JP5594526B2 - Switching power supply circuit - Google Patents

Description

  The present invention relates to a switching power supply circuit used in various electronic devices such as an LED driver, and more particularly to a switching power supply circuit having a function of controlling a constant output current.

  Conventionally, a switching power supply circuit is known as a small, lightweight and highly efficient power supply circuit, and is used as a power supply for various electronic devices. In general, it is often used as a constant voltage source that supplies a constant voltage to a load. However, it may also be used as a constant current source that supplies a constant current to a load. It is disclosed (for example, see Patent Document 1).

In the switching power supply device shown in FIG. 1 of Patent Document 1, the main switching element is used as a so-called high-side switching element arranged on the positive electrode terminal side of the input power supply. In this device, since a current detection resistor is connected in series with the load and the output current flowing through the load is directly detected, constant current control can be performed relatively easily. However, since the main switching element is arranged on the high voltage side, there is a problem that the drive circuit for the switching element becomes relatively expensive.

  As an improvement measure, a lighting fixture using a switching power supply circuit in which a main switching element is arranged on the negative electrode terminal side of an input power supply and used as a so-called low-side switching element is disclosed (for example, Patent Document 2).

  In Patent Document 2, the switching power supply circuit section has a step-down chopper circuit, and is controlled by a control circuit IC that also serves as a switching element. Switching is performed when the peak value of the current flowing through the switching element exceeds a threshold current. Current limit control to turn off the element is performed.

JP2009-148107A (FIG. 1) JP 2009-134946 A

However, the switching power supply circuit unit disclosed in Patent Document 2 has the following problems. That is, in the switching power supply circuit portion of Patent Document 2, when the input voltage is Vin, the output voltage is Vout, the inductance value (L value) of the choke coil is Lc, and the switching period of the switching element is Ts, the output current Io (choke coil) The relationship between the average value of the currents flowing through and the threshold current Ip is expressed by the following equation (1).
Io = Ip− (1/2) × ((Vin−Vout) / Lc)
× (Vout / Vin) × Ts (1)
As can be seen from the equation (1), when the L value Lc of the choke coil is sufficiently large, the output current Io is substantially equal to the threshold current Ip. However, when the L value Lc of the choke coil is increased, the size of the choke coil is increased and the choke coil is expensive. Therefore, there is a limit to increasing the L value Lc of the choke coil. As a result, the input voltage Vin Alternatively, there is a problem that the output current Io varies due to the variation of the output voltage Vout.

  The present invention has been made in view of the above-described problems, and has a simple circuit configuration, and is a switching power supply circuit capable of accurately performing constant current control of output current with respect to fluctuations in input voltage or output voltage. The purpose is to provide.

  The following aspects of the present invention exemplify the configuration of the present invention, and will be described separately for easy understanding of various configurations of the present invention. Each section does not limit the technical scope of the present invention, and some of the components of each section are replaced, deleted, or further, while referring to the best mode for carrying out the invention. Those to which the above components are added can also be included in the technical scope of the present invention.

( 1 ) A converter circuit unit including a switching element and a rectifying / smoothing circuit, a current detection circuit that is connected in series to the switching element and detects a current flowing through the switching element by converting it into a voltage, and a current flowing through a load unit A switching control unit that controls on / off of the switching element so as to be constant, and a reference voltage generation circuit that generates a reference voltage serving as a reference for a limit value of a current flowing through the switching element and outputs the reference voltage to the switching control unit And a correction signal for adjusting a reference voltage based on input / output voltage information obtained from the converter circuit unit in a switching power supply circuit that inputs a voltage from a DC voltage source and supplies DC power to the load unit. Is supplied to the reference voltage generation circuit, and the converter circuit unit includes the rectifying and smoothing circuit. Is a step-down converter circuit unit disposed on the high voltage side of the switching element, and the rectifying and smoothing circuit includes a capacitor connected in parallel with the load unit, one end of the capacitor, and the high voltage side of the switching element. A choke coil connected in series, an anode terminal connected to a connection point between the choke coil and the switching element, and a cathode terminal connected to the other end of the capacitor and the DC voltage source; The input / output voltage information is a difference voltage between an input voltage and an output voltage obtained from a connection point between the capacitor and the choke coil, and the reference voltage correction circuit is a direct current proportional to the difference voltage. A switching power supply circuit that outputs a voltage as a correction signal (claim 1 ).

