JP7141916B2 - Power controller and LLC resonant converter - Google Patents

Description

The present invention relates to power supply controllers for LLC resonant converters.

Conventionally, as one type of DC/DC converter, there is an LLC resonance type DC/DC converter (hereinafter referred to as LLC resonance converter). The LLC resonant converter is an isolated switching power supply circuit.

Conventional LLC resonant converters have been known to perform burst operation in which a switching stop period is intentionally provided in order to improve efficiency at light load. That is, in burst operation, switching operation is performed intermittently. An example of LLC resonant converter with burst operation is disclosed in US Pat.

The LLC resonant converter of Patent Document 1 is controlled by the following LLC control IC. The LLC control IC has a voltage-controlled oscillator (VCO) that oscillates at a frequency corresponding to a feedback voltage (feedback voltage) obtained by feeding back the output voltage on the secondary side of the LLC resonant converter. Based on this, the switching element of the LLC resonant converter is switching driven.

The LLC control IC includes a burst operation setting circuit, and a control circuit for switching between a switching operation state in which the oscillation output of the VCO is passed and a switching stop state in which the oscillation output is cut off based on the output of the burst operation setting circuit. have more.

The burst operation setting circuit has a correction circuit and a comparator that compares a threshold voltage output from the correction circuit and a feedback voltage. In the standby mode, the switching operation state and the switching stop state of the control circuit are switched according to the output level (H/L) from the comparator. The correction circuit generates the threshold voltage based on the bulk voltage, which is the output voltage of a PFC (power factor correction circuit) located on the front stage side of the LLC resonant converter.

JP 2017-135894 A

However, in Patent Document 1, when the feedback voltage is lower than the threshold voltage, the output level of the comparator becomes Low, resulting in a switching stop state in which the output of the oscillation signal from the control circuit is stopped. At this time, the current resonance is suddenly stopped, so there is a possibility that the transformer for insulation in the LLC resonance converter may squeal.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a power supply control device capable of suppressing the ringing of a transformer in an LLC resonance converter during burst operation.

In order to achieve the above object, one aspect of the present invention is
a first switching element to one end of which an input voltage is applied;
a second switching element having one end connected to the other end of the first switching element;
a primary winding and a resonant capacitor connected in series between a first connection node where the first switching element and the second switching element are connected, and the other end of the second switching element;
A power supply control device that drives and controls an LLC resonance converter having
an off-threshold generation circuit that generates an upper off-threshold and a lower off-threshold based on a feedback voltage obtained by feeding back the output voltage of the LLC resonant converter;
a feedback current summing circuit for summing a resonance current detection signal to each of the upper off-threshold and the lower off-threshold;
an upper comparator that compares the upper off threshold after summation by the feedback current summing circuit with the resonance voltage detection signal and outputs an upper off signal for turning off the first switching element;
a lower comparator that compares the lower off threshold after summing by the feedback current summing circuit with the resonance voltage detection signal and outputs a lower off signal for turning off the second switching element;
a hysteresis comparator that compares the feedback voltage with first and second thresholds;
has
When the hysteresis comparator detects that the feedback voltage exceeds the second threshold value, the switching operation state is shifted to the switching operation state by the first switching element and the second switching element, and the feedback voltage is switched during the switching operation state. exceeds the first threshold value, the summed amount by the feedback current summing circuit is changed for a predetermined period of time, and when the predetermined period of time elapses, switching is switched to a stopped state. , a power control device (first configuration).

Further, in the above first configuration, the off-threshold generation circuit includes:
a first resistor;
a second resistor;
a first voltage application unit that applies a first predetermined voltage to a second connection node to which one end of the first resistor and one end of the second resistor are connected;
an output current generating circuit for generating a first output current flowing through the other end of the first resistor and a second output current flowing through the other end of the second resistor based on the feedback voltage;
has
The feedback current summing circuit may draw a sink current from the other end of the first resistor and discharge a source current to the other end of the second resistor based on the resonance current detection signal (second configuration ).

Further, in the second configuration, the amounts of the sink current and the source current may be N times (N>1) the normal amount during the predetermined period (third configuration).

In the second configuration, a first constant current source draws a constant current from a line into which the sink current is drawn during the predetermined period, and a constant current is supplied to a line through which the source current is discharged during the predetermined period. (fourth configuration).

In any one of the second to fourth configurations, the feedback current summing circuit may
a first sample and hold unit that holds the resonance current detection signal when the first switching element is switched on;
a first transconductance amplifier that outputs the sink current according to the difference between the output of the first sample-and-hold unit and the resonance current detection signal;
a second sample and hold unit that holds the resonance current detection signal when the second switching element is switched on;
a second transconductance amplifier that outputs the source current according to the difference between the output of the second sample-and-hold unit and the resonance current detection signal;
(fifth configuration).

In the fifth configuration, the feedback current summing circuit level-shifts the resonance current detection signal, and outputs the level-shifted resonance current detection signal to the first sample-and-hold section, the first transconductance amplifier, A first level shift circuit that outputs to the second sample-hold section and the second transconductance amplifier may be provided (sixth configuration).

In any one of the second to sixth configurations, the output current generation circuit may
a first transistor;
a third resistor connected to one end of the first transistor;
a first error amplifier that receives the feedback voltage and the voltage of a third connection node where the first transistor and the third resistor are connected to drive the first transistor;
an upper current mirror that receives the current flowing through the first transistor and generates the first output current;
a lower current mirror that receives the output current of the upper current mirror and generates the second output current;
(seventh configuration).

In any one of the second to seventh configurations, the first voltage application section may be a voltage follower to which a second reference voltage is input (eighth configuration).

In any one of the second to eighth configurations, further comprising a second level shift circuit for level-shifting the resonance voltage detection signal and outputting it to each of the upper comparator and the lower comparator,
The first predetermined voltage may be the same as the center voltage of the resonance voltage detection signal after level shifting (ninth configuration).

Further, in any one of the first to ninth configurations, further comprising a counter,
The predetermined period may be a period during which the counter counts the number of drive signals for the first switching element and the number of the drive signals for the second switching element by a predetermined number (tenth configuration).

In any one of the first to tenth configurations, the LLC resonance converter includes a first capacitor having one end connected to a second connection node where the primary winding and the resonance capacitor are connected; a third resistor connected to the other end of the first capacitor,
The resonance current detection signal may be generated at a third connection node where the first capacitor and the third resistor are connected (eleventh configuration).

In any one of the first to eleventh configurations, the LLC resonance converter includes a second capacitor having one end connected to a second connection node where the primary winding and the resonance capacitor are connected; a third capacitor connected to the other end of the second capacitor,
The resonance voltage detection signal may be generated at a fourth connection node where the second capacitor and the third capacitor are connected (twelfth configuration).

Further, the power supply control device is any one of the first to twelfth configurations as an IC package, and includes a first external terminal to which the resonance current detection signal can be applied and a second external terminal to which the resonance voltage detection signal can be applied. The two external terminals may be included in a group of terminals with the same level of withstand voltage arranged along the same side of the IC package (13th configuration).

Further, in the thirteenth configuration, the third external terminal connectable via a diode to the application end of the AC voltage for generating the input voltage and the fourth external terminal which is a non-connection terminal are the same. A side may further include the fourth external terminal, and the fourth external terminal may be arranged between the terminal group and the third external terminal (14th configuration).

Another aspect of the present invention is an LLC resonant converter including the power control device having any one of the above configurations.

According to the power supply control device of the present invention, it is possible to suppress the ringing of the transformer in the LLC resonance converter in the burst operation.

