JP6216202B2 - Isolated switching power supply - Google Patents

Description

  The present invention relates to an insulating switching power supply device.

  2. Description of the Related Art Conventionally, an insulating switching power supply device that generates a desired output voltage from an input voltage while insulating between a primary circuit system and a secondary circuit system has been used in various electrical devices.

  As an example of the prior art related to the above, Patent Document 1 can be cited.

JP 2013-62947 A

  In general, an insulating switching power supply apparatus is configured to perform output feedback control using a photocoupler. However, in the conventional configuration using a photocoupler, reduction in long-term reliability and increase in cost due to an increase in the number of parts have been problems.

  Conventionally, there has also been proposed an insulating switching power supply apparatus that performs output feedback control using an auxiliary winding or primary winding of a transformer without using a photocoupler. However, the conventional configuration using the auxiliary winding or the primary winding has room for further improvement with respect to the accuracy of the output feedback control.

  The present invention has been made in view of the above-described problems found by the inventor of the present application, and an object thereof is to provide an isolated switching power supply device capable of performing high-precision output feedback control.

  An insulated switching power supply device according to the present invention includes a sample / hold circuit that samples / holds a feedback voltage generated by using an auxiliary winding or a primary winding of a transformer to generate a holding voltage, and according to the holding voltage. A primary current control circuit for controlling a primary current flowing through the primary winding, and the sample / hold circuit maintains a feedback voltage until the feedback voltage falls below a threshold voltage after the primary current is turned off. The period is measured, and the feedback voltage is sampled / held near the end of the feedback voltage maintaining period based on the measurement result (first structure).

  In the isolated switching power supply device having the first configuration, the sample / hold circuit repeats sampling / holding of the feedback voltage a plurality of times to compare each hold value, and based on the comparison result, It is preferable to adopt a configuration (second configuration) in which one hold value is selected as the holding voltage.

  Further, in the isolated switching power supply device having the second configuration, the sample / hold circuit detects whether or not a difference value between adjacent hold values is larger than a threshold reduction width, and based on the detection result. Thus, it is preferable to adopt a configuration (third configuration) in which the hold value immediately before the feedback voltage starts to drop sharply is selected as the hold voltage.

  Further, in the isolated switching power supply device having the third configuration, the sample / hold circuit determines that the last hold value is the holding voltage when the difference value between adjacent hold values is smaller than the threshold reduction width. It is good to make it the structure (4th structure) selected as.

  In the isolated switching power supply device having any one of the first to fourth configurations, the primary current control circuit includes an error amplifier that generates an error voltage according to a difference between the holding voltage and the first reference voltage. A detection voltage generation unit that generates a detection voltage according to the primary current, a first comparator that compares the error voltage with the detection voltage to generate a first comparison signal, and is turned off according to the first comparison signal A controller for generating a pulse for a signal, an oscillator for generating a pulse for an on signal at a predetermined frequency, a flip-flop for generating an output control signal in response to the on signal and the off signal, and the in response to the output control signal A configuration (a fifth configuration) including an output switch for turning on / off the primary current is preferable.

  Further, in the isolated switching power supply device having the fifth configuration, the primary current control circuit further includes a second comparator that compares the detection voltage with a second reference voltage to generate a second comparison signal, The controller is configured to perform one of constant voltage control according to the first comparison signal and constant current control according to the second comparison signal depending on whether or not the primary current has reached an upper limit value ( A sixth configuration) may be used.

  Further, in the isolated switching power supply device having the fifth or sixth configuration, the detection voltage generation unit fixes the detection voltage to a zero value over a predetermined mask period after the output switch is turned on. A configuration including a mask processing unit (seventh configuration) is preferable.

  The isolated switching power supply device having any one of the first to seventh configurations generates an output voltage from a transformer in which an input voltage is applied to the primary winding and an induced voltage generated in the secondary winding of the transformer. And a rectifying / smoothing unit for generating a feedback voltage from the induced voltage generated in the auxiliary winding or the primary winding of the transformer.

  Further, the insulated switching power supply device having the eighth configuration may have a configuration (9th configuration) further including an AC / DC conversion unit that generates the input voltage from an AC voltage.

  Moreover, the AC adapter according to the present invention has a configuration (tenth configuration) including the insulating switching power supply device having the ninth configuration.

  According to another aspect of the invention, there is provided an electronic apparatus comprising: the insulated switching power supply device having any one of the first to ninth configurations; and a load that operates upon receiving an output voltage from the insulated switching power supply device. The configuration is an eleventh configuration.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the insulation type switching power supply device which can perform highly accurate output feedback control.