( 2 ) A converter circuit unit including a switching element and a rectifying / smoothing circuit, a current detection circuit that is connected in series to the switching element and detects a current flowing through the switching element by converting the voltage into a voltage, and a current flowing through the load unit A switching control unit that controls on / off of the switching element so as to be constant, and a reference voltage generation circuit that generates a reference voltage serving as a reference for a limit value of a current flowing through the switching element and outputs the reference voltage to the switching control unit And a correction signal for adjusting a reference voltage based on input / output voltage information obtained from the converter circuit unit in a switching power supply circuit that inputs a voltage from a DC voltage source and supplies DC power to the load unit. Is supplied to the reference voltage generation circuit, and the converter circuit unit includes the rectifying and smoothing circuit. Is a step-down converter circuit unit disposed on the high voltage side of the switching element, and the rectifying and smoothing circuit includes a capacitor connected in parallel with the load unit, one end of the capacitor, and the high voltage side of the switching element. A choke coil connected in series, an anode terminal connected to a connection point between the choke coil and the switching element, and a cathode terminal connected to the other end of the capacitor and the DC voltage source; The input / output voltage information is a pulse voltage obtained from a connection point between the choke coil and the diode, and the reference voltage correction circuit divides and smoothes the pulse voltage. A switching power supply circuit that outputs a DC voltage proportional to the difference between the input voltage and the output voltage as a correction signal ( Claim 2 ).

  The switching power supply circuit according to the present invention includes a reference voltage correction circuit that outputs a correction signal for adjusting the reference voltage to the reference voltage generation circuit based on the input / output voltage information obtained from the converter circuit unit. Alternatively, when the output voltage fluctuates, the reference voltage is adjusted according to the fluctuation, so that it is possible to obtain a stable and highly accurate output current that is not influenced by fluctuations in the input voltage and output voltage, even with a simple circuit configuration. It becomes possible.

It is a block diagram which shows the circuit structure of the switching power supply circuit in one Embodiment of this invention. FIG. 2 is a circuit diagram illustrating an example of a specific circuit configuration of the switching power supply circuit illustrated in FIG. 1. FIG. 3 is a circuit diagram showing another example of a specific circuit configuration of the switching power supply circuit shown in FIG. 1.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a circuit diagram showing a circuit configuration of a switching power supply circuit according to an embodiment of the present invention. The switching power supply circuit 1 includes a converter circuit unit 2 including a switching element Q1 and a rectifying / smoothing circuit 8, and a switching control unit 4 for controlling on / off of the switching element Q1, and a DC voltage input from a DC voltage source Vdc. Is converted into power and DC power is supplied to the load unit 5.

The switching power supply circuit 1 includes a current detection circuit 3 connected in series to the switching element Q1 and a reference voltage generation circuit 6. The current detection circuit 3 detects a current flowing through the switching element Q1. A voltage signal corresponding to the detected current is output to the switching control unit 4, and the reference voltage generation circuit 6 generates a reference voltage that serves as a reference for the limit value of the current flowing through the switching element Q 1 and outputs the reference voltage to the switching control unit 4.

Based on the voltage signal from the current detection circuit 3 and the voltage signal from the reference voltage generation circuit 6, the switching control unit 4 turns on / off the switching element Q1 so that the output current flowing through the load unit 5 is always constant. The switching power supply circuit 1 functions as a switching power supply circuit in a constant current control mode.

Here, in the present embodiment, the converter circuit unit 2 is configured as a step-down converter circuit in which the rectifying and smoothing circuit 8 is disposed on the high voltage side of the switching element Q1, and the current detection circuit 3 includes the switching element Q1. And a detection resistor R1 for converting a current flowing through the voltage into a voltage signal. In addition, the present invention is not limited by the type of the load unit 5 connected to the switching power supply circuit 1. For example, an LED module in which a plurality of light emitting diodes are connected in series is applied as the load unit 5. It may be.

In addition to the above configuration, the switching power supply circuit 1 includes a reference voltage correction circuit 7 that outputs a correction signal for adjusting the reference voltage to the reference voltage generation circuit 6 based on input / output voltage information obtained from the converter circuit unit 2. In addition, this provides a stable and accurate output current that is not affected by fluctuations in the input voltage and output voltage.