1 is a circuit diagram showing the configuration of an AC/DC converter according to one embodiment of the present invention; FIG. 4 is a schematic diagram mainly showing a configuration for determining switching off timing in a power supply control IC; FIG. FIG. 3 is a circuit diagram showing a configuration example of an off-threshold generation circuit; FIG. 4 is a schematic diagram showing the relationship between the feedback voltage and the off-threshold; 4 is a timing chart for explaining a soft start function; FIG. 4 is a circuit diagram showing a configuration example of a feedback current summing circuit; 4 is a timing chart showing an example of level shift of a resonance current detection signal; 4 is a timing chart showing generation of sink current in the feedback current summing circuit; 4 is a timing chart showing generation of source currents in the feedback current summing circuit; 1 is a circuit diagram showing a configuration example of a power supply control IC; FIG. It is a circuit diagram which shows one structural example of an on-timing control part. 4 is a timing chart showing an operation example of an on-timing control unit; 4 is a timing chart showing signal waveforms when the load is light; 4 is a timing chart showing signal waveforms when the load is heavy; 4 is a timing chart showing a normal switching operation state; 4 is a timing chart showing a switching operation state immediately before shifting to a switching stop state; 4 is a timing chart showing burst operation according to one embodiment of the present invention; 3 is a circuit diagram showing the configuration of a power supply control IC according to a comparative example; FIG. 9 is a timing chart showing burst operation according to a comparative example; It is a circuit diagram which shows the structure of the power supply control IC which concerns on a modification.

An embodiment of the present invention will be described below with reference to the drawings.

<1. Overall configuration of AC/DC converter>
FIG. 1 is a circuit diagram showing the configuration of an AC/DC converter 5 according to one embodiment of the invention. The AC/DC converter 5 is roughly divided into a front-stage power factor correction circuit (PFC) 51 and a rear-stage LLC resonance converter 52 . The AC/DC converter 5 is applied to various power supplies such as consumer equipment (TV, PC, server, etc.) power supply, LED lighting power supply, industrial equipment power supply, OA equipment (laser printer, etc.) power supply.

The power factor correction circuit 51 is configured as a boost chopper circuit, and includes a diode bridge DB, an inductor L1, a diode D1, a capacitor C1, a switching element M1, a resistor R1, a resistor R2, and a PFC control IC1. have.

An AC voltage Vac is applied to the input end of the diode bridge DB. The output end of diode bridge DB is connected to one end of inductor L1. The other end of inductor L1 is connected to the anode of diode D1. A connection node between the inductor L1 and the diode D1 is connected to the drain of the switching element M1 configured as an n-channel MOSFET. The source of the switching element M1 is connected to the ground potential application terminal. The cathode of diode D1 is connected to one end of capacitor C1. The other end of the capacitor C1 is connected to the ground potential application end.

The PFC control IC1 controls on/off driving of the switching element M1. When the switching element M1 is turned on, energy is stored in the inductor L1, and when the switching element M1 is turned off, current flows from the inductor L1 to the output side through the diode D1, releasing the energy in the inductor L1.

The PFC control IC 1 is fed back with a voltage obtained by dividing the output voltage (=Vin) of the power factor correction circuit 51 generated on the cathode side of the diode D1 by the resistors R1 and R2, thereby performing PWM (pulse width modulation). The control drives the switching element M1. As a result, the peak of the inductor current flowing through the inductor L1 has the same waveform as the input voltage VI on the input side of the inductor L1, and the power factor can be improved.

An input voltage Vin as an output of the power factor correction circuit 51 is input to the LLC resonant converter 52 . LLC resonant converter 52 converts input voltage Vin to output voltage Vout. The LLC resonance converter 52 includes switching elements Q1 and Q2, a transformer Tr, a resonance capacitor Cr, diodes D11 and D12, a shunt regulator SR, a photocoupler PC, resistors R11 and R12, an output capacitor C10, and a power supply. and a control IC2.

LLC resonant converter 52 also includes resistors R3-R8, capacitors C2-C9, diodes D2-D5, and Zener diode Z1.

A power control IC (power control device) 2 controls the driving of the LLC resonance converter 52 . The power control IC 2 has various external terminals for establishing electrical connection with the outside. More specifically, the power supply control IC 2 has a VH terminal (pin 1), a non-connection terminal (pin 2), a PFC_IN terminal (pin 3), an FB terminal (pin 4), and a SET_SS terminal. (5th pin), ILLC terminal (6th pin), VLLC terminal (7th pin), SW terminal (8th pin), REG terminal (9th pin), VCC terminal (10th pin) , LO terminal (11th pin), GND terminal (12th pin), non-connection terminal (13th pin), HGND terminal (14th pin), HO terminal (15th pin), and HVCC terminal (16th pin) and .

The switching elements Q1 and Q2 are both configured as n-channel MOSFETs. An input voltage Vin is applied to the drain of the switching element Q1. The source of switching element Q1 is connected to the drain of switching element Q2. The source of the switching element Q2 is connected to the ground potential application end.

The transformer Tr has a primary winding Np, secondary windings Ns1 and Ns2, and an auxiliary winding Na. A connection node Ns to which switching elements Q1 and Q2 are connected is connected to one end of primary winding Np. The other end of the primary winding Np is connected to one end of the resonant capacitor Cr. The other end of resonance capacitor Cr is connected to the source of switching element Q2.

One end of secondary winding Ns1 is connected to the anode of diode D11. One end of secondary winding Ns2 is connected to the anode of diode D12. A connection node where the other end of the secondary winding Ns1 and the other end of the secondary winding Ns2 are connected is connected to an application end GND to which a ground potential is applied.

The cathode of diode D11 is connected to the cathode of diode D12. The cathode of the diode D11 is connected to the output terminal OUT together with one end of the capacitor C10. The other end of the capacitor C10 is connected to the application end GND. Thus, the secondary side of LLC resonance converter 52 is configured as a rectifying/smoothing circuit. An output voltage Vout is produced at the output terminal OUT.

Resistors R11 and R12 are connected in series between the output terminal OUT and the application terminal GND. A light-emitting element P1 included in the photocoupler PC and a shunt regulator SR are arranged between the output terminal OUT and the application terminal GND. The output terminal OUT is connected to the anode of the light emitting element P1. A cathode of the light emitting element P1 is connected to a cathode of the shunt regulator SR. The anode of the shunt regulator SR is connected to the application terminal GND.

The shunt regulator SR compares the divided voltage obtained by dividing the output voltage Vout by the resistors R11 and R12 with a reference voltage, and supplies a current between the cathode and the anode according to the difference between the divided voltage and the reference voltage. to occur. The generated current causes the light emitting element P1 to emit light. As a result, a feedback operation is performed in which the lower the output voltage Vout (the heavier the load), the smaller the light emission amount of the light emitting element P1.

A light receiving element P2 included in the photocoupler PC receives light output from the light emitting element P1. One end of the light receiving element P2 is connected to the FB terminal of the power supply control IC2, and the other end is connected to the ground potential application end. A feedback voltage Vfb is generated at the FB terminal by the current flowing through the light receiving element P2. With such a configuration, the output voltage Vout is fed back as the feedback voltage Vfb.

In the LLC resonance converter 52, the leakage inductance is increased by reducing the coupling coefficient of the transformer Tr, and the leakage inductance and the exciting inductance are used. Leakage inductance is used as a resonant inductor. A resonance inductor may be separately connected in series with the primary winding Np.

