 140 ns (= 120 + 20).

  On the other hand, when the synchronous switch element Q2 is turned off and the voltage detection unit 10 detects that no current flows from the input side to the output side of the synchronous switch element Q2 (SC2), the soft switch control unit 20 The shortening correction time corresponding to the count value of the map down counter 24 is selected from the correction amount map data 25 shown in FIG. 10, and the on-time of the synchronous switch element Q2 is shortened and corrected (SC4). The counter 24 is incremented by 1 (SC5).

  As a result of the shortening correction performed in step SC4, when the synchronous switch element Q2 is turned off, the voltage detector 10 detects that a current flows from the input side to the output side of the synchronous switch element Q2 (SC6). Then, the expansion correction process in step SC3 is executed to correct the overcorrection, and the process returns to step SC2.

  In step SC6, when it is detected by the voltage detector 10 that no current flows from the input side to the output side in the synchronous switch element Q2, the map down counter 24 is subtracted by two (SC7), and step SC4. Return to.

  That is, when it is detected for the first time that the current does not flow from the input side to the output side in the synchronous switch element Q2 by the voltage detection unit 10, it corresponds to the value 1 of the map down counter 24 shown in FIG. When the on-time of the synchronous switch element Q2 is corrected to be shortened by 200 ns, and the same detection is made for the second time, the on-time of the synchronous switch element Q2 is corrected to be shortened by 100 ns corresponding to the value 2 of the map down counter 24. When the same detection is made after the third time, the on-time of the synchronous switch element Q2 is corrected to be shortened by 50 ns corresponding to the value 3 of the map down counter 24.

  In the present embodiment, it is assumed that when the value of the map down counter 24 is 1 or 2, the shortening correction is greatly reduced to 200 ns and 100 ns, respectively, so that the shortening correction is not continuously performed.

  When the map down counter 24 has a value of 3, if it is necessary to perform a shortening correction continuously, two values of the map down counter 24 are subtracted in step SC7. As a result, the map down counter 24 Corresponding to the value 1, the on-time of the synchronous switch element Q2 is corrected to be shortened by 200 ns.

  Control characteristics with respect to the ON time of the synchronous switch element Q2 will be described based on a timing chart shown in FIG.

  Initially, the expansion correction process of step SC3 is repeated, and the on-time of the synchronous switch element Q2 gradually increases during this period TB1. After that, at time TB2, when the voltage detection unit 10 detects that no current flows from the input side to the output side in the synchronous switch element Q2, corresponding to the count value 1 of the map down counter 24, The correction is shortened to an on time obtained by subtracting 200 ns from the on time of the synchronous switch element Q2 immediately before.

  As a result, the expansion correction process in step SC3 is repeated again, and the on-time of the synchronous switch element Q2 gradually increases during this period TB3. Thereafter, at time TB4, when the voltage detection unit 10 detects that no current flows from the input side to the output side in the synchronous switch element Q2, corresponding to the count value 2 of the map down counter 24, The correction is shortened to an on time obtained by subtracting 100 ns from the on time of the synchronous switch element Q2 immediately before.

  As a result, the expansion correction process in step SC3 is repeated again, and the on-time of the synchronous switch element Q2 gradually increases during this period. At time TB5, when it is detected by the voltage detection unit 10 that no current flows from the input side to the output side in the synchronous switch element Q2, it corresponds to the count value 3 of the map down counter 24 and immediately before it. The on-time obtained by subtracting 50 ns from the on-time of the synchronous switch element Q2 is corrected to be shortened.

  Thereafter, when the extension correction process at the extension correction time of 20 ns and the reduction correction process at the reduction correction time of 50 ns are repeated, and the reduction correction process continues as at time TB6, the immediately preceding synchronous switch element Q2 Shortening correction is made to the on time obtained by subtracting 200 ns from the on time. If the subtraction value of the map down counter 24 is changed from 2 to 1 in step SC7, the shortening correction time can be set to 100 ns.

  That is, the on-time of the synchronous switch element Q2 is corrected to be greatly shortened in the initial stage according to the correction amount map data 25, and gradually shortened to be corrected. Accordingly, as the time approaches the optimum time for zero current switching. The fluctuation due to the correction is reduced. The shortening correction amount increases when the deviation from the optimal time increases due to some factor.

  In the present invention, the upper limit value of the map down counter 24 is not limited to 3, and a larger value can be counted as the upper limit value. The correction amount map data 25 corresponds to the upper limit value. Can be set, and the set value of the correction amount map data 25 is not limited to the above-described value.

