JP3010611B2 - Ringing choke converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ringing choke converter used as a low-cost constant-voltage power supply for electronic devices.

[0002]

2. Description of the Related Art FIG. 3 is a circuit diagram showing a conventional example of a ringing choke converter (also called a flyback converter). In FIG. 3, a ringing choke converter is provided between a transformer 2 having a primary winding P, a secondary winding S and an auxiliary winding A, and between the positive and negative power supply terminals IP and IN via the primary winding P of the transformer 2. Switching elements connected in series, for example, a drain (hereinafter referred to as “D”), a source (hereinafter referred to as “S”) and a current detecting resistor 6 of a MOSFET 1, and a collector thereof is a MOSFET
1 is connected to a positive power supply terminal IP via a gate (hereinafter referred to as G) and a starting resistor 3, and its emitter is connected to a negative power supply terminal IN.
And the base of the auxiliary winding A is a MOSFET
1 comprises a switching control transistor 5 connected to each S, and a capacitor 4A and a resistor 4B connected in series between the collector of the switching control transistor 5 and the positive electrode of the auxiliary winding A of the transformer 2, respectively. A drive circuit 4, an output diode 7 having an anode connected to the negative electrode of the secondary winding S of the transformer 2, and a diode connected between the cathode of the output diode 7 and the positive electrode of the secondary winding S It comprises an output capacitor 8 and positive and negative output terminals OP and ON respectively connected between both terminals of the output capacitor 8.

FIG. 4 shows the operation waveform, and at time t ₀ , the DC voltage V is applied between the positive and negative power supply terminals IP and IN.
When "in" is applied, the capacitor 4A of the drive circuit 4 is charged via the starting resistor 3, and as shown in FIG.
The voltage between G and S of SFET1, that is, the gate voltage increases. When this gate voltage exceeds the threshold value at time t ₁ , MOSFET 1 starts to turn on, DC voltage Vin is applied to primary winding P of transformer 2, and a voltage is induced in auxiliary winding A. This voltage is the G of MOSFET 1
Is positively fed back and MOSFET 1 is completely turned on.
(1), (2)｝. When the MOSFET 1 is turned on, the primary winding P of the transformer 2 has a voltage of approximately (Vin / L) · T (where L is the inductance of the primary winding P, and T is the time after the MOSFET 1 is turned on). A constantly rising primary current Ip flows {FIG. 4 (3)}. The resistance value of the current detecting resistor 6 is so small that it is ignored. Voltage drop occurs between both terminals of the current detection resistor 6 by the primary current Ip, since the voltage drop is applied between the emitter and base of the switching control transistor 5, a current value Ipp primary current Ip at time t ₂ When the switching control transistor 5 is turned on, the switching control transistor 5 is turned on.
Turns off {FIG. 4 (1), (3)}. When the primary current Ip reaches the current value Ipp, the primary coil P of the transformer 2 stores energy of ・ · L · (Ipp) ² .
When the MOSFET 1 is turned off, the output capacitor 8 is output from the negative electrode of the secondary coil S through the output diode 7.
And the stored energy is released. When the stored energy is released, the voltage of each winding of the transformer 2 decreases and returns to the initial state. On the other hand, MOSFE
When T1 is turned off, the switching control transistor 5 is turned off because the base current is cut off. This transistor 5
Is turned off, the charging of the capacitor 4A of the drive circuit 4 through the starting resistor 3 starts again. These operations are repeated to continue the oscillation, and the positive and negative output terminals OP, ON
Outputs a voltage Vout.

A capacitor 9A and a resistor 9B, which are connected in series with the primary winding P of the transformer 2, respectively, are a snubber circuit 9 provided as necessary.
Used to absorb a surge voltage generated in the primary winding P. This ringing choke converter is composed of one switching element having a large capacity, and is characterized in that the number of parts is small and the cost is low.

[0005]

In the ringing choke converter described above, the stray capacitance of the circuit, for example, the stray capacitance of the primary winding of the transformer (indicated by reference numeral 10 in FIG. 3), and the stray capacitance of the winding of the transformer. Depending on the inductance,
When a switching element, for example, a MOSFET is turned off, resonance may occur. Figure 5 is a waveform diagram showing a state where the voltage indicated by Q ₁ by the resonance in the primary winding P of the transformer 2 as shown in FIG. 5 (1) when MOSFET1 at time t ₂ is turned off is generated Since this resonance voltage Q ₁ is also induced in the auxiliary winding A, the MOSF
ET1 of G, S voltage, i.e. the resonance voltage shown in Q ₂ is superimposed on the gate voltage of the MOSFET 1, this voltage value is MOSFET 1 exceeds the threshold value of the MOSFET 1 is turned on again. Since the frequency of the resonance voltage is high, the MOSFET 1 is repeatedly turned on and off each time (FIG. 5 (2)). The larger peak current flows repeatedly (trans second current value shown in Q ₃ are the MOSFET1 its core is from time t ₁ to time t ₂ the primary current Ip flows has become close to the magnetically saturated state, its because the winding of the inductance is reduced, high peak currents of the current value as shown in Q _3).

