JPS645984Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention uses a switching operation of a switching transistor connected in series with the load to step the DC input, and stabilizes the DC input voltage lower than the DC input voltage. Regarding the step-down chopper circuit that produces a constant voltage output, more specifically, it is a step-down step-down circuit using discrete components in which the transistor that controls the on/off of the switching transistor functions as both an oscillator and an error amplifier. This invention relates to an automatic chopper circuit.

[Prior Art] A switching transistor is connected in series with a load to one of the chopper circuits that includes an energy storage element and a switching element and generates an output voltage depending on the on/off time ratio of the switching element. There is a so-called step-down chopper circuit that generates an output voltage lower than the DC input voltage.

Conventionally, this step-down chopper circuit often has a circuit configuration using a dedicated control IC. Although it depends on the output capacitance, unless the output capacitance is extremely small, individual transistors for power are used as switching elements, and individual transistors for control are used as switching elements.
Externally attached to the IC. Of course, it goes without saying that the rectifying and smoothing section, which consists of a smoothing capacitor and a diode connected in parallel with the choke coil connected in series with the load, must also be installed separately from the control IC and switching element.

In such a circuit configuration, a dedicated control
An oscillation circuit is built into the IC, and by turning on and off the oscillation transistor in the output stage, the switching transistor is turned on and off.
It controls off. The constant voltage control of the output voltage is also carried out by the control unit built into the control IC. In other words, the output voltage of the power supply (chopper circuit) is detected by a voltage dividing resistor, etc., and compared with a reference voltage, and the operation of the oscillation transistor is controlled within the control IC to provide an appropriate pulse width. That's what I do.

[Problems that the invention aims to solve] In this way, a circuit configuration that uses a dedicated control IC has a relatively small number of parts compared to a conventional circuit configuration that is assembled using only discrete components, and is easy to assemble. However, even in that case, a considerable number of resistors and capacitors must be externally connected in order for the control IC to operate properly. Of course for dedicated control
Since it uses an IC, it is inevitably more expensive compared to individual transistors, etc., and
There are certain limits to the allowable input voltage for ICs, which are usually quite low, so they also have the disadvantage of not allowing high output voltages.

The purpose of this invention is to eliminate the drawbacks of the conventional technology as described above, and to create an error amplifier for constant voltage output using a simple circuit consisting of only a few individual components without using a dedicated control IC. We have developed an improved step-down automatic chopper circuit that can function as an oscillator for driving a switching transistor and as an oscillator for driving a switching transistor, and is therefore highly reliable and inexpensive, and can also obtain a high output voltage. It is about providing.

[Means for Solving the Problems] The present invention, which can achieve the above purpose, is composed of only individual parts without using a dedicated control IC, and in particular, The oscillation and control circuits have been improved.

That is, the present invention consists of a switching transistor connected in series to the load, an oscillation transistor for controlling on/off of the switching transistor, and a smoothing transistor connected in parallel to a chiyoke coil connected in series to the load. In a step-down chopper circuit equipped with a rectifying and smoothing section including a capacitor and a diode, the oscillation transistor is connected between the base of the switching transistor and the power output to form a Darlington circuit, and
This is a step-down automatic chopper circuit in which a series circuit of a resistor and a constant voltage element is provided in parallel to a power input, and a connection point between the resistor and the constant voltage element is connected to the base of the oscillation transistor.

[Function] With this configuration, conventional dedicated control
The oscillation and control circuit part that was performed by IC is
This can be realized with only one oscillation transistor, a resistor, and a constant voltage element. In other words, one oscillation transistor and several associated components function as both an oscillator and an error amplifier in a step-down chopper circuit, which was conventionally performed using a dedicated control IC. It is possible. Therefore, the number of parts of the chopper circuit as a whole can be extremely reduced, making it possible to reduce the size and cost.

[Example] The present invention will be explained in more detail below based on the drawings. The drawing is a circuit diagram showing an embodiment of the step-down automatic chopper circuit according to the present invention. This chopper circuit includes a switching transistor _Q1 connected in series with a load _RL , an oscillation transistor _Q2 for controlling on/off of the switching transistor _Q1 , and a rectifying and smoothing section. This rectifying and smoothing section is a circuit including a chiyoke coil L connected in series with the load R _L , a smoothing capacitor C ₁ and a diode D connected in parallel.

