JPS5920269B2 - Chopper type switching regulator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a chopper type switching regulator that steps down an input power supply voltage and supplies a stable output voltage to a load.

A conventional example of a chopper type switching regulator with an overcurrent protection circuit is shown in FIG. 1 and will be described below.

The circuit shown in FIG. 1 is a switching regulator that converts the DC level by controlling the opening and closing of a transistor Q1 connected in series between a DC power source E and a load. In this switching regulator, a primary winding N of a choke transformer T is connected between a transistor Q1 and a DC power source E, and a secondary winding N2 is connected to the primary winding N. , the output of the secondary winding N2 is applied between the emitter and pace of the transistor Q. Further, a tertiary winding N3 is provided which is coupled to the primary winding NlVC, so that the energy stored in the choke transformer T is released through the tertiary winding N3VC. Also, a level setting circuit LS is connected to the base of the transistor Q1, and a resistor is connected to the transistor Q. are connected in series, and when an overcurrent occurs, the voltage drop of the resistor type causes the transistor Q,
A bypass circuit is connected to the overcurrent protection circuit that makes the transistor Q
1 is configured to convert the DC level by opening and closing the Flil legs. With this configuration, the opening and closing of the transistor Q can be controlled without a pulse width modulation circuit or the like, the circuit configuration is simple, and overcurrent protection can be provided. However, the circuit shown in Figure 1 requires three transformer windings (Nl, N2, N3).
Not only does the structure of the Chiyoke transformer T become complicated,
The elements used in the overcurrent detection circuit are useless under normal conditions.

Furthermore, since the circuit shown in FIG. 1 directly controls the switching transistor Q by the level setting circuit LS of one transistor, the gain is low and the regulation is therefore poor.

Furthermore, in the case of a high-power DC-to-DC converter, since power is required for the control system, efficiency cannot be improved unless a switching transistor with a high DC current amplification factor Hfe is selected and used. Furthermore, the oscillator circuit generally performs an operation called transistor saturation type blocking oscillation.

In this oscillation operation, by controlling the base current of the switching transistor Q1, the collector current saturation of the switching transistor Q1 is used to turn off the switching transistor Q1 and reduce the output voltage. Since the base current is supported by the DC output according to the deviation value between the reference voltage and the reference voltage, the pace current is always suppressed to the minimum necessary current value during the conduction period of the switching transistor Q. The collector-emitter saturation voltage of Q1 cannot be made sufficiently small.

Moreover, when the switching transistor Q1 is turned off, the saturation of the collector current is slow and it is insufficient to draw out the accumulated carriers.
The power loss of No. 1 is large and has been a major obstacle to improving the efficiency of this type of switching regulator. In addition, when the input voltage Vi is high or the load current is light, the output impedance of the level setting circuit LS, which shunts the pace current of the switching transistor Q, when the feedback amount of the negative feedback system is large is the base of the switching transistor Q1. Since the impedance is lower than the input impedance, the conduction trigger signal obtained from the transformer winding during blocking oscillation is absorbed into the level setting circuit LS and cannot make the switching transistor 3tQ conductive.

Furthermore, after a while without being able to conduct to the switching transistor Q1, the output voltage V.
decreases, the amount of negative feedback decreases, and conduction becomes possible again.
That is, in such a state, as shown in FIG. 2A, normal blocking oscillation does not occur, but intermittent oscillation occurs. The circuit of FIG. 1 has an output voltage V as shown in FIG. 2b. A serious drawback was that a large ripple voltage was generated in the VC, making it unable to function as a stabilized power supply, resulting in a malfunction. Furthermore, the output voltage V is stable against all fluctuation factors such as input fluctuations and load fluctuations. Therefore, it has been difficult to design a negative feedback system and an oscillation system for switching operation without malfunction. The present invention was made in view of the above-mentioned points, and it is possible to improve efficiency with a simple circuit configuration, and also to have an overcurrent protection function without the need for a special overcurrent protection circuit. The object of the present invention is to provide a chopper-type switching regulator that has high voltage stability and does not suffer from intermittent oscillation. That is, the present invention includes an input power supply that supplies power to a load, a current detection circuit, a switching transistor that connects and converts the input power supply voltage to an AC voltage, and a choke transformer that smooths the AC voltage and converts it to a DC voltage. A smoothing capacitor is connected in series, a freewheeling diode is connected between the connection point of the switching transistor and the choke transformer, and the connection point of the input power supply and the smoothing capacitor, and the oscillation circuit that drives the switching transistor is connected between its base and emitter. In a chopper-type switching regulator connected to a smoothing capacitor to obtain a DC output voltage across the smoothing capacitor, a first reference voltage is compared with the first reference voltage and an output corresponding to the deviation value is obtained.
A comparator circuit and one transistor are used, and the sum of the output of the current detection circuit and the output of the first comparator circuit is added between the base and emitter of the transistor, and the voltage drop between the base and emitter is calculated as follows. The present invention is characterized in that it has a second comparison circuit which generates a trigger signal to turn off the oscillation circuit only when the sum of the outputs exceeds the second reference voltage.