As described above, when a peak current having a large current value repeatedly flows, the MOSFET 1 is overheated, and in some cases, it may be damaged. As a countermeasure for this, for example, it is conceivable to increase the capacitance of a capacitor (indicated by 9A in FIG. 3) of the snubber circuit. However, to prevent this resonance, a large capacitor capacitance is required, which causes a cost increase.

An object of the present invention is to prevent the switching element from being repeatedly turned on and off due to resonance occurring when the switching element is turned off without increasing the capacitance of the capacitor of the snubber circuit, for example.

[0008]

In order to achieve the above object, the present invention provides a transformer having a primary winding, a secondary winding and an auxiliary winding, and a positive side and a negative side via the primary winding of the transformer. A positive-side main terminal of a switching element composed of, for example, a MOSFET connected in series between power supply terminals,
A negative side main terminal and a current detection resistor, a collector thereof is connected to a positive side power supply terminal via a control terminal and a starting resistor of the switching element, an emitter thereof is connected to a negative side power supply terminal and a negative electrode of the auxiliary winding, and a base thereof is provided. A switching control transistor respectively connected to the negative side main terminal of the switching element, and a capacitor and a resistor respectively connected in series between the collector of the switching control transistor and the positive electrode of the auxiliary winding of the transformer. A driving circuit, an output diode having an anode connected to the negative electrode of the secondary winding of the transformer, and an output capacitor connected between the cathode of the output diode and the positive electrode of the secondary winding. A ringing choke converter comprising: a resistor connected in series with the drive circuit and in parallel with each other; And connecting a diode, or an inductor.

[0009]

In the ringing choke converter according to the first aspect, since the resistor and the diode connected in parallel with each other are connected in series with the drive circuit, the resonance voltage induced in the auxiliary winding when the switching element is turned off is reduced. It is applied to the gate of the switching element via the resistance of the drive circuit and this newly provided resistance. A capacitance called a gate capacitance (11 in FIGS. 1 to 3) is provided at the gate of the switching element.
The capacitance is charged and the gate voltage rises, but the charging current due to the resonance voltage is limited by the newly provided resistor, so that the rise of the gate voltage is suppressed and the switching element is turned off. Repetition of ON / OFF is suppressed. Note that the diode connected in parallel with this resistor is used to bypass the charging current of the capacitor of the drive circuit for turning on the switching element during normal operation, which may affect the operation of the switching choke converter. There is no.

In the ringing choke converter according to the second aspect, since the inductor is connected in series with the drive circuit, the charging current of the gate capacitance of the switching element is similarly limited by this inductor, and the rise of the gate voltage is suppressed. In addition, the switching element is prevented from being repeatedly turned on and off. In general, since the frequency of the resonance voltage is high, the inductor effectively limits the high-frequency charging current due to the resonance voltage, and a relatively low-frequency charging current for turning on the switching element in a normal state. The current limiting effect is small, and the operation of the switching choke converter is not affected by this inductor.

[0011]

FIG. 1 is a circuit diagram showing an embodiment of a ringing choke converter according to the present invention. The ringing choke converter of the present invention shown in FIG. 1 has a resistor 12 and a diode 13 connected in series and parallel to each other in a driving circuit 4 of the conventional ringing choke converter shown in FIG.

As already described in the section of the problem to be solved by the invention, the switching element, for example, the MOSFE
When T1 is turned off, the stray capacitance of the circuit, for example, the stray capacitance 10 of the primary winding P of the transformer 2 and the resonance caused by the inductance of the winding of the transformer, causes the auxiliary winding A to be connected to the auxiliary winding A in FIG. resonance voltage, as shown in Q ₂ of 2) is induced, G of MOSFET 1, S voltage, i.e. the resonance voltage Q ₂ is superimposed on the gate voltage of the MOSFET 1, this voltage value exceeds the threshold value of the MOSFET 1 The MOSFET 1 repeatedly turns on and off. For this reason, the MOSFET 1 is overheated and may be damaged in some cases.

