JP2799749B2 - Control method of buck-boost converter circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method of a buck-boost converter circuit in which a primary winding voltage of a transformer is stepped up and down by a choke coil.

[Conventional technology]

FIG. 4 is a diagram for explaining a method of controlling a conventional buck-boost converter circuit. In the figure, a primary winding n1 of a choke coil 3 is connected between a DC input power supply 1 and a center tap of a transformer 2, and a secondary winding n2 is connected to the DC input power supply 1 via a diode 4. ing. Switching elements, for example, the collectors of transistors 5 and 6 are connected to both ends of the primary windings N1 and N'1 of the transformer 2 via current transformers 7 and 8, respectively, and each emitter is connected to the negative electrode of the DC input power supply 1. It is connected. The secondary winding N2 of the transformer 2 has a diode 9,
The AC input side of the full-wave bridge circuit composed of 10, 11, and 12 is connected, and the smoothing capacitor 13 is connected to the DC output side, and the DC voltage is supplied to the load 14 after being smoothed by the smoothing capacitor 13. It has a circuit configuration. The output voltage is controlled to a constant voltage by a constant voltage control signal generated based on the detected voltage, which controls the on time of the transistor. However, the maximum on time is also limited by the maximum on time signal. , Does not exceed a certain width. If the current flowing through the transistor 5 abnormally increases for some reason and a current exceeding the allowable current value of the transistor 5 flows, the collector current is reduced to prevent the transistor 5 from being destroyed. Detector 7 generates a voltage proportional to the collector current across resistor 16 via diode 15, compares this voltage with the voltage of reference power supply 17 by comparator 18, and the collector current reaches the set value. Then, the output of the comparator 18 changes from H to L, the output of the AND logic 19 changes from H to L, and the transistor 5 is turned off to protect it from overcurrent. Although the circuit configuration is omitted in FIG. 4, the same applies when the current of the transistor 6 abnormally increases for some reason. 20 is a diode, 21 to 25
Is resistance.

Next, the operation of this circuit will be described. First, a boost mode operation in which a simultaneous ON period of the transistors 5 and 6 is provided, energy is stored in the choke coil 3, and a voltage higher than the power supply voltage is applied to the primary winding of the transformer 2 will be described with reference to FIG. . When the transistor 5 is off and the transistor 6 is on, a drive signal shown in FIG. 5A is applied to the base of the transistor 5 at time to. When the transistor 5 is turned on, the current i2 flowing through the transistor 6 is reduced by the transistor i. Divide into 5 Since the primary winding of the transformer 2 is short-circuited, the DC input power supply 1
The currents i1 and i2, which are short-circuited through the next winding n1 and flow through the transistors 5 and 6, rise with a slope of E / 2L (where E is the voltage of the DC input power supply 1 and L is the inductance of the choke coil 3). At this time, the conduction of the secondary winding n2 of the choke coil 3 is prevented by the diode 4. Next, when the transistor 6 is turned off at time t1, the current i2 flowing through the transistor 6 flows into the transistor 5, and the current i1 flowing through the transistor 5 doubles as shown in FIG. 5 (c). . The slope of the current at this time is (E−Eo) / L (however, the output voltage is Eo, and the turns ratio of the transformer 4 is 1: 1). Next winding n1
Is higher than the input voltage E, and (E−
Eo) / L is negative. The current i1 flowing through the transistor 5 is the same as the current flowing through the primary winding N1 of the transistor 2, and
A current io as shown in FIG. 5 (e) flows through the next winding N2. Next, when the transistor 6 is turned on again at time t2,
The transistors i1 and i2 are shunted, the transformer 2 is short-circuited, and is in the same state as at time to. Next, at time t3, the transistor 5
Is turned off, all the current that has flowed so far flows through the transistor 6, the same current also flows through the primary winding N'1 of the transformer 2, and the current of the secondary winding flows in the opposite direction to that at time t1. Flows to Next, at time t4, the fifth
The drive signal shown in FIG. 7A is applied, and the same operation is repeated thereafter to supply output power.

Assuming that the simultaneous ON time of the transistors 5 and 6 is r and the cycle is T, the output voltage Eo during the boost mode operation is expressed by Eo = E / (1-2τ / T) (1).

