JPH0132752B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a DC-DC converter that outputs a predetermined DC voltage corresponding to a reference voltage.

Conventional configuration and its problems A DC-DC converter efficiently converts a predetermined DC voltage that is different from the voltage value of the input DC power supply by using a switching transistor that operates in a pulsed manner and a smoothing section that smooths the output pulse voltage. It is produced well and is supplied as a power supply voltage to the load section (electronic circuit). In conventional DC-DC converters, the base current of the switching transistor is kept constant when it is on. That is, assuming the maximum supply current I _{p nax} to the load section, a sufficiently large base current is supplied to the switching transistor so as to output I _{p nax} . On the other hand, the required current I _p at the load varies depending on its operating state, and is usually much smaller than the maximum supply current I _{p nax} (approximately 1/
2 to 1/10). As a result, an excessive current is supplied to the base of the switching transistor, causing the following problems.

(1) Power loss increased and conversion efficiency decreased.

(2) The amount of charge accumulated at the base of the switching transistor increased, and the accumulation time and fall time became longer, making it impossible to increase the pulse frequency of the DC-DC converter.

First, to explain (1), the maximum supply current is
If I _{p nax} = 2.5 A and the worst value h' _FE min of the DC amplification of the switching transistor is 25, then a current larger than I _B = 2.5/2.5 = 100 mA must be supplied as the base current. DC like this
- I _p as the load current of the DC converter in use
= 0.5A, then I _L = (2.5−
0.5)/25=80mA equivalent base current becomes excessive. Assuming that the voltage of the DC power supply on the input side is V _S = 15 V, a loss equivalent to P _S = V _S・ I _L = 1.2 W has occurred (in reality, it is multiplied by the on-time ratio of the switching transistor). There is a need). As a result, the efficiency of the DC-DC converter was decreasing.

Next, to explain (2), when the switching transistor changes from the on state (saturated) to the off state, the switching transistor maintains the on state until the charge accumulated in the base is exhausted. This time is called the accumulation time. Storage time is the time required to discharge the stored charge in the base and tends to increase significantly with excessive base current. If the accumulation time is long, the pulse frequency of the switching transistor is limited and cannot be made to a sufficiently high frequency (if the pulse frequency is high and its period approaches the accumulation time, the on-time ratio of the switching transistor must be reduced). (This makes it impossible to control the output voltage to the desired value.) When the pulse frequency decreases,
It is necessary to increase the capacitance of the smoothing inductance element and capacitor, which increases their size. In other words, the external size of the DC-DC converter becomes large, which is undesirable. Also, if the accumulation time is long, the fall time (when the output current is 90% of the specified value)
10%) is also large, and the collector loss associated with switching of the switching transistor is also large.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a DC-DC converter that improves the above points, has low base current loss of the switching transistor, and is capable of high-speed switching operation.

Structure of the Invention In order to achieve the above object, the present invention includes a DC power supply, a switching transistor that pulses the power supply path from the DC power supply to the load section, and a switching transistor that smooths the pulse voltage generated by the switching transistor. smoothing means for supplying a DC voltage to the load section by the smoothing means; pulse generation means for obtaining a pulse signal of a predetermined frequency with a pulse width responsive to the voltage supplied to the load section by the smoothing means; The DC-DC converter is equipped with a pulse control means for turning on and off the switching transistor at a corresponding on-time ratio, the pulse control means being proportional to or approximately equal to the DC current supplied to the load section. Current detecting means for obtaining a current signal that changes proportionally; Current mirror means receiving the current signal of the current detecting means on an input side and outputting a current proportional or substantially proportional to the current signal; and the current mirror means. pulsing means that turns the output current of the current mirror means into a pulse current by turning on and off the input current to the pulse generator according to the pulse signal of the pulse generating means; It has a supply means for supplying current including a DC component, and the current detection means, the current mirror means, and the supply means convert the base current of the switching transistor when it is on into the DC current supplied to the load section. The structure is such that the amount can be increased or decreased accordingly.