The figure which shows the whole constitution of the insulation type switching power supply device Timing chart showing an example of switching control operation Diagram for explaining switching operation between constant voltage control and constant current control The figure which shows one structural example of a sample / hold circuit Timing chart showing an example of sample / hold operation The figure which shows an example of hold value selection operation Diagram showing another method of sample / hold operation The figure which shows the example of 1 structure of AC adapter provided with the insulation type switching power supply device The figure which shows one structural example of the electronic device provided with the insulation type switching power supply device

<Overall configuration>
FIG. 1 is a block diagram showing an overall configuration of an insulated switching power supply device. The insulation type switching power supply device 1 of the present configuration example is an AC supplied from a commercial AC power supply PW while electrically insulating the primary circuit system 1p (GND1 system) and the secondary circuit system 1s (GND2 system). An AC / DC converter that converts the voltage Vac into a DC output voltage Vo and supplies it to the load Z. The transformer 10, the semiconductor device 20, the AC / DC converter 30, the power supply voltage generator 40, and the feedback voltage The generator 50 and the rectifying / smoothing unit 60 are included.

  The transformer 10 includes a primary winding 11 (number of turns Np) and a secondary winding 12 (number of turns Ns) which are electromagnetically coupled with opposite polarities while being electrically insulated between the primary circuit system 1p and the secondary circuit system 1s. including. The first end of the primary winding 11 is connected to the application end of the input voltage Vi. The second end of the primary winding 11 is connected to the ground end GND1 of the primary circuit system 1p through the semiconductor device 20. The first end of the secondary winding 12 is connected to the application end of the output voltage Vo (the power supply input end of the load Z) via the rectifying and smoothing unit 60. The second end of the secondary winding 12 is connected to the ground terminal GND2 of the secondary circuit system 1s. Note that the turns Np and Ns may be arbitrarily adjusted so that a desired output voltage Vo is obtained. For example, the output voltage Vo decreases as the number of turns Np increases or the number of turns Ns decreases. Conversely, the output voltage Vo increases as the number of turns Np decreases or the number of turns Ns increases. The transformer 10 includes an auxiliary winding 13 in addition to the primary winding 11 and the secondary winding 12. The auxiliary winding 13 is used when generating the power supply voltage Vcc and the feedback voltage Vfb.

  The semiconductor device 20 is a switching control IC that is a driving body of the transformer 10. A sample / hold circuit 21 and a primary current control circuit 22 are integrated therein.

  The sample / hold circuit 21 samples / holds the feedback voltage Vfb to generate a holding voltage Va. The configuration and operation of the sample / hold circuit 21 will be described in detail later.

  The primary current control circuit 22 basically controls the primary current Ip flowing through the primary winding 11 according to the holding voltage Va generated by the sample / hold circuit 21. The primary current control circuit 22 includes an error amplifier 221, comparators 222 and 223, a controller 224, an oscillator 225, an RS flip-flop 226, an output switch 227, and a detection voltage generation unit 228.

  The error amplifier 221 generates an error voltage Vb corresponding to the difference between the holding voltage Va applied to the inverting input terminal (−) and the reference voltage Vref1 applied to the non-inverting input terminal (+). More specifically, the error amplifier 221 reduces the error voltage Vb when the holding voltage Va is higher than the reference voltage Vref1, and increases the error voltage Vb when the holding voltage Va is lower than the reference voltage Vref1.

  The comparator 222 compares the error voltage Vb applied to the inverting input terminal (−) and the detection voltage Vd applied to the non-inverting input terminal (+) to generate a comparison signal Sa. The comparison signal Sa is at a high level when the detection voltage Vd is higher than the error voltage Vb, and is at a low level when the detection voltage Vd is lower than the error voltage Vb.

  The comparator 223 compares the reference voltage Vref2 applied to the inverting input terminal (−) and the detection voltage Vd applied to the non-inverting input terminal (+) to generate a comparison signal Sb. The comparison signal Sb is at a high level when the detection voltage Vd is higher than the reference voltage Vref2, and is at a low level when the detection voltage Vd is lower than the reference voltage Vref2.

  The controller 224 generates a pulse in the off signal S2 according to the comparison signals Sa and Sb. More specifically, the controller 224 detects a rising edge of the comparison signals Sa and Sb and generates a pulse in the off signal S2.

  The oscillator 225 generates a pulse in the ON signal S1 at a predetermined frequency.

