JPS635433Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a ripple removal circuit for removing power ripples occurring in power lines of various electronic circuits.

In general, in various electronic circuits, in order to obtain a stable operating state, a DC stabilized power supply is used to stabilize the power supply voltage against DC level fluctuations in the power supply voltage. In order to eliminate the power supply rip, a ripple filter made up of passive elements and a ripple removal circuit made up of active elements are used to remove the power supply rip.

Conventionally, as the above-mentioned ripple removal circuit, for example, one using a time constant of a resistor 14 and a capacitor 15 as shown in FIG. 1, or a negative feedback control loop using an error amplifier 24 as shown in FIG. 2 has been used. are widely used.

Conventional ripple removal circuit 10 shown in FIG.
uses an NPN transistor 13 whose collector is connected to the input terminal 11 and whose emitter is connected to the output terminal 12 as a so-called series pass element, and a resistor 14 and a capacitor 15 connected in series between the input terminal 11 and ground Connect midpoint above
It is formed by connecting the base of an NPN transistor 13.
In the conventional ripple removal circuit 10 having such a configuration, the voltage drop V _R due to the resistor 14 and the base-emitter voltage V _BE (V _BE ≒
The sum voltage V _R +V _BE 〓0.6V is the voltage drop of the power supply voltage by the ripple removal circuit 10, and the power supply ripple removal ability is determined by the time constant of the resistor 14 and capacitor 15. I get tired.
Therefore, if the resistance value of the resistor 14 is made small in order to reduce power loss, the ability to remove power supply ripples will decrease, and in order to efficiently remove power supply ripples of low frequency components, it is necessary to use the capacitor 14.
The disadvantage was that the capacity of 5 had to be extremely large.

Further, the conventional ripple removal circuit 20 shown in FIG. 2 uses a PNP transistor 23 whose emitter is connected to the input terminal 21 and whose collector is connected to the output terminal 22 as a series pass element, and the power supply ripple component on the output terminal 12 side is is amplified by the error amplifier 24 and the above PNP transistor 2
It is structured to return to the base of 3. In the ripple removal circuit 20 having such a configuration, a PNP transistor 23 as a series pass element is used.
Since the operating state of the error amplifier 24 is feedback-controlled via the error amplifier 24, the collector-emitter voltage _VCE of the PNP transistor 30 becomes a drop voltage due to the ripple removal circuit 20, resulting in less power loss. The structure is complicated, and it is also extremely difficult to set the collector-emitter voltage _VCE .

Generally, a ripple removal circuit is used to remove power supply ripples in a power supply line stabilized by a stable DC power supply, so if the power loss caused by the ripple removal circuit is large, the power supply voltage must be set high in advance. In this case, it becomes impossible to drive various electronic circuits, so it is necessary to reduce the power loss as much as possible.

Therefore, in view of the problems of the conventional examples as described above, the present invention provides a ripple removal circuit with a new configuration that can efficiently remove power supply ripples by using a capacitor with small power loss and small capacitance. It is.

Hereinafter, the present invention will be described in detail with reference to the drawings showing one embodiment.

The ripple removal circuit according to the present invention has a first transistor 33 whose emitter is connected to an input terminal 31 and whose collector is connected to an output terminal 32, as shown in the principle circuit configuration in FIG. a second transistor 34 having a conductive structure equal to that of the transistor 33 and whose emitter is connected to the output terminal 32, and the collector of the second transistor 34 is connected in series with a shunt resistor 35 for a time constant. is grounded via a resistor 36 and a capacitor 37, the base of the second transistor is grounded via the capacitor, and the base of the first transistor 33 is connected to the collector of the second transistor 34. Become.

The first transistor 33 is used as a series pass element, and is feedback-controlled via the second transistor 34 to output from the collector an output voltage Vout in which the power supply ripple component on the emitter side is suppressed. Further, the second transistor 34 constitutes a collector feedback type amplifier circuit connected to a feedback circuit having a time constant formed by the resistor 36 and the capacitor 37 in an alternating current manner, and has a frequency determined by the time constant. Feedback control of the first transistor 34 is performed using the characteristics.

The effects of the ripple removal circuit 30 according to the present invention having the above-mentioned principle structure will be explained in detail with reference to a specific embodiment shown in FIG.

That is, the ripple removal circuit 3 shown in FIG.
0 is a first transistor 33 and a second transistor 34, both of which have a PNP conductive structure.
, and the above-mentioned first
The emitter of the first transistor 33 is connected to the output terminal 32, and the collector of the first transistor 33 and the emitter of the second transistor 34 are connected to the output terminal 32. Then, the first transistor 3
The base of No. 3 is connected to the input terminal 31 via a first resistor 41 and to the collector of the second transistor 34 via a second resistor 42 . In addition, the above second PNP
The collector of the transistor 34 is connected to a third resistor 35.
It is grounded via a fourth resistor 36 and a capacitor 37 connected in series. Furthermore, the second transistor 3
The base of No. 4 is connected to the fourth resistor 43 through the fifth resistor 43.
It is connected to the connection point between the resistor 36 and the capacitor 37.

