JPS5937668B2 - switching power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a self-oscillation type switching power supply using a blocking oscillator.

Generally, the typical operation of a flyback converter is to release the magnetic energy accumulated in the transformer during the ON period of the switching circuit to the load side during the OFF period, and the switching frequency of the switching circuit and the output power are inversely proportional to each other. be.

It can be seen that it is possible to make the flyback converter constant voltage by utilizing this property and controlling the operating frequency to vary in inverse proportion to the output power as the load fluctuates. Conversely, if constant voltage control is performed, the operating frequency changes in inverse proportion to the load current as the load changes. However, such characteristics of the flyback converter cause disadvantages such as a decrease in efficiency and an increase in the size of the transformer when load fluctuations are large. On the other hand, in a forward converter, output control is performed by changing the on period or off period of the switching circuit, that is, by changing the duty ratio, and even if only the operating frequency of the switching circuit is changed, the output can be controlled. It generally has the property of not being able to be controlled.

However, in the case of a self-oscillation oscillation circuit, it is relatively easy to change the oscillation frequency, but it is difficult to change the duty ratio, which poses a problem in simplifying the circuit configuration. In view of the above points, the present invention provides a switching power supply in which output control can be performed with a simple circuit configuration using one blocking oscillator.

Embodiments of the switching power supply according to the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention, which is a single-stone blocking oscillation flyback converter.

In this figure, the oscillation transformer T1 has a primary winding L8, a secondary winding L2, a feedback winding Lf, and a rest winding Ls. The blocking oscillator 1 includes a transistor Q, a primary winding L connected to its collector side, a feedback winding Lf connected to its base side, resistors R1 to R3, and a capacitor C.
A positive voltage + is supplied to the tap of the primary winding L1, and a negative voltage V- is supplied to the emitter of the transistor Q. The pause circuit 2 is composed of a transistor Q connected via a diode D3 between one end of the pause winding Ls and the tap, a base bias resistor R4, a variable resistor R, and a capacitor C2. , the polarity of the idle winding Ls and the diode D is such that when the transistor Q1 of the blocking oscillator 1 is turned on, the induced voltage generated in the idle winding Ls reverse biases the diode D3 and forward biases the base of the transistor Q. is set.

On the other hand, a diode D is connected to the secondary winding L2 of the transformer T.
4 and a rectifying and smoothing circuit of capacitor C3 are connected, and the DC output cage pressure E. is supplied between output terminals A and B, and the DC output voltage EO is also supplied to the error amplification circuit 3. This error amplification circuit 3 includes a transistor Q3, a light emitting element DF of a photocoupler 4, and a constant voltage diode Z.
It consists of Dl, resistors R to R, and capacitor C4, and when the voltage across capacitor C4 exceeds the reference voltage determined by voltage regulator diode ZDl, voltage regulator diode ZDl breaks over and transistor Q3 is turned on. The light emitting element DF is configured to emit light. The base circuit of the transistor Q1 includes a transistor Q.
4. Photocoupler 4's light receiving element QFl diode D,
, a capacitor C5 and a resistor R8, R, a control circuit 5 is provided which is coupled to the error amplification circuit 3 via a photocoupler 4.

In the above configuration, switching of the primary side of the oscillation transformer Tl is performed as follows.

First, the transistor Q1 of the blocking oscillator 1 is turned on by the DC bias of the resistor R2, and a DC voltage is applied to the primary winding L, and the transformer Tl is excited. When the transistor Q1 is turned on, an induced voltage is generated in the idle winding Ls, and this induced voltage forward biases the base of the transistor Q2, but since the diode D3 is in the off state, the idle winding Ls is substantially open. It has become a state.

When the transistor Q1 is turned off after a certain period of time due to the oscillation operation of the blocking oscillator 1, the induced voltage in the rest winding Ls is reversed.

At this time, since the transistor Q2 is still forward biased by the carrier storage in the base region and the charging voltage of the capacitor C2, the rest winding Ls is short-circuited by the conductive diode D2 and the transistor Q2. In this state, the charge in capacitor C2 is discharged, and the base of transistor Q2 is reverse biased.
Continue until 2 turns off. During the period in which the idle winding Ls is short-circuited in this manner, the magnetic energy stored in the transformer T1 is conserved, and the induced cage pressure in the secondary winding L2 becomes almost zero. Therefore, this period is called a rest period. Now, after the end of the predetermined rest period, the transistor Q2 is also turned off, so the rest winding Ls is opened, and an induced voltage with the opposite polarity to the induced voltage when the transistor Q is on is generated in the secondary winding L2. In this way, on the primary side of the transformer T, (1) the transistor Ql is on and the primary winding L1
Excitation, (2) Transistor Ql or off, transistor Q
2 is on, the rest winding Ls is shorted, (3) the transistor Q
The three operations of turning off both Q1 and Q2 and opening the rest winding Ls are repeated in sequence.