  The RS flip-flop 226 generates a gate signal G1 (corresponding to an output control signal) in response to an ON signal S1 input to the set end (S) and an OFF signal S2 input to the reset end (R). More specifically, the RS flip-flop 226 sets the gate signal G1 to the high level at the rising edge of the on signal S1, and resets the gate signal G1 to the low level at the rising edge of the off signal S2.

  The output switch 227 conducts / cuts off the current path from the application end of the input voltage Vi to the ground end GND1 via the primary winding 11 in accordance with the gate signal G1, so that the primary current Ip flowing through the primary winding 11 is reduced. This is a switch element that is turned on / off. In this configuration example, an N-channel MOS (metal oxide semiconductor) field effect transistor is used as the output switch 227. Describing the connection relationship, the drain of the output switch 227 is connected to the second end of the primary winding 11. The source and back gate of the output switch 227 are both connected to the ground terminal GND1 via the detection voltage generation unit 228. The gate of the output switch 227 is connected to the application terminal of the gate signal G1. The output switch 227 is turned on when the gate signal G1 is at a high level, and turned off when the gate signal G1 is at a low level.

  The detection voltage generation unit 228 includes a sense resistor 228a and a mask processing unit 228, and generates a detection voltage Vd corresponding to the primary current Ip. The sense resistor 228a is connected between the output switch 227 and the ground terminal GND1, and generates a sense voltage Vc corresponding to the primary current Ip. The mask processing unit 228b performs a predetermined mask process on the sense voltage Vc to generate the detection voltage Vd. More specifically, the mask processing unit 228b fixes the detection voltage Vd to a zero value for a predetermined mask period (see times t11 to t12 in FIG. 2) after the output switch 227 is turned on. With such a configuration, it is not necessary to be affected by ringing noise of the sense voltage Vc generated when the output switch 227 is turned on, so that the stability of the switching control operation can be improved.

  The AC / DC converter 30 includes a filter 31, a diode bridge 32, and capacitors 33 and 34, and generates a DC input voltage Vin from the AC voltage Vac. The filter 31 removes noise and surge from the AC voltage Vac. The diode bridge 32 generates an input voltage Vin by full-wave rectifying the AC voltage Vac. Capacitor 33 removes harmonic noise of AC voltage Vac. The capacitor 34 smoothes the input voltage Vin. The AC / DC converter 30 may include a protective element such as a fuse.

  The power supply voltage generation unit 40 is a rectifying / smoothing circuit including a diode 41 and a capacitor 42, and generates the power supply voltage Vcc of the semiconductor device 10 from the induced voltage Vaux of the auxiliary winding 13. The winding ratio between the primary winding 11 and the auxiliary winding 13 may be appropriately set in view of the power supply voltage Vcc necessary for the operation of the semiconductor device 20.

  The feedback voltage generator 50 includes resistors 51 and 52 connected in series between the application terminal of the induced voltage Vaux and the ground terminal GND1, and generates the feedback voltage Vfb by dividing the induced voltage Vaux. The higher the output voltage Vo, the higher the induced voltage Vaux, and the higher the feedback voltage Vfb. Conversely, the lower the output voltage Vo, the lower the induced voltage Vaux, and the lower the feedback voltage Vfb. Thus, the feedback voltage Vfb varies according to the output voltage Vo. Therefore, if the feedback voltage Vfb is generated from the induced voltage Vaux of the auxiliary winding 13, output feedback control can be performed without using a photocoupler. The feedback voltage generation unit 50 may be configured to generate the feedback voltage Vfb from the switch voltage Vsw appearing at the connection node between the primary winding 11 and the output switch 227.

  The rectifying / smoothing unit 60 includes a rectifying diode 61 and a smoothing capacitor 62, and rectifies and smoothes the induced voltage generated in the secondary winding 12 to generate the output voltage Vo. The connection relationship will be described. The anode of the diode 61 is connected to the first end of the secondary winding 12. Both the cathode of the diode 61 and the first terminal of the capacitor 62 are connected to the application terminal of the output voltage Vo. A second terminal of the capacitor 62 is connected to the ground terminal GND2.

<Switching control operation>
FIG. 2 is a timing chart showing an example of the switching control operation. In order from the top, the ON signal S1, the OFF signal S2, the gate signal G1, the sense voltage Vc (primary current Ip), the detection voltage Vd, and the comparison signal Sa. Is depicted.

  When a pulse is generated in the on signal S1 at time t11, the gate signal G1 is set to a high level, and the output switch 227 is turned on. During the ON period of the output switch 227, since the primary current Ip flows from the application terminal of the input voltage Vi to the ground terminal GND1 via the primary winding 11 and the output switch 227, electric energy is stored in the primary winding 11. It is done.

