JP3183411B2 - Ringing choke converter protection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a protection circuit for a ringing choke converter.

More specifically, the present invention controls a gate potential of a switching element by flowing a starting current into a capacitor included in a driving circuit of the switching element for switching a DC input voltage. The present invention relates to a protection circuit for a ringing choke converter having a circuit for performing the above.

[0003]

2. Description of the Related Art FIG. 7 shows a power supply circuit of a ringing choke converter type conventionally known. Where 1
Is a switching element (MOS FET), 2 is a current detection resistor, 3 is a transistor, 4 is a switching control circuit,
5 is a starting resistor, 6 is a drive circuit, 7 is a converter transformer, 8 is an output circuit, 9 is an output voltage detection circuit, and 10 is a photocoupler.

In the circuit shown in FIG. 7, the DC input voltage Vi
n, and outputs a stabilized DC voltage to the secondary side by a ringing choke converter including the converter transformer 7, the switching element 1, and the like. Here, the output of the output voltage detection circuit 9 is sent to the switching control circuit 4 via the photocoupler 10, and controls the on / off of the switching element 1 to keep the output voltage constant. Further, the drive circuit 6 turns on the gate of the switching element 1.
Transmits off-drive energy.

FIG. 8 shows an example of the voltage and current waveforms of the switching element 1 when the output is short-circuited.

When the switching element 1 is turned on, its gate
The rain current is Vin / L · t (L: converter transformer
7 primary winding P₁ Of the resistance 2
The transistor 3 is turned on by the rise of the terminal voltage,
Primary winding P of the power transformer 7 ₁ Has (1/2) Li
_p ^Two(I_p Is the switch when transistor 3 is turned on
Energy of the switching element 1). Soshi
When the switching element 1 is turned off, the converter transformer
From the secondary winding S of the
Primary winding P with forward voltage₁ Energy stored in
Consume.

[0007]

[0006] However, before the energy stored in the converter transformer primary winding P ₁ is completely consumed, as shown in FIG. 8, the switching element 1
(The gate voltage is generated by charging the capacitor C with the starting current flowing through the starting resistor 5) exceeds the threshold value of the switching element 1, a DC current flows through the switching element 1. This switching element 1
Loss increases.

For example, in FIG.
When a wide input power supply is configured without switching of 0V (Vin = 140, 280V), 100V AC (Vin = 140
When the input voltage is increased from V) to 200 V AC (Vin = 280 V), the starting current of the starting resistor 5 is doubled.
As a result, to charge the capacitor C at twice the speed,
The direct current of the switching element 1 began to flow quickly, and the loss of the switching element 1 increased remarkably, resulting in a defect that the switching element 1 was eventually damaged.

In FIG. 7, when the output is short-circuited, only the forward voltage of the diode included in the output circuit 8 consumes the energy stored in the converter transformer 7, and the energy release time is shorter than that at the time of output of the rated voltage. become longer.

On the other hand, since the starting current of the starting resistor 5 increases in proportion to the rise of the DC input voltage Vin, the charging time of the capacitor included in the drive circuit 6 is inversely proportional, and the starting time of the switching element 1 is short. Become. If the startup time is shorter than the energy release time, the DC current of the switching element 1 flows and the loss of the switching element 1 increases significantly, and eventually the switching element 1 is damaged.

For this reason, conventionally, a countermeasure has been taken by using a constant current circuit using an expensive transistor with a high withstand voltage instead of the starting resistor 5.

It is therefore an object of the present invention to provide a protection circuit for a ringing choke converter in which the start-up time is kept constant even when the input voltage changes significantly.

It is another object of the present invention to provide a protection circuit for a ringing choke converter which protects a switching element even when an output is overloaded or short-circuited.

[0014]

SUMMARY OF THE INVENTION The present invention controls a gate potential of a switching element by causing a starting current to flow into a capacitor included in a driving circuit of the switching element for switching a DC input voltage. A ringing choke converter having a circuit for performing the determination, determining a magnitude of the DC input voltage or the output voltage; a plurality of resistors connected in parallel to supply the starting current to the capacitor; And shunt means for preventing a current flowing through a specific one of the plurality of resistors from flowing into the capacitor in response to the output of the plurality of resistors.

[0015]

Further, the present invention provides a ringing having a circuit for controlling a gate potential of a switching element by flowing a starting current into a capacitor included in a driving circuit of the switching element for switching a DC input voltage. The choke converter includes a determining means for determining the magnitude of the DC input voltage or the output voltage, and a switching means for connecting an auxiliary capacitor in parallel with the capacitor in response to an output of the determining means. .

[0017]

According to the present invention, as shown in FIG. 1 as an example, a current flowing through a specific resistor among a plurality of starting resistors is prevented from flowing into the capacitor.

[0018]

Further, according to the present invention, as shown in FIGS. 3 and 5, for example, an auxiliary capacitor is connected in parallel with the capacitor in response to the output of the determination means.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention. In this figure, 1 is a switching element (MOS FET),
2 is a current detection resistor, 3 is a transistor, 4 is a switching control circuit, 5 is a starting resistor, 6 is a drive circuit, 7 is a converter transformer, 8 is an output circuit, 9 is an output voltage detection circuit,
Reference numeral 10 denotes a photocoupler, 11 denotes a diode, 12 denotes a capacitor, 13 denotes a Zener diode, 14 denotes a resistor, 15 denotes a transistor, 16 denotes a starting resistor, and 17 denotes a diode.

