JPH08242581A - Ringing choke converter - Google Patents

Abstract

(57) [Abstract] [Object] The present invention is directed to a ringing choke converter (Ri
The present invention relates to improvement of the output control circuit of the nging choke converter (RCC). INDUSTRIAL APPLICABILITY The present invention can be applied to a switching power supply device to reliably control an output voltage, and moreover, it is possible to reliably prevent an output current from becoming excessive. [Structure] In FIG. 1, a diode D ₃ for improving the switching characteristics of the transistor Q ₂ is inserted in parallel with R ₃ .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of an output control circuit of a ringing choke converter (RCC).

[0002]

2. Description of the Related Art A conventional ringing choke converter will be described below.

FIG. 3 is a conventional basic circuit diagram. When the input power supply voltage E _i is turned on, the switching main transistor Q ₁ is turned on through the starting resistor R ₁ , whereby the voltage induced in the feedback winding NB of the output transformer T and the base resistor R ₂ cause the main transistor Q ₁ to turn on. A constant base current flows. In this case, the voltage induced in the secondary winding N ₂ is blocked by the rectifying diode D ₁ , and no current flows through the smoothing capacitor C ₂ and the load RL. On this occasion,
The input power supply voltage E _i is applied to the primary winding N ₁ of the transformer T, and the current of the primary winding N ₁ , that is, the collector current of the transistor Q ₁ increases linearly to store energy in the primary winding N _1. To be However, since the base current is constant, when the collector current of the transistor Q ₁ reaches a certain value, it cannot be further increased, and thereafter, the voltage induced in the primary winding N ₁ is reduced, and thus the base current is also reduced. Due to such a feedback reproducing action, the transistor Q ₁
Turns off rapidly. At the same time, the secondary winding N _{2 of the} transformer T
Induces a voltage in the direction to make the diode D ₁ conductive,
The energy stored in the primary winding N ₁ is supplied to the capacitor C ₂ and the load RL through the diode D ₁ . Eventually, the transistor Q ₁ is turned on again and the diode D ₁ is cut off. However, the current supply is continued by the discharge of the capacitor C ₂ to the load RL, and then the above operation is repeated. The voltage detection unit A includes a voltage detector IC ₁ having a built-in reference voltage, a photocoupler light emitting unit PD for outputting the reference voltage, and resistors R ₄ , R ₅ for dividing the output voltage E _o . In the control circuit section B, Q ₂ is a control transistor connected between the base and emitter of the main transistor Q ₁ , and R ₃ and C ₄ are resistors and capacitors forming a time constant circuit at both ends of the feedback winding NB. Connected and also resistor R ₃
The connection point a of the capacitor C ₄ is connected to the base of the control transistor Q ₂ .

Next, PT is the photocoupler light receiving portion connected between one end of the feedback winding NB and the connection point a, by which the charging time constant of the capacitor C ₄ is adjusted. Incidentally, C ₃ is a capacitor for improving the off-characteristics of the main transistor Q ₁ , and D ₂ is a diode for preventing sneaking of the base starting current.

[0005]

However, in the above-described conventional configuration, the constant voltage control and the overcurrent protection may not perform the desired operation depending on the switching characteristics of the transistor Q ₂ in FIG.

An object of the present invention is to ensure that the constant voltage control and the overcurrent protection operate.

[0007]

In order to solve the above problems, the present invention provides a time constant circuit composed of a photocoupler, a resistor and a capacitor, and a diode connected in parallel with the resistor to provide a diode in FIG. The switching characteristics of the Q ₂ transistor are improved.

[0008]

With this configuration, the constant voltage control and the overcurrent protection operation are surely performed.

[0009]

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

The difference between the present invention and the prior art is that in FIG.
Q₂To improve the switching characteristics of the transistor
Resistance R₃In parallel with diode D₃To connect
It R ₃And Q₂C connected between the base and emitter of_FourTo
Adjust the charging time more and the charging voltage is Q₂Reached the threshold of
Then Q₂Turns on.

Next, when C ₄ is discharged and becomes lower than the threshold value, Q ₂ is turned off, but when C ₄ is delayed, Q ₂ is always on or the charging time cannot be controlled. There is.

In order to improve this, the charge voltage of C ₄ is discharged at D ₃ and the on / off control of Q ₂ is surely performed.