  As described above, the detection voltage Vd is fixed to a zero value for a predetermined mask period (time t11 to t12) after the output switch 227 is turned on, and ringing noise of the sense voltage Vc is masked. .

  Thereafter, when the detection voltage Vd becomes higher than the error voltage Vb at time t13 and the comparison signal Sa rises to a high level, a pulse is generated in the off signal S2 at time t14. As a result, the gate signal G1 is reset to a low level, and the output switch 227 is turned off. During the OFF period of the output switch 227, an induced voltage is generated in the secondary winding 12 that is electromagnetically coupled to the primary winding 11, and the secondary voltage from the secondary winding 12 to the ground terminal GND2 via the diode 61 is generated. A current Is flows. At this time, an output voltage Vo obtained by half-wave rectifying the induced voltage of the secondary winding 12 is supplied to the load Z.

  Further, when the output switch 227 is turned off at time t14, the primary current Ip is cut off, so that both the sense voltage Vc and the detection voltage Vd fall to zero values, and the comparison signal Sa becomes low level. After time t14, basically the same switching control operation as described above is repeated.

  As described above, according to the insulation type switching power supply device 1 of this configuration example, the output voltage Vo is generated from the AC voltage Vac while electrically insulating the primary circuit system 1p and the secondary circuit system 1s. The load Z can be supplied. Note that the flyback method employed in the isolated switching power supply device 1 of this configuration example is advantageous in terms of cost reduction because it has fewer parts than the forward method that requires a smoothing inductor.

<Constant voltage control and constant current control>
FIG. 3 is a diagram for explaining a switching operation between the constant voltage control and the constant current control. When the difference between the output voltage Vo and the target voltage Vtarget is small and the error voltage Vb is lower than the reference voltage Vref2, the controller 224 is turned off according to the comparison result (= comparison signal Sa) between the error voltage Vb and the detection voltage Vd. Pulse generation of the signal S2 is performed. This state corresponds to a state in which the primary current Ip has not reached the upper limit value Ilimit and constant voltage control according to the comparison signal Sa is performed (reference characters CV [constant in columns (A) and (B)). voltage]).

  On the other hand, when the difference between the output voltage Vo and the target voltage Vtarget becomes large and the error voltage Vb becomes higher than the reference voltage Vref2, the controller 224 determines the comparison result (= comparison signal Sb) between the reference voltage Vref2 and the detection voltage Vd. Accordingly, pulse generation of the off signal S2 is performed. This state corresponds to a state in which the primary current Ip reaches the upper limit value Ilimit and constant current control is performed in accordance with the comparison signal Sb (reference symbols CC [constant current in columns (A) and (B)). ]).

  Thus, the controller 224 performs either one of constant voltage control according to the comparison signal Sa and constant current control according to the comparison signal Sb depending on whether or not the primary current Ip has reached the upper limit value Ilimit.

<Sample / hold circuit>
FIG. 4 is a diagram illustrating a configuration example of the sample / hold circuit 21. The sample / hold circuit 21 of this configuration example includes a comparator 211, a timing generator 212, a sample / hold unit 213, a difference processing unit 214, a comparison processing unit 215, a control unit 216, and a selector 217. .

  The comparator 211 compares the feedback voltage Vfb applied to the non-inverting input terminal (+) and the threshold voltage Vth applied to the inverting input terminal (−) to generate a comparison signal S10. The comparison signal S10 is at a high level when the feedback voltage Vfb is higher than the threshold voltage Vth, and is at a low level when the feedback voltage Vfb is lower than the threshold voltage Vth.

  The timing generator 212 detects the pulse edge of the comparison signal S10 to thereby maintain a feedback voltage maintaining period from when the primary current Ip is turned off until the feedback voltage Vfb falls below the threshold voltage Vth (see symbols T1 to T4 in FIG. 5). ) And the timing signals S11 to S14 are generated so that the feedback voltage Vfb is sampled / held near the end of the feedback voltage maintaining period based on the measurement result. Note that the off timing of the primary current Ip (measurement start timing of the feedback voltage maintaining periods T1 to T4) is based on the falling edge of the gate signal G1 or the rising edge of the off signal S2, instead of the rising edge of the comparison signal S10. You can decide. The operation of the timing generator 212 will be described in detail later.

