JPS607906B2 - DC-DC converter circuit - Google Patents

Description

[Detailed description of the invention] The present invention relates to a DC-DC converter circuit.

Figure 1 shows a DC using external switching.
- A conventional example of a constant voltage circuit using a DC converter is shown. Transistor Q, . , Q, 2 are Darlint-connected switching output stages, configured to have a common collector, and connected to a mono-multi vibrator (hereinafter referred to as "mono-multi") 2 via transistors Q, 3. Therefore, the switching conduction period of the transistor Q,2 in the output stage corresponds to the time constant of the monomultiplier 2. Mono Multi 2 is Astable Multi Viprator (hereinafter referred to as Astable Multi) 1
The voltage comparator 3 controls the duty. The voltage switched by transistor Q,2 is applied to diodes D, . , inductance L, , capacitor C, . A constant voltage circuit is formed by controlling the monomulti 2 via the DC amplifier 3 for feedback. In order to qualitatively explain the efficiency of the constant voltage circuit using the DC-DC converter shown in FIG.
, 2 is assumed to be 50%, and the unstable voltage is assumed to be 12V.

The voltage at the emitter of transistor Q8 is shown in FIG. That is, assume that the transistors Q and 2 are in the ON state and the output current is, for example, 30 hA. Transistor Q, . , Q,2, the base current of transistor Q,2, which is the control current of the switching output stage, is 300.
'100≠3hA, so transistors Q, . The base current of is known as 0.0. When the resistor r is set to IKQ~0, the voltage drop due to the resistor is equal to the voltage drop of the transistor Q, . , Q, about 0 of the voltage drop across the base semiconductor junction of 2
．． It can be ignored compared to 7V. Therefore, the emitter potential of transistor Q,2 when conductive is 10.6V'. Also, the moment transistors Q and 2 switch from conducting to non-conducting,
Inductance L,. Because the current of transistor Q. operates in the direction of maintaining continuity due to its action, the current of transistor Q. 2
From the moment -J becomes non-conducting, the inductance L, . are diodes D, . Supplied from ground via. Therefore, when transistor Q,2 is cut off, transistor Q
, 2 is connected to the diode D, . The forward voltage drop is approximately 0.8V. Therefore, the transistor Q,
2 is turned ON and FF with a duty of 50%, the average voltage of the transistor Q and 2 becomes 49V as shown by Va in FIG. Output current: 30hA
Then, the current flowing through the transistors Q and 2 is approximately 15 hA since the duty is 50%. Also, circuits 1, 2, and 3 that control switching of transistors Q and 2
Let the circuit current of 1 shoe be A. Also, the inductance L, .
Assuming that the resistance component is 0.60, and assuming that the switching is completely ON and FF without any transient phenomenon, calculate the input/output efficiency shown in FIG. The average voltage ya of the transistor Q, 2 is 4.9V as shown in Figure 2, but the output voltage of the converter circuit in Figure 1 is Va-06 due to the resistance of the inductance L, 0.6Q. ×0.3〒4.7V, so the output power is 4.7×0.3=1.41W. However, the input power is 12V×0.
3×0.5 (Due7i)=1.8W. Also, if the resistor r2 is set to 0, the resistor r2 is grounded through the transistor Q,3 when the transistor Q,2 is not conductive.
, consumes 12'3 x 0.5 = 2hA. Therefore, the stove, 2
, 17mA x 12V≠0.2W in combination with the circuit current of 3.
It will be consumed. Therefore, the input/output efficiency is; Hatao;;
o-7o5, which is a typical efficiency of conventional switching power supplies of about 70%. The present invention realizes a circuit configuration that can further increase the efficiency to about 90%,
One embodiment will be described below based on the drawings.

FIG. 3 shows a configuration in which the voltage drop across the switching element during conduction can be reduced by making the switching output stage emitter-grounded.

