JP3003437B2 - Voltage converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage conversion circuit for converting a relatively low input voltage into a desired high voltage, and more particularly to a voltage conversion device having a reduced number of circuit components.

[0002]

2. Description of the Related Art Electronic devices using a battery as a power supply source are particularly common in consumer devices. The voltage that can be supplied by the battery and the voltage used in the electronic device do not always match, and therefore, it is necessary to convert the voltage of the battery, that is, boost the voltage and supply it to the electronic circuit. As such a booster circuit, a booster circuit conventionally called an up-converter is used, and a booster circuit is provided so as to be able to cope with a particularly low input voltage.
The types are used in parallel. FIG. 3 shows a conventional booster circuit configured in two types in parallel.

In FIG. 3, a coil 1 and a transistor 2
Are connected in series between the power supply line 3 and the ground 4, and the anode of the diode 5 is connected to the connection point between the coil 1 and the transistor 2. The output of the oscillating circuit 6 is connected to the gate of the transistor 2 via the gate circuit 15 to turn on / off the transistor 2. The output of the PWM circuit, which changes according to the value of the output voltage 11, is connected to the gate of the transistor 12 via the gate circuit 16 to turn on / off the transistor 12.
Turn off. The booster circuits 7 and 8 configured in this way are connected in two stages in parallel, the cathodes of the diodes 5 and 9 are connected, and a boosted output voltage is taken out therefrom. The extracted output is supplied to a smoothing circuit 10, and a smoothed DC voltage is extracted from an output 11. The output of the smoothing circuit 10 is provided to a level detection circuit 13 and a PWM circuit 14.

When the transistor 2 is turned off from on by a pulse output from the oscillation circuit 6, a voltage higher than the voltage on the power supply line 3 is generated at a connection point between the coil 1 and the diode 5, and the voltage gradually decreases. Thereafter, when the transistor 2 is turned on again, the voltage becomes substantially equal to the ground voltage.
Therefore, a voltage fluctuation in response to the pulse output from the oscillation circuit 6 appears at the anode of the diode 5, and when the fluctuation is rectified by the diode 5, a voltage higher than the voltage on the power supply line 3 is obtained.

When the smoothed voltage output from the diode 5 becomes higher than a predetermined voltage, the transistor 2 is turned off, and the transistor 12 is supplied with a pulse from the PWM circuit 14. The second stage booster circuit 8 performs the same operation as the booster circuit 7, and outputs a boosted voltage from the diode 9.

When the output voltage from the output 11 reaches a predetermined voltage, the level detection circuit 13 supplies a low-level voltage to the gate 15 and stops the supply of pulses from the oscillation circuit 6 to the transistor 2. When the pulse supply is stopped,
A pulse is supplied from the PWM circuit 14 to the gate of the transistor 12, and the booster circuit 8 starts operating.

[0007]

As described above,
By using a booster circuit connected in parallel in two stages and switching from the first stage to the second stage for operation, a relatively low voltage can be efficiently converted to a target high voltage.
Since such a booster circuit is used for a relatively small device, it is required to reduce the size of the circuit. Therefore, there is a strong demand for downsizing the components of the booster circuit and reducing the number of components.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and includes two sets of coils and diodes that are separately used by the first-stage and second-stage booster circuits.
An object of the present invention is to provide a voltage conversion device that can be replaced with a set of coils and diodes without impairing the smooth operation of a booster circuit.

[0009]

According to the present invention, there is provided a voltage conversion apparatus comprising: first switching means for repeating conduction and cutoff operations according to a predetermined first frequency signal; predetermined second switching means; Second switching means 22 for repeating conduction and cutoff operations in accordance with the frequency signal; coupled to the power supply voltage 20, the first switching means, and the second switching means, to make the first switching means or the second switching means conduct and cut off. Boosting means 23 and 27 for boosting the power supply voltage by this means; connected to the boosting means and smoothing means 31 for smoothing the output voltage; connected to the smoothing means, and responding to the fact that the smoothed output voltage has reached a predetermined reference voltage. A switching signal for stopping the operation of the first switching means and starting the operation of the second switching means Characterized in that it is composed; that comparison means.