Further, in order to achieve the above object, the present invention includes a DC power source, a switching transistor that pulses and connects the power supply path from the DC power source to the load section, and a switching transistor that smooths the pulse voltage generated by the switching transistor. smoothing means for supplying DC voltage to the load section; pulse generation means for obtaining a pulse signal of a predetermined frequency with a pulse width responsive to the voltage supplied to the load section by the smoothing means; and a pulse generation means corresponding to the pulse width of the pulse signal. The DC-DC converter is provided with a pulse control means for turning on and off the switching transistor at a certain on-time ratio, the pulse control means being proportional or substantially proportional to the DC current supplied to the load section. a current detecting means for obtaining a changing current signal; and a first circuit receiving the current signal of the detecting means on an input side and outputting a current proportional or substantially proportional to the current signal.
and a first current mirror means in which the output current of the first current mirror means is made into a pulse current by turning on and off the input current to the first current mirror means by a pulse signal of the pulse generating means. pulsing means, first supply means for supplying the pulsed current including a DC component as a base current when the switching transistor is turned on, and a common connection terminal connected to the emitter side of the switching transistor; The second current mirror means has an output terminal connected to the base side, and the input current of the second current mirror means is turned on and off by the pulse signal of the pulse generating means. a second supply means for supplying a current to short-circuit between the base and emitter of the switching transistor from the output terminal of the switching transistor; The base current when the switching transistor is on is increased or decreased in accordance with the DC current supplied to the load section, and the base current is accumulated when the switching transistor is off by the second current mirror means and the second supply means. It is configured to form a charge discharge path.

DESCRIPTION OF EMBODIMENTS The present invention will be described below based on illustrated embodiments. FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, the switching transistor 12 is turned on and off by a high frequency pulse signal (approximately 100KHz), and is connected to the DC power supply 11 (V _S = 15V).
The power supply path from the load unit 20 to the load unit 20 is intermittent in a pulse manner. This pulse voltage V _i is smoothed by a smoothing section 13 consisting of a freewheeling diode 32, an inductance element 33, and a capacitor 34, and the on-time ratio of the switching transistor 12 (ratio of on-time to one on-off cycle) ) is converted into a DC voltage proportional to
0. The voltage V _p applied to the load section 20 is detected by the voltage detection section 14 . Voltage detection section 14
The output voltage V _d becomes V _d =V _p /2, assuming that the values of the resistors 35 and 36 are equal. On the other hand, the reference voltage generating section 15 including a constant voltage diode 37 and resistors 38, 39, and 40 outputs a predetermined reference voltage _Vr obtained by dividing the Zener voltage generated by the diode 37 by resistors 38 and 39. Detection voltage V _d and reference voltage V _r
is input to the pulse signal generator 16, and a high frequency pulse signal A having a pulse width corresponding to the voltage difference between the two is obtained.

FIG. 2 shows a specific example of the configuration of the pulse signal generator 16. V _r and V _d are input to a differential amplifier 43,
The difference between the two is amplified by a predetermined gain. The oscillator 44 oscillates a sawtooth wave D of approximately 100 KHz, and this sawtooth wave D and the amplified output E of the differential amplifier 43 are compared by a comparator 45 to produce a high frequency pulse signal A. That is, the frequency of the high frequency pulse signal A is the oscillation frequency of the oscillator 44 (approximately 100 KHz).
The pulse width is determined by the differential voltage V _r −V _d .

The output pulse signal A of the pulse signal generator 16 is input to the pulse controller 17 to obtain a current pulse C for controlling the switching transistor 12 on and off. In the pulse control section 17, the current detection section 18 detects the DC current I _p supplied to the load section 20, and the pulse supply section 19 generates a current pulse signal C having a peak value corresponding to the output B. ,
The signal is supplied to the base of the switching transistor 12.

FIG. 3 shows a specific example of the configuration of the current detection section 18. _I0 is detected as a voltage drop across a resistor 51 inserted in series in the current path, and a first emitter follower consisting of a transistor 52 and a constant current source 53, a transistor 54 and a resistor 55 (when the switch 57 is on, the resistor 56 is also It is converted into a current _i1 by a second emitter follower consisting of a In other words, the base-emitter voltages V _BE of the transistors 52 and 54 are canceled out, so that i ₁ = k ₁ · I ₀ (1) k ₁ = R ₅₁ /R ₅₅ (2) when off). Here, R ₅₁ and R ₅₅ are the resistance values of resistors 51 and 55,
Usually, R ₅₅ ≧100·R ₅₁ is set so that the current i ₁ is sufficiently smaller than I ₀ . Here, R ₅₁ =
0.1Ω, R ₅₅ = 250Ω, and i ₁ = I ₀ /2500. After the current _i1 is reversed by a current mirror formed by transistors 58 and 59, it is supplied to a constant current source 6.
It is added to the current I ₂ of 0 and becomes the output signal B. In other words, B=i ₁ +I ₂ (3). Here, I ₂ =0.05mA.