The upper switching element Q1 and the lower switching element Q2 are complementarily turned on and off by gate drive signals GH and GL, respectively. Note that the term “complementary” here includes a switching operation including a dead time, which is a period during which both switching elements are turned off. Also, the on-duty of both the switching elements Q1 and Q2 is approximately 50%.

One input of diode bridge DB is connected to the anode of diode D2 and the other input to the anode of diode D3. The cathodes of diodes D2 and D3 are connected to one end of resistor R3. The other end of resistor R3 is connected to the VH terminal. As a result, the AC voltage Vac is full-wave rectified by the diodes D2 and D3 and input to the VH terminal. The VH terminal is used to charge a capacitor C8, which will be described later, to start the power supply control IC2 at startup.

A PFC_IN terminal is connected to a connection node between the resistors R1 and R2.

The SET_SS terminal is connected to one end of the capacitor C5. The other end of the capacitor C5 is connected to the ground potential application end. Resistor R7 is connected in parallel with capacitor C5. The SET_SS terminal is used for soft start setting. Soft start will be described later.

A connection node N1 between the primary winding Np and the resonance capacitor Cr is connected to one end of the capacitor C3. The other end of capacitor C3 is connected to one end of resistor R6. The other end of the resistor R6 is connected to the ground potential application end. The ILLC terminal is connected to a connection node between capacitor C3 and resistor R6. A resonance current detection signal VIS obtained by converting the resonance current into a voltage signal is generated at the ILLC terminal.

The connection node N1 is also connected to one end of the capacitor C4. The other end of capacitor C4 is connected to one end of capacitor C6. The other end of the capacitor C6 is connected to the ground potential application end. The VLLC terminal is connected to a connection node between capacitors C4 and C6. A resonance voltage detection signal VCR is generated at the VLLC terminal.

The connection node Ns is connected to one end of the capacitor C2. The other end of capacitor C2 is connected to one end of resistor R4. The other end of resistor R4 is connected to one end of resistor R5. The other end of the resistor R5 is connected to the ground potential application end. A connection node between the resistors R4 and R5 is connected to the SW terminal. The SW terminal is connected to the cathode of the Zener diode Z1. The anode of the Zener diode Z1 is connected to the ground potential application end.

The switch voltage SW generated at the connection node Ns rises from 0V to the input voltage Vin or falls from the input voltage Vin to 0V due to charging or discharging of the parasitic capacitance when the switching elements Q1 and Q2 are both off. A switch voltage detection signal VSW that detects the rise and fall of such switch voltage SW is generated at the SW terminal. Note that the Zener diode Z1 clamps the switch voltage detection signal VSW with a forward voltage when the switch voltage detection signal VSW becomes negative.

The REG terminal is connected to one end of capacitor C9. The other end of the capacitor C9 is connected to the ground potential application end. An internal voltage Vreg is generated at the REG terminal.

The VCC terminal is connected to one end of capacitor C8. The other end of the capacitor C8 is connected to the ground potential application end. One end of the auxiliary winding Na is connected to the ground potential application end. The other end of auxiliary winding Na is connected to the anode of diode D5 via resistor R8. The cathode of diode D5 is connected to the connection node between the VCC terminal and capacitor C8. Thereby, the voltage generated by the auxiliary winding Na is rectified and smoothed by the diode D5 and the capacitor C8 to become the power supply voltage Vcc generated at the VCC terminal. The power supply voltage Vcc is also used as a power supply for the PFC control IC1.

The LO terminal is connected to the gate of switching element Q2. A gate of the switching element Q2 is driven by a gate drive signal GL output from the LO terminal. The GND terminal is connected to the ground potential application terminal.

The HGND terminal is connected to the connection node Ns. A capacitor C7 is connected between the HVCC terminal and the HGND terminal. The anode of diode D4 is connected to the connection node between the REG terminal and capacitor C9. The cathode of diode D4 is connected to the HVCC terminal. A capacitor C7 and a diode D4 are used for bootstrapping to generate a gate drive signal GH having a voltage higher than the drain voltage (=Vin) for turning on the switching element Q1.

The HO terminal is connected to the gate of switching element Q1. A gate of the switching element Q1 is driven by a gate drive signal GH output from the HO terminal.

<2. Return path configuration>
Next, the configuration of the feedback path in the power supply control IC 2 will be described in detail. FIG. 2 is a schematic diagram showing a main part of the configuration for determining the switching off timing in the power supply control IC 2. As shown in FIG.

As shown in FIG. 2 , the power supply control IC 2 has an off-threshold generation circuit 21 , a feedback current summing circuit 22 , a DC level shift circuit 23 , an upper comparator 24 and a lower comparator 25 .

The off-threshold generation circuit 21 generates the upper off-threshold VTHH and the lower off-threshold VTHL based on the feedback voltage Vfb generated at the FB terminal. The feedback current summing circuit 22 sums the resonance current detection signal VIS generated at the ILLC terminal with the upper OFF threshold VTHH to generate an upper OFF threshold VTHH', and sums the resonance current detection signal VIS with the lower OFF threshold VTHL. to generate the lower OFF threshold VTHL'.

The DC level shift circuit 23 level-shifts the resonance voltage detection signal VCR generated at the VLLC terminal, and outputs a level-shifted resonance voltage detection signal VCR'. The resonance voltage detection signal VCR' is input to the non-inverting input terminal (+) of the upper comparator 24, and the upper off-threshold value VTHH' is input to the inverting input terminal (-). The upper comparator 24 outputs an upper OFF signal H_OFF switched from Low to High at the timing when the resonance voltage detection signal VCR' exceeds the upper OFF threshold VTHH'. At this time, the switching element Q1 is turned off from on.

On the other hand, the resonance voltage detection signal VCR' is input to the inverting input terminal of the lower comparator 25, and the lower off-threshold value VTHL' is input to the non-inverting input terminal. The lower comparator 25 outputs the lower OFF signal H_OFF switched from Low to High at the timing when the resonance voltage detection signal VCR' falls below the upper OFF threshold VTHH'. At this time, the switching element Q2 is turned off from on.

This feedback configuration determines the off timing of the switching elements Q1 and Q2, and controls the output voltage Vout to match the target value. Particularly in this embodiment, since the feedback path includes information on the resonance current, the load response of the LLC resonance converter 52 becomes faster, and the phase compensation design becomes easier.

<3. Configuration of OFF Threshold Generation Circuit>
Next, a specific configuration example of the off-threshold generation circuit 21 described above will be described. FIG. 3 is a circuit diagram showing a configuration example of the off-threshold generation circuit 21. As shown in FIG.

The off-threshold generation circuit 21 shown in FIG. 3 has an output current generation circuit 211, a resistor R21, a constant current source CI21, a transconductance amplifier TA21, a resistor R212, a resistor R213, and an operational amplifier A21.

A predetermined power supply voltage V21 is applied to one end of the resistor R21, and the other end is connected to the FB terminal. A current flows through the resistor R21 according to the current flowing through the light receiving element P2, and the feedback voltage Vfb is generated.

The output current generation circuit 211 is a circuit that generates the upper side output current IoH and the lower side output current IoL based on the feedback voltage Vfb. The output current generation circuit 211 has, for example, an error amplifier EA21, a transistor M21, a resistor R211, an upper current mirror PM, and a lower current mirror NM.

A feedback voltage Vfb is applied to one non-inverting input terminal of the error amplifier EA21, and a predetermined reference voltage V211 is applied to the other non-inverting input terminal. The output terminal of the error amplifier EA21 is connected to the gate of the transistor M21 configured as an n-channel MOSFET. The source of the transistor M21 is connected to the ground potential application end via the resistor R211. A connection node N211 between the source of the transistor M21 and the resistor R211 is connected to the inverting input terminal of the error amplifier EA21.

