JPH114578A - Voltage converter device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To partially control an output voltage and to prevent a resonance voltage from increasing excessively, by connecting a magnetic amplifier to the secondary coil winding circuit of a forward type voltage transformer, and controlling the pulse width of a secondary output pulse from the forward type voltage transformer. SOLUTION: In a switching voltage conversion device with a switching element 20, a forward type voltage transformer 7, and a flyback type voltage transformer 22, an oversaturation choke coil 11 is connected to a secondary coil winding 10 of the forward type voltage transformer 7. Then, the oversaturation choke coil 11 constitutes a magnetic amplification circuit with a rectifier 13, a resistor 14, and a voltage detection circuit 16 and controls a pulse width so that the output voltage can be maintained constantly. In this case, to prevent a resonance voltage from increasing excessively when an input voltage is high, voltage control due to the magnetic amplification circuit is performed when the control is shallow. When the control becomes deep, the control is shifted to a primary side PWM control, thus performing the stabilization control of an output voltage within an entire operation range.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching-type voltage converter widely used as a power supply device for electronic equipment.

[Prior Art] A primary winding of a flyback type and a forward type voltage transformer are connected in series, a secondary winding is connected in parallel, and a pulse width is controlled by a control circuit provided in a primary circuit. Voltage converters for controlling have already been developed and some have been put to practical use. As an automatic voltage switching circuit and an inrush current prevention circuit, a technique using a triac as a switching element is widely used.

[Problems to be Solved] It is well known that a voltage resonance operation is an ideal operation mode in a switching type voltage converter. However, a complete voltage resonance type voltage converter has not been realized yet. Also, triacs used in conventional automatic voltage switching circuits and inrush current prevention circuits have high forward voltages, which causes a reduction in power efficiency of the device. Furthermore, a major disadvantage of voltage resonance operation is the generation of its high resonance voltage.

According to the present invention, a flyback type and a forward type voltage transformer having a primary winding connected in series to a voltage transformer circuit are used. The output voltage is partially controlled by controlling the pulse width of the secondary output pulse from the forward type voltage transformer by the magnetic amplifier provided in the secondary winding circuit of the voltage transformer of , The output voltage was controlled by the primary PWM. In addition, an automatic voltage switching circuit and a rush current prevention circuit using a MOSFET with low power loss are provided so as to be able to automatically respond to either the 100 V area or the 200 V area. Further, in order to prevent a high resonance voltage, which is a drawback of the voltage resonance operation, a voltage clamp circuit using a MOSFET is provided.

[Operation] One of the reasons why the voltage resonance operation could not be completed in the conventional technology is that when the resonance operation approaches the end, the secondary circuit becomes conductive and the resonance voltage is clamped at that time. It was to be. In the present invention, the control of the output voltage from the forward type voltage transformer is partially performed by the magnetic amplifier circuit provided on the secondary side. In this case, the saturable choke coil connected to the secondary output circuit of the forward type voltage transformer is OF
While in the F state, the primary circuit and the secondary circuit are electrically separated, so the primary side resonance operation is independent of the state of the secondary circuit, and the resonance operation can be completed. Becomes On the other hand, since the resonance voltage generated with the resonance operation increases in proportion to the input voltage and the output power, the peak value becomes a very high value in a high input voltage and a high output operation, and a practical device is used. An obstacle to realization. In the present invention, in order to prevent this phenomenon, by simultaneously performing the primary side PWM, it is possible to prevent an excessive rise of the resonance voltage and realize a final stabilization of the output voltage. or,
According to the present invention, a reduction in power efficiency of the device is prevented by employing a MOSFET having a low ON resistance value in the automatic voltage switching circuit and the inrush current prevention circuit. Further, in the present invention, a semiconductor device having a withstand voltage as low as possible is used, and in order to prevent an increase in cost and a decrease in power efficiency,
The voltage clamp circuit by OSFET was adopted.

