JPH04185280A - Resonant switching power source circuit - Google Patents

Abstract

PURPOSE:To lower the internal loss of a switching by constituting a voltage detection circuit simply out of a transistor and a diode only, and turning on the transistor with the timing that the voltage of a resonant transistor becomes a specified value or less. CONSTITUTION:An optional circuit, which has the function of detecting the minimum point of the voltage VDS between the oscillating electrodes to be controlled, preferably, the minimum point of the first vibration and turning on the switching element with this timing, can be used for a voltage detection circuit (a transistor Q0, a resistor R9, and a diode D2), and by this voltage detection circuit, the timing of the energy transmission from the resonant capacitor CRES to the secondary coil L2 of a transformer 50 being completed is detected. When turning on the switching element SW by this timing, the energy charged in the resonant capacitor CRES is consumed little inside the switching element SW.

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a switching power supply circuit that utilizes series resonance between an isolation transformer and a capacitor.

(b) Prior Art A conventional switching power supply circuit will be explained with reference to FIG.

The main circuit of the switching power supply circuit is a transformer (72) that isolates its output DC0UT from the input power supply DCIN.
, a switching element SW that controls switching of the current of the secondary coil L1 of this transformer (72), and a control circuit (6) that drives this switching element SW at a predetermined timing.
0), and in order to prevent noise due to large current switching and high voltage switching, or to prevent destruction of switching elements SW etc. due to this noise, a snubber circuit consisting of resistor R2□, capacitor C2□, and diode D22, and resistor R2 □, a snubber circuit consisting of a capacitor C21, a snubber circuit consisting of a resistor R23 and a capacitor C24, and inductances such as bead cores (80) are added at designated points in the circuit in order to suppress steep rises and falls and suppress noise generation. has been done.

Control circuit (60) often provided as an integrated circuit
are pulse generator (62), and gate (64)
, a flip-flop (66), a buffer +681, and a comparator (70). The pulse generator (62) operates at a constant frequency determined by the OR time constant of a capacitor connected between the terminal TPIN and the built-in resistor, or synchronized with the trigger pulse by supplying a trigger pulse from the outside. Operate on frequency.

Next, the operation of this switching power supply circuit will be explained.

The control circuit (60) is started by the input power supply D CI N supplied to the terminal V0° via the resistor R2D, and after starting, it is rectified by the diode D2° and the capacitor C2°.
It operates by three outputs on the tertiary coil of the smoothed transformer (72).

Now, if the pressure of the comparator (70) is at a high level.

The flip-flop (66) is a pulse generator (62).
) is set by the output voltage (f84) at the rising edge of the pulse generator (62), and is reset at the falling edge of the output from the pulse generator (62). The switching element SW is driven by the buffer (68) based on the set output Q of the flip-flop (66). Therefore, the transformer (72
) changes at a predetermined time constant based on the switching operation of the switching element SW, and induces a voltage in the secondary coil L2 and the tertiary coil L3 of the transformer (72).

The negative circuit current of the transformer (72) is detected by the current detection resistor R81.
1N and is input to the inverting input terminal of the comparator (70).

Input power supply D CI N voltage is low (or pressure DC0
When the primary circuit current detected by the current detection resistor RSEN becomes equal to or higher than the set value 78 due to an increase in the current in the a, the comparator (70) outputs a low level to the AND gate (64), and this The AND gate (64) blocks the set signal input from the pulse generator (62) to the flip-flop (66). As a result, average value control of the -order circuit current is performed. Therefore, in a switching power supply circuit with such an operation method, the on/off of the switching element SW is controlled by the input power supply D CI, except immediately after startup.
This is performed randomly based on the voltage value of N and the current value of output DC0UT.

(c) Problems to be Solved by the Invention Conventional switching power supply circuits require multiple snubber circuits and bead cores composed of diodes, resistors, and capacitors with good switching or frequency characteristics. It has the disadvantage that it cannot meet the demand for lower prices. The addition of the snubber circuit and bead core not only limits the operating frequency of the switching power supply circuit, but also has the disadvantage that power is consumed in the snubber circuit, reducing the efficiency of the switching power supply circuit.

That is, in a switching power supply circuit that reduces noise, exchange efficiency decreases, and in a switching power supply circuit that increases exchange efficiency, noise becomes a problem. Therefore, it has not been possible to realize a switching power supply circuit that has contradictory technical requirements such as noise reduction and high exchange efficiency.

Furthermore, since large currents and high voltages are switched, a large amount of power is consumed inside the switching elements that turn on and off with a finite slope, resulting in a disadvantage that the efficiency of the switching power supply circuit is reduced.