Next, a step-down mode operation in which a simultaneous off period of the transistors 5 and 6 is provided and a voltage obtained by subtracting the voltage of the choke coil 3 from the power supply voltage is applied to the primary winding of the transformer 2 will be described with reference to FIG. . First, transistors 5, 6
Is off and the current _in2 flows through the secondary winding n2 of the choke coil 3, and at time to, the sixth
When the drive signal shown in FIG. 6A is applied and the transistor 5 is turned on, the current i1 flowing through the transistor 5 rises with a slope of (E−Eo) / L as shown in FIG. 6C. The current i1 flowing through the transistor 5 is the primary winding N1 of the transformer 2.
6 (g) is the same as the current flowing through the secondary winding N2.
A current io flows as shown in FIG. Next, when the transistor 5 is turned off at time t1, the current flowing through the primary winding N1 of the transformer 2 is cut off, and the current of the choke coil 3 is reduced to the secondary winding n2.
Is fed back to the DC input power supply 1. The slope of the current i _n2 of the secondary winding n2 of the transformer 2 in time decreases with E / L. Next, when the transistor 6 is turned on at time t2, a current similar to that at time to flows through the primary winding N'1 of the transformer 2, and the secondary winding
A current io as shown in FIG. 6 (g) flows in N2 in a direction opposite to that at time to. Next, when the transistor 6 is turned off at time t3, the current flowing through the primary winding N'1 of the transformer 2 is cut off, and the current of the choke coil 3 is fed back to the DC input power supply 1 via the secondary winding n2. You. Next, at time t4, the drive signal shown in FIG. 6A is applied to the base of the transistor 5, and the same operation is repeated thereafter to supply output power.

Assuming that the ON time of the transistor is T _ON and the cycle is T, the output voltage Eo in the step-down mode operation is expressed by Eo = (2−T / 2T _ON ) E (2)

In the case of a buck-boost converter, in normal operation, the input current is continuous, and efficient boost mode operation is used because the current is not fed back to the input. Step-down is performed only in abnormal conditions such as output overcurrent, short circuit and startup. Mode usage is a common usage. In addition, when the current of the transistor 5 abnormally increases for some reason, such as an output short circuit or an overcurrent at the time of starting, and a current exceeding the allowable current value of the transistor 5 flows, the transistor 5 is not destroyed. To prevent this, the collector current is detected by the current transformer 7 and the diode 15
A voltage proportional to the collector current is generated at both ends of the resistor 16 through the comparator, and the voltage is compared with the voltage of the reference power supply 17 by a comparator.
The output of the comparator 18 transitions from H to L when the collector current reaches the set value.
Is changed from H to L, and the transistor 5 is turned off to protect it from overcurrent.

[Problems to be solved by the invention]

However, in such a conventional buck-boost converter circuit, once turned off, it does not turn on until the next cycle. Therefore, over-current detection shortens the on-period of transistors 5 and 6 and increases the off-period. , All the energy stored in the choke coil 3 returns to the DC input power supply 1, and the initial value of the choke coil 3 starts from zero when the next transistors 5, 6 are turned on, as shown in FIG. Since the energy is not sufficiently transmitted to the output, if a heavy load such as a rated load is connected and started, there is a problem that the start-up does not occur or the start-up takes time. To solve this, increase the inductance value of the choke coil 3 so that it does not return to the DC input power supply 1 during one cycle, or set the current limit value of the transistors 5 and 6 to normal. Even if the off-period becomes longer due to the current limiting operation, the current of the choke coil 3 remains sufficiently, and the power can be transmitted to the secondary side of the transformer 2 at the next on. However, in this case, there is a problem that the choke coil 3 and the transistors 5 and 6 are not only expensive but also heavy and large.

[Means for solving the problem]

In order to eliminate the above disadvantages, the present invention provides a DC input power supply, a plurality of switching elements, a transformer, a choke coil for raising and lowering a primary winding voltage of the transformer, and a secondary winding voltage of the transformer. In a buck-boost converter circuit including a rectifying / smoothing circuit for rectifying and smoothing, a current flowing through the switching element is detected, and when the current increases and reaches a first set value, the switching element is turned off. The energy stored in the choke coil is fed back to the DC input power supply via a secondary winding, and the secondary winding current of the choke coil is detected, and the current decreases to reach a second set value. When the switching element is within the on-time of the constant voltage control signal and within the on-time of the maximum on-time signal, the switching element is turned on again. There is provided a method of controlling the converter circuit.

[Action]

Within the on-time of the constant voltage control signal and the on-time of the maximum on-time signal, even when the switching element is turned off due to current limitation, the secondary winding current of the choke coil is reduced to a constant value. Since the switching element conducts again, the above problem can be solved.

