JP3574033B2 - Boost chopper circuit - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a boost chopper circuit, and more particularly to a boost chopper circuit that supplies boosted DC power to audio equipment mounted on a vehicle.
[0002]
[Prior art]
Higher power amplifiers are being used in automotive audio equipment year by year. When the power exceeds a certain power, a boost chopper circuit for boosting the battery voltage is required, and the amplifier is driven by the boosted DC voltage.
[0003]
FIG. 4 shows a conventional boost chopper circuit.
[0004]
The boost chopper circuit includes an input terminal VIN and a ground terminal GND to which a DC voltage from a battery is applied, a coil L1, a switch SW1 including a transistor or a MOSFET for switching a current to the coil L1, a coil L1, and a switch. A diode D1 for extracting and rectifying energy to be stored in the coil L1 from an output terminal which is a connection point of the switch SW1, a rectifying capacitor C1, a comparator OP1 for comparing an output voltage VOUT with a reference voltage Ref1, and a comparator OP1 And an output terminal VOUT for outputting an output voltage vout.
[0005]
Next, the operation of the boost chopper circuit will be described. The input voltage vin from the battery is 14.4 V if the battery is new, and the output voltage vout is set to 17 V. The comparator OP1 compares whether the output voltage vout is high or low with respect to the reference voltage Vref1, and outputs a high-level output signal when it is high and a low-level output signal when it is low.
[0006]
FIG. 5 shows a relationship between the output voltage vout and the reference voltage Vref1. The horizontal axis is time t. When the output voltage vout becomes lower than the reference voltage Vref1, the output signal of the comparator OP1 outputs a low level, and the switch SW1 is turned off by a drive signal from the PWM drive circuit PWM. At that time, the energy stored in the coil L1 is rectified by the diode D1 and charged in the capacitor C1, and the output voltage vout increases. Next, when the output voltage vout becomes higher than the reference voltage Vref1, the output signal of the comparator OP1 outputs a high level, and the switch SW1 is turned on by the drive signal from the PWM drive circuit PWM. At that time, a current flows through the coil L1 via the switch SW1, and energy is stored. On the other hand, the electric charge charged in the capacitor C1 is discharged, and the output voltage vout decreases. As described above, the boost chopper circuit operates so that the output voltage vout becomes equal to the reference voltage Vref1. For example, when the reference voltage Vref1 is set to 2.5V, when the output voltage vout is set to 17V, 2.5V is compared by resistance division. What is necessary is just to supply to the device OP1.
[0007]
When driving the amplifier with the battery voltage of 14.4V,
Po = Vcc ² / RL
Therefore, assuming that the efficiency is 100%, an output of about 51 W can be obtained with a load of 4Ω (RL). Actually, the output of 40 to 45 W is the limit from the battery voltage of 14.4 V. When boosting to 17 V by the boost chopper circuit, 60 W of output is obtained for each channel in four channels in consideration of efficiency.
[0008]
[Problems to be solved by the invention]
In such a step-up chopper circuit, as shown by a dotted line in FIG. 2, when the input voltage vin of the battery changes over time, the input current iin from the battery increases to maintain the output voltage vout. This is because the input voltage vin × input current iin = output voltage vout × output current iout in the boost chopper circuit.
Is established. Therefore, when the output voltage vout is set to 17 V and the output current iout is set to 15 A, when the input voltage vin drops from 14.4 V to 10 V, the input current iin increases from 18.2 A to 25.5 A. For this reason, in the audio equipment for vehicles, the rank of fuses in the set must be upgraded, and in some cases, power must be supplied directly from the battery with dedicated wiring, and the fuses in the set are blown immediately There was a problem.
[0009]
[Means for Solving the Problems]
The present invention has been made in view of the above problems, and has a switch for switching a DC input power supply via a coil, a rectifying circuit for rectifying energy stored in the coil to obtain a boosted output voltage, and a rectifying circuit for obtaining a boosted output voltage. In a boost chopper circuit including a comparator for comparing a voltage, an output for comparing an input voltage with the output voltage is input to the comparator, and the output voltage has an input voltage dependency. .
[0010]
More specifically, a switch for switching a DC input power supply via a coil, a rectifier circuit for rectifying energy stored in the coil when the switch is off to obtain a boosted output voltage, In a step-up chopper circuit including a first comparator for comparing a reference voltage and a drive circuit for performing pulse width modulation of the switch with an output signal of the first comparator, the input voltage is level-shifted by a second reference voltage. An output of a second comparator for comparing a voltage with the output voltage is input to the first comparator.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
An embodiment of a boost chopper circuit according to the present invention will be described with reference to FIGS.
[0012]
FIG. 1 shows a circuit diagram of a boost chopper circuit of the present invention.