(Means for solving the bridge problem) The present invention was made in view of the above problem, and includes a transformer that insulates the output from the input power source, a switching element that controls the primary coil current of this transformer, and a switching element that controls the primary coil current of this transformer. a control circuit that is driven at a predetermined timing, a resonant capacitor connected between the controlled electrodes of the switching element, and a resonant capacitor that detects the voltage of the tertiary coil of the isolation transformer and detects the voltage of the resonant capacitor at a timing when the voltage of the resonant capacitor reaches a predetermined value. The problem of the conventional switching power supply circuit described above is solved by a resonant switching power supply circuit composed of a voltage detection circuit that triggers a voltage to turn on a switching element.

(e) The oscillating voltage of the working resonance capacitor is detected, and the switching element is turned on at the timing when the voltage of this resonance capacitor reaches a predetermined value, so the voltage level and current level at which the switching element cuts off are set to arbitrarily low values. This reduces the power consumed inside the switching element. Additionally, this reduces the level of switching noise, making a snubber circuit unnecessary.

Furthermore, since the switching element is turned on at the minimum point of the charge level of the resonant capacitor, the charging energy of the resonant capacitor is effectively transmitted to the secondary side, and the charging energy consumed inside the switching element is reduced.

Furthermore, since the voltage detection circuit is simple, consisting only of transistors and diodes, and the transistor is turned on at the timing when the voltage of the resonant capacitor becomes less than a predetermined value, there is no reduction in operating speed due to saturation of the transistor.

Furthermore, to obtain the voltage waveform of the resonant capacitor from the tertiary coil of the relatively low voltage transformer.

There is no need to design a voltage detection circuit with high voltage resistance.

(F) Embodiment A resonant switching power supply circuit (hereinafter simply referred to as a switching power supply circuit) of the present invention will be explained with reference to FIGS. 1 to 4.

Referring to FIG. 1, the switching power supply circuit of the present invention includes a switching element S that uses a transformer (50) for insulating the pressure DCOUT from the input power supply DC+N, a power MO3FET, or a high-speed type IGET.
W, a resonant capacitor CRIII connected between the controlled electrodes of the switching element SW, a control circuit (20) that drives the switching element SW at a predetermined timing, an output voltage detection circuit (52), and a transformer ( 50) Voltage detection circuit that detects from the tertiary coil (transistor Q0, resistor R9, diode D2)
Consists of etc. Although a switching power supply circuit in which a capacitor as a snubber circuit is connected in parallel between the controlled electrodes of the switching element SW is known, the operation of the switching power supply circuit of the present invention is clearly different from that kind. It is.

The control circuit (20), as shown in the block diagram in FIG. . A comparator (22) that detects the rise of the power supply voltage, a reference voltage circuit (34) that outputs 5 reference voltages VR1, v8 based on the eight comparators (22), and a three-man OR gate (34). 24+.

Capacitor C3 and resistor R4 (first
A clock generator (26), a flip-flop (28), a differential amplifier (30), a comparator (3), which outputs a narrow pulse at a frequency set by the
2) Push-pull connected transistors Q1 and Q2
It consists of

In this embodiment, an output voltage detection circuit (52) is provided in the output circuit on the secondary side of the transformer (50), and the voltage detection circuit (transistor Q0,
Resistor R8, diode D2) output and independent control circuit (2
0) is controlled.

In this embodiment, the voltage detection circuit (transistor Q, resistor R8, diode D2) determines the timing at which the power switch element SW is turned on (minimum point of VDll), while the output connected to the output circuit A voltage detection circuit (52) determines the timing at which the power switch SW is turned OFF based on a control signal via the photocoupler PC. As a result, high pressure conditions and transformer (50
) is a switching regulator whose circuit operates at a frequency according to the resonance conditions of the capacitor C□8.

The basic switching operation of the embodiment will first be explained with reference to FIGS. 1 and 2.

The switching power supply circuit of the present invention connects the terminal V via the resistor R. . It is activated by the input power supply DCIN supplied to the

This terminal V. During the unstable operation period when the voltage of 0 changes,
Terminal ■. . A comparator (22) that compares the voltage of VB with the reference voltage VB and a three-way OR gate (24) that inverts and inputs the comparison output turn off the transistor Q1 and turn on the transistor Q2, turning on the control circuit (2 (1) output OU
T is kept at a low level. Therefore, the switching element SW is off at this timing.

Next, the flip-flop (28) is turned on by the pulse of a certain period outputted by the clock generator (26), and when the output pulse of the clock generator (26) becomes low level, the three-way OR gate (24) outputs a non-inverted output. It outputs a low level as the output, and a high level as the inverted output. And this three-man power game) (2
The output of 4+ turns on the transistor Q1 and turns off the transistor Q2, so that the output OUT of the control circuit (20) becomes high level, and the switching element SW is turned on.