FIG. 4 shows a specific example of the configuration of the pulse supply section 19. When the pulse signal A is "L" (approximately 0V), the transistor 72 is turned off. Diodes 73, 74, transistors 75, 76, resistor 7
7 and 78 constitute a current mirror circuit, and a current C obtained by multiplying the output current B of the current detection section 18 by a predetermined gain k ₂
(If the emitter area of the transistor 76 is made large, the gain k ₂ is determined by the ratio of the resistors 77 and 78, and here k ₂ =100).
When the pulse signal A is "H" (approximately equal to V _S ), the output current C of the current mirror circuit becomes zero. That is, the current pulse C corresponding to the pulse signal A is as follows: C={k ₂ ·B (A="L") 0 (A="H") (4).

The current pulse C is the switching transistor 12
The base current becomes the base current, which turns the switching transistor 12 on and off.

Next, the voltage control operation of the embodiment shown in FIG. 1 will be explained. When the switching transistor 12 is turned on, the voltage V _S (15 V) of the DC power supply 11 is output (Vi≈V _S ), and power is supplied to the load section 20 via the inductance element 33 . When the switching transistor 12 is turned off, the freewheel diode 32 becomes conductive and supplies the energy stored in the inductance element 33 to the load section 20.
As a result, the voltage _Vp applied to the load section 20 is smoothed by the diode 32, inductance element 33, and capacitor 34 of the smoothing section 13, and has a value corresponding to the on-time ratio of the switching transistor 12.

The voltage V _p of the load section 20 is detected by the voltage detection section 14, and the detected voltage V _d is compared with the reference voltage V _r of the reference voltage generation section 15, and a high frequency pulse width corresponding to the difference voltage between the two is generated. A pulse signal A is generated by a pulse signal generator 16, and the on-time ratio of the switching transistor 12 is controlled via a pulse controller 17. As a result, the switching transistor 12, the smoothing section 1
3. A voltage feedback loop is constituted by the voltage detection section 14, the pulse signal generation section 16, and the pulse control section 17, and control is applied so that the detected voltage V _d matches the reference voltage V _r . That is, the applied voltage V _p of the load section 20 is controlled to a predetermined value (here, 5 V).

Next, the effect of reducing base current loss in this embodiment will be explained. Assuming I _{p nax} = 2.5 A and h _FE min = 25, 100 mA is required as the base current of the switching transistor 12, and if 100 mA is supplied as the base current regardless of the load current, I ₀
It has already been explained that when = 0.5A, a base current loss equivalent to 80mA occurs. In this embodiment, the base current of the switching transistor 12 when it is turned on is made responsive (proportional) to the current I ₀ supplied to the load section 20 by the operation of the current detection section 18 and the pulse supply section 19 of the pulse control section 17. It is increased when I ₀ is large, and decreased when I ₀ is small.
Therefore, the base current loss when I ₀ is small is significantly reduced. For example, when I ₀ = 0.5A,
Since i ₁ = 0.2 mA and B = i ₁ + I ₂ = 0.25 mA, C
= _k2・B=25mA. As a result, (100
-25) = base current loss equivalent to 75mA is reduced. This corresponds to 1.5V×0.075A×1/3=0.375W when the on-time ratio is V _p /V _S =1/3. Here, the value of the resistor 51 for current detection is R ₅₁ =
Because it is sufficiently small at 0.1Ω, the loss is 0.1×
0.52=0.025W, which is small. Such a base current loss reduction effect becomes large when the current I ₀ to the load section 20 is small. Therefore, the DC-DC converter of this embodiment is extremely effective when supplying the DC voltage V _p to a load where the supply current I ₀ changes significantly.