[0013]
The boost chopper circuit includes an input terminal VIN and a ground terminal GND to which a DC voltage from a battery is applied, a coil L1, a switch SW1 including a transistor or a MOSFET for switching a current to the coil L1, a coil L1, and a switch. A diode D1 for extracting and rectifying energy to be stored in the coil L1 from an output terminal, which is a connection point of SW1, and a rectifying capacitor C1, a voltage obtained by shifting the output voltage vout and the input voltage vin by a second reference voltage Vref2. (Operational amplifier) OP2, which compares the first reference voltage Vref1 with the output of the second comparator OP2, and the output of the comparator OP1 modulates the pulse width. PWM drive circuit PWM and output terminal for outputting output voltage vout It is composed of a OUT.
[0014]
Next, the operation of the boost chopper circuit will be described. The input voltage vin from the battery is 14.4 V if the battery is new, and the output voltage vout is set to 17 V. The second comparator OP2 compares whether the voltage obtained by shifting the input voltage vin higher by the second reference voltage Vref2 with respect to the output voltage vout is higher or lower. If the voltage is higher, the output voltage vout is output. A voltage obtained by shifting the voltage vin higher by the second reference voltage Vref2 is output. The first comparator OP1 receives the reference voltage Vref1 and the output of the second comparator OP2, and compares them.
[0015]
In a normal state, a voltage obtained by shifting the input voltage vin higher by the second reference voltage Vref2 is set higher than the output voltage vout. Therefore, the output voltage vout is output from the second comparator OP2, and the first comparator OP1 Compares the output voltage vout with the reference voltage Vref1 to determine whether the output voltage is high or low. When the output voltage vout is high, a high-level output signal is output. When the output voltage vout becomes lower than the reference voltage Vref1, the output signal of the comparator OP1 outputs a low level, and the switch SW1 is turned off by a drive signal from the PWM drive circuit PWM. At that time, the energy stored in the coil L1 is rectified by the diode D1 and charged in the capacitor C1, and the output voltage vout increases. Next, when the output voltage vout becomes higher than the reference voltage Vref1, the output signal of the comparator OP1 outputs a high level, and the switch SW1 is turned on by the drive signal from the PWM drive circuit PWM. At that time, a current flows through the coil L1 via the switch SW1, and energy is stored. On the other hand, the electric charge charged in the capacitor C1 is discharged, and the output voltage vout decreases.
[0016]
The feature of the present invention lies in the operation when the battery becomes old and the input voltage vin drops. That is, when the voltage obtained by shifting the input voltage vin higher by the second reference voltage Vref2 becomes lower than the output voltage vout, the second comparator OP2 outputs a voltage obtained by shifting the input voltage vin higher by the second reference voltage Vref2. The first comparator OP1 compares whether the voltage obtained by shifting the input voltage vin higher than the reference voltage Vref1 by the second reference voltage Vref2 is higher or lower, and outputs a high-level output signal when it is high and a low-level output signal when it is low. Is output. Therefore, when the voltage obtained by shifting the input voltage vin higher by the second reference voltage Vref2 becomes lower than the reference voltage Vref1, the output signal of the comparator OP1 outputs a low level, and the switch SW1 is turned off by the drive signal from the PWM drive circuit PWM. I do. At that time, the energy stored in the coil L1 is rectified by the diode D1 and charged in the capacitor C1, and the output voltage vout increases. Next, when a voltage obtained by shifting the input voltage vin higher by the second reference voltage Vref2 becomes higher than the reference voltage Vref1, the output signal of the comparator OP1 outputs a high level, and the switch SW1 is turned on by the drive signal from the PWM drive circuit PWM. Turn on. At that time, a current flows through the coil L1 via the switch SW1, and energy is stored. On the other hand, the electric charge charged in the capacitor C1 is discharged, and the output voltage vout decreases. That is, the voltage control is performed in a state where the output voltage vout is reduced from the input voltage vin lower than the set 17 V to a voltage shifted higher by the second reference voltage Vref2.
[0017]
As shown by the solid line in FIG. 2, in the step-up chopper circuit of the present invention, when the input voltage vin drops due to the aging of the battery, the output voltage vout also drops to a voltage obtained by shifting the input voltage vin higher by the second reference voltage Vref2. So
Input voltage vin × input current iin = output voltage vout × output current iout
From the relational expression, it is possible to prevent an increase in the input current iin, and it is possible to maintain the input current iin substantially constant by an optimal design. Therefore, when the output voltage vout is set to 17 V and the output current iout is set to 15 A, and the input voltage vin is reduced from 14.4 V to 10 V, the output voltage vout can be reduced to 13 V by designing the second reference voltage Vref2 to 3 V. , The input current iin can be maintained from 18.2A to 19.5A. At this time, the output of the amplifier decreases due to the decrease of the output voltage vout, but there is no problem since the output of the amplifier when the input voltage vin is 14.4 V (normal) satisfies the catalog value.
[0018]
FIG. 3 shows a circuit diagram of a more specific boost chopper circuit. 1 and 4 have the same reference numerals.
[0019]
Here, the second comparator OP2 is more specific. The second comparator OP2 includes a PNP transistor TR, a Zener diode ZD that generates a second reference voltage Vref2, and bias resistors R4, R5, and R6. The emitter of the transistor TR is connected to the line of the output terminal VOUT, the bias resistor R5 is connected between the base and the emitter, the Zener diode ZD connected to the input terminal VIN and the bias resistor R6 are connected to the base, and the collector is connected to the bias resistor R6. The output voltage vout is connected through a resistor R4 to a connection point between the resistors R1 and R2 of the series-connected divided resistors R1, R2, and R3. Therefore, the second comparator OP2 is an error amplifier composed of one transistor.