[0010]

The voltage supplied from the battery is supplied to the booster. The boosting means boosts the voltage applied from the battery according to the first switching means which conducts and cuts off with a predetermined repetition signal from the oscillating means. Similarly to the first switching means, the second switching means repeats the conduction and cutoff operations to increase the output voltage of the battery. The boosted voltage is applied to the smoothing means and smoothed. When the smoothed voltage reaches the reference voltage, the comparing means stops the operation of the first switching means and outputs a switching pulse for starting the operation of the second switching means. The first switching means and the second switching means share one boosting means.

[0011]

FIG. 1 is a circuit diagram of a voltage converter for explaining an embodiment of the present invention. A battery 20 composed of batteries such as a manganese battery, an alkaline battery, and a mercury battery,
In general, it is used as a power source for an electronic circuit mounted in the electronic device or as a power source when a motor is provided. The output of the battery 20 is input to the booster circuit 28. One end of the coil 23 in the booster circuit 28 is connected to the power supply line 24 and the other end is connected to the MOS transistor 25 and M
Connected to each drain of OS transistor 29. MO
The source of S transistor 25 is grounded, and the gate is connected to the output of AND circuit 26. In order to ensure the operation even when the output voltage of the battery 20 is low, a MOS transistor 25 having a low gate threshold voltage Vth is used. The source of the MOS transistor 29 is grounded, and the gate is connected to the output of the AND circuit 52. MO
As the S transistor 29, a power MOS transistor such as an LD.MOS transistor manufactured by Motorola is used to obtain a low on-resistance by applying a high gate voltage. An anode of a diode 27 is connected to a connection point between the coil 23 and each drain of the MOS transistor 25 and the MOS transistor 29. The cathode of the diode 27 is connected to the smoothing circuit 31.

One end of the smoothing coil 32 of the smoothing circuit 31 is connected to the cathode of the diode 27 and the capacitor 33, and the other end is connected to the capacitor 34 and to the output Vout of the voltage converter. Capacitor 3
3, 34 perform a smoothing action together with the coil 32.

The output of the smoothing circuit 31 is connected to a non-inverting input of a hysteresis comparator 36 of a comparison circuit 35,
A reference voltage Vref is applied to the inverting input. The output of the comparator 36 is input to the AND circuits 26 and 52.

The pulse output from the oscillation circuit 43 is frequency-divided by a frequency dividing circuit 42 and a repetition pulse 1 of about 128 KHz
Is output. A part of the frequency-divided pulse is further frequency-divided by a PWM circuit 44, which is another frequency dividing circuit, and is output as a repetition pulse 2 of about 32 KHz. Repetitive pulse V
1 (see also FIG. 2) is input to the AND circuit 26, while
The repetition pulse V2 is input to the AND circuit 52. The output of the AND circuit 26 is the MO of the first switching circuit 21.
The AND circuit 5 is connected to the gate of the S transistor 25 and
The output of the second switching circuit 22 is connected to the gate of the MOS transistor 29 of the second switching circuit 22. First switching circuit 21, AND circuit 26, frequency dividing circuit 42, and oscillation circuit 4
The power to 3 is supplied from a battery 20, although the power lines to them are omitted in FIG. Second switching circuit 22, smoothing circuit 31, frequency dividing circuit 44, comparing circuit 3
Although power to the AND circuit 52 and the AND circuit 52 is omitted in FIG. 1, the output of the smoothing circuit 31 is supplied.