  The sample / hold unit 213 includes analog switches SW11 to SW14, capacitors C1 to C4, and N-channel MOS field effect transistors N1 to N4, and performs a sample / hold operation of the feedback voltage Vfb according to the timing signals S11 to S14. I do. The first ends of the analog switches SW11 to SW14 are all connected to the application end of the feedback voltage Vfb. The second ends of the analog switches SW11 to SW14 are connected to the output ends of the hold values V11 to V14, respectively. The control ends of the analog switches SW11 to SW14 are connected to the application ends of the timing signals S11 to S14, respectively. The capacitors C1 to C4 are connected between the output terminals of the hold values V11 to V14 and the ground terminal, respectively. The transistors N1 to N4 are connected between the output terminals of the hold values V11 to V14 and the ground terminal, respectively. The gates of the transistors N1 to N4 are all connected to the application terminal of the enable signal ENB.

  The analog switches SW11 to SW14 are turned on when the timing signals S11 to S14 are at a high level, respectively, and are turned off when the timing signals S11 to S14 are at a low level. The on period of the analog switches SW11 to SW14 corresponds to the sampling period of the sample / hold unit 213, and the capacitors C1 to C4 are charged by the feedback voltage Vfb. On the other hand, the off period of the analog switches SW11 to SW14 corresponds to the hold period of the sample / hold unit 213, and the charging voltages of the capacitors C1 to C4 are held as the hold values V11 to V14. The transistors N1 to N4 are turned off when the enable signal ENB is at a low level (logic level when enabled) and turned on when the enable signal ENB is at a high level (logic level when disabled). When the transistors N1 to N4 are turned on, the capacitors C1 to C4 are discharged and the hold values V11 to V14 are reset to zero values.

  The difference processing unit 214 includes current output amplifiers AMP1 to AMP3 and resistors R1 to R3, and generates difference values V21 to V23 between adjacent hold values. The inverting input terminal (−) of the current output amplifier AMP1 is connected to the output terminal of the hold value V11. Both the non-inverting input terminal (+) of the current output amplifier AMP1 and the inverting input terminal (−) of the current output amplifier AMP1 are connected to the output terminal of the hold value V12. Both the non-inverting input terminal (+) of the current output amplifier AMP2 and the inverting input terminal (−) of the current output amplifier AMP3 are connected to the output terminal of the hold value V13. The non-inverting input terminal (+) of the current output amplifier AMP3 is connected to the output terminal of the hold value V14. The output terminals of the current output amplifiers AMP1 to AMP3 are connected to the output terminals of the difference values V21 to V23, respectively. The resistors R1 to R3 are connected between the output terminals of the difference values V21 to V23 and the ground terminal, respectively.

  As the hold value V11 is lower than the hold value V12, the current output amplifier AMP1 increases the difference value V21 by flowing more current through the resistor R1. As the hold value V12 is lower than the hold value V13, the current output amplifier AMP2 increases the difference value V22 by flowing more current through the resistor R2. As the hold value V13 is lower than the hold value V14, the current output amplifier AMP3 increases the difference value V23 by flowing more current through the resistor R3.

  The comparison processing unit 215 includes comparators CMP1 to CMP3, and compares the difference values V21 to V23 with the reference voltage Vref (corresponding to the threshold reduction width) to generate comparison signals S21 to S23. The comparison signals S21 to S23 are at a high level when the difference values V21 to V23 are higher than the reference voltage Vref, respectively, and are at a low level when the difference values V21 to V23 are lower than the reference voltage Vref. In this configuration example, a configuration in which three comparators CMP1 to CMP3 are provided in parallel has been described as an example. However, the configuration of the comparison processing unit 215 is not limited to this, and for example, a single comparator is sometimes used. By using the division, the difference values V21 to V23 and the reference voltage Vref may be sequentially compared.

  The control unit 216 generates a switching signal S30 for the selector 217 based on the comparison signals S21 to S23. The operation of the control unit 216 will be described in detail later.

  The selector 217 selectively outputs any one of the hold values V11 to V14 as the hold voltage Va according to the switching signal S30.

<Sample / hold operation>
FIG. 5 is a timing chart showing an example of the sample / hold operation. In order from the top, the gate signal G1, the feedback voltage Vfb, the primary current Ip, the secondary current Is, the comparison signal S10, the timing signals S11 to S14, and The holding voltage Va is depicted.

  At time t21, when the gate signal G1 is set to the high level and the output switch 227 is turned on, the primary current Ip flows and energy is stored in the transformer 10.

