JPS605773A - Dc-dc converter - Google Patents

Abstract

PURPOSE:To reduce the base current loss of a switching transistor by outputting a pulse having a peak value in response to a DC current supplied to a load, and supplying the pulse as a control current of the transistor. CONSTITUTION:A switching transistor 12 is turned ON or OFF by a high frequency pulse signal from a pulse supply unit 19. The applied voltage to a load 20 is detected by a voltage detector 14, the detecting voltage and a reference voltage are inputted to a pulse signal generator 16, and the high frequency pulse signal of the pulse width in response to the differential voltage of both is outputted. This signal is applied through a pulse controller 17 to the transistor 12. The output of a current detector 18 is applied to a pulse supply unit 19, and the peak value of the current to the transistor 12 is controlled in response to a load current.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention 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 through the operation of a switching transistor that operates in a pulsed manner and a smoothing section that smoothes the output pulse voltage. In conventional DC-DC converters, the base current when the switching transistor is on is kept constant.In other words, the maximum supply current to the load Assuming IOmax, a sufficiently large base current was supplied to the switching transistor to output Iomax.On the other hand, the required current at the load section was 1
o varies depending on its operating conditions and is usually much smaller than the maximum supply current Iomax (approximately 1/2 to '/1o
degree). As a result, 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 increases, and the accumulation time and fall time become large.
, the pulse frequency of the DC-DC converter could not be increased.

Trout, (1)! To elaborate, the maximum supply current is 1
If omax = 2.51A and the worst value of DC amplification of the switching transistor hpEmin = 25, then IB = 2.5/15 = 1 as the base current.
A current greater than 00mA must be supplied. In this way, if Io=0.5A is not required as the load current when the C-DC converter is in use, I L
= (2,5-0,5)/25 = The base current equivalent to 80mA becomes excessive. The voltage of the DC power supply on the input side is V
If S" is 15V, a loss equivalent to PS-Vc, 4t, = 1.2W has occurred (actually, it is necessary to multiply by the on-time ratio of the switching transistor)
. As a result, the efficiency of the DC-DC converter was decreasing.

Next, to explain (2), the switching transistor changes from the on state (saturated) to the off state! 71 When switching, the switching transistor remains on until the charge stored in the base is exhausted.

This time is called the accumulation time (A).

The storage time is the time required to discharge the accumulated charge in the base, and tends to increase significantly with excessive base current. If the accumulation time is large (1) [In this case, the switching transistor's 7sll pulse frequency power is limited and cannot be made to a sufficiently high frequency.0 [When the pulse frequency is high and its period approaches the accumulation time, the switching The on-time ratio of the transistor cannot be reduced (and the output voltage cannot be controlled to the desired value). As the pulse frequency becomes lower, it is necessary to increase the capacity of smoothing inductance elements and capacitors, and their shapes become larger. That is, the external size of the DC-DC converter becomes large, which is not preferable. Also, if the accumulation time is long,
The fall time (time for the output current to change from 90% to 10% of the predetermined value) is also long, and the collector loss associated with the 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-mentioned object, the present invention includes a DC power source, a switching transistor that randomly connects and disconnects the power supply path from the DC 1 to the load section, and a pulse voltage smoothed by the switching transistor. smoothing means for supplying DC voltage to the load section; voltage detection means for detecting the voltage supplied to the load section; and reference voltage generation means for obtaining a reference voltage.

pulse signal generating means for obtaining a high frequency pulse signal with an on-time ratio corresponding to the difference between the output of the voltage detecting means and the output of the reference voltage generating means; and the switching transistor in response to the output pulse of the pulse signal generating means. on/off
The pulse control means has a current detection means for detecting the DC current supplied to the load section, and a peak value responsive to the output of the current detection means. The device includes a pulse supply means for obtaining a current pulse in response to an output pulse of the pulse signal generation means, and is configured to supply the current pulse of the pulse supply means as a control current of the switching transistor.