The error amplifier EA21 compares the higher one of the voltages applied to the two non-inverting inputs with the voltage at the inverting input. Thereby, when the feedback voltage Vfb is higher than the reference voltage V211, the voltage of the connection node N211 is controlled to be the feedback voltage Vfb, and otherwise, the voltage of the connection node N211 is controlled to be the reference voltage V221. be done. Therefore, the reference voltage V211 defines the lowest value of the voltage of the connection node N211.

The drain of transistor M21 is connected to the input end of upper current mirror PM. One output end of upper current mirror PM is connected to the input end of lower current mirror NM, and the other output end is connected to one end of resistor R212 at connection node NH. An output end of the lower current mirror NM is connected to one end of the resistor R213 at a connection node NL.

Current I211 flows through resistor R211 according to the voltage of connection node N211. Upper current mirror PM receives current I211 and outputs current I212 and upper output current IoH. The lower current mirror NM receives the current I212 and outputs the lower output current IoL.

A connection node NC between the resistor R212 and the resistor R213 is connected to the output terminal of the operational amplifier A21. A predetermined reference voltage V212 is applied to the non-inverting input terminal of the operational amplifier A21. The output terminal of the operational amplifier A21 is connected to the inverting input terminal of the operational amplifier A21. Since the voltage follower is configured by the operational amplifier A21 in this way, the same voltage Vnc as the reference voltage V212 is generated at the connection node NC.

At the connection node NH, a voltage higher than the voltage Vnc by the voltage drop across the resistor R212 corresponding to the upper output current IoH is generated as the upper OFF threshold VTHH (FIG. 2). At the connection node NL, a voltage lower than the voltage Vnc by the voltage drop across the resistor R213 corresponding to the lower output current IoL is generated as the lower OFF threshold VTHL (FIG. 2).

As a result, as schematically shown in FIG. 4, the higher the feedback voltage Vfb, the greater the deviation between the upper off-threshold value VTHH and the lower off-threshold value VTHL around the voltage Vnc (=V212).

Further, in the configuration shown in FIG. 3, the non-inverting input terminal of the transconductance amplifier TA21 is connected to the SET_SS terminal. A constant current from the constant current source CI21 flows into the connection node between the transconductance amplifier TA21 and the SET_SS terminal. The output terminal of the transconductance amplifier TA21 is connected to the connection node between the FB terminal and the resistor R21, and is also connected to the inverting input terminal of the transconductance amplifier TA21. The transconductance amplifier TA21 only sinks the sink current IS21 to the output terminal and does not discharge the source current from the output terminal.

The configuration using such a transconductance amplifier TA21 is intended for soft start, and the soft start will be described with reference to the timing chart of FIG. The waveform of the output voltage Vout and the waveform of the feedback voltage Vfb1 shown in FIG. 5 show the case where the soft start function is not provided. In this case, when the power supply control IC 2 is activated at timing ts, the feedback voltage Vfb1 rises from 0V to the power supply voltage V21, and the output voltage Vout rises from 0V.

At the timing te when the output voltage Vout reaches the target value REF, the feedback voltage Vfb1 drops to a stable value, but the drop takes time, so an overshoot OS occurs in the output voltage Vout as shown in FIG. do.

On the other hand, in this embodiment, the constant current source CI21 starts charging the capacitor C5 externally connected to the SET_SS terminal from the start timing ts, and the voltage Vss (FIG. 5) generated at the SET_SS terminal starts to rise. do. At this time, even if the feedback voltage Vfb (Vfb2 in FIG. 5) tries to become higher than the voltage Vss, the sink current IS21 is absorbed by the transconductance amplifier TA21 so that the feedback voltage Vfb is controlled to match the voltage Vss. Therefore, the voltage Vss and the feedback voltage Vfb increase while matching.

After the feedback voltage Vfb reaches the stable value Vs, even if the voltage Vss further increases, the feedback voltage Vfb maintains the stable value Vs, so that the voltage Vss and the feedback voltage Vfb diverge. At this time, the overshoot of the output voltage Vout is suppressed.

<4. Configuration of Feedback Current Summing Circuit>
Next, a specific configuration example of the above feedback current summing circuit 22 will be described. FIG. 6 is a circuit diagram showing a configuration example of the feedback current summing circuit 22. As shown in FIG.

The feedback current summing circuit 22 shown in FIG. 6 includes resistors R221 to R224, an error amplifier 221, a capacitor C221, a transconductance amplifier 222, a capacitor C222, a transconductance amplifier 223, a switch SW221, a switch SW222, have

A resistor R221 and a resistor R222 are connected in series between the terminal to which the predetermined power supply voltage V22 is applied and the ILCC terminal. A connection node between the resistors R221 and R222 is connected to the non-inverting input terminal of the error amplifier 221 . Resistors R223 and R224 are connected in series between the output end of the error amplifier 221 and the ground potential application end. A connection node between the resistors R223 and R224 is connected to the inverting input terminal of the error amplifier 221 .

As a result, for example, if the resistance ratio between the resistors R221 and R222 is 1:1 and the resistance ratio between the resistors R223 and R224 is also 1:1, the error amplifier At the output end of 221, a resonance current detection signal VIS' centered at the same voltage as the power supply voltage V22 (2 V as an example in FIG. 7) is generated. That is, the resonance current detection signal VIS is level-shifted to the resonance current detection signal VIS'.

The output terminal of the error amplifier 221 is connected to the inverting input terminal of the transconductance amplifier 222 and also connected to the non-inverting input terminal of the transconductance amplifier 222 via the switch SW221. A connection node between the switch SW221 and the transconductance amplifier 222 is connected to one end of the capacitor C221. The other end of the capacitor 221 is connected to the ground potential application end. The switch SW221 and the capacitor 221 constitute a sample hold circuit.

As shown in the timing chart of FIG. 8, at timing t81 when the gate drive signal GH is switched from Low to High and the switching element Q1 is switched from off to on, the switch SW221 is switched from on to off. A voltage V222 generated at the non-inverting input terminal of 222 is held at the value of the resonance current detection signal VIS' at the switching timing. On the other hand, the resonance current detection signal VIS' is directly input to the inverting input terminal of the transconductance amplifier 222 (broken line in FIG. 8).

The transconductance amplifier 222 sinks a sink current I222 having a current value proportional to the difference ΔVH between the voltage at the non-inverting input terminal and the voltage at the inverting input terminal. Therefore, as shown in FIG. 8, as the difference ΔVH increases from timing t81, the sink current I222 increases.

At timing t82 when the gate drive signal GH is switched from High to Low and the switching element Q1 is switched from ON to OFF, the switch SW221 is switched from OFF to ON. As a result, the voltage V222 matches the resonance current detection signal VIS'. Therefore, the difference ΔVH becomes zero, and the sink current I222 stops flowing.

On the other hand, the output terminal of the error amplifier 221 is connected to the inverting input terminal of the transconductance amplifier 223 and also connected to the non-inverting input terminal of the transconductance amplifier 223 via the switch SW222. A connection node between the switch SW222 and the transconductance amplifier 223 is connected to one end of the capacitor C222. The other end of the capacitor 222 is connected to the ground potential application end. The switch SW222 and the capacitor 222 constitute a sample hold circuit.