  Thereafter, at time t22, when the gate signal G1 is set to the low level and the output switch 227 is turned off, the primary current Ip is cut off and the secondary current Is starts to flow. At this time, the feedback voltage Vfb becomes higher than the threshold voltage Vth, and the comparison signal S10 becomes high level.

  Thereafter, when the energy stored in the transformer 10 is exhausted and the secondary current Is does not flow, the feedback voltage Vfb becomes lower than the threshold voltage Vth at time t23, and the comparison signal S10 falls to the low level.

  The timing generator 212 measures the feedback voltage maintaining periods T1 to T4 (corresponding to the high level period of the comparison signal S10) until the feedback voltage Vfb falls below the threshold voltage Vth after the primary current Ip is turned off. A moving average value for N cycles is calculated to obtain an average feedback voltage maintaining period Tave.

  Then, the timing generator 212 uses the average feedback voltage maintaining period Tave and a predetermined shift period Tx (for example, 100 μs) to sample the feedback voltage Vfb near the end of the feedback voltage maintaining periods T1 to T4 (immediately before time t23). Timing signals S11 to S14 are generated so as to perform / hold.

  Specifically, after the comparison signal S10 rises to a high level, the timing generator 212 first performs a sample / hold operation at a timing (Tave-4Tx) obtained by subtracting four times the shift period Tx from the average period voltage maintenance period Tave. The timing signal S14 is generated so that Thereafter, the timing generator 212 sequentially performs a sample / hold operation at a timing (Tave-3Tx, Tave-2Tx, Tave-Tx) obtained by subtracting 3 times, 2 times, and 1 time of the shift period Tx from the average period voltage maintaining period Tave. Timing signals S13, S12, and S11 are generated so as to perform the above. Note that the high level period Td (corresponding to the sampling period) of the timing signals S11 to S14 may be set to the same value (for example, 100 μs).

  By such timing control, the sample / hold circuit 21 of this configuration example repeats the sample / hold operation of the feedback voltage Vfb a plurality of times to obtain a plurality of hold values V11 to V14, and the comparison results (more accurate) In this case, any one hold value is selectively output as the hold voltage Va based on a difference value V21 to V23 between adjacent hold values and the reference voltage Vref.

  In the example of this figure, after completion of the sample / hold operation in the off period (time t22 to t24), the holding voltage Va is updated without delay when the next period on period (time t24 to t25) ends. It has been broken. However, the update timing of the hold voltage Va is not limited to this, and the hold voltage Va can be updated at an arbitrary timing during the off period (time t25 to t26) of the next cycle.

  After time t25, basically, the same sample / hold operation as described above is repeated, whereby the feedback voltage Vfb immediately before the secondary current Is becomes zero is sequentially held as the holding voltages Va1 to Va4.

  Note that when generating the timing signals S11 to S14, the average feedback voltage maintaining period Tave is not calculated, and the feedback voltage maintaining period of the immediately preceding cycle can be used as a reference.

<Hold value selection operation>
FIG. 6 is a diagram illustrating an example of a hold value selection operation by the control unit 216. As shown in the column (A) of this figure, when the secondary current Is does not become zero during the off period Toff of the output switch 227 (so-called current continuous mode), the feedback voltage Vfb is kept until the output switch 227 is turned on. Almost no decrease. Accordingly, since the difference values V21 to V23 between the adjacent hold values are all lower than the reference voltage Vref (corresponding to the threshold reduction width), the comparison signals S21 to S23 are all at the low level. Accordingly, the control unit 216 receiving this selects the hold value V11 acquired last (latest timing) as the hold voltage Va.

  On the other hand, as shown in the columns (B) to (D) of this figure, when the secondary current Is has a zero value during the off period Toff of the output switch 227 (so-called current discontinuous mode), the secondary current Is The feedback voltage Vfb starts to drop sharply after the value becomes zero, and eventually falls below the threshold voltage Vth. For example, as shown in the column (B) of this figure, when the feedback voltage Vfb suddenly decreases after the hold value V12 is acquired, the comparison signal S21 becomes high level, and the comparison signals S22 and S23 become low level. . Accordingly, the control unit 216 receiving this selects the hold value V12 immediately before the feedback voltage Vfb starts to drop sharply as the hold voltage Va.

  Further, as shown in the column (C) of this figure, when the feedback voltage Vfb suddenly decreases after the hold value V13 is acquired, the comparison signals S21 and S22 are at a high level and the comparison signal S23 is at a low level. . Accordingly, the control unit 216 that receives this selects the hold value V13 immediately before the feedback voltage Vfb starts to drop sharply as the hold voltage Va.