Here, the present invention is significantly different from the prior art in the connection structure of the oscillation transistor _Q2 and the circuitry associated therewith. That is, in this invention,
The oscillation transistor _Q2 is connected between the base of the switching transistor _Q1 and the power output. In this example, a switching transistor
A PNP power transistor is used as _Q1 ,
Its base is connected via the base current limiting resistor _R2
Connected to the collector of NPN oscillation transistor _Q2 . Also, the emitter of the oscillation transistor _Q2 is
It is connected to the connection between the chiyoke coil L and the smoothing capacitor _C1 , that is, to the power output. In other words, switching transistor Q ₁ and oscillation transistor Q ₂
constitutes a Darlington circuit. Further, a series circuit of a resistor R ₁ and a constant voltage element (a Zener diode ZD in this embodiment) is provided in parallel with the power input, and a connection portion between the resistor R ₁ and the Zener diode ZD and the oscillation transistor Q It is connected to the base of ₂ . Note that a positive feedback capacitor _C2 is attached between the base and emitter of the oscillation transistor _Q2 . Although this positive feedback capacitor _C2 is not particularly necessary in principle, it is desirable to install it in order to stably connect the oscillation operation of the oscillation transistor _Q2 .

Now, the operation of this circuit is as follows. First, when the DC input voltage V _IN is applied to the power supply input, a voltage is applied from the resistor R ₁ to the base of the oscillation transistor Q ₂ , and the oscillation transistor Q ₂ is turned on (conducting state).
becomes. Thereby switching transistor
_Q1 is also turned on and a voltage is generated at the power supply output.
Here, when the input voltage V _IN exceeds the Zener voltage V _ZD of the Zener diode ZD, the oscillation transistor
The base voltage of Q ₂ will be established at the Zener voltage V _ZD . The output voltage V _OUT tries to rise further, but the output voltage V _OUT is lower than the Zener voltage V _ZD
When the voltage of the oscillating transistor _Q2 exceeds the sum of the base-emitter voltage V _BE (V _OUT ≧ V _ZD + V _BE ),
This time, oscillation transistor _Q2 is turned off (non-conducting state)
becomes. Thereby switching transistor
Since Q ₁ is also turned off, power supply to the power supply output is stopped. Then, the energy stored in the chiyoke coil L is transferred to the load R _L and the diode D.
released through. As the energy is released, the output voltage V _OUT decreases, so the output voltage V _OUT eventually becomes the Zener voltage V _ZD and the oscillation transistor.
It is lower than the sum of the base-emitter voltage V _BE of Q ₂ (V _OUT < V _ZD + V _BE ). Then, the oscillation transistor _Q2 is turned on again, the switching transistor _Q1 is also turned on, and the output voltage _VOUT increases.

Thereafter, such a cycle is repeated, and self-oscillation is performed. Therefore, according to the present invention, the output voltage
V _OUT is the Zener voltage V _ZD and the oscillating transistor Q ₂
It is controlled to a constant value determined by the sum of the base-emitter voltage _VBE . Therefore, by appropriately selecting and using constant voltage elements, it is possible to easily accommodate chopper circuits having different output voltages.

[Effects of the invention] Since the present invention is a step-down self-excited chopper circuit configured as described above, the oscillation/control circuit portion can be assembled with only a few individual parts, so the number of parts as a whole is significantly reduced. This makes the circuit simpler, more reliable, significantly smaller and cheaper, and if the parts used have sufficient withstand voltage, the output voltage can be increased, and so on. It can produce excellent practical effects.

[Brief explanation of drawings]

The drawing shows an embodiment of a step-down self-excited chopper circuit according to the present invention. Q ₁ ... switching transistor, Q ₂ ... oscillation transistor, L ... chiyoke coil, C ₁ ...
...Smoothing capacitor, D...Diode, _R1 ...
Resistor, ZD... Zener diode.

Claims (1)

[Scope of utility model registration request] It includes a switching transistor connected in series with the load, an oscillation transistor that controls on/off of the switching transistor, and a smoothing capacitor and a diode connected in parallel with a chiyoke coil connected in series with the load. In a step-down chopper circuit equipped with a rectifying and smoothing section, the oscillation transistor is connected between the base of the switching transistor and the power output to form a Darlington circuit, and a resistor and a constant voltage are connected in parallel to the power input. A step-down self-excited chopper circuit comprising a series circuit with an element, and a connection point between the resistor and the constant voltage element and a base of the oscillation transistor.