Furthermore, if the configuration of this embodiment is adopted, the base current C when the switching transistor 12 is on increases or decreases in proportion to the control current I ₀ to the load section 20, so the supply current I ₀ is Even if it is made larger than _{p nax} , the switching transistor 12 normally operates on and off.

Note that when the output voltage of the DC-DC converter increases from the state where the applied voltage V _p of the load section 20 is zero, the initial base current of the switching transistor 12 corresponds to I ₂ of the constant current source 60. (C = k ₂ · I ₂ = 5 mA), and although the switching transistor 12 is not completely turned on, as the voltage V _p applied to the load section 20 increases, the current I ₀
becomes large, the output B of the current detection section 18 becomes large, the base current C becomes large, and the switching transistor 12 comes to perform complete on/off operation, supplying a predetermined voltage and current to the load section 20. It becomes like this. In other words, positive feedback occurs transiently, and the voltage V ₀ applied to the load section 20 rapidly increases.
It quickly settles down to a predetermined value. In order to operate such positive feedback operation stably and to reduce base current loss, it is desirable to set as follows.

Even when the supply current _I0 to the load section 20 is zero, a predetermined small base current is supplied to the switching transistor 12 (when turned on).

The conversion gain k ₁ from the supply current I ₀ to the output B in the current detection unit 18 and the base current C of the switching transistor 12 from B in the pulse supply unit 19
The total product of the transfer gain k ₂ to the switching transistor 12 and the current amplification h _FE of the switching transistor 12 k ₁・k ₂・h _FE is 1
Make it. Actually switching transistor 1
_{Since the current} amplification _{degree h FE of} During current operation, the switching transistor 12 is not turned on sufficiently, increasing power loss.Furthermore, if k ₁ · k ₂ · h _FE is too large, excessive base current may be supplied to the switching transistor 12. (The effect of reducing base current loss becomes smaller.) k ₁・k ₂・
In order to bring _hFE as close to 1 as possible, a switch 57 is provided in the current detection section 17 (see FIG. 3) of the above-described embodiment. That is, when h _FE of the switching transistor 12 is large, the switch 57 is turned off to make k ₁ small, and when h _FE is small, the switch 57 is turned on to make k ₁ large.

In the above-mentioned embodiment, since the base current of the switching transistor is brought close to the required value, the amount of charge stored in the base is small, and the storage time and fall time are also short. In order to further reduce these times, conventionally a resistor (1KΩ) was installed between the base and emitter of the switching transistor 12.
degree) was connected. However, in this configuration, an extra current (0.7V/1KΩ=
0.7 mA), and the effect of reducing the accumulation time and fall time by the resistor was not sufficient.

FIG. 5 shows the configuration of the pulse supply section 19 provided in the pulse control section 17 that has improved these points. The overall configuration is the same as that shown in FIG. 1, and the pulse signal generating section 16 and current detecting section 18 are the same as those shown in FIGS. 2 and 3, and their explanation will be omitted. The pulse supply section 19 (included in the pulse control section 17) in FIG. 5 includes an on-current supply section 101 (corresponding to first means) that supplies a current pulse to turn on the switching transistor 12;
It is constituted by an off-current supply device 102 (corresponding to second means) that supplies a current pulse to turn off the switching transistor 12.

When pulse signal A is “L”, transistor 7
2 and 112 are turned off, and when on current is supplied, 101
operates, a base current C=I _B1 =k ₂ ·B is supplied to the switching transistor 12, and the switching transistor 12 is turned on. At this time, each transistor 115, 1 of the off-current supply device 102
17 and 118 are off, and their output current I _B2 is zero.