Next, an embodiment of the present invention will be described.
This will be described with reference to the drawings. FIG. 1 is a block circuit diagram of an embodiment of a voltage converter according to the present invention. In the figure, 1, 1 'indicates an input terminal from which AC input power is supplied. 2 is an inrush current prevention circuit, and 3
Is a rectifying bridge. Reference numeral 4 denotes an automatic voltage switching circuit, and reference numerals 5 and 6 denote smoothing capacitors having the same capacitance. The control circuit 19 drives the switching element 20 by generating pulse power at the set frequency. 7 and 22
Are forward type and flyback type voltage transformers, respectively. Voltage transformers 7 and 22 are
Each has a primary winding 8 and 23 and a secondary winding 10
And 24. The capacitor 21 forms a leakage inductance of the voltage transformer and an LC resonance circuit. When the parasitic capacitance of the switching element is sufficiently large, this capacitor can be omitted. Rectifiers 12 and 25 are connected to the secondary windings of each voltage transformer, respectively, and convert high-frequency power generated in the secondary windings into a DC pulsating flow. This pulsating current is converted into flat DC power by the condenser 15 and supplied to the load via the output terminals 17 and 17 '. A saturable choke coil 11 is connected to the secondary winding 10 of the forward type voltage transformer 7. This saturable choke coil comprises a rectifier, 13,
The resistor 14 and the voltage detection circuit 16 constitute a magnetic amplification circuit, and perform a pulse width control operation so as to keep the output voltage constant. If necessary, the magnetic amplification circuit
As shown in FIG. 2, by adding a saturable choke coil 11 'and a rectifier 13', it can be provided also in a secondary winding circuit of a flyback type voltage transformer. Even if the magnetic amplifier circuit is used alone, the output voltage can be controlled in the entire operation range.However, if the entire operation region is controlled only by the magnetic amplifier circuit, when the input voltage is high, the resonance voltage also increases. When the control is shallow, it is better to perform voltage control mainly by the magnetic amplifier circuit, and shift to the primary-side PWM control as the control becomes deeper. The deepest control point of the magnetic amplifier circuit can be set by the value of the resistor 14. Further, as a simpler method, by omitting the magnetic amplifier circuit and connecting a resistor of an appropriate value to the rectifier 12 in parallel, the saturable choke coil 11
Almost the same effect can be obtained by always supplying a constant reset current.

Further, as shown in FIG. 3, the secondary winding 24 of the flyback type voltage transformer is connected so as to operate in series with the secondary winding 10 of the forward type voltage transformer. Things are also possible. In this case, the output circuit of the forward type voltage transformer is independently connected to the voltage detection circuit 1.
6 'must be provided. And, of course,
The set voltage value of the voltage detection circuit 16 ′
Must be lower than the set voltage value.

FIG. 4 is a circuit diagram of an inrush current prevention circuit. Here, [FIG. 4] (a) shows an inrush current prevention circuit provided on the AC input wiring, and [FIG. 4] (b)
FIG. 3 is a circuit diagram of an inrush power prevention circuit provided on a DC power wiring. In the figure, 30 and 31 are MOSFETs
The resistors 32 and 35, the rectifier 37, and the capacitor 33 connected to the gate terminal form a bias circuit and a delay circuit, and the constant voltage diode 34 plays a role of a protection circuit. When a power switch (not shown) is turned on and the input AC power is applied to the input terminals 1 and 1 ′, the current slowly flows through the resistor 36.
The smoothing capacitors 5 and 6 are charged. Resistor 3 at the same time
Through 5 and rectifier 37, current flows into the gate terminal and charges capacitor 33 slowly. When the voltage between both ends of the capacitor 33 reaches the gate transition voltage of the MOSFET, the MOSFET shifts to the ON state, and the input power is supplied to the smoothing capacitor through the MOSFETs 5 and 6. [FIG. 4] (b) is an inrush current prevention circuit used in a DC circuit. In this case,
Since the flowing current is direct current, only one MOSFET is required.

FIG. 5 is a circuit diagram of an automatic voltage switching circuit. In the figure, 41 and 42 are MOSFETs
Is the main switching element of the circuit. MOSFET4
The source electrodes 1 and 42 are connected in opposite directions by source electrodes, and their drain electrodes are connected to an intermediate connection point between the input terminal 1 'and the smoothing capacitors 5 and 6, respectively. When a voltage is applied to the circuit, current flows through resistor 46, charging capacitor 44;
When the voltage across the capacitor 44 reaches the gate transition voltage value of the MOSFET, the MOSFETs 41 and 42
The state transits to the N state, and the input terminal 1 'is directly connected to the intermediate connection point between the smoothing capacitors 5 and 6, and the rectifier circuit operates as a voltage doubler rectifier circuit. In this case, the resistors 46 and 43 and the capacitor 44 form a bias circuit and a delay circuit, and the constant voltage diode 45 prevents an abnormal voltage from being applied to the gate electrode. Here, the delay circuit is set to an appropriate time constant so that the circuit does not operate abnormally immediately after the application of the input voltage or at the moment of a power interruption. Resistor 4
8, 50, 52 capacitor 51 constant voltage diode 49
And the NPN transistor 47 form a voltage detection circuit. When the input AC voltage rises and the rectified DC voltage value rises and the voltage at the connection point of the resistors 48 and 50 reaches the set voltage value of the constant voltage diode, the current becomes NPN.
The current flows to the base electrode of the transistor 47 and the transistor 4
7 turns ON. As a result, the gate electrodes of the MOSFETs 41 and 42 are short-circuited, and the MOSFETs 41 and 42 transition to the OFF state. Then, the connection between the input terminal 1 'and the intermediate connection point between the smoothing capacitors 5 and 6 is disconnected, and the rectifier circuit returns to a normal full-wave rectifier circuit.