As a result, the voltage across the secondary winding L becomes as shown in FIG. 2A. In this figure, the section where the voltage is zero is the pause period. Second
The voltage induced in the secondary winding L2 as shown in Figure A is rectified and smoothed by a diode D4 and a capacitor C3 to form a DC output voltage E.

The output voltage is supplied to the load via output terminals A and B. In this case, the DC output voltage E. When becomes larger than a predetermined set value, the constant voltage diode ZD breaks over, the transistor Q3 becomes conductive, the light emitting element DF emits light, and as a result, the resistance of the light receiving element QF becomes low. Therefore, transistor Q
4 becomes conductive, diode D5 and capacitor C
A negative voltage rectified and smoothed by transistor Q4 is applied to the base of transistor Q1 through transistor Q4, thereby increasing the oscillation frequency of locking oscillator 1. In this case, since the rest period is almost constant regardless of the oscillation frequency, as shown in FIG. 2B, the secondary winding L2
The duty ratio of the voltage waveform decreases as the oscillation frequency increases. Therefore, the DC output voltage E. decreases due to the synergistic effect of increasing the oscillation frequency and decreasing the duty ratio, and stabilization control is executed. According to the first embodiment, the oscillation transformer T1 is provided with the rest winding Ls, and a rest period is provided in which the winding Ls is short-circuited, so that it is possible to change the oscillation frequency and the duty ratio.

Therefore, the range of variation in oscillation frequency can be made smaller than in conventional flyback converters. Therefore, it is possible to reduce the size and weight of the transformer, improve its efficiency, and stabilize its operation when no load is applied. FIG. 3 shows a second embodiment of the present invention, which is a locking type blocking oscillation forward converter.

In this figure, the oscillation transformer T2 has primary windings L, 2
The locking oscillator 1 has a secondary winding L3 and a feedback winding Lf, and the configuration of the locking oscillator 1 is the same as that of the first embodiment. The secondary winding L3 of the oscillation transformer T2 has a tap in the middle,
It consists of an output winding section L3O and a pause control winding section L38.

A rectifying and smoothing circuit consisting of diodes D6, D7, a choke coil Lc, and a capacitor C6 is connected to the output winding L3O, and a DC output voltage E is connected thereto. or between output terminals A and B. In addition, the pause control winding part L
38, transistors Q to Q7, tie auto D8
, constant voltage diode ZD2, resistors RlO to R17,
An error amplification control circuit 6 consisting of a variable resistor VR2 and capacitors C7 and C8 is connected.

In the above configuration, when the transistor Q1 of the blocking oscillator 1 is turned on, the primary winding L, is excited, and the
An induced voltage with a polarity that turns on the diode D6 and turns off the diode D8 is generated in the next winding L3.

Therefore, the pause control winding L38 is substantially open and does not affect the operation, and the voltage across the output winding L3O is rectified and smoothed by the diodes D6, D7, the choke coil Lc, and the capacitor C6, and becomes a direct current. Output voltage E. The output voltage is supplied to the load via output terminals A and B. At this time, the base of the transistor Q5 of the error amplification control circuit 6 is connected to a voltage obtained by dividing the DC output voltage EO by a resistor Rl, a variable resistor VR2, and a resistor R12, and a rectified rectangular wave of a diode D6. A voltage obtained by superimposing a triangular wave integrated by the capacitors R and O and the capacitor C8 is applied. Therefore, transistor Q
The base voltage of No. 5 stops the reference voltage determined by the constant voltage diode ZD2 for a certain period of one cycle. During this period, transistors Q5 and Q6 are turned on and transistor Q7 is forward biased. After a certain period of time, when the transistor Q1 turns off, the induced voltage in the secondary winding L3 is reversed and the diode D8 turns on, and during the forward bias period of the transistor Q7, both the diode D8 and the transistor Q7 turn on and stop. Control winding portion L38 is short-circuited.

This short-circuited period becomes a rest period, and the transformer T
The magnetic energy stored in the secondary winding L3 is conserved and the magnetic energy stored in the secondary winding L3
The voltage becomes almost zero. The rest period ends when the transistor Q7 turns off, the rest control winding L38 becomes open, and the output winding L3O receives an induced voltage that is opposite in polarity to the induced voltage when the transistor Q is on. occurs. As a result of repeating the above operations, the collector voltage of the transistor Ql changes as shown in FIG. 4A, and the anode voltage of the diode D8 changes as shown in FIG. 4B.