When pulse signal A is “H”, transistor 7
2,112 turns on, and the on-current supply device 101
current mirror circuit (diodes 73, 74,
Transistors 75, 76 and resistors 77, 78) are turned off, and current I _B1 becomes zero. A constant current source consisting of a resistor 121, a diode 122, and a transistor 123 is connected to the transistor 7 of the current mirror circuit.
5 and 76 are configured to switch from on to off at high speed. The current value is about 1 mA, which is sufficiently smaller than I _B1 . Off current supply device 10
Since transistor 112 of No. 2 is on, a predetermined current i ₃ determined by resistors 113, 114, 116 and transistor 115 flows. Its value is i ₃
= about 0.3mA. Current i ₃ is transistor 1
17, 118 and resistors 119, 120, the off-state current I _B2 =3 mA is amplified by a predetermined factor (approximately 10 times) to the base of the switching transistor 12. The emitter area of the output side transistor 118 of the current mirror circuit is 10 times that of the diode-connected transistor 117, and the value of the resistor 119 is set to 1.
20 is set to 10 times the current amplification factor (resistance 119 is set to 100Ω and resistor 120 is set to 10Ω to reduce the voltage drop there. In reality, there are no resistors 119 and 120. (current mirror operation is performed). A common connection end of the current mirror circuit is connected to the emitter side of the switching transistor 12, and a collector (output end) of the output transistor 118 is connected to the base of the switching transistor 12. Therefore, the output current I _B2 of the off-current supply device 102 rapidly discharges the charge accumulated between the emitter and base of the switching transistor 12, and the accumulation time and fall time are significantly shortened. . In fact, the off-current
I _B2 decreases as the accumulated charge is discharged, and when the charge is exhausted, I _B2 =0. Therefore, even if the off-state current I _B2 is increased, no substantial power loss occurs.

As the high-frequency pulse signal A changes from "H" to "L" to "H", on-current I _B2 and off-current I _B2
are generated in a complementary or substantially complementary manner, causing the switching transistor 12 to turn on and off at high speed.

The off-state current supply 102 having such a configuration has a remarkable effect of speeding up the switching of the switching transistor 12, and unlike a conventional DC-DC converter, the on-current supply has a constant current pulse (I ₀ Even if the system does not respond (no response), a significant effect can be obtained.

In the embodiment described above, the supply current I ₀ to the load section 20
Since the switching transistor 12 is supplied with a base current proportional to There is a risk of causing FIG. 6 shows the configuration of the current detection section 18 provided in the pulse control section 17 that improves this point. The overall configuration is almost the same as that in FIG. 1, and its explanation will be omitted. The current detection section 18 in FIG.
A proportional current generator 201 outputs a current B that is proportional to the current I ₀ supplied to 0, and an overcurrent generator that operates to reduce the reference voltage V _r of the reference voltage generator 15 when the current I ₀ becomes larger than a predetermined value. It is composed of a detector 202. The proportional current generator 201 has the same configuration as the current detection section shown in FIG. 3, and its operation is also the same. A predetermined voltage I ₄ and R ₂₂₁ is generated by the current I ₄ of the constant current source 219 of the overcurrent detector 202 and the resistor 221 (resistance is R ₂₂₁ ), and the current
The voltage drop R ₅₁ · I ₀ due to I ₀ and the predetermined voltage R ₂₂₁ · I ₄ are compared by the differential transistors 214 and 215 (the base-emitter voltage of the transistor 52 and the forward voltage of the diode 220 cancel each other out). ).
The collector currents of transistors 214 and 215 are compared by a current mirror of transistors 216 and 217, and depending on the difference, transistor 21
A base current of 8 is supplied and current amplified to an output current of ₅ . That is, I _{p nax} = (R ₂₂₁ /R ₅₁ )・I ₄
Then, when I ₀ ≦I _{p nax} , i ₅ = 0, and I ₀
>I _{p nax} , i ₅ increases in response to (I ₀ −I _{p nax} ). Output current i ₅ of overcurrent detector 202
is applied to the reference voltage _Vr point of the reference voltage generating section 15 (the connection point between the resistors 38 and 39 in FIG. 1). Therefore, when I ₀ becomes larger than I _{p nax} , the reference voltage V _r becomes smaller, and the voltage V _p applied to the load section 20 also becomes smaller due to the operation of the voltage feedback loop. As a result, the supply current _I0 to the load section 20 is prevented from becoming excessive (for example, even if the load section 20 is momentarily short-circuited, the maximum supply current is
I _{p nax} ). As a result, current breakdown and thermal breakdown of the switching transistor 12 are prevented.

In the above-mentioned embodiment, a fixed frequency pulse width modulation type using a sawtooth wave oscillator was explained as an example, but the present invention is not limited to such a case.
It goes without saying that a method using self-sustained oscillation may also be used. Furthermore, it is not limited to a step-down type DC-DC converter, but may be a step-up type, a reverse voltage type, or a DC-DC converter using a transformer, and it goes without saying that the present invention includes these converters. others,
Various modifications can be made without changing the spirit of the invention.