  In the above-described embodiment, the correction amount map data is used when the on-time of the synchronous switch element Q2 is shortened and corrected. However, the correction amount map data may be used when the expansion correction is performed. Correction amount map data may be used for both of the expansion correction.

  When the map counter value at the initial stage of control is small, the shortening correction time or the decompression correction time is long, and the shortening correction time or the decompression correction time gradually decreases as the map counter value increases. By setting the value, it is possible to quickly approach zero-current switching and reduce switching loss due to subsequent fluctuations.

  The above-described three modes of correction control by the soft switch control unit 20 (a constant correction time, a variable correction time based on a voltage fluctuation history, and a variable correction time based on correction amount map data) may be appropriately combined. For example, the expansion correction may be performed with a variable correction time based on a voltage fluctuation history, and the shortening correction may be performed with a variable correction time based on correction amount map data.

  In the above-described embodiment, the output voltage adjustment switch element Q1 and the synchronous switch element Q2 have been described as being configured by n-channel MOS-FETs. However, both switch elements Q1 and Q2 are configured as bipolar transistors. There may be. In this case, it is necessary to provide a separate flywheel diode between the collector terminal and the emitter terminal of the bipolar transistor.

  In the above-described embodiment, the logic circuit 122 provided in the voltage detection unit 10 is configured by the NAND circuit 122A. However, the switching element voltage Vds when the synchronous switching element Q2 is switched from on to off is described. As long as it has a gate function that allows the output signal from the comparison circuit 11 to pass based on the output signal from the delay circuit 121, the NAND circuit is not limited to the same, and a NOR circuit or the like It is possible to configure with an arbitrary gate circuit capable of realizing the above function.

  In addition, the soft switch control unit 20 has a time period between the time when a predetermined time elapses from the time when the synchronous switch element Q2 is turned on and the time when the predetermined time elapses after the time when the synchronous switch element Q2 is turned off. A software filter for detecting the output signal may be provided. In this case, the mask circuit 12 realized by a hardware circuit becomes unnecessary.

  In the above-described embodiment, the configuration in which the comparison circuit 11 is provided with the coupling capacitor C3 for cutting off the DC component in the path from the connection point of both the switch elements Q1 and Q2 to the non-inverting input terminal of the comparator 111 has been described. However, as shown in FIG. 12, the connection point of both the switch elements Q1 and Q2 and the non-inverting input terminal of the comparator 111 may be directly connected without using the coupling capacitor C3.

  In this case, the cathode of the diode D3 constituting the constant voltage source 110 is connected to the drain terminal of the synchronous switch element Q2.

  In the above-described embodiment, the constant voltage source 110 is configured by the constant current source 112 and the diode D3. However, the constant voltage source 110 is not limited to such a circuit configuration, and is illustrated in FIG. As described above, a constant voltage circuit 113 that generates a reference voltage Vth using a Zener diode or a known constant voltage circuit 113 that generates a reference voltage Vth using an operational amplifier can be used.

  In the above-described embodiment, the correction amount map data provided in the soft switch control unit 20 has been set in advance as a fixed value. However, the correction amount map data is provided at the connection point between the switch elements Q1 and Q2. By configuring so as to be variably set based on the inductance value of the connected booster coil, it is possible to configure a general-purpose switching regulator that can handle a coil having an arbitrary inductance value.

  Further, the soft switch control unit 20 includes a plurality of sets of correction amount map data corresponding to inductance values of a plurality of boosting coils that may be used, and is automatically detected by the software switch control unit 20 or the Based on the inductance value set and input to the software switch control unit 20, correction amount map data adapted from a plurality of sets of correction amount map data may be adopted.

  In the embodiment described above, the initial value of the on-time of the synchronous switch element is set to a fixed value in advance. However, the initial value is configured to be variably set based on the inductance value of the boost coil. May be.

  Further, a plurality of initial values are stored in the storage unit corresponding to the inductance values of a plurality of boosting coils that may be used in the soft switch control unit 20 and automatically detected by the software switch control unit 20 Alternatively, an initial value adapted from a plurality of initial values may be adopted based on the inductance value set and input to the software switch control unit 20.

  In the above-described embodiment, the voltage detection unit 10 that detects the presence / absence of a current flowing from the input side to the output side at the moment when the synchronous switch element Q2 is turned off based on the potential difference V1 generated by the parasitic diode D2, Although the software switch control unit 20 has been described to control the off timing of the synchronous switch element Q2, the presence or absence of current flowing from the output side to the input side at the moment when the synchronous switch element Q2 is turned off is determined. The voltage detection unit 10 may be configured to detect based on the reverse potential difference V2 generated by the on-resistance of the synchronous switch Q2, and the software switch control unit 20 may be configured to control the off timing of the synchronous switch element Q2. .