As shown in the timing chart of FIG. 9, at timing t91 when the gate drive signal GL is switched from Low to High and the switching element Q2 is switched from off to on, the switch SW222 is switched from on to off. A voltage V223 generated at the non-inverting input terminal of 223 is held at the value of the resonance current detection signal VIS' at the switching timing. On the other hand, the resonance current detection signal VIS' is directly input to the inverting input terminal of the transconductance amplifier 223 (broken line in FIG. 9).

The transconductance amplifier 223 discharges a source current I223 having a current value proportional to the difference ΔVL between the voltage at the non-inverting input terminal and the voltage at the inverting input terminal. Therefore, as shown in FIG. 9, as the difference ΔVL increases from timing t91, the source current I223 increases.

At timing t92 when the gate drive signal GL is switched from High to Low and the switching element Q2 is switched from ON to OFF, the switch SW222 is switched from OFF to ON. As a result, the voltage V223 matches the resonance current detection signal VIS'. Therefore, the difference ΔVL becomes zero, and the source current I223 stops flowing.

<5. Determining Off Timing of Switching Element>
FIG. 10 is a circuit diagram showing a more specific internal configuration of the power supply control IC2. As shown in FIG. 10, in the power supply control IC 2, the off-threshold generation circuit 21 and the feedback current summing circuit 22 are connected. More specifically, the connection node NH and the output end of the transconductance amplifier 222 are connected at the connection node NH2, and the connection node NL and the output end of the transconductance amplifier 223 are connected at the connection node NL2.

An upper off-threshold VTHH' (FIG. 2) is generated at the connection node NH2, and a lower off-threshold VTHL' (FIG. 2) is generated at the connection node NL2.

When the sink current I222 does not flow, the upper off-threshold VTHH' matches the upper off-threshold VTHH because the upper output current IoH flows through the resistor R212 as it is. As the amount of the sink current I222 flowing increases, the current flowing through the resistor R212 decreases, so the upper off-threshold VTHH' becomes lower than the upper off-threshold VTHH.

When the source current I223 does not flow, the lower output current IoL flows through the resistor R213 as it is, and the lower OFF threshold VTHL' matches the lower OFF threshold VTHL. As the amount of the source current I223 flowing increases, the current flowing through the resistor R213 decreases, so that the lower off-threshold VTHL' rises above the lower off-threshold VTHL.

Here, as shown in FIG. 10, the DC level shift circuit 23 (FIG. 2) is configured by series connection of resistors R231 and R232 between the application terminal of the power supply voltage V23 and the application terminal of the ground potential. be. A connection node N23 between the resistors R231 and R232 is connected to the VLLC terminal.

The resonance voltage detection signal VCR centered on 0 V generated at the VLLC terminal by the DC level shift circuit 23 is changed to the resonance voltage detection signal VCR centered on the voltage obtained by dividing the power supply voltage V23 by the resistors R231 and R232. ' is level-shifted.

The connection node N 23 is connected to the non-inverting input terminal of the upper comparator 24 and to the inverting input terminal of the lower comparator 25 . The connection node NH2 is connected to the inverting input terminal of the upper comparator 24, and the connection node NL2 is connected to the non-inverting input terminal of the lower comparator 25. FIG. As a result, the upper comparator 24 compares the resonance voltage detection signal VCR' with the upper OFF threshold VTHH', and outputs the upper OFF signal H_OFF as a comparison result. Further, the lower comparator 25 compares the resonance voltage detection signal VCR' with the lower OFF threshold VTHL', and outputs the lower OFF signal L_OFF as a comparison result.

An output terminal of the upper comparator 24 is connected to one input terminal of the AND circuit A1. The other input terminal of AND circuit A1 is connected to the output terminal of falling edge detection section 27 . Since the output of the falling edge detector 27 is High in the switching operation state, the output of the AND circuit A1 corresponds to the level of the upper OFF signal H_OFF. The output terminal of the AND circuit A1 is connected to the reset terminal of the upper D flip-flop DH. A gate drive signal GH is output from the Q output terminal of the upper D flip-flop DH. A gate drive signal GH is applied to the gate of the switching element Q1 via the HO terminal.

As a result, when the resonance voltage detection signal VCR' exceeds the upper OFF threshold value VTHH', the upper comparator 24 switches the upper OFF signal H_OFF to High, resets the upper D flip-flop DH, and switches the gate drive signal GH to Low. and the switching element Q1 is switched off.

The output terminal of the lower comparator 25 is connected to one input terminal of the AND circuit A2. The other input terminal of AND circuit A2 is connected to the output terminal of falling edge detection section 27 . As will be described later, the output of the falling edge detector 27 is High in the switching operation state, so the output of the AND circuit A2 corresponds to the level of the lower side off signal H_OFF. The output terminal of the AND circuit A2 is connected to the reset terminal of the lower D flip-flop DL. A gate drive signal GL is output from the Q output terminal of the lower D flip-flop DL. A gate drive signal GL is applied to the gate of the switching element Q2 via the LO terminal.

As a result, when the resonance voltage detection signal VCR' falls below the lower-side OFF threshold value VTHL', the lower-side comparator 25 switches the lower-side OFF signal L_OFF to High, resets the lower-side D flip-flop DL, and resets the gate drive signal GL. is switched low and switching element Q2 is switched off.

<6. Determining ON Timing of Switching Element>
Also, as shown in FIG. 10, the power supply control IC 2 has a configuration for controlling the ON timing of switching. The on-timing control section 26 outputs an upper-side on-signal QH and a lower-side on-signal QL. The upper ON signal QH is input to one input terminal of the AND circuit A3, and the output of the minimum dead time section DT1 is input to the other input terminal via the inverter IV1.

An output terminal of the AND circuit A3 is connected to one input terminal of the OR circuit OR1. The other input terminal of the OR circuit 1 is connected to the output terminal of the rising edge detector 28 . Since the output of the rising edge detector 28 is Low in the switching operation state, the output of the OR circuit OR1 corresponds to the output level of the AND circuit A3. The output terminal of the OR circuit OR1 is connected to the clock terminal of the upper D flip-flop DH.

When the minimum dead time unit DT1 detects that the gate drive signal GL is switched to Low, it starts counting, and after counting a predetermined period corresponding to the minimum dead time, inputs the output switched to Low to the inverter IV1. Even if the on-timing control unit 26 switches the upper ON signal QH to High, if the predetermined period has not yet been counted, the signal input from the inverter IV1 to the AND circuit A3 is Low. output is held low. After that, when the predetermined period is counted, the output of the inverter IV1 is switched to High, so the output of the AND circuit A3 is switched to High. When the upper ON signal QH is switched to High after counting the predetermined period, the output of the AND circuit A3 is switched to High at that time.

When the output of the AND circuit A3 is switched to High, the gate drive signal GH output from the Q output terminal of the upper D flip-flop DH is switched to High, and the switching element Q1 is switched to ON. In this way, the dead time (simultaneous OFF period) from when the switching element Q2 is turned off until when the switching element Q1 is turned on is adjusted, and the dead time is ensured to be equal to or longer than the minimum dead time.

The lower ON signal QL is input to one input terminal of the AND circuit A4, and the output of the minimum dead time section DT2 is input to the other input terminal via the inverter IV2. The output terminal of the AND circuit A4 is connected to the clock terminal of the lower D flip-flop DL.

When the minimum dead time unit DT2 detects that the gate drive signal GH is switched to Low, it starts counting, and after counting a predetermined period corresponding to the minimum dead time, inputs the output switched to Low to the inverter IV2. Even if the lower ON signal QL is switched to High by the ON-timing control unit 26, if the predetermined period has not yet been counted, the signal input from the inverter IV2 to the AND circuit A4 is Low. The output of A4 is held low. After that, when the predetermined period is counted, the output of the inverter IV2 is switched to High, so the output of the AND circuit A4 is switched to High. When the lower ON signal QL is switched to High after counting the predetermined period, the output of the AND circuit A4 is switched to High at that time.