Next, the circuit configuration of the switching power supply circuit according to the present embodiment and the operation and effect thereof will be described in detail based on a specific example shown in FIG.
In the switching power supply circuit 1a shown in FIG. 2, the rectifying and smoothing circuit 8 includes a capacitor C1, a choke coil L1, and a diode D1, and the capacitor C1 is connected in parallel with the load unit 5 and one end of the capacitor C1. And the choke coil L1 is connected in series between the high voltage side of the switching element Q1. The other end of the capacitor C1 is connected to the positive side of the DC voltage source Vdc. The diode D1 has a cathode terminal connected to the positive side of the DC voltage source Vdc together with the other end of the capacitor C1, and an anode terminal connected to the switching element. It is connected to the connection point between Q1 and choke coil L1.
Furthermore, one end of the detection resistor R1 constituting the current detection circuit 3 is connected to the low voltage side of the switching element Q1, and the other end of the detection resistor R1 is connected to the negative electrode side (ground side) of the DC voltage source Vdc. The

Here, in the switching power supply circuit 1a, the switching element Q1 is composed of a MOSFET, and the switching element Q1 is connected to the drain terminal of the MOSFET on the high voltage side and to the source terminal of the MOSFET on the low voltage side.

The switching control unit 4 includes a switch drive circuit 9 and a current limit control circuit 10, and a reference voltage generation circuit 6 includes a reference voltage source Vcc, and a positive side and a negative side (ground side) of the reference voltage source Vcc. Two resistance elements R2 and R3 connected in series are provided.
The current limit control circuit 10 of the switching control unit 4 includes a voltage signal a generated at a connection point between the two resistance elements R2 and R3 of the reference voltage generation circuit 6, a detection resistance R1 of the current detection circuit 3, and a switching element Q1. The voltage signal b generated at the connection point is input, and the control signal c is input from the current limit control circuit 10 to the switch drive circuit 9. Then, the switch drive circuit 9 outputs a drive signal (in this case, a gate drive signal) d for turning on / off the switching element Q1 to the switching element Q1.

  Here, the current limit control circuit 10 is composed of, for example, a comparator circuit, and compares the input voltage signals a and b, and uses a signal whose positive / negative logic is inverted according to the magnitude relationship as the control signal c. It may be output.

  The reference voltage correction circuit 7 includes two resistance elements R4 connected in series between the connection point between the capacitor C1 and the choke coil L1 of the rectifying and smoothing circuit 8 and the negative side (ground side) of the DC voltage source Vdc. R5 is provided, and the connection point between these resistance elements R4 and R5 is connected to the connection point between the two resistance elements R2 and R3 of the reference voltage generation circuit 6.

In the switching power supply circuit 1a, the constant current control of the output current Io by the switching control unit 4 is performed as follows. First, when the switching element Q1 is turned on by the gate drive signal d output from the switch drive circuit 9, a choke current is supplied from the DC power source Vdc to the switching element Q1 and the current detection circuit 3 via the load unit 5 and the choke coil L1. The current value increases as the on-time of the switching element Q1 elapses.
At this time, the choke current is detected by being converted into a voltage signal b by the detection resistor R1 of the current detection circuit 3, and this voltage signal b (hereinafter also referred to as a detection voltage signal) is detected by the current limit control circuit of the switching control unit 4. 10 is output.

On the other hand, a voltage signal a from the reference voltage generation circuit 6 is input to the current limit control circuit 10 of the switching control unit 4, and this voltage signal a (hereinafter also referred to as a reference voltage signal) limits the output current Io. Used as a reference voltage for reference of values. That is, when the choke current increases and the level of the detection voltage signal b reaches the level of the reference voltage signal a, the current limit control circuit 10 turns off the switching element Q1 with respect to the switch drive circuit 9. A control signal c for commanding is output.

  The switch drive circuit 9 to which the control signal c is input outputs a gate drive signal d for turning off the switching element Q1, and the switching element Q1 is turned off. At this time, the choke current is maintained as a regenerative current flowing from the choke coil L1 to the load portion 5 via the diode D1 by the back electromotive force generated in the choke coil L1, and this current value is equal to the off time of the switching element Q1. Decreases over time.

In the switching control unit 4, a predetermined switching cycle is normally set in advance. When the sum of the on time and the off time reaches the switching cycle, the switching control unit 4 again turns on the switching element Q1. The driving is performed so as to be in the on state, and thereafter the on / off operation of the switching element Q1 is repeated. As a result, the choke current is controlled to be substantially constant within a range below the limit value determined by the reference voltage signal a, and at this time, the output current Io (average value of the choke current) is expressed by the above formula (1). .