  In this case, as shown in FIG. 14, in the comparison circuit 11 incorporated in the voltage detection unit 10, the source terminal of the synchronous switch element Q2 is connected to the non-inverting input terminal, and the drain terminal is connected to the inverting input terminal. What is necessary is just to comprise with the comparator 114.

  That is, the voltage detection unit 10 detects whether or not the timing for turning off the synchronous switch element Q2 is later than the zero current switching.

  The soft switch control unit 20 determines that a current flows from the output side to the input side when the synchronous switch element Q2 is turned off based on the voltage fluctuation detected by the voltage detection unit 11. Sometimes, the on-time of the synchronous switch element Q2 is corrected to be short, and when it is determined that no current is flowing into the input side, the on-time of the synchronous switch element Q2 is corrected to be long. Such a correction process can be realized in the same way as the flowcharts shown in FIGS. 5, 7, and 9 described above.

  In the above-described embodiment, the step-up half-bridge switching regulator has been described. However, the present invention can also be applied to a step-down half-bridge switching regulator.

  For example, as shown in FIG. 15, an output voltage adjustment switch element Q1 that adjusts the output voltage and the output voltage adjustment switch element Q1 are connected in series, and complementarily turn on when the output voltage adjustment switch element Q1 is off. The synchronous switch element Q2, the voltage detector 10 for detecting the voltage at the connection point of both switch elements when the synchronous switch element Q2 is turned off, and the synchronous switch based on the voltage fluctuation detected by the voltage detector 10 A step-down half-bridge switching regulator can be configured by including the soft switch control unit 20 that adjusts the turn-off timing of the element Q2.

  More specifically, the source terminal of the output voltage adjustment switch element Q1 is connected to the input voltage terminal IN, and the drain terminal is connected to the output voltage terminal OUT with the step-down coil L2 interposed therebetween. The drain terminal of the synchronous switch element Q2 is connected to the output voltage terminal OUT with the step-down coil L2 interposed therebetween, and the source terminal is grounded. That is, both switch elements Q1, Q2 are connected in series between the input terminal IN and the ground.

  As shown in FIG. 16, the half-bridge type switching regulator according to the present invention is incorporated into a control unit 400 including a microcomputer that controls power supply to a load 200 of equipment fed from the switching regulator 300A. The electronic device 100 can be configured.

  The control unit 400 includes a low-voltage (for example, DC5V) switching regulator 300B, a microcomputer fed from the switching regulator 300B, and peripheral circuits such as a MOS-FET 600 that feeds the load 200. For example, the load 200 The MOS-FET 600 is controlled by detecting the current flowing through the resistor R connected in series to the load 200. In the figure, reference numeral 500 denotes a battery for supplying power to the half-bridge type switching regulator 300A and the low-voltage switching regulator 300B according to the present invention.

  When the load 200 is a magnet clutch of an in-vehicle air conditioner, the electronic device 100 is an in-vehicle electronic control unit for the air conditioner, and the electronic device 100 is a motor that is a power source of power steering. Becomes an in-vehicle electronic control unit for power steering for controlling the motor.

  The specific configuration of the switching regulator including the soft switch control unit described above is not limited to the configuration shown in the embodiment, and can be changed and designed as appropriate within the scope of the effects of the present invention. Moreover, each aspect of the correction control by the soft switch control unit described above can be appropriately combined in a range where the effects of the present invention can be achieved.