Further, in order to achieve the above object, the present invention includes a DC power supply, a switching transistor that pulse-intermittents a power supply path from the DC power supply to a load, and a pulse voltage generated by the switching transistor that is smoothed to a smoothing means for supplying DC voltage to the load section; a voltage detection means for detecting the voltage supplied to the load section; and a base r for obtaining a reference voltage.
(← Voltage generating means, m pulse signal generating means for obtaining a high frequency pulse signal with an on time ratio corresponding to the difference between the output of the distribution voltage detecting means and the output of the reference voltage generating means, and pulse control means for turning on and off the switching transistor; the pulse control means includes first means for supplying a pulsed base current to the switching transistor; and second means for discharging the charge accumulated between its emitter and base when turned off, said second means
The switching transistor has a current mirror circuit whose common connection end is connected to the transmitter side and whose output end is connected to the base side, and is complementary or substantially complementary to the pulse current of the first means. The second pulse current
It is configured to be input to the current mirror circuit of the means.

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 (6) is turned on and off by a high frequency pulse signal (approximately 100 KH2),
DC power supply Ql) (V5=15V) to load section (1)
The power supply path to the circuit is intermittent in pulses.

This pulse voltage Vi is applied to the freewheel diode (b), the inductance element (to), and the capacitor (b).
The DC voltage is smoothed by a smoothing section consisting of a switching transistor (b), and converted into a DC voltage proportional to the on-time ratio (ratio of on-time to one cycle of on/off), and supplied to the load member. The voltage vo applied to the load section (a) is detected by the voltage detection section α◆. Voltage detection part Q
The output voltage Vd of No. 4 becomes Vd-Vo/2, assuming that the values of the resistances (to) and (to) are equal. On the other hand, the constant voltage diode (b) and the resistor C! A standard consisting of 4 (to) rings.
The voltage generating section (c) outputs a predetermined reference voltage vr obtained by dividing the Zener voltage generated by the diode by the resistor (2). The detection voltage Vd and the reference voltage Vr are input to a pulse signal generating section a, 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 O. Vr and Vd are input to a differential amplifier, and the difference between IIti1 is amplified to a predetermined gain. Oscillator) is approximately 100K
A sawtooth wave H2 is oscillated, and this sawtooth wave and the amplified output E of the differential amplifier are compared by a comparator (c) to produce a high frequency pulse signal A. That is,
The frequency of the high-frequency pulse signal A is determined by the oscillation frequency (approximately 100 KHz) of the oscillator θ◆, and the pulse width is determined by the differential voltage Vr-Vd.

The output pulse signal A of the pulse signal generator O is input to the pulse controller (b), and the switching transistor (b)
A current pulse C is obtained to control the on/off. The pulse control section Q'h controls the direct current 1. supplied to the load section (E). is detected by the current detection section (G), and a current pulse signal C having a peak value corresponding to the output B is sent to the pulse supply section (1).
1 produced by the switching transistor (6)
The signal is supplied to the base of tI.

FIG. 8 shows a specific example of the configuration of the voltage ε detection section (g).

l as the voltage drop across a resistor inserted in series with the current path.

The first transistor consisting of transistor Akira 4 and constant current sister
Emitter follower, transistor and resistor - (
Switch i5? The current 11 is replaced by a second emitter follower consisting of a resistive terminal (also added when l is on). In other words, the base-emitter voltage VBE of the transistor 62 and the foundation are canceled out, resulting in i1 = kt, Io - (1) R51... (2) k1'''' Rss (when the switch is off) It's time for this.
s1. Rss is the resistance value of resistance superiority and -, and 1 piece'h
The current 11 is made to be sufficiently smaller than IO by setting Rss≧100·R51. Here, Rs.
t=0.1Ω.

Set R55 = 250Ω, i1 = I (1/2500
G, t,).・The 1st ward style is transistor■
After the current mirror is reflected, the current I2 of the constant current source and the force 11 are summed, and the output signal B becomes t). That is, B=i1+I2 (3). Here, it is set to hI2-0.05mA.

FIG. 4 shows a specific example of the configuration of the pulse supply section a. When pulse signal A is "L" (approximately OV).

Transistor (7 days will be off. Diode US 9
<, transistor ffl f7Q, resistance (c) (to)
constitutes a current mirror circuit, and outputs a current C which is the output current B of the current detection section (G) doubled to a predetermined gain. is determined by the ratio of resistance Qη and σ mallet, here kz = 100). Pulse signal A is “H” [
(approximately equal to Vs), the output current C of the current mirror circuit becomes zero. That is, the current pulse C corresponding to the pulse signal A is 2.B(A=L) C=t OCA=H) (4).

The current pulse C becomes a base current of the switching transistor (6), and turns the switching transistor (2) on and off.