  Similarly, as shown in the column (D) of this figure, when the feedback voltage Vfb suddenly drops after the hold value V14 is acquired, the comparison signals S21 to S23 are all at the high level. Accordingly, the control unit 216 receiving this selects the hold value V14 immediately before the feedback voltage Vfb starts to drop sharply as the hold voltage Va.

  Note that the number of times of sampling / holding the feedback voltage Vfb is not limited to four times, and may be five times or more and three times or less. However, it should be noted that if the number of times of sampling / holding is excessively increased, the circuit scale and power consumption increase unnecessarily. In addition, when the number of samples / holds is set to one, the circuit scale is minimized, but the difference process of the hold value cannot be performed. Therefore, the feedback voltage Vfb immediately before the secondary current Is becomes zero is accurately determined. Note that it is difficult to sample / hold.

<Another method of sample / hold operation>
FIG. 7 is a diagram showing another method of sample / hold operation. As a first alternative method, as shown in the column (X) of this figure, a method of setting the start timing T11 and the end timing T12 of the sample / hold operation starting from the off timing (time t31) of the output switch 227. Can be considered. However, in this method, it is very difficult to sample / hold the feedback voltage Vfb immediately before the secondary current Is becomes zero (time t32). Further, the sample / hold operation has a restriction that it must be executed after the ringing of the feedback voltage Vfb converges until the secondary current Is becomes zero. In view of such a restriction, the start timing T11 and the end timing T12 of the sample / hold operation are very severely limited, so that the set application range is narrowed.

  As a second alternative method, as shown in the column (Y) of this figure, after setting the start timing T11 of the sample / hold operation starting from the off timing (time t31) of the output switch 227, feedback is performed. A method is conceivable in which the sample / hold operation is repeated many times until the voltage Vfb starts to drop sharply. According to this method, it is possible to sample / hold the feedback voltage Vfb immediately before the secondary current Is becomes zero (time t32). However, in this method, the number of times of sample / hold is greatly increased, which causes an unnecessary increase in circuit scale and power consumption.

  On the other hand, according to the above-described sample / hold circuit 21, the minimum necessary starting from the timing at which the feedback voltage Vfb falls below the threshold voltage Vth after the primary current Ip is turned off (time t23 in FIG. 5). Since the sample / hold operation is performed, the above-described problem of the different method does not occur.

<Application>
The use of the insulating switching power supply device 1 will be described. The insulating switching power supply device 1 is preferably used for a power supply block of an AC adapter or an electronic device.

  FIG. 8 is a diagram illustrating a configuration example of an AC adapter including the insulating switching power supply device 1. The AC adapter 800 includes a plug 802, a housing 804, and a connector 806. Plug 802 is supplied with commercial AC voltage VAC (corresponding to AC voltage Vac in FIG. 1) from an outlet (not shown). The insulating switching power supply device 1 is mounted inside the housing 804. An output voltage VOUT (corresponding to the output voltage Vo in FIG. 1) generated by the insulating switching power supply device 1 is supplied from the connector 806 to the electronic device 810. Examples of the electronic device 810 include a notebook PC, a digital still camera, a digital video camera, a mobile phone, and a mobile audio player.

  FIG. 9 is a diagram illustrating a configuration example of an electronic device including the insulating switching power supply device 1. In addition, the front view of the electronic device 900 is drawn in the (A) column in the figure, and the rear view of the electronic device 900 is drawn in the (B) column in the drawing. Note that the electronic device 900 illustrated in the figure is a display device, but the type of the electronic device 900 is not particularly limited, and may be an electronic device including a power supply device such as an audio device, a refrigerator, a washing machine, or a vacuum cleaner. That's fine.

  Plug 902 is supplied with commercial AC voltage VAC (corresponding to AC voltage Vac in FIG. 1) from an outlet (not shown). The insulating switching power supply device 1 is mounted inside the housing 904. The output voltage VOUT (corresponding to the output voltage Vo in FIG. 1) generated by the insulating switching power supply 1 is a load (microcomputer, DSP [digital signal processor], power supply circuit, lighting device) mounted inside the housing 904. , Analog circuit, and digital circuit).

<Other variations>
The configuration of the present invention can be variously modified in addition to the above-described embodiment without departing from the gist of the invention. That is, the above-described embodiment is an example in all respects and should not be considered as limiting, and the technical scope of the present invention is not the description of the above-described embodiment, but the claims. It should be understood that all modifications that come within the meaning and range of equivalents of the claims are included.