[0020]
Next, the circuit operation will be described.
[0021]
When the battery has a normal input voltage vin, the output voltage vout is 17 V, the input voltage vin is 14.4 V, and the Zener voltage of the Zener diode ZD that generates the second reference voltage Vref2 is 3 V. Since it is reverse biased between the base and the emitter, it is off and does not operate. For this purpose, the output voltage vout is voltage-divided by the dividing resistors R1, R2, R3, and for example, 2.5 V, which is equal to the first reference voltage Vref1, is input to the first comparator OP1 from the resistor R3, and as described above, the normal comparator OP1 Voltage control is performed to keep the output voltage vout at 17V.
[0022]
When the battery becomes old and the input voltage vin drops to, for example, 12 V, the transistor TR is turned on by the resistor R5, and a current flows through the transistor TR to increase the voltage drop of the divided resistors R2 and R3. For this reason, the voltage drop generated in the dividing resistor R3 becomes 2.5 V or more, and a voltage higher than the first reference voltage Vref1 of the first comparator OP1 is input as a detection output of the output voltage vout, so that the first comparator OP1 Becomes a high level, acts in a direction to turn off the switch SW1, and lowers the output voltage vout. Specifically, the output voltage vout is reduced to 15.6 V which is the sum of the input voltage vin, the zener voltage, and the base-emitter voltage 0.6 V for turning on the transistor TR.
[0023]
【The invention's effect】
According to the present invention, a switch for switching a DC input power supply via a coil, a rectifier circuit for rectifying energy stored in the coil to obtain a boosted output voltage, and a comparator for comparing the output voltage with a reference voltage In the step-up chopper circuit, the input voltage is reduced by responding to the decrease of the input voltage by inputting the output for comparing the input voltage and the output voltage to the comparator. Can also provide a boost chopper circuit that suppresses an increase in input current. As a result, the in-vehicle audio equipment has an advantage that the rank in the fuse in the set does not need to be increased because the input current does not increase, and there is no need to supply power directly from the battery through dedicated wiring.
[0024]
A switch for switching a DC input power supply via a coil, a rectifier circuit for rectifying energy stored in the coil when the switch is off to obtain a boosted output voltage, and providing the output voltage and a first reference voltage. In a boost chopper circuit comprising a first comparator to be compared and a drive circuit for performing pulse width modulation of the switch with an output signal of the first comparator, a voltage obtained by level-shifting the input voltage by a second reference voltage and the output An output of a second comparator for comparing a voltage with the input is input to the first comparator, and the output voltage is decreased in response to the decrease of the input voltage. Thus, it is possible to provide a step-up chopper circuit in which the voltage is suppressed. The second comparator has an advantage that it can be composed of only one transistor and few circuit components.
[0025]
Therefore, in the present invention, pattern design and thermal design in consideration of an increase in the input current when the input voltage is reduced can be eliminated. It is also possible to exchange as desired.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a boost chopper circuit of the present invention.
FIG. 2 is a diagram illustrating characteristics of the present invention and a conventional boost chopper circuit.
FIG. 3 is a diagram for explaining a more specific circuit of the boost chopper circuit of the present invention.
FIG. 4 is a diagram illustrating a conventional boost chopper circuit.
FIG. 5 is a diagram illustrating operation waveforms of the present invention and a conventional boost chopper circuit.
[Explanation of symbols]
L1 Coil OP1 First comparator OP2 Second comparator PWM PWM drive circuit SW1 Switch D1 Diode C1 Capacitor

Claims (2)

A switch for switching an input voltage obtained from a DC input power supply consisting of a battery through a coil ,
A rectifier circuit that rectifies the energy stored in the coil to obtain a boosted output voltage ;
In a boost chopper circuit having a comparator for comparing the output voltage with a reference voltage,
An output obtained by comparing the output voltage with a voltage obtained by shifting the input voltage higher by a certain value is input to the comparator instead of the output voltage, and the output voltage has dependency on the input voltage. , boost chopper circuit, characterized in that also the input voltage is reduced to suppress the increase of the input current. A switch for switching an input voltage obtained from a DC input power supply consisting of a battery through a coil ,
A rectifier circuit for rectifying energy stored in the coil when the switch is off to obtain a boosted output voltage ;
A first comparator for comparing the output voltage with a first reference voltage ;
A PWM drive circuit for pulse width modulating a signal for controlling on / off of the switch with an output signal of the first comparator.
Instead the output from the second comparator for comparing the higher shifted voltage and the output voltage by a value corresponding to the input voltage to the boost voltage to the output voltage, input to the first comparator, the output voltage boost chopper circuit, characterized in that said is responsive to a decrease in the input voltage is lowered, the input voltage is suppressed an increase in the input current is also reduced.

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