When the output of the AND circuit A4 is switched to High, the gate drive signal GL output from the Q output terminal of the lower D flip-flop DL is switched to High, and the switching element Q2 is switched to ON. In this manner, the dead time from when the switching element Q1 is turned off until when the switching element Q2 is turned on is adjusted, and the dead time is ensured to be equal to or longer than the minimum dead time.

<7. Configuration of ON Timing Control Unit>
Next, a specific configuration of the on-timing control section 26 will be described. FIG. 11 is a circuit diagram showing a configuration example of the on-timing control section 26. As shown in FIG.

As shown in FIG. 11 , the on-timing control section 26 has a transistor 261 , comparators 262 and 263 , inverters 264 and 265 , D flip-flops 266 and 267 , and AND circuits 268 and 269 .

The drain of the transistor 261, which is an n-channel MOSFET, is connected to the SW terminal. A reference voltage V261 is applied to the gate of the transistor 261 . The source of transistor 261 is connected to the inverting input of comparator 263 as well as the non-inverting input of comparator 262 .

A reference voltage V262 is applied to the inverting input terminal of the comparator 262 . The output end of comparator 262 is connected to the input end of inverter 264 . The output of inverter 264 is connected to the clock terminal of D flip-flop 266 . A ground potential is applied to the non-inverting input terminal of the comparator 263 . The output terminal of the comparator 263 is connected to the input terminal of the inverter 265 . The output end of inverter 265 is connected to the clock terminal of D flip-flop 267 .

The output end of inverter 264 is connected to one input end of AND circuit 269 . The output end of inverter 265 is connected to one input end of AND circuit 268 . The output CT output from the counter 29 shown in FIG. 10 is input to the other input terminals of the AND circuits 268 and 269 . The output terminal of AND circuit 268 is connected to the reset terminal of D flip-flop 266 . The output terminal of the AND circuit 269 is connected to the reset terminal of the D flip-flop 267 .

The Q output terminal of the D flip-flop 266 outputs the upper ON signal QH, and the Q output terminal of the D flip-flop 267 outputs the lower ON signal QL.

The operation of the on-timing control section 26 will be described using the timing chart shown in FIG. Note that FIG. 12 shows the switch voltage SW, the switch voltage detection signal VSW, the upper ON signal QH, and the lower ON signal QL in order from the top.

At timing t121 when both the switching elements Q1 and Q2 are turned off by turning off the switching element Q2, the switch voltage SW starts rising from 0 V due to the charging of the parasitic capacitance by the resonance current. Then, at timing t122, the switch voltage SW reaches the input voltage Vin (hereinafter, 400 V as an example). At this time, at timing t121, the switch voltage detection signal VSW rises from 0V to a predetermined voltage Vin' after being divided by resistors R4 and R5, and falls to 0V at timing t122.

The transistor 261 limits the switch voltage detection signal VSW input to the drain to a predetermined voltage lower than the reference voltage V261 by the threshold voltage Vgs between the gate and the source. Therefore, the switch voltage detection signal VSW of the voltage Vin' is limited to the predetermined voltage. Comparator 262 compares the limited signal with reference voltage V262. As a result, at timing t121, the output of the comparator 262 is switched to High, and the output of the AND circuit 269 is switched to Low. As will be described later, since the output CT is High in the switching operation state, the outputs of the AND circuits 268 and 269 correspond to the output levels of the inverters 265 and 264. FIG. Therefore, the D flip-flop 267 is reset and the lower ON signal QL is switched to Low.

Then, at timing t122, the output of the inverter 264 is switched to High, and the upper ON signal QH output from the D flip-flop 266 is switched to High. As a result, the switching element Q1 is turned on when the switch voltage SW reaches 400 V, so hard switching of the switching element Q1 can be avoided.

After timing t122, the switch voltage SW is maintained at 400 V, and the switching element Q1 is turned off at timing t123, thereby turning off both the switching elements Q1 and Q2. At this time, the resonance current starts discharging the parasitic capacitance, and the switch voltage SW starts falling from 400V. Then, at timing t124, the switch voltage SW reaches 0V. At this time, the switch voltage detection signal VSW falls from 0V to -Vf (Vf: forward voltage) by clamping the Zener diode Z1 at timing t123, and rises to 0V at timing t124.

As a result, at timing t123, the output of the comparator 263 is switched to High, and the output of the AND circuit 268 is switched to Low. Therefore, the D flip-flop 266 is reset and the upper ON signal QH is switched to Low. At timing t124, the output of the inverter 265 is switched to High, and the lower ON signal QL output from the D flip-flop 267 is switched to High. As a result, the switching element Q2 is turned on when the switch voltage SW reaches 0V, so hard switching of the switching element Q2 can be avoided.

After timing t124, the switch voltage SW is maintained at 0 V, and when the switching element Q2 is turned off at timing t125 and both the switching elements Q1 and Q2 are turned off, the switch voltage SW starts rising from 0 V as described above. .

<8. Waveform example in switching operation>
Here, FIG. 13 is a timing chart showing each signal waveform when the load of the LLC resonance converter 52 is light. FIG. 14 is a timing chart showing each signal waveform when the load of LLC resonance converter 52 is heavy. 13 and 14 show, in order from the top, the resonance voltage detection signal VCR, the resonance voltage detection signal VCR', the resonance current detection signal VIS, and the gate drive signals GH and GL. Note that the resonance voltage detection signal VCR' is shown together with the upper off-threshold value VTHH' and the lower off-threshold value VTHL'.

Also, the resonance voltage detection signal VCR' is an example in which the center of the resonance voltage detection signal VCR is level-shifted from 0V to 2V. That is, this is the case where the power supply voltage V23 (FIG. 10) is 4V and the resistance ratio between the resistors R231 and R232 is 1:1. Also, the voltage Vnc (=V212) is set to 2V as an example.

In the heavy load case shown in FIG. 14, the value of the feedback voltage Vfb is higher than in the light load case shown in FIG. In both FIGS. 13 and 14, when the gate drive signal GH is switched to the ON level (High), the sink current I222 begins to flow and the upper OFF threshold VTHH' is lowered. Then, the gate drive signal GH is switched to the off level (Low) at the timing when the resonance voltage detection signal VCR' exceeds the upper off threshold value VTHH'. Also, in both FIGS. 13 and 14, when the gate drive signal GL is switched to the ON level (High), the source current I223 begins to flow and the lower OFF threshold VTHL' rises. Then, the gate drive signal GL is switched to the off level (Low) at the timing when the resonance voltage detection signal VCR' falls below the lower off threshold VTHL'.

<9. Burst operation>
Also, the power supply control IC 2 shown in FIG. 10 has a configuration for performing a burst operation. Specifically, the power control IC 2 has a comparator CP1, a counter 29, a falling edge detector 27, a rising edge detector 28, and an OR circuit OR2.

A non-inverting input terminal of the comparator CP1 is connected to the FB terminal. The comparator CP1 is a hysteresis comparator that compares the feedback voltage Vfb generated at the FB terminal with the first threshold th1 and the second threshold th2. First threshold th1<second threshold th2, the first threshold th1 is set to 0.1 V, and the second threshold th2 is set to 0.15 V, for example.