When the switching element SW is turned on, the transformer (50)
A current that rises at a predetermined time constant flows through the second coil L of . This current is I s! by the current detection resistor R, □.
s and compared with the reference voltage vs of the comparator (32). Therefore, the flip-flop (28) is reset at the timing when r1lItN becomes larger than the reference voltage Vs, and the switching element SW is turned off.

When the switching element SW is turned off, the resonant capacitor CR1,s connected in parallel between the controlled electrodes is charged with a predetermined time constant, and then the secondary coil L1 of the transformer (50) and the resonant capacitor Cl1l! Since a series resonant circuit is formed by S, the circuit current oscillates. Therefore, the minimum point of this oscillating voltage is detected by the voltage detection circuit (transistor Q0, resistor R, diode D2), and the clock generator (26) is triggered at that timing.
Switching element SW is turned on again.

The switching power supply circuit of the present invention induces a voltage in the secondary coil L2 by repeating the ON operation and OFF operation of the switching element SW just described.

The present invention will be described in further detail with reference to FIGS. 3(A) and 4(B) and FIGS. 4(A) and 4(B). In addition, Fig. 3 (A)
(B) schematically shows the waveforms of the controlled inter-electrode voltage VOS and current IDl9 of the switching element SW of the conventional switching power supply circuit and the switching power supply circuit of the present invention, respectively. Referring to these waveforms, the voltage VOg between the controlled electrodes of the switching element SW and the current . It should be noted that the phase of 8 is shifted and the voltage/current product of the switching element SW becomes small.

In a conventional switching power supply circuit that controls the current of a high inductance circuit by forcibly turning on and off the switching element SW at any time, as shown in FIG. 3(A), especially when the switching element SW is turned off ( It is understood that a high level of noise occurs at the rise of Vt+g). Also, because the switching element SW operates at a finite speed.

It is also understood that the internal loss of the switching element SW, which is represented by the product of the controlled interelectrode voltage VI)s and the current IDII, increases at the timing of the rise and fall of VD8. On the other hand, in the present invention in which a series resonant circuit is formed by the negative coil L of the transformer (50) and the resonant capacitor CR□, the relatively large capacity resonant capacitor CR18 is connected in series with the circuit. The high inductance circuit is not opened when the switching element SW is turned off, and noise is suppressed.

Furthermore, since the voltage waveform of the resonant capacitor CRRfi is obtained from the tertiary coil of the relatively low-voltage transformer, a low-voltage diode can be used in the voltage detection circuit, eliminating the need for a high-voltage design.

Referring to FIG. 3(B), in the switching power supply circuit of the present invention, the controlled interelectrode voltage VD immediately after the switching element SW is turned off, that is, the voltage of the resonant capacitor C□8, increases with a predetermined time constant due to charging. , remains at a constant level until the energy transfer to the secondary coil L2 of the transformer (50) is completed, and then vibrates (only the oscillatory decreasing tendency is shown at the left end of the drawing).

Voltage detection circuit of the present invention (transistor Q0, resistor Rs,
For the diode D, use any circuit that has the function of detecting the minimum point of the oscillating controlled interelectrode voltage VDg, preferably the first minimum point of vibration, and turning on the switching element SW at this timing. It is possible,
This voltage detection circuit detects the timing at which energy transfer from the resonant capacitor OR18 to the secondary coil 2 of the transformer f50 is completed.

When the switching element SW is turned on with this timing, the energy charged in the resonant capacitor CRE11 is less consumed inside the switching element SW, and at the timing of the rise and fall of VDI+, the controlled interelectrode voltage DIl The internal loss of the switching element SW, which is represented by the product of the current I0 and the current I0, is suppressed.

In this embodiment, the emitter is used as a voltage detection circuit and a control circuit (20
) power terminal■. . A specific circuit is illustrated that includes a transistor Q0 connected to the transistor Q0, a resistor R6 connected to the base of the transistor Q0 and the controlled electrode of the switching element SW, and a level shift diode D2.

Next, the detection level of this voltage detection circuit and the transformer (50
) will be explained with reference to FIGS. 4(A) and 4(B).

Controlled inter-electrode voltage V. S oscillates as shown in FIG. 4(A), and the first vibration extreme value V8 becomes the minimum value. Fourth
As shown in Figure (B), this extreme value ■8 is mainly due to the turns ratio R=L2 of the secondary coil and primary coil of the transformer (50).
It has been known through research by the inventors of the present invention that this is dominated by /L+.