The zero voltage section in FIG. 4B is the rest period. On the other hand, the base voltage of transistor Q has a waveform as shown in Figure 4C, which is a triangular wave superimposed on DC, and transistor Q
It repeats a monotonous increase when it is on and a monotonous decrease when it is off. During the period in which the base voltage of the transistor Q5 exceeds the reference voltage Er determined by the constant voltage diode ZD2 in FIG. 4C, the transistor Q7 is turned on as shown in FIG. 4D. Now, the DC output voltage E.

When becomes larger than a predetermined set value, the base voltage of the transistor Q shown in FIG. 4C increases, and the triangular wave shifts upward. As a result, the period exceeding the reference voltage Er increases,
The on period of transistor Q7 also becomes longer. This results in
As the rest period in which the rest control winding L38 of the secondary winding L3 is short-circuited becomes longer, the duty ratio of the waveform shown in FIG. 4B decreases, and the DC output voltage E. is controlled in a decreasing direction and stabilization control is executed. According to the second embodiment, a tap is provided on the secondary winding L3 of the oscillation transformer T2 to divide it into the output winding L3O and the pause control winding L38, and the pause control winding L35 is short-circuited. Since a rest period is provided and this rest period is controlled, it is possible to change the duty ratio of the voltage waveform appearing in the secondary winding L3, and the blocking oscillator can be used to control the stabilization of the forward converter. It has the advantage of being realized with a simple configuration. Note that in each of the above embodiments, the error amplification circuit, the control circuit,
The configuration of the error amplification control circuit can be changed as appropriate.

Furthermore, in the oscillation transformer T, it is of course possible to configure the output winding section and the pause control winding section with independent windings. As described above, according to the present invention, a switching power supply that can perform output control with a simple circuit configuration is obtained.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a first embodiment of the switching power supply according to the present invention, Fig. 2 is a waveform diagram for explaining the operation of the first embodiment, and Fig. 3 is a circuit diagram showing the second embodiment. , FIG. 4 is a waveform diagram for explaining the operation of the second embodiment. 1... Blocking oscillator, 2... Pause circuit, 3... Error amplification circuit, 4...
Photo cutlet, 5... Control circuit, 6...
...Error control circuit, C1 to C8...Capacitor, Dl to D8...Diode, TlT2...
...Oscillation transformer, L1 ...Lth winding,
L2, L3...Secondary winding, Lf...Feedback winding, Ls...Stop winding, L3O...
・Output winding section, L38... Pause control winding section, Q
, to Q7...transistor, R1 to Rl,
...Resistor, ZDl, ZD2 ... Constant voltage diode.

Claims (1)

[Claims] 1. A transformer T_1 having at least a primary winding L_1 and a secondary winding L_2, a first switching element Q_1 that switches the primary winding L_1, and another winding of the transformer T_1. a second switching element Q_2 for short-circuiting Ls or a part of the secondary winding L_2; and a rectifier circuit for rectifying the voltage induced in the secondary winding L_2 during the off period of the first switching element Q_1. and a control circuit 5 that controls the switching frequency,
1 during the on period of the first switching element Q_1.
The next winding L_1 is excited and this first switching element Q
At the beginning of the off period of T_1, the second switching element Q_2 is turned on, and a part of the other winding Ls or the secondary winding L_2 is short-circuited to conserve the magnetic energy of the transformer T_1. A switching power supply characterized in that, when the output of the rectifier circuit increases, the switching frequency is increased via the control circuit 5 to stabilize the output. 2. A transformer T_2 having at least a primary winding L_1 and a secondary winding L_3, a first switching element Q_1 that switches the primary winding L_1, and another winding of the transformer T_2 or the secondary winding. A second switching element Q_7 for short-circuiting a part of L_3, and a rectifier circuit for rectifying the voltage induced in the secondary winding L_3 during the ON period of the first switching element Q_1, The primary winding L_1 is excited during the ON period of the switching element Q_1, and the first switching element Q_1 is energized.
At the beginning of the off period of 1, the second switching element Q_7 is turned on and the other winding or the secondary winding L
A rest period is provided by short-circuiting a part of the transformer T_2 to conserve the magnetic energy of the transformer T_2, and when the output of the rectifier circuit increases, the second switching element Q
A switching power supply characterized in that the on-period of _7 is lengthened and the output is stabilized by controlling the inactive period to become longer.