When the output voltage Vout of the LLC resonant converter 52 becomes equal to or lower than the target voltage, the feedback voltage Vfb exceeds the second threshold th2, and the output BST of the comparator CP1 is switched to High. Then, the counter 29 outputs the output CT switched to High to the rising edge detection section 28 and the on-timing control section 26 . When the rising edge detection unit 28 detects the rise of the output CT, it rises from Low to High and then immediately falls to Low to output to the OR circuit OR1. As a result, the gate drive signal GH output from the upper D flip-flop DH is switched to High, shifting to the switching operation state. At this time, in the on-timing control unit 6, the outputs of the inverters 265 and 264 input to the AND circuits 268 and 269 are validated by the output CT that has risen to High.

Also, when the output BST is switched to High as described above, the transconductance amplifier 222 sets the sink current I222 to a normal current amount, and the transconductance amplifier 223 sets the source current I223 to a normal current amount.

Then, when the output voltage Vout rises and exceeds the target voltage, the feedback voltage Vfb starts to drop. When the feedback voltage Vfb falls below the first threshold th1, the output BST is switched to Low. Then, the counter 29 starts counting the number of pulses of the gate drive signal based on the output of the OR circuit OR2 to which the gate drive signals GH and GL are input.

When the output BST is switched to Low as described above, the transconductance amplifier 222 sets the sink current I222 to n times the normal current amount, and the transconductance amplifier 223 sets the source current I223 to n times the normal current amount. set in quantity. Note that n is a value greater than 1 and is set to 3, for example.

When the counter 29 counts m pulses, it switches the output CT to Low. Note that m can be any value from 4 to 32, for example, 8. Then, the falling edge detection unit 27 detects the fall of the output CT, and outputs an output that instantaneously rises to High after falling from High to Low to the AND circuits A1 and A2. As a result, the upper D flip-flop DH and the lower D flip-flop DL are reset, the gate drive signals GH and GL are set to Low, and the switching is stopped. At this time, the output CT switched to Low causes the outputs of the AND circuits 268 and 269 to be Low in the on-timing control unit 26, the upper ON signal QH and the lower ON signal QL to be Low, and the gate drive signal Prevents GH and GL from becoming High.

Then, when the output voltage Vout drops and becomes equal to or lower than the target voltage, the feedback voltage Vfb exceeds the second threshold th2, and the state shifts to the switching operation state again as described above. In this manner, a burst operation is performed in which switching operations are performed intermittently.

FIG. 15 is a timing chart showing the upper off-threshold VTHH' and the lower off-threshold VTHL' with respect to the resonance voltage detection signal VCR' when the sink current I222 and the source current I223 are normal current amounts. FIG. 16 is a timing chart showing the upper off-threshold value VTHH' and the lower off-threshold value VTHL' with respect to the resonance voltage detection signal VCR' when the sink current I222 and the source current I223 are n times the normal amount. is.

As shown in FIG. 16, when the sink current I222 and the source current I223 are n times the normal current amount, the lower off-threshold value VTHH' falls faster and the lower off-threshold value VTHL' rises faster. The timing is advanced and the switching frequency is increased. In this embodiment, as described above, even if the output BST is switched to Low, the output CT does not become Low immediately, and the sink current I222 and the source current I223 is made n times the normal current amount, and the switching frequency is increased. As a result, the resonance current can be gradually reduced, and the ringing that occurs in the transformer Tr can be suppressed.

Moreover, in order to explain the effect of this embodiment, a comparison with a comparative example will be shown. FIG. 18 is a circuit diagram showing the configuration of the power supply control IC 2 according to the comparative example. In the configuration of FIG. 18, the difference from the configuration according to the present embodiment (FIG. 10) is that the output BST of the comparator CP1 is directly applied to the falling edge detection section 27, the rising edge detection section 28, and the on-timing control section 26. to enter.

FIG. 19 shows a timing chart showing a burst operation with such a configuration according to the comparative example. FIG. 19 shows gate drive signals GH, GL, output BST, resonance voltage detection signal VCR', resonance current I_LLC, and feedback voltage Vfb in order from the top. Note that the resonance voltage detection signal VCR' is shown together with the upper off-threshold value VTHH' and the lower off-threshold value VTHL'.

When the feedback voltage Vfb exceeds the second threshold at timing t191 and the output BST is switched to High, the gate drive signal GH is set to High by the rising edge detector 28, and the switching operation state is entered. Then, when the feedback voltage Vfb drops and falls below the first threshold th1 at timing t192, the output BST is switched to Low. Then, the gate drive signals GH and GL are set to Low by the falling edge detector 27, and the switching is stopped.

In this case, the resonance current I_LLC abruptly decreases at the time of transition to the switching stop state, which causes noise in the transformer Tr.

On the other hand, FIG. 17 shows a timing chart showing burst operation by the configuration (FIG. 10) of this embodiment. Note that FIG. 17 also shows the output CT in addition to the output BST. In this embodiment, even if the output BST switches to Low at timing t172 after transitioning to the switching operation state at timing t171, the output CT is maintained at High, and the counter 29 starts counting the gate drive signals GH and GL. be done. When m (here, 8) pulses of the gate drive signal are counted, the output CT is switched to Low at timing t173, the gate drive signals GH and GL are set to Low, and the switching is stopped.

During counting of the gate drive signal (timing t172 to t173), the amount of current by the transconductance amplifiers 222 and 223 is increased, the switching frequency is increased, and the resonance current I_LLC is gradually decreased. As a result, noise generated in the transformer Tr can be suppressed.

<10. Variation>
FIG. 20 is a circuit diagram showing the configuration of the power supply control IC 2 according to one modification. The configuration of the modification shown in FIG. 20 differs from the configuration shown in FIG. 10 in that constant current sources CI222 and CI223 are provided.

Constant current source CI 222 draws constant current from a line that sinks current I 222 with transconductance amplifier 222 . A constant current source CI223 applies a constant current to a line that sources a current I223 through a transconductance amplifier 223.

When the output BST is High, the constant current sources CI222 and CI223 do not flow current, and when the output VST is Low, the constant current sources CI222 and CI223 flow constant current. As a result, when the feedback voltage Vfb falls below the first threshold th1 and the output BST is switched to Low, a constant current is added to the sink current I222 and the source current I223, thereby increasing the upper OFF threshold VTHH'. The amount of fall and the amount of rise of the lower-side off-threshold VTHL' are increased, the off-timing is advanced, and the switching frequency is increased. That is, the switching frequency can be increased by a method different from the configuration shown in FIG.

<11. Terminal Arrangement of Power Supply Control IC>
Here, the terminal arrangement of the power control IC 2 (FIG. 1) will be described. In the following description, the terminals are described as the 1st pin to the 16th pin.

FIG. 1 is a top view of a power supply control IC 2 as an IC package. In the power control IC 2, an IC chip is fixed to a support (copper frame or the like). The IC chip is connected to a lead frame (copper frame or the like) and an Au wire or the like. The 1st to 16th pins shown in FIG. 1 are configured as a lead frame. The support, IC chip, and lead frame are sealed with a sealing material such as molding resin.

In the power control IC 2, which has a rectangular shape as viewed from above, the 1st to 8th pins are arranged in order along the first side, and the 9th to 16th pins are arranged in order along the second side opposite to the first side. be done. The 1st to 8th pins are opposed to the 16th to 9th pins in a one-to-one manner.

The 1st and 14th to 16th pins are terminals to which a voltage rising up to about 400 V, for example, is applied, and are high withstand voltage terminals. The 2nd to 8th pins are terminals with a low withstand voltage (for example, 10 V or less). The 9th to 11th pins are terminals with a medium withstand voltage (for example, 40 V or less).