An embodiment of the present invention is shown in FIG. 3 and will be described in detail below.

In the figure, a closed circuit is constructed by the input power source E, the emitter-collector of a switching transistor Q1 connected to its base with a starting resistor R, the primary winding N of a choke transformer T, and a smoothing capacitor C2. ing.

Further, a load current is connected to both ends of the smoothing capacitor C. A base input circuit consisting of a secondary winding N2, } of a transistor T, a parallel circuit of diodes D, D2, a capacitor C1, and a resistor R2 is connected in series between the base and emitter of a switching transistor Q. It is connected. The base input circuit, the switching transistor Q1, the primary winding N of the choke transformer T, the smoothing capacitor C2, and the starting resistor R1 constitute a blocking oscillation circuit, as well as the freewheeling diode D3 and the choke transformer. The primary winding N, of T, and the smoothing capacitor C2 constitute a reset loop for the excitation energy of the choke transformer T.

The switching regulator configured as described above is
This power supply is generally called a chopper, and has an output voltage V lower than the input voltage Vi of the input power supply E across the smoothing capacitor C2.

It is well known that this can be obtained, and the basic operation is also well known, so the explanation will be omitted. Furthermore, in the circuit of FIG. 3, a resistor R4 for detecting current is connected in series between the DC power source E and the emitter of the switching transistor Q, and a series circuit of the resistor R4 and the DC power source E is formed. are resistor R3, collector-emitter of transistor Q2,
A series circuit of eight Zener diodes and eight Zener diodes are connected in parallel.

A variable resistor VR is connected to both ends of the smoothing capacitor C2, and its movable terminal is connected to the base of the transistor Q2. Here, the operating current and voltage waveforms of each part of the circuit shown in FIG. 3 are shown in FIG.

In FIG. 4, the collector current 1cNb of the switching transistor Q1 is the primary current 1r. ．．
c is the current detection circuit output V2 and the voltage V across the resistor R,
and the base-emitter voltage VBE of transistor Q3.
It is a waveform.

In the chopper type switching regulator configured in this way, the output voltage V of the variable resistor R detects the voltage across the smoothing capacitor C2.

And a Zener diode? A reference voltage 2 is compared by the transistor Q2, and an output voltage V corresponding to the deviation value is obtained across the resistor R3 connected to the collector of the transistor Q2. In addition, a voltage V2 proportional to the triangular wave input current of the switching transistor Q1 is applied across the resistor R4.
I am getting . Therefore, the sum voltage of the voltages Vl and V2 obtained across the resistors R3 and R4 is applied between the base and emitter of the transistor Q3. As a result, the sum voltage of the voltages V, , V2 and the base voltage of the F transistor Q3 are
The sum voltage (V, +
V2) exceeds the voltage BO, the transistor Q3
The output shown in d in FIG. 4 is obtained at the collector of the transistor Q1, and the base current of the switching transistor Q1 is cut off by the collector output. Furthermore, the blocking oscillator circuit is rapidly shut off by drawing out the base storage carrier of switching transistor Q1. Therefore, the output voltage.

The output V of the transistor Q2 changes according to the deviation value of the voltage of the Zener diode 8, and the voltage V
2 will also change.

The peak value of the triangular wave input current proportional to the voltage V2 is controlled according to the deviation value of the reference voltage η, and the output voltage V is stable based on the well-known Chopper relational expression (4). is obtained. (where TO is the oscillation period and TON is the conduction period of the switching transistor Q.

That is, in the blocking oscillator circuit of the present invention, there is no diversion of the pace current due to negative feedback control during the conduction period of the switching transistor Q1, and a sufficiently large pace current is supplied from the secondary winding N2 of the transformer T to control the switching transistor Q1. Reduces collector-emitter saturation voltage.