FIG. 4(B) is a characteristic diagram showing the coil turns ratio R=L2/L1 in a power supply circuit with an output voltage of about 120 to 130 V used for, for example, a CTV or CRT display.

Graph ■ in FIG. 4(B) indicates the turns ratio R=L2/L.

The controlled interelectrode voltage VDII when = 1.0, that is, the residual voltage ■8 of the resonant capacitor Can5, is shown, and the graph ■ shows the residual voltage of the resonant capacitor CRIII when the turns ratio R = L2/L + = 0, 75. It shows voltage ■8. From the same figure, it is easy to understand that in order to reduce the power consumed by the switching element SW, it is preferable to reduce the turns ratio R of the transformer (50) to lower the residual voltage ■R of the resonant capacitor CR□. Ru.

On the other hand, as a reaction to the above, the voltage applied to the switching element SW increases, but the voltage of the secondary high-speed diode D3 decreases, so a high-performance diode with a low VF that has a faster switching speed than a low breakdown voltage There is an advantage that it can be used.

According to the present invention, the oscillating voltage of the resonant capacitor is detected and the switching element is turned on at the timing when the voltage of the resonant capacitor reaches a predetermined value. ) The power consumed inside the switching element is reduced.

Additionally, this reduces the level of switching noise, making the snubber circuit and bead core unnecessary.

Furthermore, since the switching element is turned on at the minimum point of the charging charge level of the resonant capacitor, the charging energy of the resonant capacitor is effectively transmitted to the secondary side, which has the advantage of reducing the charging energy consumed inside the switching element.

Furthermore, since the voltage detection circuit is simple, consisting only of transistors and diodes, and the transistor is turned on at the timing when the voltage of the resonant capacitor falls below a predetermined value, there is no reduction in operating speed due to saturation of the transistor.

Furthermore, since the voltage waveform of the resonant capacitor is obtained from the relatively low voltage tertiary coil of the transformer, it is not necessary to design the voltage detection circuit to have a high withstand voltage.

(G) Effects of the Invention As described above, according to the present invention, (+1) ON/OFF of the switching element is controlled by the voltage level;
This is done at a timing when the current level is low.

Switching noise level is reduced.

Therefore, a snubber circuit and a bead core are not required, and the switching power supply circuit can be made smaller and lower in price.

(2) Since the switching element turns on at the minimum point of the charging charge level of the resonant capacitor, the charging energy of the resonant capacitor is effectively transmitted to the secondary side.

The charging energy consumed inside the switching element is reduced.

(3) Since the switching element is turned on and off at a timing when the voltage level and current level are low, and the temporal phase relationship is shifted from each other, the internal loss of the switching element, which is calculated by the product of voltage and current, is reduced.

(4) Since the voltage waveform of the resonant capacitor is obtained from the relatively low-voltage tertiary coil of the transformer, a low-voltage diode can be used in the voltage detection circuit, eliminating the need for a high-voltage design.

Therefore, since a low voltage diode can be used, the generated noise can be significantly suppressed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a block diagram of a control circuit used in the embodiment, and FIG.
B) are voltage and current waveform diagrams of the switching elements of the conventional example and the embodiment of the present invention, respectively. Figures 4 (A) and 4 (B) are diagrams explaining the residual voltage of the resonant capacitor, and the residual voltage of the resonant capacitor and insulation. FIG. 5 is a block diagram of a conventional example. (20)...Control circuit, (50)...Transformer, (52)...Pressure voltage detection circuit, SW...Switching element, CR15...Resonance capacitor, P
C...Photocoupler RswN...Current detection resistor. Requester Sanyo Electric Co., Ltd. agent Patent attorney 100% Takuji and two others Figure 3 (△) Figure 4 (Δ) Figure 4 (B)

Claims (4)

[Claims] (1) an isolation transformer, a switching element that controls the primary coil current of the isolation transformer, a control circuit that drives the switching element at a predetermined timing, a resonant capacitor connected between the controlled electrodes of the switching element; A resonant switching power supply circuit comprising a voltage detection circuit that detects a voltage of a tertiary coil of an isolation transformer and triggers the control circuit to turn on a switching element at a timing when the voltage of the resonant capacitor reaches a predetermined value. (2) The resonant switching power supply circuit according to claim 1, wherein the voltage detection circuit detects a minimum point of the oscillating voltage of the resonant capacitor. (3) The resonant switching power supply circuit according to claim 1, wherein the output circuit on the secondary side includes an output voltage detection circuit, and the control circuit is controlled by the output of the output voltage detection circuit independently of the output of the voltage detection circuit. . (4) Power MOSFET as the switching element
2. The resonant switching power supply circuit according to claim 1, wherein the resonant switching power supply circuit uses: