JPH03195362A - Ringing choke converter - Google Patents

Abstract

PURPOSE:To keep an output voltage constant stably by reducing a period or continuity of switching elements according to the rise of a power voltage. CONSTITUTION:When a power voltage Vi rises, the first FET 7 is turned OFF, an induced voltage VA of a main winding L1a rises, and the threshold of the current is steep. Simultaneously, an induced voltage VB of an auxiliary winding L1b also rises, and the time until an output of an integrating circuit 11 reaches the threshold value of a gate bias voltage of the second FET 9 is reduced. Accordingly, the timing for ON starting of the second FET 9 is quickened, and an ON period of the first FET 7 is reduced. As a result, a level of the current supplied to the main winding L1a is kept in the same level as that of the power voltage Vi in a normal time, and accordingly, a quantity of energy stored in a transformer 3 has also the same level, so that a secondary side output voltage VOUT remains unchanged and is stabilized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a DC-DC converter that steps up (or steps down) a DC voltage to a predetermined voltage.

[Prior Art] Conventionally, as one type of DC-DC converter, a transformer is provided with a main winding and an auxiliary winding on the next side, and an output winding on the first secondary side, and a DC power supply. A positive feedback circuit that applies positive feedback to the switching element by returning the voltage induced in the auxiliary winding by the current flowing to the next winding to the bias side of the switching element. A ringing choke converter (hereinafter referred to as RCC) is known, which is equipped with the following and steps up or steps down a DC voltage through self-excited oscillation (switching) of a switching element.

[Problem to be solved by the invention] This type of RCC has a problem in that the output voltage fluctuates due to fluctuations in the power supply voltage and changes in the load on the output side, and the development of circuit technology for output stabilization is desired. ing. In particular, RCC is often used as an auxiliary power supply for other DC-DC converters, and in this case, the output voltage becomes unstable due to fluctuations in the power supply voltage rather than due to load fluctuations.
Measures against this are required.

As one measure against this, in RCCs that use bipolar transistors as switching elements, the positive feedback circuit is
When the voltage of the auxiliary winding exceeds a predetermined value, a base current control circuit is provided that divides and reduces the base current of the transistor, and the output voltage (the output voltage and the auxiliary winding voltage are in a proportional relationship) reaches the rated voltage. If the threshold is exceeded, it is possible to reduce the base current and turn off the transistor, thereby shortening the on-period of the transistor, suppressing the voltage rise, and stabilizing the output voltage.

However, bipolar transistors have a large collector-emitter forward voltage drop, resulting in large collector losses and large power consumption losses.

Furthermore, although the base bias current is smaller than the collector current, its power consumption cannot be ignored. Therefore, in place of bipolar transistors, for example, well-known field effect transistors (hereinafter referred to as FETs), which have a very small forward voltage drop and do not require bias current, may be used.
However, the technique for stabilizing the output voltage in an RCC using bipolar transistors cannot be applied to an RCC using an FET as a switching element to stabilize the output voltage.

In other words, the drain current of an FET is controlled by the gate voltage, and only a very small amount of current flows from the gate to the source, so the on-period of the FFT cannot be shortened using the base current control circuit described above. It is from.

Therefore, an object of the present invention is to provide a ringing choke converter that stabilizes the output voltage by controlling the bias voltage of the switching element according to the power supply voltage. '-[Means for Solving the Problems] 4 The gist of the present invention is to provide a transformer having a main winding and an auxiliary winding on the primary side and a secondary winding on the secondary side, and a direct current a switching element that connects and disconnects current from a power source to the main winding; a bias circuit that applies the voltage induced in the auxiliary winding to the switching element as a bias voltage; and a bias voltage that is output from the bias circuit. the transformer; A ringing choke connected to a secondary winding, comprising a rectifying element that becomes conductive when the main winding stops energizing and passes current from the secondary winding, and a smoothing circuit that smoothes the output of the rectifying element. It's in the converter.

[Function] According to the ringing choke converter of the present invention configured as described above, when the switching element conducts and current flows from the DC power supply to the main winding of the transformer, a voltage approximately proportional to the power supply voltage is generated. are induced in the main winding and the auxiliary winding, respectively. Then, the bias circuit applies the induced voltage of the auxiliary winding to the switching element as a bias voltage, so that the switching element continues to be in a conductive state. on the other hand,
When the induced voltage of the auxiliary winding is input to the integrating circuit, the output voltage of the integrating circuit increases with a predetermined time constant relative to the induced voltage, and this output voltage is applied to the auxiliary switching element as a bias voltage.

Therefore, the auxiliary switching element is turned on and the bias voltage output from the bias circuit is controlled, thereby cutting off the conduction of the switching element. When the power supply voltage rises, the induced voltage in the auxiliary winding rises, and the output voltage of the integrating circuit rises steeply, so that the auxiliary switching element starts conducting conduction earlier, and therefore the switching element's cut-off timing also becomes earlier.

[Example] An embodiment of the present invention will be described below with reference to the drawings.

First, FIG. 1 is an electrical circuit diagram showing a ringing choke converter according to an embodiment of the present invention.

As shown in the figure, a ringing choke converter (hereinafter referred to as
RCC) is provided with a main winding Lla and an auxiliary winding Llb on the negative side, and a main winding Lla on the secondary side.
A transformer 3 is provided with a secondary winding L2 wound with a polarity opposite to that of the transformer 3, and a first field effect transistor (hereinafter referred to as a first FET) that connects and disconnects current from the DC power supply 5 to the main winding Lla. 7, a second field effect transistor (hereinafter referred to as a second FET) 9 as an auxiliary switching element, and an integrating circuit 1 whose output side is connected to the gate of the second FET 9 and whose input side is connected to one end of the auxiliary winding Llb. , 1st FE
A rectifier diode DRE provided in the secondary winding L2 and a rectifier diode DRE provided in the secondary winding L2 of the transformer 3 so that the voltage induced in the secondary winding L2 of the transformer 3 is in the forward direction when T7 is turned off.
A smoothing capacitor C3M is provided for smoothing the secondary side output of.

One end of the main winding Lla of the transformer 3 is connected to the positive electrode of the DC power source 5 , and the other end is connected to the negative electrode of the DC power source 5 via the drain-source of the first FET 7 . On the other hand, the auxiliary winding Llb has one end connected to the source of the first FET 7 and the gate thereof via the starting resistor R, and the other end connected to the first FET 7 via the capacitor C and the resistor R2.
and the input side of the integrating circuit. In other words, the voltage VB induced in the auxiliary winding Llb is not applied to the gate of the first FET7.
The structure is such that an induced voltage VB is applied to the gate of 9 via an integrating circuit 1.

Further, the gate of the first FET7 is connected to a resistor R3 and a resistor R4.
is connected to the positive electrode side of the DC power source 5 via the resistor R3 and the negative electrode side of the DC power source 5 via the resistor R3 and the capacitor C2, and is also connected to the drain of the second FET 9, and further connected to the drain of the second FET 9, and further connected to the drain of the second FET 9. The source of the second FET 9 is connected to the source of the second FET 9. In other words, when the second FET9 turns on, the first FET9 turns on.
The potential difference between the gate and source of ET7 disappears, and the first F
ET7 is configured to turn off.

Note that the turns ratio between the main winding Lla and the auxiliary winding Llb is determined so that the induced voltage VB of the auxiliary winding Llb is equal to or higher than the gate bias voltage of the second FET 9. Further, the respective sizes of the resistor R3, the starting resistor R1, and the resistor R4 are set so that the voltage across the starting resistor R1 exceeds the threshold of the gate bias voltage VGSI of the first FET 7 when the switch 5 is turned on. ing.

Integrating circuit [1] is a well-known CR circuit consisting of a resistor R5 and a capacitor C3, which is provided with a bypass circuit [3] that bypasses the resistor R5. Bypass circuit] 3 is the second
A diode D which is in the forward direction with respect to the gate bias voltage VGS2 of FET9] and a constant voltage diode TZ which is in the reverse direction with respect to the bias voltage VGS2 and whose anode is connected to the anode of the diode D1 via the resistor R6. It is configured as a series circuit.

When the induced voltage VB is generated, the output voltage of the integrating circuit 1] rises with the time constant of the integrating circuit 1]. Auxiliary winding L
When the induced voltage VB of lb further increases and exceeds a predetermined voltage (breakdown voltage vZ of the voltage regulator diode TZ), the voltage regulator diode TZ becomes conductive and the resistor R5 and the resistor R
6 are connected in parallel, and the time constant of the integrating circuit] is changed. In other words, the charging time of capacitor C3 is shortened.]
1 output voltage is the gate bias voltage V of the second FET 9
Since the time required to exceed the GS2 threshold VS is shortened,
The second FET 9 turns on faster.

The operation of the RCCI will be explained below with reference to FIG.

First, when the switch 15 is turned on, the bias voltage V GSI is applied to the gate of the first FET 7, and the first FET
The channel between the drain and source of 7 is opened and the DC power supply 5
Current begins to flow from the main winding Lla of the transformer 3 to the main winding Lla of the transformer 3. Then, a voltage V is applied to the main winding Lla approximately in proportion to the power supply voltage V1.
A is induced, and a voltage VB is also induced in the auxiliary winding Llb. This induced voltage VB is returned to the gate of the first FFT 7, and the bias voltage VGSI increases. Therefore,
The channel width of the first FET 7 is expanded to completely conduct between the drain and the source. Further, since a leakage bias current (extremely small current) is supplied to the gate of the first FET 7 by the capacitor C2, the first FFT 7 can continue to be in the on state. In FIG. 2, the induced voltage VB is shown with the forward bias direction of the first FET 7 as a positive voltage.

During the ON period of the first FFT 7, the current flowing through the main winding Lla increases the inductance of the main winding L]a, and the time t
Then, it becomes (Vi*t)/L, which increases in proportion to time. That is, the length of the ON period of the first FET 7 determines the current level and therefore the amount of energy stored in the transformer 3. During the ON period of the first FET 7, a voltage in the opposite direction to the rectifying diode DRE1 is generated in the secondary winding L2 of the transformer 3, so no current flows to the secondary side of the transformer 3.

On the other hand, the induced voltage VB is input to the integrator 11. The output voltage (=VGS2) of the tongue integrator 1 reaches the threshold VS of the gate bias voltage VGS2 of the second FET 9 after a predetermined time. Therefore, the second FFT9 turns on and the first FFT9 turns on.
FET7 turns off.

Then, in the transformer 3, the main winding Lla and the auxiliary winding Llb
In this case, a voltage is generated in the direction in which the current continues to flow through the main winding Lla, and the induced voltage VB becomes a negative potential.

Therefore, the output voltage of the integrating circuit (=VGS2)
is inverted to a negative potential, and the second FET 9 is also turned off.

Then, the charge accumulated in the capacitor C3 is transferred to the resistor R5.
, is collected from the auxiliary winding Llb to the DC power supply 5. In addition,
Diode D] prevents discharge from capacitor C3 through voltage regulator diode TZ, and capacitor C3
The negative potential of is adjusted.

At this time, a forward voltage VC is generated in the secondary winding L2 of the transformer 3 with respect to the rectifier diode DRE, so current flows from the rectifier diode DRE to the capacitor 2 CSM, charging the capacitor C3M and loading the load. Outputs voltage VOUT to. Then, when the energy stored in the transformer 3 is released to the secondary side, the current flowing through the rectifier diode DRE becomes zero, and the rectifier diode DRE is turned off.

The moment the rectifier diode DRE turns off, the first F
Bias voltage VGSI is applied to the gate of ET7, and current is supplied from DC power supply 5 via resistor R3, so
The first FET 7 is turned on, and self-oscillation of the first FET 7 continues.

In this way, in RCCl, the first FET 7 oscillates at a constant frequency, thereby boosting the DC voltage to a predetermined voltage VOUT and outputting it to the external load LD.

