JPS6245513Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention is an improved DC that can obtain a stable high output voltage even when the input voltage is low, and can control the output voltage on and off by changing the reference voltage. -Relates to DC converters.

A step-up DC-DC converter is a device that chops the DC input using a transistor and smoothes it using a filter to obtain a DC voltage higher than the input. Techniques such as width control are employed. A conventional circuit configuration is, for example, as shown in FIG. 1, and the converter main body operates in the following manner in principle. When the switch SW is turned on, the resistance R ₄
Through this, the current of I _B1 flows into the base of the oscillation transistor Q ₁ , the transistor Q ₁ begins to turn on, and the collector current I _C begins to flow. When the collector current I _C continues to increase, a current I _B2 flows due to the induced power from the base winding N _B , and the base current I
_B becomes I _B1 + I _B2 . When the current amplification factor of the oscillation transistor Q ₁ is h _fe , the transistor Q 1 remains on as long as I≦h _fe・I _B is satisfied, but when the collector current I _C further increases, the transistor Q ₁ turns _on . The base current becomes insufficient, and the transistor _Q1 moves out of the saturation region, and some voltage is generated between the collector and emitter of transistor Q1. As a result, the collector winding voltage E ₁ decreases by that amount, and the base winding voltage E _B also decreases, so that the base current becomes further insufficient, and the transistor Q ₁ is turned off instantaneously.
The current flowing through the output diode D ₁ flows while the oscillation transistor Q ₁ is off, and when the transistor Q ₁ is on, the anode side potential V _A ″ of the output diode D ₁ is lower than the output voltage V _OUT . The potential is low, and the output current is the smoothing capacitor C ₂
This is covered by the discharge current of .

Now, the output voltage can be made constant by using the parts shown by the broken lines in Figure 1, that is, the output dividing resistors R ₁ , R ₂ ,
This is performed by a constant voltage control circuit consisting of a comparator IC and a control transistor _Q2 . That is, the output divided sense potential V _A of the output voltage dividing resistors R ₁ and R ₂ and the reference potential V _REF are compared by the comparator IC, and the voltage difference amplified output is supplied to the control transistor Q ₂ and the oscillation transistor Q ₁ The oscillation pulse width is controlled by controlling the base current of the oscillation pulse, thereby making the output voltage constant.

However, with this configuration, the comparator
Since a power supply voltage is required for the IC, if the input voltage is less than the power supply voltage of the comparator IC (+V _CC standard...usually 5V), it becomes uncontrollable, and there are problems in that it becomes expensive. Also, it is possible to compare and amplify the divided sense potential and the reference potential using a transistor instead of a comparator IC.
Reference potential V _R at low input voltage (e.g. 5V or less)
Even if _{the EF} is lowered (for example, 0.5V), the divided sense potential is not high enough to control the comparison and amplification transistor and the control transistor _Q2 , so the oscillation transistor _Q1 cannot be completely turned off, resulting in instability. Invite action. In other words, in order to completely control the comparison amplification and control transistors even when the output voltage is low, the bleeder ratio of resistors R ₁ and R ₂ must be made small, but this will reduce the divided sense potential during normal oscillation. Since the voltage becomes too high, the reference potential must be increased, and it becomes impossible to generate the reference voltage inside the converter. Therefore, even if a transistor is used instead of a comparator IC, it will be difficult to freely vary the output voltage down to a low input voltage, and it will be difficult to freely vary the output voltage down to a low input voltage.
There are problems such as the inability to perform off control.

The purpose of this invention is to eliminate the above-mentioned drawbacks of the conventional technology, to enable output voltage control and output on/off control from a low input voltage of about 2 to 3 V, and to provide an inexpensive, highly variable output voltage range. An object of the present invention is to provide an improved step-up DC-DC converter that can be used in a wide range of applications.

In order to achieve this purpose, the present invention uses a transistor for voltage comparison and amplification, and is configured to insert a diode or Zener diode on the ground side of the divided resistance circuit, which is a feature of the present invention. .

Hereinafter, the present invention will be explained in detail based on the drawings.
FIG. 2 is a circuit diagram showing an embodiment of the present invention.
The boost converter body may be exactly the same as shown in FIG. In the present invention, a diode D _x is forward connected to the ground side of the dividing resistor circuit consisting of R ₁ and R ₂ , and a PNP transistor Q ₃ for comparison and amplification is used to connect the divided sense potential V _A ′ and the reference potential V _REF . It is configured to compare and amplify. That is, the transistor _Q3 has its emitter connected to the divided sense potential point, its base connected to the reference potential point, and its collector connected to the base of the control transistor _Q2 . A transistor Q ₄ and a resistor R ₃ are connected to the voltage comparison transistor Q ₃ in a latch configuration.