  The present invention can be used for an insulating switching power supply device used in various fields (such as the home appliance field, the automobile field, and the industrial machine field).

1 Insulation type switching power supply 1p Primary circuit system (GND1 system)
1s Secondary circuit system (GND2 system)
10 Transformer 11 Primary winding 12 Secondary winding 13 Auxiliary winding 20 Semiconductor device (switching control IC)
21 Sample / Hold Circuit 211 Comparator 212 Timing Generator 213 Sample / Hold Unit 214 Difference Processing Unit 215 Comparison Processing Unit 216 Control Unit 217 Selector 22 Primary Current Control Circuit 221 Error Amplifier 222, 223 Comparator 224 Controller 225 Oscillator 226 RS Flip-Flop 227 Output Switch (N-channel MOS field effect transistor)
228 Detection voltage generation unit 228a Sense resistor 228b Mask processing unit 30 AC / DC conversion unit 31 Filter 32 Diode bridge 33, 34 Capacitor 40 Power supply voltage generation unit 41 Diode 42 Capacitor 50 Feedback voltage generation unit 51, 52 Resistance 60 Rectification smoothing unit 61 Diode 62 Capacitor PW Commercial AC power supply Z Load SW11-SW14 Analog switch C1-C4 Capacitor N1-N4 N-channel MOS field effect transistor AMP1-AMP3 Current output amplifier R1-R3 Resistance CMP1-CMP3 Comparator 800 AC adapter 802 Plug 804 Housing 806 Connector 900 Electronic device 902 Plug 904 Housing

Claims (10)

A sample / hold circuit that samples / holds the feedback voltage generated using the transformer auxiliary winding or primary winding to generate a holding voltage;
A primary current control circuit for controlling a primary current flowing in the primary winding in accordance with the holding voltage;
Have
The sample / hold circuit measures a feedback voltage maintaining period from when the primary current is turned off until the feedback voltage falls below a threshold voltage, and based on the measurement result, the feedback near the end of the feedback voltage maintaining period. An insulated switching power supply device characterized in that voltage sampling / holding is performed a plurality of times, each hold value is compared, and any one hold value is selected as the hold voltage based on the comparison result . The sample / hold circuit detects whether or not a difference value between adjacent hold values is larger than a threshold reduction range, and based on the detection result, the hold value immediately before the feedback voltage starts to drop sharply is determined. 2. The insulated switching power supply device according to claim 1 , wherein the insulating switching power supply device is selected as a holding voltage. 3. The insulation type according to claim 2 , wherein the sample / hold circuit selects the last hold value as the hold voltage when the difference values between the adjacent hold values are all smaller than the threshold reduction width. Switching power supply. The primary current control circuit includes:
An error amplifier that generates an error voltage according to a difference between the holding voltage and the first reference voltage;
A detection voltage generation unit that generates a detection voltage according to the primary current;
A first comparator for comparing the error voltage and the detection voltage to generate a first comparison signal;
A controller for generating a pulse in an off signal in response to the first comparison signal;
An oscillator that generates a pulse in the ON signal at a predetermined frequency;
A flip-flop that generates an output control signal in response to the on signal and the off signal;
An output switch for turning on / off the primary current in response to the output control signal;
The insulated switching power supply device according to any one of claims 1 to 3 , further comprising: The primary current control circuit further includes a second comparator that compares the detection voltage with a second reference voltage to generate a second comparison signal;
The controller performs either one of constant voltage control according to the first comparison signal and constant current control according to the second comparison signal depending on whether or not the primary current has reached an upper limit value.
The insulation type switching power supply device according to claim 4 characterized by things. The said detection voltage production | generation part contains the mask process part which fixes the said detection voltage to a zero value over the predetermined | prescribed mask period after the said output switch is turned on, The Claim 4 or Claim 5 characterized by the above-mentioned. Isolated switching power supply. A transformer in which an input voltage is applied to the primary winding;
A rectifying / smoothing unit that generates an output voltage from an induced voltage generated in the secondary winding of the transformer;
A feedback voltage generator for generating the feedback voltage from an induced voltage generated in the auxiliary winding or primary winding of the transformer;
The insulated switching power supply device according to any one of claims 1 to 6 , further comprising: The insulated switching power supply device according to claim 7 , further comprising an AC / DC converter that generates the input voltage from an AC voltage. An AC adapter comprising the insulated switching power supply device according to claim 8 . The insulated switching power supply device according to any one of claims 1 to 8 ,
A load that operates by receiving supply of an output voltage from the isolated switching power supply device;
Electronic equipment having

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