Next, the voltage control operation of the embodiment shown in FIG. 1 will be explained. When the switching transistor @ turns on, the voltage Vs (15V) of the DC power supply (l) is output and V in CVi
s) supplying power to the load member via the inductance element Z; When the switching transistor υ is turned off, the freewheeling diode () becomes conductive and supplies the energy stored in the inductance element to the load member. As a result, it is smoothed by the diode (to) of the smoothing part a, the inductance element, and the capacitor (b),
The pressure Vo applied to the load member has a value corresponding to the on-time ratio of the switching transistor (2).

The voltage vO of the load section is detected by the voltage detection section α→, and the detected voltage Vd is compared with the reference voltage Vr of the reference voltage generation section. The high-frequency pulse signal A) is generated by the pulse signal generator CI, and the on-time ratio of the switching transistor (2) is controlled via the pulse controller a'tt.As a result, the on-time ratio of the switching transistor (2) is
), smoothing section (transformer), voltage detection section 04, pulse signal generation section CI [9 and pulse control section Q? ) constitutes a voltage feedback loop, and control is applied so that the detected voltage Vd matches the reference voltage Vr. That is, the voltage Vo applied to the load section (1) is controlled to a predetermined value (here, 5V).

Next, the effect of reducing base current loss in this embodiment will be explained. Iomax ss 2.5A, hFEmi
If H=25, the switching transistor (
It has already been explained that 100 mA is required as the base current for (b), and if 100 mA is supplied as the base current regardless of the load current, a base current loss equivalent to 80 mA will occur when Io" is 0.5 A. In this implementation In the example,
The switching transistor (6
) is the supply current I to the load section (7) when it is on.
It changes in response (proportional) to o, increasing when IO is large and decreasing when IO is small. Therefore b 1
The base current loss when 0 is small is significantly reduced.

For example, when I,=0.5A, it=0.
2mA b B =il + I2 = 0.25mA
Therefore, C=R2・B=25mA.

As a result, the base current loss equivalent to (100-25)=75 mA is reduced. This changes the on-time ratio to Vo
/Vs -”/B, 15VX0.075A
Corresponds to X1/3 = 0.875W. Here, since the value of the current detection resistor Ell is sufficiently small as R51=0.1Ω, its loss is o,1 x O,52=0.
It is small at 0.025W. Such a base current loss reduction effect becomes large when the current IO to the load section (e) is small. Therefore, when supplying the DC voltage vO to a load where the supply current I0 changes significantly, the DC()C
Converters are extremely effective.

In addition, if the configuration of this embodiment is used, the base current C when the switching transistor @ is on is the load section (1
) increases or decreases in proportion to the supply current Io to ), so even if the supply current IO is made larger than Iomax, the switching transistor (2) normally turns on and off.

Note that when the applied voltage vO of the load section (4) is zero, the DC
- When the output voltage of the DC converter increases (increasing), the initial base current of the switching transistor 0 sweep will be a value corresponding to 12 of the constant current source (C=2・I 2
= 5 mA), and the switching transistor (2
) is not completely turned on, but as the voltage Vo applied to the load section (7) increases, the current IO also increases, the output B of the current detection section (G) increases, and the base current C increases, causing the switching transistor to (l is full on
It turns off, and the load section starts supplying a predetermined voltage and current. That is, positive feedback occurs transiently, and the voltage Vo applied to the load section (E) increases rapidly and 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.

(c) to enable a predetermined small base current to be supplied to the switching transistor (2) even when the supply current IO to the load section (e) is zero (when turned on).

■ A conversion gain kl from the supply current Io to the output B in the current detection section (to), and a transfer gain of 2 from B to the base current C of the switching transistor (b) in the pulse supply section (1'), The total product kl- of the current amplification degree hFE of the switching transistor (b) is set to 1 by 2·hFE. In reality, the current amplification degree hF of the switching transistor (b)
Since E is likely to fluctuate, it is preferable to set 0.8≦ and 1・R2・hFE≦5 − (5) (if 2・hFE is too small for kl−, the switching transistor during high current operation (b) will not be turned on sufficiently, resulting in increased power loss.Also, if bkl・R2・hFE is too large, excessive base current will be supplied to the switching transistor (b), resulting in base current loss. (The reduction effect will be smaller.)
.

In order to bring kl·lo -hFE as close to 1 as possible, a switch extension η is provided in the current detection unit α (see FIG. 8) of the above-described embodiment. That is, when hFE of the switching transistor (6) is large, the switch fIη is turned off to make the value 1 smaller, and when hFE is small, the switch is turned on to make the value 1 larger.