Now, the transistor _Q3 has a divided sense potential V
_A ' and the reference potential V _REF are compared and amplified, and the difference voltage is used to supply the base current I _B to the control transistor Q ₂ .
₃ to control the oscillation transistor _Q1 and stabilize the output voltage. In other words, when the divided sense potential V _A ' becomes lower than the reference voltage V _REF , _the base current I _B3 stops flowing and the control transistor _{Q 2} turns _off. The amount increases by the amount that is lost, and the on-time width of transistor _Q1 increases, increasing the output voltage. Conversely, when the divided sense potential V _A ' becomes higher than the reference potential V _REF , the base current I _B
3 flows, the control transistor _Q2 turns on,
Since the collector current I _C2 flows, the base current I _B of the oscillation transistor Q ₁ becomes I _B = (I _B1 + I _B2 ) - I _C2 , and the on time of the transistor Q ₁ becomes shorter and the output voltage decreases. In this way, the output voltage is stabilized. Note that the function of the transistor _Q4 is to prevent the output voltage from becoming unstable when the reference voltage V _REF changes slightly. That is, as mentioned above, transistors Q ₃ and Q ₄ have a latch configuration, so that even if some ripple voltage is superimposed on the reference voltage V _REF , it does not affect the oscillation operation of the oscillation transistor Q ₁ . It works.

By the way, in the circuit shown in FIG. ₂ , the minimum value Vmin of the _divided sense voltage V _A ' is
is a value (approximately 2V) that allows linear operation. The divided sense potential changes depending on the output voltage and the resistance division ratio, and the situation is as shown in FIG. Figure A shows the conventional example, and Figure B shows the case of the present invention. As is clear from these figures, in the case of FIG. 3A, the values of the divided sense potentials V _A1 and V _A2 differ greatly between when the output voltage is low and when the output voltage is high. In other words, V _A
Since control is not possible unless ≧Vmin or higher, in order to be able to control down to a low output voltage, the bleeder ratio must be increased, and if this is done, V _A will become too large at a high output voltage. On the other hand, in FIG. 3B, the ground level is always raised by V _Dx (forward voltage drop of silicon diode ≒ 0.7V), so R ₁ :R ₂
By setting a large ratio, there is no large difference in the values of V _A ' and V _A ' whether the output voltage is low or high, and moreover, it can be made larger than Vmin.
If 0.7V, which is the forward voltage drop of a silicon diode, is insufficient for V _Dx , a plurality of diodes may be connected in series, or a Zener diode may be used.

As described above, according to the present invention, since the change in the divided sense potential V _A ' is small, even if the variable range of the reference voltage is small (2 to 3 V), the output voltage variable range can be made large (10 to 20 V, etc.). I can do it. Furthermore, even when the input voltage is low (for example, about 2 to 3 V) and the oscillation transistor Q ₁ has stopped oscillating, the divided sensor potential V _A ' is given a potential sufficient to control the transistors Q ₂ and Q ₃ . Reference potential V _REF
By lowering the potential to a sufficiently low potential, the oscillation operation of the oscillation transistor _Q1 can be completely stopped, in other words, the output can be turned off.

Regarding the conventional example, when stabilizing at a high output voltage, the dividing resistor ratio R ₁ /
Since R ₂ is small, when the oscillation transistor Q ₁ stops oscillating at a low input voltage, the divided sense potential V _A becomes very low, making it impossible to control the transistors Q ₂ and Q ₃ , and causing the oscillation transistor Q ₁ to stop oscillating. It becomes impossible to maintain the stopped state. In other words,
The operation of the oscillation transistor _Q1 becomes unstable, and the output cannot be controlled on and off by manipulating the reference voltage V _REF . Conversely, when stabilizing at a low output voltage, the ratio of dividing resistors R ₁ / R ₂
If the reference voltage V _REF is made large, it becomes possible to control the output on and off by manipulating the reference voltage V REF, but in order to stabilize the output voltage at a high output voltage, the reference voltage V _REF must be made quite high, and the self V within the unit of
When creating _REF , the circuit configuration becomes extremely difficult.

As described above, the present invention is configured such that a diode or Zener diode is inserted on the ground side of the divided sense resistor circuit, and a transistor is used to compare and amplify the differential voltage.
Output voltage control and output on/off control can be performed even with input voltages as low as ~3V, and since it can be manufactured with a small number of parts without using an IC, it is inexpensive and has a very wide variable range of output voltage. It has excellent practical effects such as being able to take
For example, it is extremely useful for circuits that generate voltages of more than 10 V with low input voltage, such as DC-DC converters for cameras, and DC-DC converters for hand-held calculators that are powered by two or three batteries. It is.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the prior art, Fig. 2 is a circuit diagram showing an embodiment of the present invention, Fig. 3A is an explanatory diagram showing a conventional divided sense potential, and Fig. 3B is a divided FIG. 2 is an explanatory diagram showing a sense potential. Q ₁ ...Oscillation transistor, Q ₂ ...Control transistor, Q ₃ ...Comparison and amplification transistor, D _x
... Diode, R ₁ , R ₂ ... Dividing resistor.

Claims (1)

[Scope of utility model registration request] In the DC-DC converter that controls the oscillation and stopping of the input side oscillation transistor based on the potential difference between the divided sense potential from the output voltage dividing resistor circuit connected to the output side and the reference potential, and obtains a boosted constant voltage output. Insert a diode or Zener diode on the ground side of the dividing resistor circuit, connect the emitter of the PNP transistor for comparison and amplification to the divided sense potential point, and connect the base to the reference potential point, and use the collector current to oscillate the input side. A step-up DC-DC converter that can control down to low input voltages and is characterized by controlling the oscillation and stopping of the transistor.