In this ringing choke converter,
Since the resistor 12 and the diode 13 connected in parallel with each other in series with the drive circuit 4 are connected, the resonance voltage Q ₂ induced in the auxiliary winding A when the MOSFET 1 is turned off is newly provided with the resistor 4 of the drive circuit 4. MOS through the resistor 12
Added to the gate of FET1. The gate of the MOSFET 1 has a capacitance 11 called a gate capacitance. The capacitance 11 is charged and the gate voltage rises. However, the charging current of the gate capacitance due to the resonance voltage is reduced by a newly provided resistor 12. , The rise of the gate voltage is suppressed, and the MOSFET 1 is prevented from being repeatedly turned on and off. Note that the diode 13 connected in parallel with the resistor 12 is for bypassing the charging current of the capacitor 4A of the drive circuit 4 for turning on the MOSFET 1 in a normal state, thereby affecting the operation of the switching choke converter. Will not be given.

FIG. 2 is a circuit diagram showing another embodiment of the ringing choke converter according to the present invention. FIG. 2 shows an inductor 14 instead of a resistor 12 and a diode 13 connected in series and connected in series to the drive circuit 4 of FIG.
Are connected. The charging current of the gate capacitance 11 of the MOSFET 1 due to the resonance voltage induced in the auxiliary winding A when the MOSFET 1 is turned off is determined by this inductor.
Similarly, the current is limited and the rise of the gate voltage is suppressed.
Repetition of ON / OFF of the FET 1 is suppressed. Generally, the frequency of the resonance voltage is a high frequency of, for example, about several KHz or more, and the inductor 14 effectively limits the high-frequency charging current due to the resonance voltage.
The current limiting effect is small for a charging current of a relatively low frequency for turning on the FET 1, for example, about several hundred Hz or less, and the operation of the switching choke converter is not affected by this inductor.

[0015]

According to the ringing choke converter of the present invention, the switching element is turned on by a resonance voltage generated when the switching element is turned off by connecting a resistor and a diode or an inductor connected in series with the drive circuit and in parallel with each other. -Since the turning-off is not repeated, a serious accident that may cause the switching element to overheat and possibly be damaged can be prevented at low cost.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram showing another embodiment of the ringing choke converter of the present invention.

FIG. 3 is a circuit diagram showing an example of a conventional ringing choke converter.

4 is an operation waveform diagram of the ringing choke converter shown in FIG.

5 is an operation waveform diagram when resonance occurs when the MOSFET is turned off in the ringing choke converter shown in FIG. 3;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 switching element (MOSFET) 2 transformer 3 starting resistor 4 drive circuit 5 switching control transistor 6 current detecting resistor 7 output diode 8 output capacitor 12 resistor 13 diode 14 inductor

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 3/28 H02M 3/338

Claims (3)

(57) [Claims] A transformer having a primary winding, a secondary winding and an auxiliary winding, and a positive side of a switching element connected in series between a positive side power supply terminal and a negative side power supply terminal via the primary winding of the transformer. A main terminal, a negative-side main terminal and a current detecting resistor, and a collector thereof is connected to a positive power supply terminal via a control terminal and a starting resistor of the switching element, and an emitter thereof is connected to a negative power supply terminal and a negative electrode of the auxiliary winding. A switching control transistor whose base is connected to the negative main terminal of the switching element, and a capacitor connected in series between a collector of the switching control transistor and a positive electrode of the auxiliary winding of the transformer. And a drive circuit comprising a resistor, an output diode having an anode connected to the negative electrode of the secondary winding of the transformer, A ringing choke converter comprising an output capacitor connected between a cathode of a diode for use and a positive electrode of the secondary winding, wherein a resistor and a diode connected in parallel with each other in series with the drive circuit are connected. A ringing choke converter characterized by the following. 2. A transformer having a primary winding, a secondary winding and an auxiliary winding, and a positive side of a switching element connected in series between a positive side power supply terminal and a negative side power supply terminal via the primary winding of the transformer. A main terminal, a negative-side main terminal and a current detecting resistor, and a collector thereof is connected to a positive power supply terminal via a control terminal and a starting resistor of the switching element, and an emitter thereof is connected to a negative power supply terminal and a negative electrode of the auxiliary winding. A switching control transistor whose base is connected to the negative main terminal of the switching element, and a capacitor connected in series between a collector of the switching control transistor and a positive electrode of the auxiliary winding of the transformer. And a drive circuit comprising a resistor, an output diode having an anode connected to the negative electrode of the secondary winding of the transformer, In ringing choke converter comprising a connected output capacitor between the cathode of the use diode and a positive electrode of the secondary winding, a ringing choke converter, characterized in that the inductor is connected to the drive circuit in series. 3. A ringing choke converter according to claim 1, wherein said switching element comprises a MOSFET.