In the above-described 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 (about IKQ) was connected between the base and emitter of a switching transistor. However, in such a configuration, an extra current (0.7V/IKΩ=0
．． 7+nA), and the effect of reducing the storage time and fall time by the resistor was not sufficient.

FIG. 5 shows the configuration of the pulse supply section α provided in the pulse control section a''tr that has improved these points.The overall configuration is the same as that in FIG. and the current detection section (g) have the same configuration as shown in FIGS. 2 and 8, and their explanation will be omitted.

The pulse supply unit 0s (included in the pulse control unit αη) in FIG. 5 is an on-current supply unit (101) (first
) and an off-current supply (corresponding to the means of
102) (corresponding to the second means).

When the pulse signal A is “L”, the transistors (7 and (
112) is turned off, the on-current supply device (101) operates, and the base current C=IBl''k2・B is supplied to the switching transistor (6), and the switching transistor (2) is turned on. Current supply (
102), each transistor (115) (117) (11
8) is off, and its output current IB2 is zero.

When the pulse signal A is “H”, the transistor rJa(1
12) turns on, and the current mirror circuit (diode (c) +741.) of the on-current supply device (101), transistor ff119 fff9, resistor ff7H71111
) is turned off, and the current IB1 becomes zero. Resistance (121
), a diode (122), and a transistor (128), the constant current source is configured so that the current mirror circuit's transistor (amplifier) changes from on to off at high speed.The current value is about 1 mA, and the current value is about 1 mA, Since the transistor (112) of the off-current supply device (102) is on, the resistance (118) (1
14) (116), a predetermined current i3 determined by the transistor (115) is applied.

Its value is about i3=0.8mA. The current i3 is
Transistors (117) (118), resistors (119) (
120) by a current mirror circuit consisting of
The base G of the switching transistor (b) is amplified by about 10 times) and supplies an off-current lBz''JmA.

The emitter area of the output side transistor (118) of the current mirror circuit is the diode-connected transistor (118).
17), the value of the resistor (119) is 10 times that of the resistor (120), and the current amplification factor is 10 times (the resistor (119) is 100Ω, (1
20) is set to 10Ω to reduce the voltage drop there. In reality, current mirror operation is performed even without resistors (119) and (120). The common connection end of the current mirror circuit is connected to the emitter side of the switching transistor (b), and the collector (output end) of the output transistor (118) is connected to the base of the switching transistor (b). Therefore, the off-current supply (10
2) The output current IBz rapidly discharges the charge accumulated between the emitter and base of the switching transistor @, and the accumulation time and fall time are significantly shortened. In reality, the off-state current IB2 decreases as the accumulated charge is discharged, and when there is no charge (IB2=0), there is no substantial power loss even if the off-state current IB2 is increased. .

High frequency pulse signal A is “H” //L” //H”...
・As the on-current IB1 and off-current IB1 change, the on-current IB1 and off-current I
B2 is generated in a complementary or substantially complementary manner, and turns the switching transistor (2) on and off at high speed.

The off-current supply device (102) having such a configuration has a remarkable effect of speeding up the switching of the switching transistor (6), and unlike the conventional DC-DC converter, the on-current supply device generates a constant current pulse ( IO).

This is something that can have a big effect.

In the above-mentioned embodiment, since the base current proportional to the supply current IO to the load section (e) is supplied to the switching transistor (6), if a short circuit occurs in the load, for example, an excessive current will not be generated. There is a risk that the current will flow to the switching transistor (2) and cause current breakdown or thermal breakdown of the switching transistor (6). The configuration of the current detection unit (to) provided in the pulse control unit αη that improves this point is shown in the sixth example.
As shown in the figure. The overall configuration is almost the same as that in FIG. 1, and its explanation will be omitted. The current detection section (c) in FIG. 6 detects the current I supplied to the load section.