Next, the operation of the voltage converter of FIG. 1 will be described with reference to the timing chart of FIG. When the power switch of the electronic device is turned on, the output voltage of the battery 20 is supplied to the first switching circuit 21. Power is also supplied to the second switching circuit 22 via the power supply line 24, but the operation is prohibited because a low-level voltage is applied to the gate of the MOS transistor 29. First
A control pulse derived from the oscillation circuit 43 is applied to the gate of the MOS transistor 25 of the switching circuit 21 via the AND circuit 26 (the other input of the AND circuit 26 is given a low-level signal. ). MOS transistor 25 repeats the conduction and cutoff operations in response to the applied control pulse. When the MOS transistor 25 is turned on, a current flows from the battery 20 via the coil 23 and the MOS transistor 25, so that a low-level voltage (drain-source voltage) is applied to the anode of the diode 27. Next, when the MOS transistor 25 is turned off, the current flowing in the coil 23 tends to flow from the MOS transistor 25 to the diode 27. However, since the input resistance to the diode side becomes higher than the on-resistance of the MOS transistor 25, , An induced voltage is generated at both ends. This induced voltage is applied to a smoothing circuit 31 via a diode 27, and after being smoothed, an external output terminal OUTP
It is output from the UT and applied to the non-inverting input of the comparator 36 of the comparison circuit 35.

The comparator 36 outputs the output voltage V of the smoothing circuit.
out is compared with the reference voltage Vref. When the output voltage Vout reaches the reference voltage Vref, the comparator 36 outputs a high-level switching pulse Vcont as shown in FIG. When the switching pulse Vcont becomes high level, the application of the control pulse from the frequency dividing circuit 42 to the gate of the MOS transistor 25 is stopped. As a result, the MOS transistor 25 is turned off, and the first switching circuit stops operating.

The high-level switching pulse Vcont from the comparator 36 activates the operation of the second switching circuit 22. That is, the second switching circuit takes over the operation of the first switching circuit 21 and continues the boosting operation of the boosting circuit 28. Thus, the output voltage of the smoothing circuit 31 is continuously output from the external output terminal OUTPUT.

[0018]

As described above, according to the present invention, the number of components can be reduced by sharing and unifying the coils and diodes used in the first and second switching circuits, thereby reducing cost and mounting area. The effect of is obtained.
Further, since the control circuit is simplified, a stable power supply system can be relatively easily configured.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a voltage converter according to an embodiment of the present invention.

FIG. 2 is a signal waveform diagram of each part of the voltage conversion device for explaining the operation of the voltage conversion device shown in FIG.

FIG. 3 is a circuit diagram for explaining a conventional technique.

[Explanation of symbols]

 Reference Signs List 20 battery 21 first switching circuit 22 second switching circuit 25, 29 MOS transistor 26, 52 AND circuit 27 diode 28 booster circuit 31 smoothing circuit 32 coil 33, 34 capacitor 35 comparison circuit 36 comparator 42 frequency dividing circuit 44 PWM circuit 43 Oscillator circuit 54 External output terminal

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H02M 3/155 H02J 1/00 304

Claims (2)

(57) [Claims] 1. A voltage converter for receiving a DC power supply voltage, boosting the voltage, and outputting the boosted voltage: first switching means for repeating conduction and cutoff operations according to a predetermined first frequency signal; conduction according to a predetermined second frequency signal And a second switching means for repeating the switching operation; and being coupled to the power supply voltage, the first switching means, and the second switching means, to conduct and interrupt the first switching means or the second switching means. Boosting means for boosting the power supply voltage by; a smoothing means connected to the boosting means for smoothing the output voltage; connected to the smoothing means, and in response to the smoothed output voltage reaching a predetermined reference voltage, Outputting a switching signal for stopping the operation of the first switching means and starting the operation of the second switching means A voltage conversion device comprising: Said first and second switching means are MOS transistors each having a grounded source, drain and gate; the boosting means has one end connected to the output of the power supply and the other end connected to the MOS transistor; A voltage converter comprising: a coil connected to each drain of a transistor; and a diode having an anode connected to the other end of the coil and a cathode serving as an output of the boosting means.