Moreover, as shown in C and d of FIG. 4, the sum voltage (V,
+V2) is the base-emitter voltage VBT of transistor Q! When it exceeds j, the base current of the switching transistor Q1 can be drawn out for the first time, and even the base storage carrier can be drawn out sufficiently. As a result, the switching transistor Q1 is quickly shut off, so power loss can be significantly reduced, and as a result, power conversion efficiency can be improved. When the load becomes heavier, the peak value of the collector current of the switching transistor Q increases, and the voltage V2 across the resistor R4, which is proportional to this peak current, becomes the base-emitter voltage VBT! of the transistor Q. j
When the peak current exceeds 1, the switching transistor Q1 is turned off in the same manner as described above, and the peak value is held constant, so that the output current 1 flowing through the load is proportional to the peak current.

can be held constant. Thereby, it is possible to have a current carrying protection function called an output voltage droop type.
In other words, the transistor Q3 and which achieves the overcurrent protection function
Since the output of the transistor Q is further amplified even under a steady load, the gain of the negative feedback system is large, and the stability of the output voltage VO is improved without increasing the number of parts compared to the conventional example. be able to. Furthermore, since the collector current is zero when the switching transistor Q is turned on, the output V2 of the current detection circuit 1 is also zero, and the sum voltage (V1 + V2) does not exceed the base-emitter voltage BO of the transistor Q3, resulting in negative feedback control. has been stopped.

Therefore, all of the current obtained from the secondary winding N2 of the transformer T contributes to turning off the switching transistor Q1, and when the input voltage 1 increases or the load current becomes lighter, the current becomes negative. Even if the amount of negative feedback in the feedback system increases, normal locking oscillation can be maintained. Therefore, intermittent oscillation does not occur. According to the inventor's experiments, in the conventional example, the rated load is 50 to 60
% or less, while intermittent oscillation occurs in a light load state of less than 2% of the rated load, in the embodiment shown in Fig. It can work.

Further, while the conventional example shown in FIG. 1 requires three transformer windings, the embodiment shown in FIG. 3 only requires two, which allows for a simpler transformer configuration than the conventional example.

That is, the present invention has many improvements as described above, and can be realized with a very simple circuit configuration. Then the third
A modified embodiment of the figure is shown in FIG.

In the figure, 0M is a well-known one-shot multi-circuit equipped with an output terminal a that outputs a cutoff trigger signal that keeps the switching transistor Q in an off state for a certain period of time in response to a trigger input, and a trigger input terminal b.

The other circuit components are the same as the circuit components in FIG. 3, and the circuit in FIG. 5 has the same basic operation as the circuit in FIG. 3, so a description thereof will be omitted. The one-shot multi-circuit 0M can be configured by applying the trigger output obtained to the collector of the transistor Q3, which controls the peak value of the triangular wave input current according to the deviation value between the output voltage VO and the reference voltage V2, to the trigger input terminal b. , switching transistor Q1 for a certain period T.
A cutoff signal for turning off only the FF is obtained at the output terminal a.
As a result, the on period T of the switching transistor Q1 increases. N is the output voltage. It is controlled according to the deviation value between the voltage and the reference voltage 2. Therefore, switching transistor Q1
Since the off period of is constant, is there a relationship between chiyotsupa? Stable output voltage based on V. is obtained. That is, the embodiment shown in FIG. 5 not only provides the same effects as those described above, but also requires only one transformer winding, making it possible to realize the present invention with the simplest transformer configuration.

Further, another embodiment of the present invention is shown in FIG.

The circuit shown in FIG. 6 has almost the same circuit configuration as the circuit shown in FIG. 3, but the current detection circuit 10 has a primary winding N3 and a secondary winding N3.
4 and a resistor R4' connected in parallel to the secondary winding N4. In this way, compared to the case where a resistor as shown in FIG. 3 is used as the current detection circuit 10, since the embodiment of FIG. 6 uses a current transformer CT, the secondary winding of the current transformer CT The current detected by N4 can be converted into voltage by resistor RJ, and the voltage can be boosted by the primary/secondary turns ratio. Therefore, the primary winding voltage of the current transformer CT is small enough to obtain a voltage comparable to the base-emitter voltage VBO of the transistor Q3. In other words, the circuit shown in FIG. 6 can drastically reduce the insertion loss of the current detection circuit 10 and further improve the efficiency. Furthermore, a modified embodiment of FIG. 6 is shown in FIG.