In this case, the load current is 30 A, which is exactly the same as the conventional example shown in Figure 1.
, assuming a duty of 50% and a power supply voltage of 12V, ``By flowing about 18 hA as the base current of transistor Q through resistor r, the voltage drop of transistor Q can be reduced to about 0.2V or less.In this case. As shown in Fig. 4, the collector potential of the transistor Q can be set to 11.8V when it is turned on.The potential when it is OFF can be set to -Q8V.
Then, the average potential Va is 85.5V.
The output current is 30 hA, and the resistance of inductance L is 0.
．． 60, the output voltage is 5.5-0.6×0.3±
It becomes 5.3V, and the output power is 5.3 x 0.3 = 1.59
It becomes W. If the circuit currents of i, 2, and 3 (same as in Figure 1) are 18 hA in total, and the base current of transistor Q is 15'2 = 7.5 mA since the duty is 50%, the total is 15 + 7.5 characters. 23 hA, and since the input current of transistor Q is 50% duty, it is 3 hA.
00/2=15 mhA. Therefore, the input power is 12×
(The efficiency is approximately 76%, which is higher than the conventional example shown in Figure 1.) Figure 5 shows an example of the configuration according to the present invention.
It can be increased to 0%. In the configuration shown in Figure 2, the base current of the switching output stage was consumed through the resistor and transistor Q2. It is characterized in that it is used as a circuit current by flowing it through the diode D2 and the capacitor C2, rectifying it to a constant voltage there, and using it as a power source for the control circuit consisting of circuits 1 and 2. In the case of FIG. voltage 1
If the voltage is 2V, the base current of the transistor Q is 15hA, and the Zener potential of the Zener diode D2 is 6V, the resistance r3 can be set by selecting a value of about 4000. FIG. 6 shows a specific example of a constant voltage circuit using the present invention. Transistors Q4 and Q5 constitute an asteful multiplier, and the collector waveform of transistor Q4 is shown in FIG. 7a. This oscillation frequency is approximately 30KHz,
Determine the switching frequency of the transistor. From the collector of transistor Q5, capacitor C8, resistor r,
A negative pulse generated at the trailing edge shown in FIG. 7a through a differential circuit of 7 triggers a monomulti 2 consisting of transistors Q and Q7. Transistor Q? The output waveform of is shown in FIG. 7b. a in FIG. 7 through resistors r2 and r4,
The waveform b is applied to the base of transistor Q2, and transistor Q2 conducts during the to period shown in FIG. 7c. Therefore, during this period, the base current of transistor Q3 becomes low. Flows through the transistor Q2, so that the base current of the transistor Q is applied to the Zener diode D2 and the capacitor C2 through the emitter-collector of the transistor Q3 and the resistor 3, and is rectified. The collector potential of transistor Q is c as shown in Figure 7d.
The switching voltage corresponds to the diode D, ,
The output voltage Vout is averaged by a filter section including an inductance L and a capacitor C, and further reduced by an inductance L2 and a capacitor C6 to obtain an output voltage Vout. The output voltage is applied to the base of the voltage comparison transistor false via the voltage adjustment volume VR, and is compared with the Zener potential of the Zener diode D2 connected to the emitter of the transistor Q9. When the output voltage Von becomes higher than the set value, more base current of transistor Q flows, which lowers the collector potential of transistor Q9, more base current flows of transistor Q8, and as a result, more collector current of transistor Q flows. , Figure 7b
The time constant bm of the monomulti 2 shown in FIG. Therefore, the conduction period (ta+blood) of the transistor Q2 becomes shorter, the conduction period of the transistor Q becomes shorter, the duty of the transistor Q becomes smaller, and the average voltage is controlled to decrease. When the output voltage Vout falls below the set value, it is corrected in the opposite direction to that described above. Note that the resistor r is for initial oscillation, and if the resistor r were not present, the potential of the capacitor C2 would be zero at the moment when the input voltage Vin was applied, so the collector potential of the transistors Q4 and Q7 would be zero potential, and the collector potential of the transistor Q2 would be zero. is cutoff, the base current of transistor Q3 flows, and transistor Q is not conductive. Therefore, capacitor C2 is not charged and transistor Q does not oscillate. The capacitor C2 is charged by inserting a resistor r, and the transistor Q4
, Q5's Asteful Multi 1 oscillates. conducts, and the base current connects capacitor C2 to Zener diode D via resistor r3.
It can be charged up to a potential of 2. Therefore, the resistance r may have a sufficiently larger value than the resistance r3, and the power consumption by the resistance r can be sufficiently reduced. Furthermore, as is clear from the explanation of Fig. 6, the base current of the transistor Q is rectified into a constant voltage by the energizing diode D2, and is used as the circuit power supply for circuits 1 and 2, and at the same time as the reference voltage of the voltage comparator. We are using.

Furthermore, in the present invention, the diode D of the switching output section,
By using a Schottky diode, the constant voltage circuit can be designed to have a very high efficiency of about 92%.
Naturally, when the output current becomes large, the voltage obtained by rectifying the base current of the transistor Q is used not only to supply the circuit power supply of the control circuit consisting of 1 and 2, but also to the other circuit 6 (Fig. 5). It can be used as a power source. Furthermore, the switching element is not limited to transistors. As described above, according to the present invention, the switching output stage has an emitter-grounded configuration, and the control current of the switching element of the switching output stage is rectified to be used as the circuit power supply current of at least the control circuit of the switching output stage, so that the input/output efficiency can be improved. This can be increased to about 90%.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of the conventional example, Figure 2 is a waveform diagram of each part,
Fig. 3 is a configuration diagram illustrating the reduction in voltage drop in the switching element when the switching output stage is emitter-grounded and conductive, Fig. 4 is a waveform diagram of each part, and Fig. 5 is an embodiment of the present invention. FIG. 6 is a diagram showing a specific circuit example, and FIG. 7 is a waveform diagram of each part thereof. 1... Astable multivibrator, 2... Mono multivibrator, 3... Voltage comparator, Q
,...Switching output stage (mitter grounded type), D
2.…” Zener diode. Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7

Claims (1)

[Scope of Claims] 1. A DC device characterized in that the switching output stage has an emitter-grounded configuration, and the control current of the switching element of the switching output stage is rectified to be used as the circuit power supply current of at least the control circuit of the switching output stage. -DC converter circuit. 2. The DC-DC according to claim 1, characterized in that the control current of the switching element is rectified to a constant voltage using a Zener diode and a capacitor to serve as a circuit power supply and as a reference voltage for constant voltage control. converter circuit.