  Here, if the reference voltage correction circuit 7 is not provided, the reference voltage signal a is generated by dividing the voltage of the reference voltage source Vcc of the reference voltage generation circuit 6 by the two resistance elements R2 and R3. This signal is normally constant regardless of fluctuations in the input voltage Vin and the output voltage Vout. However, as shown in the equation (1), the output current Io depends not only on the limit value of the choke current (corresponding to Ip in the equation (1)) but also on the input voltage Vin and the output voltage Vout. Therefore, when the limit value of the choke current is constant, the output current Io varies due to the variation of the input voltage Vin or the output voltage Vout.

  Therefore, the switching power supply circuit 1a includes a reference voltage correction circuit 7, and improves the accuracy of the output current Io by adjusting the reference voltage signal a in accordance with fluctuations in the input voltage Vin and the output voltage Vout.

Specifically, in the switching power supply circuit 1a, a difference voltage (Vin−Vout) between the input voltage Vin and the output voltage Vout is generated at the connection point between the capacitor C1 and the choke coil L1 of the rectifying and smoothing circuit 8. Therefore, the reference voltage correction circuit 7 receives this difference voltage (Vin−Vout) as input / output voltage information, and the input voltage is divided by the resistance elements R4 and R5, and is proportional to the difference voltage (Vin−Vout). The direct current voltage is output to the reference voltage generation circuit 6 as a correction signal.

  In the configuration example shown in FIG. 2 as the switching power supply circuit 1a, the connection point of the resistance elements R4 and R5 of the reference voltage correction circuit 7 and the connection point of the resistance elements R2 and R3 of the reference voltage generation circuit 6 are directly connected. Therefore, the output of the correction signal from the reference voltage correction circuit 7 is integrated with the generation of the reference voltage signal a by the reference voltage generation circuit 6 as one voltage dividing process by the resistance elements R2, R3, R4, and R5. To be implemented. Therefore, in this example, the voltage signal e shown in FIG. 2 is not the correction signal itself output from the reference voltage correction circuit 7 to the reference voltage generation circuit 6, but the reference voltage signal a corrected by the correction signal. It is the same signal.

  In the switching power supply circuit 1a, by providing the reference voltage correction circuit 7 in this way, the reference voltage signal a reflects the fluctuation of the input / output voltage. For example, when the input voltage Vin is constant, if the output voltage Vout increases, the difference voltage (Vin−Vout) decreases. Therefore, the reference voltage has a constant ratio determined by the resistance values of the resistance elements R2, R3, R4, and R5. The signal a (and therefore the choke current limit value) also decreases, and the increase in the output current Io is suppressed. Conversely, when the input voltage Vin is constant, if the output voltage Vout decreases, the differential voltage (Vin−Vout) increases. Therefore, the reference voltage is determined at a constant ratio determined by the resistance values of the resistance elements R2, R3, R4, and R5. The voltage signal a (and hence the choke current limit value) also increases, and the decrease in the output current Io is suppressed.

  As described above, according to the switching power supply circuit 1a, when the input voltage Vin or the output voltage Vout varies, the reference voltage signal a is adjusted according to the variation. Therefore, the input voltage Vin can be achieved with a simple circuit configuration. In addition, it is possible to obtain a stable and accurate output current Io that is not affected by fluctuations in the output voltage Vout.

  Next, another example of the switching power supply circuit in the present embodiment will be described with reference to FIG. However, the switching power supply circuit 1b shown in FIG. 3 is the same as the switching power supply circuit 1a shown in FIG. 2 except for the configuration of the reference voltage correction circuit 7a. Will be described.

  In the switching power supply circuit 1b, the reference voltage correction circuit 7a is connected in series between the connection point between the choke coil L1 and the diode D1 of the rectifying and smoothing circuit 8 and the negative electrode side (ground side) of the DC voltage source Vdc. Two resistance elements R4 and R5 are provided, and the connection point between these resistance elements R4 and R5 is connected to the connection point between the two resistance elements R2 and R3 of the reference voltage generation circuit 6. In the reference voltage correction circuit 7a, a capacitor C2 is connected in parallel with the resistor element R5.

  In the switching power supply circuit 1b, a pulsed voltage is generated at the connection point between the choke coil L1 and the diode D1 of the rectifying and smoothing circuit 8 according to the on / off operation of the switching element Q1, and the pulsed voltage The average corresponds to the difference voltage (Vin−Vout) between the input voltage Vin and the output voltage Vout. Therefore, the reference voltage correction circuit 7a inputs this pulse voltage as input / output voltage information, and the voltage is divided and smoothed by the resistance elements R4 and R5 and the capacitor C2, thereby obtaining a differential voltage (Vin− A DC voltage proportional to Vout) is output to the reference voltage generation circuit 6 as a correction signal.