Next, the voltage control operation will be described. FIG.
4A shows the voltage V _{CE of the} main transistor Q _{1 .}
Waveform diagram, FIG. 4B shows a voltage waveform diagram of the feedback (base) winding, FIG. 4C shows a voltage waveform diagram of the capacitor C ₄ (point a), and the current flowing through the photocoupler light receiving unit PT and the resistor R _3. And a time constant circuit formed by the capacitor C ₄ ,
When the point potential exceeds the voltage (V _BE ) of the control transistor Q ₂ , the transistor Q ₂ turns on and absorbs the base current of the main transistor Q ₁ to turn it off. When the loss of each part of the converter is ignored, the relationship between the output voltage E _o and the ON time T _ON of Q ₁ can be approximated as shown in (Equation 1).

[0014]

[Equation 1]

Where E _i is the input voltage, I _o is the output current, and K
₁ and K ₂ are constants. When the output voltage is detected and the current of the transistor of the photocoupler is changed to control T _ON , the output voltage E _o can be kept constant by (Equation 1).

Next, the overcurrent protection operation will be described. When the output voltage is controlled to be constant as described above, the load current is increased or the input voltage (E _i )
Is decreased, the on-time (T _ON ) of the main transistor Q ₁ is increased and the frequency is decreased. Therefore, when the input voltage (E _i ) is the lowest and the maximum load current (I _OMAX ), the on-time (T _ON ) is the maximum (T _ONMAX ). This is expressed by (Equation 2).

[0017]

[Equation 2]

Now, if the current of the photocoupler light receiving portion PT via the voltage detecting portion A is set to be zero, the charging time constant of the capacitor C ₄ becomes the maximum for the output current beyond this, and the main time at this time is set. When the on-time (T _ON ) of the transistor Q ₁ is T _OC , it becomes (Equation 3).

[0019]

(Equation 3)

This T _OC time does not extend the T _ON width any more, no matter how the load current is increased. When these relationships are expressed by the output voltage and current, the output characteristics are as shown in FIG. 5, and the load current increases up to the output current I _OC corresponding to T _OC , but even if a load is further increased, the T _ON width Does not increase and becomes a drooping character. The voltage EB generated in the base winding in FIG. 1 (FIG. 4 (b)) is the voltage generated in the forward direction E _BF
Since the voltage generated in the opposite direction to the E _BN reverse voltage E _BN proportional to the output voltage E _o, if E _o is a constant voltage E
_BN is also constant, the forward voltage E _BF becomes shorter charging time of the capacitor C ₄ higher E _i is proportional to E _i T _OC
Becomes smaller. Therefore, if EB is optimally designed, I _OC
Can also minimize changes with input voltage.

[0021]

FIG. 2 shows how the characteristics are improved by the present invention. After the improvement in FIG. 2A and the improvement in FIG. 2B before the improvement, the constant voltage control and the overcurrent protection operation are surely performed.

As is apparent from the above description, according to the present invention, the output voltage can be reliably controlled, and the output current can be prevented from becoming excessively large. Extremely large.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a linking choke converter according to an embodiment of the present invention.

FIG. 2A is an output characteristic diagram of the linking choke converter circuit of the embodiment. FIG. 2B is an output characteristic diagram of the conventional linking choke converter circuit.

FIG. 3 is a circuit diagram of a conventional linking choke converter.

4A is a voltage waveform diagram of a main transistor Q ₁ , FIG. 4B is a voltage waveform diagram of a feedback (base) winding, and FIG. 4C is a voltage waveform diagram of a capacitor C ₄ .

FIG. 5 is an output characteristic diagram of a linking choke converter circuit according to an embodiment of the present invention.

[Explanation of symbols]

E _i Input voltage E _o Output voltage I _o Output current PD Light emitting part PT Light receiving part T Transformer N ₁ Primary winding N ₂ Secondary winding A Voltage detecting part B Control circuit R ₁ , R ₂ , R ₃ , R ₄ , R ₅ resistor Q ₁ , Q ₂ transistor D ₁ , D ₂ , D ₃ diode C ₁ , C ₂ , C ₃ , C ₄ capacitor IC ₁ constant voltage control IC

Claims (1)

[Claims] 1. A leakage transformer having a primary winding, a secondary winding, a feedback winding, and optionally a control winding, a collector connected to the primary winding, and a base and an emitter connected to the feedback winding. A rectifying diode is connected to the switching main transistor and the secondary winding, and it has a time constant circuit consisting of a photocoupler and a resistor and a capacitor for performing voltage control operation and overcurrent protection operation, and is connected in parallel to the resistor. Ringing choke converter characterized by having an improved diode.