A proportional current generator (201) that outputs a current B proportional to
The overcurrent detector (202) operates to reduce the reference voltage Vr of the reference voltage generator (g) when the current IO becomes larger than a predetermined value. The proportional current generator (201) has the same configuration as the current detection section shown in FIG. 8, and its operation is also the same. Overcurrent detector (2
Current I4 of constant current source (219) of 02) and resistance (221
) (resistance is R221), the specified voltage I4・R
221 and voltage drop R51・1 due to current IO
0 and a predetermined voltage r<ul-14, the differential transistor (21
4) and (215) are compared (base-emitter voltage of transistor value 4 and diode (220')
forward voltages are canceled out). Transistor (214)
The collector current of and (215) is the transistor (216)
and (217), and the base current of the transistor (218) is supplied according to the difference, and the current is amplified to become the output current i5. Sunaitsuchis Iomax=()yamato(tob IO≦Iomax
When IO>Iomax, i6 increases in response to (lo-1,)max). The output current ib of the overcurrent detector (202) is applied to the reference constant voltage VrO point (the connection point between the resistor (c) and the resistor (c) in FIG. 1) of the reference voltage generator (g). Therefore s IO
is 1. When it becomes larger than max, the reference voltage Vr becomes smaller, and the voltage Vo applied to the load section 4 also becomes smaller due to the operation of the voltage feedback loop. As a result, load section (1)
This prevents the supply current IO from becoming excessive (for example, even if the load section (a) is momentarily short-circuited, the maximum supply current is limited to about I6max). As a result, current breakdown and thermal breakdown of the switching transistor (6) are prevented.

In the above-mentioned embodiments, 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 automatic oscillation may also be used. In addition to step-down type DC-DC converters, DC-DC converters that use step-up type, reverse voltage type, or transformers are also available.
It goes without saying that a C converter may be used and is included in the present invention. In addition, various cracks and shapes are possible without changing the gist of the present invention.

Effects of the Invention The DC-DC converter of the present invention reduces the base current loss of the switching transistor by &1 Jt2, and shortens the storage time and fall time of the switching transistor. Therefore, if a DC-DC converter for DC m-voltage reduction of 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 the drawing]

FIG. 1 is a 1pY diagram representing an embodiment of the present invention, FIG. 2 is a specific configuration diagram of the pulse signal generator (lf19), FIG. 8 is a specific configuration diagram of the current detection unit (g), and FIG. Figure 4 is a specific configuration diagram of the pulse supply section 01, and Figure 5 is the pulse supply section O.
Other configuration diagram of I1. FIG. 6 is another configuration diagram of the current detection section Oen. 0υ...DC power supply, (2)...Switching I transistor, Time...Smoothing part, α4...Voltage detection part, 0
G...Reference voltage generation section, (1...Pulse signal generation section, α...Pulse control section, (G)...Current detection section,
(a) Pulse control unit, (7) Negative counter agent Yoshihiro Morimoto Figure 2 43 Figure 4 2

Claims (1)

[Scope of Claims] 1. A DC power source, a switching transistor that connects and connects the power supply path from the DC power source to the load section in a pulsed manner, and a DC voltage that smooths the pulse voltage from the switching transistor to supply the DC voltage to the load section. smoothing means for supplying;
Voltage detection means for detecting the voltage supplied to the load section, reference voltage generation means for obtaining a reference voltage, and high-frequency pulses having an on-time ratio according to the difference between the output of the voltage detection means and the output of the reference voltage generation means. A pulse signal generating means for obtaining a signal, and a pulse control means for turning on and off the switching transistor in response to an output pulse of the pulse signal generating means, the pulse control means supplying a signal to the load section. and a pulse supply means for obtaining a current pulse having a peak value responsive to the output of the current detecting means and responsive to the output pulse of the pulse signal generating means, A DC()C converter in which a current pulse from the pulse supply means is supplied as a control current to the switching transistor. 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, and a smoothing means that smoothes the pulse voltage from the switching transistor to supply the DC voltage to the load section.
@if A voltage detection means for detecting the voltage supplied to the load section, a reference voltage generation means for obtaining a reference voltage, and an on-time ratio according to the difference between the output of the voltage detection means and the output of the reference voltage generation means. The device includes a pulse signal generation means for generating a high frequency pulse signal, and a pulse control means for turning on and off the switching transistor according to the high frequency pulse signal, and the pulse control means is configured to generate a pulse signal for turning on the switching transistor. a first means for supplying a base current; and a second means for discharging the charge accumulated between the emitter and base of the switching transistor when the switching transistor is turned off; The means has a current mirror circuit whose common connection end is connected to the emitter side of the switching transistor and whose output end is connected to the base side, and the means has a current mirror circuit whose common connection end is connected to the emitter side of the switching transistor and whose output end is connected to the base side, and which generates a pulse that is complementary or substantially complementary to the pulse current of the first means. DC-DC current input to the current mirror circuit of the second means
converter.