Here, suppose that the power supply voltage V1 has increased beyond the rated voltage for some reason. In this case, when the first FET 7 is turned on, the induced voltage VA of the main winding [a] is the power supply voltage Vi
is higher than when it is normal, and the rise of the current flowing through the main winding Lla becomes steep. At the same time, as shown by the broken line in FIG. 2, the induced voltage VB of the auxiliary winding Llb also increases, so that the output (=vGS2) of the integrator circuit]1 is transferred to the second FET9 (
7) The time required for the gate bias voltage VGS2 to reach the threshold value vS becomes shorter. Therefore, since the second FET 9 starts turning on earlier, the first FET 7 also turns off earlier, and the on period of the first FET 7 is shortened. As a result, the current level flowing through the main winding Lla is the power supply voltage V1
Since the amount of energy stored in the transformer 3 remains at the same level as during normal operation, the secondary output voltage VOUT remains stable without changing.

However, as described above, as the power supply voltage Vi increases, the first
Even if the ON period of the on-off duty of FET7 is shortened, the output voltage VOUT will still be affected by the forward voltage drop of the rectifier diode DRE, the resistance value of each winding Lla, Llb, and L2, and the first
Due to the influence of the turn-on time of FET7, the output voltage VO
It may not be possible to suppress the rise in UT. In particular, the higher the power supply voltage V1 is, the more easily the output voltage VOUT increases, and when the power supply voltage V1 increases significantly, the output voltage VOUT
will rise. In this way, when the power supply voltage V1 increases significantly and the induced voltage VB of the auxiliary winding Llb also increases beyond the breakdown voltage vZ, the constant voltage diode TZ becomes conductive in the integrating circuit 11. be done. Therefore, the output voltage (=VG
S2) reaches the threshold value VS of the gate bias voltage VGS2 of the second FET9 in a shorter time, so the gate bias voltage of the first FET7
turns off faster.

This greatly shortens the on period of the first FET7,
Since the amount of energy stored in the transformer 3 remains at the previous level, the rise in the secondary output voltage VOIJT is suppressed and stabilized.

As described above, in this embodiment, as the power supply voltage V1 rises, the on period of the on-off duty of the first FET 7 is shortened to maintain the output voltage V OUT at a predetermined level, and furthermore, the power supply voltage V1 increases significantly. , when the induced voltage VB of the auxiliary winding Llb rises above a predetermined level (VZ), the first F
The on-period of ET7 is further shortened to suppress the rise in output voltage VOUT. Therefore, even if the power supply voltage V1 increases significantly, the output voltage VOUT can be stably maintained at a predetermined level.

Furthermore, since FETs are used as switching elements, there is less loss in power consumption and less heat generation than in conventional RCCs using bipolar transistors.

[Effects of the Invention] As explained above, according to the present invention, the conduction period of the switching element is shortened as the power supply voltage increases.
Even if the power supply voltage increases, the output voltage can be kept stable.

[Brief explanation of drawings]

FIG. 1 is an electric circuit diagram of a ringing choke converter according to an embodiment, and FIG. 2 is an explanatory diagram showing the operation timing of the ringing choke converter. ]...Ringing choke converter 3...Transformer 5...DC power supply 7...First field effect transistor 9...Second field effect transistor]]...Integrator circuit Ll meter... Main winding Llb...Auxiliary winding L2...
・Secondary winding 6- TZ... Constant voltage diode C1... Capacitor DRE... Rectifier diode

Claims (1)

[Scope of Claims] A transformer including a main winding and an auxiliary winding on the primary side and a secondary winding on the secondary side, and a switching element that cuts off and on energization of the main winding from a DC power source. , a bias circuit that applies a voltage induced in the auxiliary winding to the switching element as a bias voltage; an auxiliary switching element that interrupts conduction of the switching element by controlling the bias voltage output from the bias circuit; an integrating circuit that stores the voltage induced in the auxiliary winding at a predetermined time constant and outputs it as a bias voltage to the auxiliary switching element; A ringing choke converter comprising: a rectifying element that is electrically conductive and passing current from the secondary winding; and a smoothing circuit that smoothes an output of the rectifying element.