[0022] In FIG. 1, when the input voltage Vin is high, when FET on, the voltage of the MOSFET driving auxiliary winding P ₂ increases in proportion to the input voltage. Using this voltage,
For example, in order to bypass the current flowing through the starting resistor 5 when the input AC 100 V becomes 200 V, the transistor 15 is turned on, and the charging time of the capacitor included in the drive circuit 6 is set to the same time as when the AC 100 V is applied. Try to eliminate the direct current.

[0023] That is, through the auxiliary winding P ₂ diodes 11, creates a voltage proportional to the input voltage Vin at capacitor 12, the voltage zener diode 13 (FET
When the voltage exceeds the input voltage at which DC current starts to flow through the transistor 1, the transistor 15 is turned on, and the starting resistor 16 is grounded. For this reason, the charging time of the capacitor included in the drive circuit 6 becomes constant, so that the DC current of the FET 1 can be eliminated.

In this embodiment, output short-circuit protection can be achieved with inexpensive components.

FIG. 2 shows a second embodiment of the present invention. This embodiment differs from the first embodiment in that a diode 27 and a resistor 28 connected in series are inserted between the capacitor side of the drive circuit 6 and the collector of the transistor 15.

That is, as shown in FIG. 1, the starting current is bypassed by the diode 27, the resistor 28 and the transistor 15 without employing the configuration in which the two starting resistors 5 and 16 are provided. As in the embodiment, output short-circuit protection can be achieved with inexpensive components.

FIG. 3 shows a third embodiment of the present invention. In this embodiment, when the input voltage Vin increases, the capacitor 1
By using the fact that the charging voltage of the second embodiment becomes higher, the relay 19 is turned on, and the capacitor 20 is connected in parallel with the capacitor included in the drive circuit 6 to provide the same protection as in the first and second embodiments. It is assumed that.

FIG. 4 shows a fourth embodiment of the present invention. In this embodiment, a ringing choke converter (hereinafter referred to as RC
In C), when the output is short-circuited or overloaded, the output voltage is detected to detect a decrease in the output voltage, and the startup current is bypassed to lengthen the startup time at short-circuit and overload.

That is, when the output voltage becomes shorter than the voltage of the zener diode included in the overload / short detection circuit 40 plus the forward voltage of the photocoupler at the time of short circuit and overload,
This photocoupler is turned on, and the diode 27 and the resistor 2
8. The starting power is bypassed via the transistor 15. For this reason, the charging time of the drive circuit 6 (the time when the switching element 1 is turned off) becomes longer, and the DC current of the switching element 1 can be eliminated.

FIG. 5 shows a fifth embodiment of the present invention. In this embodiment, the diode 50 from P ₂ winding of the converter transformer 7, creating a voltage proportional to the output voltage at the capacitor 12, this voltage falls below the operating voltage of the relay 52, B contact of the relay 52 is restored, By connecting the capacitor 20 in parallel with the capacitor included in the drive circuit 6, the same protection as in the embodiment of FIG. 4 can be provided.

In other words, P _{2 of the} converter transformer 7
Since the negative voltage of the winding is proportional to the voltage of the S winding,
Utilizing this voltage, the contact 52 is normally opened by operating the relay 52 of the B contact that bypasses the starting current.
At the time of overload or short circuit lowers the voltage of the P ₂ and S windings, bypass the starting current relay 52 is restored, it is intended to eliminate the DC current of the switching element 1.

FIG. 6 shows a sixth embodiment of the present invention. The operation of the present embodiment is basically the same as that of FIG. 4, and the startup current is bypassed via the diode 27 and the resistor 28 when the output is short-circuited and when the output is overloaded.

According to the embodiments shown in FIGS. 4 to 6, short circuit protection and overcurrent protection of the output can be achieved with inexpensive components.

[0034]

According to the present invention, since the starting current is bypassed to a portion other than the capacitor of the drive circuit only when the input voltage is increased, even when the input voltage changes greatly,
The start-up time is kept constant and the output overload,
The switching element can be protected even during a short circuit.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the present invention.

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a third embodiment of the present invention.

FIG. 4 is a circuit diagram showing a fourth embodiment of the present invention.

FIG. 5 is a circuit diagram showing a fifth embodiment of the present invention.

FIG. 6 is a circuit diagram showing a sixth embodiment of the present invention.

FIG. 7 is a circuit diagram showing a conventional technique.

FIG. 8 is a waveform chart showing the operation of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Switching element (MOS FET) 2 Current detection resistor 3 Transistor 4 Switching control circuit 5 Start-up resistor 6 Drive circuit 7 Converter transformer 8 Output circuit 9 Output voltage detection circuit 10 Photocoupler 11 Diode 12 Capacitor 13 Zener diode 14 Resistance 15 Transistor 16 Start Resistance 17 Diode

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 3/28

Claims (1)

(57) [Claims] 1. A ringing choke converter having a circuit for controlling a gate potential of a switching element by flowing a starting current into a capacitor included in a driving circuit of the switching element for switching a DC input voltage. Determining means for determining the magnitude of the DC input voltage or output voltage; a plurality of resistors connected in parallel to supply the starting current to the capacitor; and in response to an output of the determining means, A protection circuit, comprising: a shunt means for preventing a current flowing through a specific one of the plurality of resistors from flowing into the capacitor.