  The switching power supply circuit 1b has the same effects as the switching power supply circuit 1a with the above configuration.

  As mentioned above, although this invention was demonstrated using preferable embodiment, this invention is not limited to embodiment mentioned above. For example, the converter circuit unit 2 may be a step-down converter circuit of a type in which the rectifying and smoothing circuit 8 is disposed on the low voltage side of the switching element Q1. The input / output voltage information input to the reference voltage correction circuits 7 and 7a may be obtained from the connection point between the positive side of the reference power source Vcc and the cathode of the diode D1. Furthermore, although the above-described embodiment has been described on the assumption that the switching power supply circuit operates in the continuous current mode, the present invention can also be applied to the operation in the critical mode or the discontinuous current mode.

1, 1a, 1b: switching power supply circuit, 2: converter circuit unit, 3: current detection circuit, 4: switching control unit, 5: load unit, 6: reference voltage generation circuit, 7, 7a: reference voltage correction circuit, 8 : Rectifying and smoothing circuit, 9: switch drive circuit, 10: current limit control circuit, a: voltage signal (reference voltage signal), b: voltage signal (detection voltage signal), c: control signal, d: drive signal (gate drive) Signal), e: voltage signal (reference voltage signal), C1, C2: capacitor, D1: diode, Io: output current, L1: choke coil, Q1: switching element, R1: detection resistor, R2, R3, R4, R5 : Resistance element, Vdc: DC voltage source, Vin: Input voltage, Vout: Output voltage

Claims (2)

A converter circuit unit including a switching element and a rectifying / smoothing circuit, a current detection circuit that is connected in series to the switching element and detects a current flowing through the switching element by converting the voltage into a voltage, and a current flowing through the load unit is constant A switching control unit that controls on / off of the switching element, and a reference voltage generation circuit that generates a reference voltage that serves as a reference for a limit value of a current flowing through the switching element and outputs the reference voltage to the switching control unit. In a switching power supply circuit that inputs a voltage from a DC voltage source and supplies DC power to the load unit,
A reference voltage correction circuit that outputs a correction signal for adjusting a reference voltage to the reference voltage generation circuit based on input / output voltage information obtained from the converter circuit unit;
The converter circuit unit is a step-down converter circuit unit in which the rectifying and smoothing circuit is disposed on a high voltage side of the switching element, and the rectifying and smoothing circuit includes a capacitor connected in parallel to the load unit, and the capacitor A choke coil connected in series between one end of the switching element and the high voltage side of the switching element, an anode terminal is connected to a connection point between the choke coil and the switching element, and a cathode terminal is connected to the other end of the capacitor and A diode connected to the DC voltage source,
The input / output voltage information is a difference voltage between an input voltage and an output voltage obtained from a connection point between the capacitor and the choke coil, and the reference voltage correction circuit corrects a DC voltage proportional to the difference voltage. features and to Luz switching power supply circuit to output as a signal. A converter circuit unit including a switching element and a rectifying / smoothing circuit, a current detection circuit that is connected in series to the switching element and detects a current flowing through the switching element by converting the voltage into a voltage, and a current flowing through the load unit is constant A switching control unit that controls on / off of the switching element, and a reference voltage generation circuit that generates a reference voltage that serves as a reference for a limit value of a current flowing through the switching element and outputs the reference voltage to the switching control unit. In a switching power supply circuit that inputs a voltage from a DC voltage source and supplies DC power to the load unit,
A reference voltage correction circuit that outputs a correction signal for adjusting a reference voltage to the reference voltage generation circuit based on input / output voltage information obtained from the converter circuit unit;
The converter circuit unit is a step-down converter circuit unit in which the rectifying and smoothing circuit is disposed on a high voltage side of the switching element, and the rectifying and smoothing circuit includes a capacitor connected in parallel to the load unit, and the capacitor A choke coil connected in series between one end of the switching element and the high voltage side of the switching element, an anode terminal is connected to a connection point between the choke coil and the switching element, and a cathode terminal is connected to the other end of the capacitor and A diode connected to the DC voltage source,
The input / output voltage information is a pulsed voltage obtained from a connection point between the choke coil and the diode, and the reference voltage correction circuit divides and smoothes the pulsed voltage to obtain an input voltage. features and to Luz switching power supply circuit to and outputs a DC voltage as a correction signal proportional to the difference between the output voltage and the.

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