Effects of the Invention As described above, according to the present invention, the base current of the switching transistor when it is on can be increased or decreased according to the DC current supplied to the load section by the current detection means, the current mirror means, and the supply means. This has the following effects.

(a) Since the base current of the switching transistor when it is on corresponds to the current supplied to the load, the switching transistor can be turned on reliably.

(b) The base current loss of the switching transistor can be reduced when the supply current is small.

(c) The base excess current of the switching transistor is reduced, the amount of charge stored in the base is reduced, and the discharge time is also shortened. That is, high-speed switching of the switching transistor becomes possible.

Therefore, if a DC-DC converter for a DC voltage source for measuring equipment or electromechanical equipment is constructed based on the present invention, it will become a compact, highly efficient, and power-saving power supply source.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, and FIG.
FIG. 3 is a specific configuration diagram of the pulse signal generator 16, FIG. 3 is a specific configuration diagram of the current detection unit 18, FIG. 4 is a specific configuration diagram of the pulse supply unit 19, and FIG. 5 is a specific configuration diagram of the pulse supply unit 19. Another configuration diagram of the section 19, FIG. 6 is another configuration diagram of the current detection section 18. 11... DC power supply, 12... Switching transistor, 13... Smoothing section, 14... Voltage detection section, 15... Reference voltage generation section, 16... Pulse signal generation section, 17... Pulse control section, 18 ... Current detection section, 19 ... Pulse control section, 20 ... Load section.

Claims (1)

[Scope of Claims] 1. A DC power supply, a switching transistor that pulses and connects a power supply path from the DC power supply to the load unit, and a pulse voltage from the switching transistor that is smoothed and supplied to the load unit. a smoothing means, a pulse generating means for obtaining a pulse signal of a predetermined frequency with a pulse width responsive to the voltage supplied to the load section by the smoothing means, and the switching at an on-time ratio corresponding to the pulse width of the pulse signal. A DC-DC converter equipped with a pulse control means for turning on and off a transistor, the pulse control means controlling a current for obtaining a current signal that changes in proportion or substantially proportion to the DC current supplied to the load section. a detection means; a current mirror means which receives the current signal of the current detection means on its input side and outputs a current proportional or approximately proportional to the current signal; pulsing means that turns the output current of the current mirror means into a pulse current by being turned on and off by a pulse signal; and a supply that supplies the pulse current including a DC component as a base current when the switching transistor is turned on. The DC current detecting means, the current mirror means, and the supplying means increase or decrease the base current of the switching transistor when it is on in accordance with the DC current supplied to the load section. -DC converter. 2. A DC power source, a switching transistor that pulses and connects the power supply path from the DC power source to the load section, a smoothing means for smoothing the pulse voltage from the switching transistor and supplying the smoothed voltage to the load section, and pulse generating means for obtaining a pulse signal of a predetermined frequency with a pulse width responsive to the voltage supplied to the load section by the means; and turning on and off the switching transistor at an on-time ratio corresponding to the pulse width of the pulse signal. The DC-DC converter is equipped with a pulse control means for controlling the current, and the pulse control means includes a current detection means for obtaining a current signal that changes in proportion or approximately proportion to the DC current supplied to the load section; A first receiving the current signal of the detection means on the input side and outputting a current proportional or substantially proportional to the current signal.
and a first current mirror means in which the output current of the first current mirror means is made into a pulse current by turning on and off the input current to the first current mirror means by a pulse signal of the pulse generating means. pulsing means, first supply means for supplying the pulsed current including a DC component as a base current when the switching transistor is turned on, and a common connection terminal connected to the emitter side of the switching transistor; The second current mirror means has an output terminal connected to the base side, and the input current of the second current mirror means is turned on and off by the pulse signal of the pulse generating means. a second supply means for supplying a current to short-circuit between the base and emitter of the switching transistor from the output terminal of the switching transistor; The base current when the switching transistor is on is increased or decreased in accordance with the DC current supplied to the load section, and the base current is accumulated when the switching transistor is off by the second current mirror means and the second supply means. A DC-DC converter that is characterized by forming a charge discharge path.