〔Example〕

FIG. 1 is a diagram for explaining one embodiment of the present invention. In the figure, the current flowing through the transistor 5 is detected by the current transformer 7 and the current of the secondary winding n2 of the choke coil 3
The current flowing through the current transformer and the current detected by the current transformer 26 are converted into a voltage by the resistor 16 and compared with the reference voltage 17 by the comparator 18.
The AND of a constant voltage control signal for controlling the output voltage to a constant voltage and a maximum on-time signal for limiting the maximum on-time of the transistor 5 is obtained by an AND logic 19, and the base of the transistor 5 is controlled by the AND output. is there. Incidentally, 2
7 is a diode and 28 is a resistor.

 Next, the operation will be described as follows.

A detection resistor for detecting the current flowing through the transistor 5
When the current at both ends of the comparator 16 becomes equal to the first set value Er (voltage of the reference power supply 17), the output of the comparator 18 changes from H to L.
, The output of the AND logic 19 is changed to L, and the transistor 5 is turned off. When the transistor 5 is turned off, a current _in2 flows through the secondary winding n2 of the choke coil 3, and the energy of the choke coil 3 is fed back to the DC input power supply 1,
A detection current flows through the secondary winding of the current transformer 26, and a voltage is generated at the resistor 16. When the output of the comparator 18 is L, the voltage at the + input terminal is given by: Er · R ₂₃
/ (R ₂₂ + R ₂₃ ), which is smaller than when H. As shown in FIG. 2, the current i _{n2 of the} secondary winding n2 of the choke coil 3
Decreases, the voltage drop of the resistor 16 decreases, and the second set value Er
When the output becomes equal to R ₂₃ / (R ₂₂ + R ₂₃ ), the output of the comparator 18 transitions to H. If the constant voltage control signal and the maximum on-time signal which are the other input signals of the AND logic 19 are H, The output of the AND logic 19 transits to H again to make the transistor 5 conductive. Then, the current i1 flowing through the transistor 5 increases again to supply power to the load 14. Then, the current flowing through the transistor 5 increases again, and the detection resistance 16
When the voltage between both ends reaches the first set value Er, the transistor 5 is turned off again. In the description, the transistor 5 has been described, but the transistor 6 has a similar control method.

FIG. 3 is a diagram showing another embodiment. This embodiment is an embodiment in which the present invention is applied to a bridge type step-up / step-down converter circuit, and has almost the same operation as the embodiment described with reference to FIG. In the figure, reference numerals 5 ', 6', 29 denote transistors, 30 denotes a drive power supply, and 31, 31 'denote drive transformers.

〔The invention's effect〕

As described above, the present invention provides a DC input power supply, a plurality of switching elements, a transformer, a choke coil for raising and lowering the primary winding voltage of the transformer, and a
In a step-up / step-down converter circuit having a rectifying / smoothing circuit for rectifying and smoothing the next winding voltage, a current flowing through the switching element is detected, and when the current increases and reaches a first set value, switching is performed. The element is turned off, the energy stored in the choke coil is fed back to the DC input power supply via the secondary winding, and the secondary winding current of the choke coil is detected. If the switching element is within the on-time of the constant voltage control signal and within the on-time of the maximum on-time signal when the set value is reached,
A step-up / step-down converter circuit control method characterized by turning on a switching element again. Since the present invention has such features, it can be started without any problem even under heavy load, and the inductance value of the choke coil and the current capacity of the transistor can be reduced. Therefore, it is possible to reduce the size and weight, and
Choke coils and transistors are inexpensive and economical.

[Brief description of the drawings]

1 and 2 are diagrams for explaining one embodiment of the present invention, FIG. 3 is a diagram for explaining another embodiment of the present invention, and FIGS. 4 to 7 are conventional examples. FIG. 1 DC input power supply 2 Transformer 3 Choke coil 4,9-12,15,20,27 Diode 5,5 ', 6,6', 29 Switching element 7,8,26 ... … Current transformer 13… Smoothing capacitor 14… Load 16,21-25,28… Resistance 17… Reference power supply 18… Comparator 19… and logic 30… Drive power supply 31… Drive transformer

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-56-107778 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H02M 3/00-3/44

Claims (1)

(57) [Claims] 1. A DC input power supply, a plurality of switching elements, a transformer, a choke coil for raising and lowering a primary winding voltage of the transformer, and a rectifying and smoothing circuit for rectifying and smoothing a secondary winding voltage of the transformer. In the step-up / step-down converter circuit comprising: a switching element that detects a current flowing through the switching element and, when the current increases and reaches a first set value, turns off the switching element; Energy 2
It is fed back to the DC input power supply through the next winding,
When the secondary winding current of the choke coil is detected and the current decreases and reaches the second set value, the switching element is within the on-time of the constant voltage control signal and within the on-time of the maximum on-time signal. A method of controlling a buck-boost converter circuit, wherein the switching element is turned on again in such a case.