In the embodiment configured as described above, the second transistor 34 constitutes a collector feedback type amplifier circuit using the fourth resistor 36 as a feedback resistor, and in terms of direct current, the collector voltage Vc and the base potential V _B It operates in a state where they are approximately equal. Therefore, the sum of the base-collector voltage V _CE1 in the first transistor 33 and the base-emitter voltage V _BE2 in the second transistor 34 is equal to
It is approximately equal to the sum of the base-emitter voltage V _BE1 in No. 3 and the voltage drop V _Dr due to the second resistor 42, and the following equation holds true: V _CE1 +V _BE2 ≈V _BE1 +V _Dr. And in this example,
The first transistor 33 and the second transistor 34 have the same conductive structure.
Since PNP type transistors are used, the base-emitter voltages V _BE1 and V _BE2 are approximately equal, and the collector-emitter voltage of the first transistor 33 is
V _CE1 , that is, the voltage drop caused by the ripple removal circuit 30, can be arbitrarily set by the resistance value of the second resistor 42, and can be lowered to 0.1V or less. Furthermore, since the temperature dependence of each of the base-emitter voltages V _BE1 and V _BE2 is approximately equal, DC-like output level fluctuations due to temperature changes in the ripple removal circuit 30 can be made extremely small. Note that the second resistor 42 can be omitted as OΩ in principle.

Furthermore, in the embodiment with the above-described configuration, the base of the second transistor 34 is grounded via the capacitor 37 in an AC manner, so that the power ripple component on the output terminal 32 side is amplified by the second transistor 34. and the first transistor 3
Returned to the base of 3. Therefore, by the action of the feedback loop formed via the second transistor 34, the AC power supply ripple component on the input terminal 32 side is removed on the output terminal 32 side, and the output voltage +Vout without power supply ripple is generated. is obtained at the output terminal 32.

In the above-described embodiment, when the ratio of the voltage fluctuation on the output terminal 32 side to the voltage fluctuation on the input terminal 31 side, that is, the ripple removal coefficient, was actually measured, an experimental result of 20 to 40 dB was obtained.

Furthermore, in the embodiment configured as described above, the fourth resistor 36 serving as the feedback resistor of the second transistor 34 is configured so that the first transistor 33 has a collector current Ic as small as necessary for feedback control of the second transistor 34. The first transistor 3
If the gain of 4 is α, a small current of Ic/α needs to be fed back to the base of the first transistor 34, so that a large resistance value can be set.

Therefore, the fourth resistor 36 and capacitor 37
The capacitor 37 has a smaller capacitance than the conventional example described above.
can be used to eliminate power supply ripples of low frequency components.

Note that in the above embodiment, each transistor 33,
34, a PNP type transistor is used to remove the power supply voltage rip for the positive power supply voltage +Vin line, but each of the above transistors 33,
By using an NPN transistor as 34, it is possible to eliminate power supply ripples on the negative power supply voltage -Vin line.

As is clear from the description of the embodiments described above, according to the present invention, the transistor has a first transistor having an emitter connected to an input terminal and a collector connected to an output terminal, and a conductive structure equal to that of the first transistor. a second transistor whose emitter is connected to the output terminal; the collector of the second transistor is grounded via a shunt resistor, a time constant resistor connected in series, and a capacitor; The base of the first transistor is grounded via the capacitor, and the base of the first transistor is connected to the collector of the second transistor to form a ripple removal circuit, which reduces power loss with a simple configuration. It is possible to provide a ripple removal circuit that can efficiently remove power supply ripples of low frequency components even when using a small capacitance capacitor, and the intended purpose can be fully achieved.

[Brief explanation of drawings]

FIGS. 1 and 2 are circuit diagrams showing conventional examples of ripple removal circuits. FIG. 3 is a circuit diagram showing the basic circuit configuration of the ripple removal circuit according to the present invention. FIG. 4 is a circuit diagram showing a specific embodiment of the present invention. 30... Ripple removal circuit, 31... Input terminal, 32... Output terminal, 33, 34... First and second transistor, 35, 36... Resistor, 3
7... Capacitor.

Claims (1)

[Scope of utility model registration request] a first transistor whose emitter is connected to the input terminal and whose collector is connected to the output terminal;
a second transistor having a conductive structure equal to that of the transistor and having an emitter connected to the output terminal, and the collector of the second transistor is connected to a shunting resistor, a time constant resistor and a capacitor connected in series. and ground through the second
A ripple removal circuit comprising: a base of a transistor grounded via the capacitor; and a base of the first transistor connected to a collector of the second transistor.