Since the voltage is directly input to the 1st pin from the terminal to which the AC voltage Vac is applied, the adjacent 2nd pin is used as a non-connecting terminal and is separated from the 3rd pin.

The 3rd to 8th pins are arranged as a group at the lower side of the paper on the first side in order to avoid adjacent short-circuiting between the high-voltage terminal and the medium-voltage terminal.

As for the 9th to 11th pins, the 13th pin is used as a non-connection terminal in order to avoid a short circuit with a high withstand voltage terminal.

Since the 14th to 16th pins are high voltage terminals, they are arranged as a group on the upper side of the paper on the second side in order to avoid adjacent short circuits between the intermediate voltage terminals and the low voltage terminals. However, since the voltage difference between the 14th to 16th pins is only about 30 V, there is no problem even if the pins are shorted.

Although the embodiments of the present invention have been described above, various modifications of the embodiments are possible within the scope of the present invention.

INDUSTRIAL APPLICABILITY The present invention can be used for LLC resonance converters used as power sources for various devices.

1 PFC control IC
2 power control IC
21 OFF threshold generation circuit 211 output current generation circuit 22 feedback current summing circuit 221 error amplifier 222, 223 transconductance amplifier 23 DC level shift circuit 24 upper comparator 25 lower comparator 26 ON timing control unit 261 transistor 262, 263 comparator 264, 265 Inverters 266, 267 D flip-flops 268, 269 AND circuit 27 Falling edge detector 28 Rising edge detector 29 Counter 5 AC/DC converter 51 Power factor correction circuit 52 LLC resonance converter DB Diode bridge L1 Inductor D1 to D5 Diode M1 Switching Element R1~R8 Resistor C1~C9 Capacitor Z1 Zener diode Q1, Q2 Switching element Cr Resonant capacitor Tr Transformer Np Primary winding Ns1, Ns2 Secondary winding Na Auxiliary winding D11, D12 Diode PC Photocoupler P1 Light emitting element P2 Light receiving Element SR Shunt regulator C10 Output capacitor R11, R12 Resistor DH Upper D flip-flop DL Lower D flip-flop CP1 Comparator A1 to A4 AND circuit IV1, IV2 Inverter OR1, OR2 OR circuit DT1, DT2 Minimum dead time part CI222, CI223 Constant current source

Claims (15)

a first switching element to one end of which an input voltage is applied;
a second switching element having one end connected to the other end of the first switching element;
a primary winding and a resonant capacitor connected in series between a first connection node where the first switching element and the second switching element are connected, and the other end of the second switching element;
A power supply control device that drives and controls an LLC resonance converter having
an off-threshold generation circuit that generates an upper off-threshold and a lower off-threshold based on a feedback voltage obtained by feeding back the output voltage of the LLC resonant converter;
a feedback current summing circuit for summing a resonance current detection signal to each of the upper off-threshold and the lower off-threshold;
an upper comparator that compares the upper off threshold after summation by the feedback current summing circuit with the resonance voltage detection signal and outputs an upper off signal for turning off the first switching element;
a lower comparator that compares the lower off threshold after summing by the feedback current summing circuit with the resonance voltage detection signal and outputs a lower off signal for turning off the second switching element;
a hysteresis comparator that compares the feedback voltage with first and second thresholds;
has
When the hysteresis comparator detects that the feedback voltage exceeds the second threshold value, the switching operation state is shifted to the switching operation state by the first switching element and the second switching element, and the feedback voltage is switched during the switching operation state. exceeds the first threshold value, the summed amount by the feedback current summing circuit is changed for a predetermined period of time, and when the predetermined period of time elapses, switching is switched to a stopped state. , power control unit. The off-threshold generation circuit is
a first resistor;
a second resistor;
a first voltage application unit that applies a first predetermined voltage to a second connection node to which one end of the first resistor and one end of the second resistor are connected;
an output current generating circuit for generating a first output current flowing through the other end of the first resistor and a second output current flowing through the other end of the second resistor based on the feedback voltage;
has
2. The power supply control according to claim 1, wherein said feedback current summing circuit sucks a sink current from the other end of said first resistor and discharges a source current to the other end of said second resistor based on said resonance current detection signal. Device. 3. The power supply control device according to claim 2, wherein the current amount of said sink current and said source current is N times (N>1) a normal amount during said predetermined period. a first constant current source that draws a constant current from a line into which the sink current is drawn during the predetermined period;
a second constant current source applying a constant current to the line from which the source current is discharged during the predetermined period;
3. The power control apparatus of claim 2, further comprising: The feedback current summing circuit is
a first sample and hold unit that holds the resonance current detection signal when the first switching element is switched on;
a first transconductance amplifier that outputs the sink current according to the difference between the output of the first sample-and-hold unit and the resonance current detection signal;
a second sample and hold unit that holds the resonance current detection signal when the second switching element is switched on;
a second transconductance amplifier that outputs the source current according to the difference between the output of the second sample-and-hold unit and the resonance current detection signal;
5. The power control device according to any one of claims 2 to 4, comprising: The feedback current summing circuit level-shifts the resonance current detection signal, and transfers the level-shifted resonance current detection signal to the first sample-and-hold section, the first transconductance amplifier, the second sample-and-hold section, and 6. The power control device according to claim 5, comprising a first level shift circuit that outputs to said second transconductance amplifier. The output current generation circuit is
a first transistor;
a third resistor connected to one end of the first transistor;
a first error amplifier that receives the feedback voltage and the voltage of a third connection node where the first transistor and the third resistor are connected to drive the first transistor;
an upper current mirror that receives the current flowing through the first transistor and generates the first output current;
a lower current mirror that receives the output current of the upper current mirror and generates the second output current;
7. The power control device according to any one of claims 2 to 6, comprising: 8. The power supply control device according to claim 2, wherein said first voltage applying section is a voltage follower to which a first reference voltage is input. further comprising a second level shift circuit for level-shifting the resonance voltage detection signal and outputting it to each of the upper comparator and the lower comparator;
9. The power control device according to claim 2, wherein said first predetermined voltage is the same as a central voltage of said resonance voltage detection signal after level shifting. further having a counter,
10. The predetermined period according to any one of claims 1 to 9, wherein the counter counts the number of drive signals for the first switching element and the number of drive signals for the second switching element by a predetermined number. A power control unit as described. The LLC resonance converter includes a first capacitor having one end connected to a fourth connection node where the primary winding and the resonance capacitor are connected, and a fourth resistor connected to the other end of the first capacitor. , further having
11. The power control device according to claim 1, wherein said resonance current detection signal is generated at a fifth connection node where said first capacitor and said fourth resistor are connected. The LLC resonance converter includes a second capacitor having one end connected to a fourth connection node where the primary winding and the resonance capacitor are connected, and a third capacitor having the other end connected to the second capacitor. , further having
12. The power control device according to claim 1, wherein said resonance voltage detection signal is generated at a sixth connection node where said second capacitor and said third capacitor are connected. The power supply control device according to any one of claims 1 to 12 as an IC package,
The first external terminal to which the resonance current detection signal can be applied and the second external terminal to which the resonance voltage detection signal can be applied are formed in a group of terminals having the same level of breakdown voltage and arranged along the same side of the IC package. included. a third external terminal connectable via a diode to an application end of an AC voltage for generating the input voltage;
a fourth external terminal that is a non-connection terminal;
on the same side,
14. The power control device according to claim 13, wherein said fourth external terminal is arranged between said terminal group and said third external terminal. An LLC resonant converter comprising a power control device according to any one of claims 1 to 14.

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