JPS63262059A - Control system for 2-element forward switching regulator - Google Patents

Abstract

PURPOSE:To inexpensively enhance the efficiency by providing a difference at the switching velocities of two switching elements, delaying faster turn-ON and delaying a slower turn-OFF. CONSTITUTION:A 2-element forward type switching regulator has two switching elements 2 driven ON, OFF by a controller 11, and supplies power through its transformer 4 to a load. In this case, the elements 2 use an element 2-1 having fast switching velocity like an FET, and an element 2-2 having a slow switching velocity like a triple diffused bipolar transistor. The ON signal of the element 2-1 is delayed by the controller 11, and the OFF signal of the element 2-2 is delayed. Thus, the regulator can be inexpensively operated in high frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a control system for a two-stone forward switching regiator.

PRIOR ART AND THEIR PROBLEMS There are various circuit systems for switching regulators, but in recent years the two-stone forward system has become more popular as it is suitable for high input voltages, provides a large capacity output, and is easy to downsize. As shown in FIG. 3, this two-stone forward type switching regulator has a series circuit of a switching element 2'-1 and a diode 3-1 and a series circuit of a switching element 2'-2 and a diode 3-1 between the terminals of a DC power supply 1.
2, and connect the primary winding 4 of the transformer 4 between the connection points of the switching elements and diodes of each series circuit.
-1 and each switching element 2'-1, 2'-2
A signal to turn on and off simultaneously is applied from the control circuit 11' to generate a rectangular wave voltage in the primary winding 4-1, and a rectangular wave voltage according to the turns ratio with the primary winding 4-1. Secondary winding 4
-2. The rectangular wave voltage obtained in this way is rectified by diode 5, and then connected to reactor A/6 and capacitor 7.
A desired DC voltage is obtained between the output terminals 919' by the smoothing circuit consisting of the above and the feedback diode 8. Note 1
0 is a dummy load. Such a two-stone forward type switching regulator has the advantage of increasing the switching frequency and making it easier to downsize, since the control circuit 11 applies a signal to turn on and off two switching elements at the same time, as shown in Figure 4. However, in order to reduce switching loss, it is necessary to use a high-speed switching element such as an FET, which has the disadvantage of being expensive.

OBJECT OF THE INVENTION The present invention solves the disadvantages of a two-stone forward type switching regulator by providing a difference in the switching speeds of two switching elements used in a two-stone forward type switching regulator, thereby delaying the turn-on of the switching element with a faster switching speed, and increasing the switching speed. The purpose of this invention is to obtain an inexpensive and highly efficient control method for a two-stone forward type switching regiator by delaying the turn-off of slow switching elements so that switching losses occur only in switching elements with fast switching speeds. shall be.

The control system for the two-stone forward switching regiator of the present invention uses an element with a fast switching speed as one of two switching elements that turn on and off at the same time, and an element with a slow switching speed as the other. This delays the turn-on of fast-speed iron elements and the turn-off of slow-switching devices.

EXAMPLES The present invention will be explained below using examples. FIG. 1 is a circuit diagram for explaining the control system of the two-stone forward switching regulator of the present invention, and parts having the same functions as those in FIG. 3 are given the same reference numerals. In FIG. 1, 2-1 is an element with a fast switching speed (hereinafter simply referred to as a "fast element"). X2-2 is an element with a slow switching speed (hereinafter simply referred to as "a fast element").
"Slow element". ). As the fast element 2-1, there is an FIT or a ring emitter type bipolar transistor, which has short turn-on time and turn-off time and can reduce switching loss even at a switching frequency that is one higher, but is expensive. On the other hand, the slow element 2-2 is a triple diffusion type or epitaxial type bipolar transistor, and its turn-on time and turn-off time are about one order of magnitude longer than the fast element 2-1. In the control method of the present invention, the control circuit 11 delays the ON signal for the fast element 2-1 and delays the OFF signal for the slow element. The control circuit 11 will be explained with reference to FIG. In Figure 2, 20
is a pulse generator, and I is used to control the switching regulator.
From the pulse width controlled output of
25.

26.27, NAND game) 28, NOR gate 2
9 to the amplifier 30.31. amplifier 30
The above-described control system can be realized by inputting the output of the amplifier 31 to the fast element 2-1 and inputting the output of the amplifier 31 to the slow element 2-2. These four inverters 24 and 25.

26e27. One HAND gate 28. One 1+ NOR gate 29 housed in the 16-pin circuit 0 is commercially available, so the control circuit 11 is connected to this one I
It can be configured by simply adding O.