The circuit of FIG. 7 connects the current detection circuit 20 to a
It is connected in series between the primary winding N, and the smoothing capacitor C2. In the current detection circuit 20, a current flows from the switching transistor Q1 through the primary winding N1 of the choke transformer T, and a current for resetting the excitation energy of the choke transformer T flows continuously through the freewheel diode D3. There is. Therefore, since the peak current detected by the current detection circuit 20VC is detected between the turn-off start time and the complete turn-off time, the cutoff trigger signal from the transistor Q3 is generated by the switching transistor Q. The cutoff trigger signal is applied to turn it off, and continues to be applied even after it is cut off. Therefore, the switching transistor Q
Not only is the switching loss of 1 lower,
It is possible to increase the safety margin of the transistor. Although the present invention has been described above based on each embodiment, it should be understood that the present invention is not limited to the above-mentioned embodiments, but can be further modified based on the technical idea described in the claims. Probably.

According to the present invention, efficiency can be improved with a simple circuit configuration as described above, a special overcurrent protection function can be shared, the output voltage is highly stable, and intermittent oscillation does not occur. It is possible to provide a chip type switching regulator that has a number of features such as:

[Brief explanation of the drawing]

Fig. 1: A circuit diagram showing a conventional example, Fig. 2: A diagram showing the operating voltage waveform of the circuit in Fig. 1, Fig. 3: A circuit diagram showing an embodiment of the present invention, Fig. 4: Fig. 3 5: A circuit diagram showing a modified embodiment of FIG. 3. FIG. 6: A circuit diagram showing another embodiment of the present invention.
Figure: A circuit diagram showing a modified embodiment of FIG. 6. E... Input power supply, Q1... Switching transistor, Q2, Q,... Transistor, R1... Starting resistor, R2, R3, R4...
...Resistance, T...Chiyoke transformer (N, .
l-order winding, N2: secondary winding), ? ...Zener diode, Dl, D2 ...Diode, D
3...Freewheel diode, VR...
...Variable resistor, C1...Capacitor, C2
...Smoothing capacitor, R, ...Load.

Claims (1)

[Scope of Claims] 1. An input power source that supplies power to a load, a current detection circuit, a switching transistor that intermittents the input power supply voltage and converts it into an AC voltage, and a choke transformer that smooths the AC voltage and converts it into a DC voltage. and a smoothing capacitor are connected in series, a freewheeling diode is connected between the connection point of the switching transistor and the choke transformer, and the connection point of the input power supply and the smoothing capacitor, and an oscillation circuit that drives the switching transistor is connected between its base and emitter. A chopper switching regulator that obtains a DC output voltage across a smoothing capacitor, the chopper switching regulator comprising: a first comparison circuit that compares the output voltage with a first reference voltage and obtains an output corresponding to a deviation value; and one transistor. The sum of the output of the current detection circuit and the output of the first comparator circuit is added between the base and emitter of the transistor, and the voltage drop between the base and emitter is used as a second reference voltage,
A chopper type switching regulator comprising a second comparator circuit that generates a trigger signal to turn off the oscillation circuit only when the sum of the outputs exceeds a second reference voltage. 2 A secondary winding is provided in the choke transformer, and the 2
The chopper type according to claim 1, wherein the oscillation circuit is constituted by a blocking oscillation circuit in which the next winding is connected between the base and emitter of the switching transistor, and a choke transformer is shared by the smoothing circuit and the oscillation circuit. switching regulator. 3 determining an off period of the switching transistor;
2. The chopper type switching regulator according to claim 1, wherein the oscillation circuit is constituted by a one-shot multi-circuit having a trigger input terminal triggered by the output of the second comparison circuit. 4. The chopper type switching regulator according to claim 1, wherein the current detection circuit is constructed of a resistor. 5. A primary winding that conducts a detection current, a secondary winding that converts the current detected by the primary winding, and a resistor that converts the current obtained by the secondary winding into a voltage. 2. The chopper-type switching regulator according to claim 1, wherein the current detection circuit is constituted by a current transformer having a current transformer. 6. The current detection circuit according to claim 1, characterized in that the current detection circuit is connected in series between an input power source that supplies power to a load and a switching transistor that turns on and off the input power source and converts it into an alternating current voltage. Chopper type switching regulator. 7. The chopper type switching regulator according to claim 1, wherein the current detection circuit is connected in series between the choke transformer and the smoothing capacitor.