(A) is a circuit diagram showing a conventional step-up switching regulator, and (b) is a timing chart showing the basic operation of zero current switching of the step-up switching regulator. Circuit diagram of a step-up half-bridge switching regulator having a voltage detector that detects whether or not the timing at which the synchronous switch element is turned off is earlier than zero-current switching (A) is a voltage variation explanatory diagram of the inter-switch element voltage Vds showing the basic operation of one cycle of zero current switching with respect to the synchronous switch, and (b) is an essential part of the inter-switch element voltage Vds during ideal zero current switching. Voltage fluctuation explanatory diagram, (c) is a voltage fluctuation explanatory diagram of the main part of the voltage Vds between switch elements when turned off earlier than ideal zero current switching, and (d) is turned off later than ideal zero current switching. Of voltage fluctuations of the main part of the inter-switch element voltage Vds when Voltage fluctuation explanatory diagram of the main part illustrating the potential difference appearing in the voltage Vds between the switch elements when the synchronous switch element is turned on and off. Control flow chart of zero current switching by the soft switch controller shown in FIG. Circuit diagram showing another embodiment of the step-up type half-bridge type switching regulator Control flow chart of zero current switching by the soft switch controller shown in FIG. Circuit diagram showing another embodiment of the step-up type half-bridge type switching regulator Control flow chart of zero current switching by the soft switch controller shown in FIG. Illustration of correction amount map data Explanatory drawing which shows the fluctuation | variation of the ON time of the synchronous switch controlled by the soft switch control part shown in FIG. 2 is a circuit diagram of a step-up type half-bridge switching regulator when a coupling capacitor is removed from the circuit diagram shown in FIG. Circuit diagram of step-up half-bridge switching regulator showing another embodiment of constant voltage source Circuit diagram of a step-up half-bridge switching regulator having a voltage detector that detects whether or not the timing at which the synchronous switch element is turned off is later than zero-current switching Circuit diagram of step-down half-bridge switching regulator showing another embodiment Illustration of an electronic device equipped with a half-bridge type switching regulator

Explanation of symbols

10: Voltage detection unit 11: Comparison circuit 12: Mask circuit 20: Soft switch control unit 20a: Output voltage adjustment unit 20b: Zero current control unit 21: Up counter 22: Down counter 23: Correction control unit 24: Map down counter 25 : Correction amount map data (storage unit)
112: Constant current source 300: Switching regulator 400: Control unit 700: Electronic device C3: Coupling capacitors D1, D2: Parasitic diode D3: Reference voltage generating diode L1: Boosting coil Q1: Output voltage adjusting switch element Q2: Synchronous Switch element

Claims (10)

  An output voltage adjustment switch element that adjusts an output voltage, a synchronous switch element that is connected in series with the output voltage adjustment switch element and that is complementarily turned on when the output voltage adjustment switch element is turned off, and when the synchronous switch element is turned off A voltage detection unit that detects a voltage at a connection point of both switch elements, and a soft switch control unit that adjusts a turn-off timing of the synchronous switch element based on a voltage variation detected by the voltage detection unit. Half-bridge type switching regulator.   2. The half-bridge type according to claim 1, wherein the voltage detection unit includes a comparison circuit that detects a change in voltage across the synchronous switch element, and a mask circuit that extracts an output from the comparison circuit when the synchronous switch element is turned off. Switching regulator.   The comparison circuit includes an input voltage via a coupling capacitor at an input side terminal of the synchronous switch element, a diode having one end grounded to form a predetermined reference voltage, and a constant current source connected in series to the diode. The half-bridge type switching regulator according to claim 2, which compares an input voltage from a constant voltage source.   The soft switch control unit extends the on-time of the synchronous switch element when it is determined that a current flows out to the output side when the synchronous switch element is turned off due to a voltage variation detected by the voltage detection unit. 4. The half-bridge type switching regulator according to claim 1, wherein the half-bridge type switching regulator corrects and corrects the on-time of the synchronous switch element to be shortened when it is determined that a current flows into the input side. 5.   5. The half-bridge type switching regulator according to claim 4, wherein the soft switch control unit corrects the on-time of the synchronous switch element to extend or shorten for a predetermined time.   5. The half-bridge type according to claim 4, wherein the soft switch control unit varies the on-time extension correction amount or the reduction correction amount of the synchronous switch element based on a past voltage fluctuation history detected by the voltage detection unit. Switching regulator.   The soft switch control unit is configured to generate the synchronization switch based on a voltage variation history detected in advance by the voltage detection unit and correction amount map data in which an extension correction amount or a shortening correction amount of the on-time of the synchronization switch element is set. The half-bridge type switching regulator according to claim 4, wherein the on-time of the element is corrected for expansion or shortening.   The half-bridge type switching regulator according to claim 7, wherein the correction amount map data is set based on an inductance value of a step-up coil or a step-down coil connected to a connection point between the two switch elements.   The half bridge according to any one of claims 1 to 8, wherein an initial value of an on-time of the synchronous switch element is set based on an inductance value of a step-up coil or a step-down coil connected to a connection point between the two switch elements. Type switching regulator.   An electronic apparatus comprising: the half-bridge type switching regulator according to any one of claims 1 to 9; and a control unit that controls power supply to the load based on a current or voltage flowing in a load of the power-supplied apparatus.