Since the ON signal of the control circuit 11 configured as described above is first applied to the slow element 2-2, the slow element 2-2 is turned on first, that is, the resistance between the collector and emitter becomes low.

When this resistance becomes sufficiently low, an on signal is applied from the control circuit 11 to the fast element 2-1, and the DC power source 1 changes the speed from the fast element 2-1 to the transformer 40 primary winding 4-1 to the slow element 2-2. Current flows in the path. Switching loss occurs when the voltage and current rise and fall when the switching element transitions from on to off or from off to on, but when the slow element 2-2 turns on first, no current is flowing. , switching loss does not occur when the slow element 2-2 is turned on, and switching loss occurs only in the fast element 2-1 when the fast element 2-1 turns on and current begins to flow. However, this switching loss is It is extremely small. Next, the off signal of the control circuit 11 is first applied to the fast element 2-1, so the fast element 2-1 is first applied to the fast element 2-1.
Although switching loss occurs due to the rise of the voltage and the fall of the current, the switching loss is extremely small.

At this time, the slow element 2-2 remains on, but the current is cut off by the fast element 2-1 being turned off, so even if an off signal is applied to the slow element 2-2, the slow element 2- 2, only switching loss due to circulating current, which will be described later, occurs. On the other hand, when the fast element 2-1 turns off first and the current is cut off, the excitation energy of the primary winding 4-1 of the transformer 4 generates a voltage of the polarity shown in the primary winding 4-1. However, while the slow element 2-2 is on, a circulating current flows through the slow element 2-2 and the diode 3-1, so that the current flows between the drain and source of the fast element 2-1, which is off. The voltage applied to the diode 3-1 never becomes higher than the sum of the DC power supply voltage and the forward voltage of the diode 3-1. When the slow element 2-2 is then turned off, switching loss occurs when the circulating current flowing through the slow element 2-2 is cut off, but since the flowing current is small, the switching loss is also extremely small.

At this time, if the excitation energy of the primary winding 4-1 of the transformer 40 remains, the voltage generated in the primary winding 4-1 of the transformer 4 tends to become even higher, but the diode 3-2
As a current begins to flow through the path → DC power supply 1 → diode 3-1, the voltage applied between the drain and source of the fast element 2-1 and between the collector and emitter of the slow element increases from the DC power supply voltage to the diode 5. The voltage rises to the sum of the forward voltage of -1.3-2 and is clamped. Then, the current flowing through the path stops flowing as the excitation energy of the primary winding 4-1 of the transformer 4 disappears, and the above-described operation is repeated after waiting for the next ON signal to be applied.

Since the control method is as described above, switching loss occurs only in the switching element that delays turn-off, and if an element with a high switching speed is used as the switching element, efficiency can be increased. Further, since almost no switching loss occurs in a switching element that delays turn-off, even if an element with a slow switching speed is used as the switching element, the device can be constructed at low cost without reducing efficiency.

Effects of the Invention As described in detail in the embodiment, the control method of the two-stone forward switching regulator of the present invention can generate switching loss in only one of the two switching elements. Using a fast switching speed element such as FIT as the switching element,
If you use an element with a slow switching speed such as a triple diffused Paipov transistor as the other switching element,
It is possible to increase the frequency of a two-stone forward type switching regulator by using one lFET whose price is about three times that of a piebolat fungistor.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram for explaining the control system of the two-stone forward type switching regulator of the present invention, Fig. 2 is its control circuit diagram, and Fig. 3 is the control system of the conventional two-stone forward type switching regulator. Circuit diagram 1 for explaining Figure 4 is an output waveform diagram of the control circuit◎ 1...DC power supply 11-11'...Control circuit 2
0...Pulse generator

Claims (2)

[Claims] (1) Connect two series circuits of a switching element and a diode between the DC power supply terminals, connect the primary winding of a transformer between the connection points of each switching element and the diode, and turn on each switching element at the same time. In the control method of a two-wheel forward type switching regulator, which rectifies and smoothes the rectangular wave voltage induced in the secondary winding by turning it off to obtain the desired DC voltage, one of the two switching elements has a switching speed control. A control method for a two-stone forward type switching regulator, characterized in that a fast element is used and an element with a slow switching speed is used, and the turn-on of the fast-switching speed element is delayed, and the turn-off of the slow-switching speed element is delayed. (2) The element with a fast switching speed is a FET or a ring emitter type bipolar transistor, and the element with a slow switching speed is a triple diffusion type or epitaxial type bipolar transistor. Control method for stone forward type switching regulator.