FIG. 6 is a circuit diagram of a resonance voltage clamp circuit. In the figure, a drain electrode of a MOSFET 60 is connected to a secondary winding 10 of a forward type voltage transformer.
And the source electrode is connected to the capacitor 64. The constant voltage diode 61, the resistor 62, and the capacitor 63 form a constant voltage circuit for keeping the base electrode of the MOSFET 60 at a constant voltage. As the voltage developed on winding 10 falls gradually into resonance, capacitor 64 is charged negatively by the parasitic diode of MOSFET 60. When the resonance voltage starts to fall after the peak value, while the charge voltage of the capacitor 64 is lower than the voltage of the constant voltage circuit, the charge of the capacitor 64 is discharged through the MOSFET because the MOSFET 60 is in the ON state. When the voltage of the capacitor 64 becomes lower than the sum of the voltage of the low voltage circuit and the transition voltage of the MOSFET 60, the MOSFET 60 changes to OFF, the discharge of the capacitor 64 stops, and the constant voltage is maintained. In the next resonance cycle, the resonance voltage drops freely until the charging voltage of the capacitor 64 is reached, but when the charging voltage is reached, charging of the capacitor 64 starts through the parasitic diode of the MOSFET. The capacitance of the capacitor 64 is such that the peak value of the resonance voltage is equal to the voltage of the constant voltage circuit,
It is set to stop at a point slightly higher than the sum of the transition voltages of the SFETs. Therefore, the resonance voltage is clamped at that voltage. This circuit can similarly clamp the resonance voltage on the primary side if a high withstand voltage P-channel MOSFET is used.

[Effects of the Invention] As described in detail above, according to the present invention, voltage resonance operation is possible in almost the entire operation range, noise generation is small, and power conversion efficiency is high, and the voltage of the switching system is high. It is possible to provide a conversion device. In addition, it is possible to provide a 100V / 200V automatic switching circuit and an inrush current prevention circuit with low power loss.

[0011]

[Brief description of the drawings]

FIG. 1 is a block circuit diagram showing one embodiment of a voltage conversion device according to the present invention.

FIG. 2 is a partial circuit diagram when a magnetic amplifier is connected to both output circuits.

FIG. 3 is a partial circuit diagram in a case where secondary windings of two voltage transformers are connected in series.

FIG. 4A is a partial circuit diagram of an inrush current prevention circuit provided in an AC input circuit. (B) is a partial circuit diagram of an inrush current prevention circuit provided in the DC circuit.

FIG. 5 is a partial circuit diagram of an input voltage automatic switching circuit.

FIG. 6 is a partial circuit diagram of a resonance voltage clamp circuit.

[Explanation of symbols]

1, 1 'input terminal 2 inrush current prevention circuit 3 rectifying bridge 4 automatic input voltage switching circuit 5, 6 primary smoothing capacitor 7 forward type voltage transformer 8 primary winding 10 same as above secondary winding 11, 11' saturable Choke coil 12,13,13'18,25
Rectifiers 14, 32, 36, 43, 46, 48, 50, 52, 6
2 Resistor 15 15 'Secondary smoothing capacitor 16, 16' Voltage detection circuit 17, 17 'Output terminal 19 Control circuit 20, 30, 31, 41, 42, 50
MOSFETs 21, 27, 33, 44, 51, 53, 54
Capacitors 34, 45, 49, 51 Constant voltage diode

Claims (4)

[Claims] The present invention has two voltage transformers, a flyback type and a forward type, in which a primary winding is connected in series, and a leakage flux of the primary winding and a capacitor connected in parallel with the primary winding. Perform resonance operation,
In the switching type voltage converter, the output voltage is controlled by controlling the pulse width of the secondary output of the forward type voltage transformer by a magnetic amplification circuit connected to the secondary winding of the forward type voltage transformer. A voltage converter characterized by partially controlling and performing a final output voltage stabilization operation by a primary PWM. 2. A primary rectifier circuit comprising a rectifier bridge and two or two sets of series-connected smoothing capacitors of equal capacity as main components, wherein one of the input terminals and one of the two smoothing capacitors are connected. A MOSFE in which the intermediate connection points are connected in opposite directions with the source electrode being the connection point, and the bias electrode and the voltage detection circuit are connected to the gate electrode
An input voltage switching circuit, wherein T is connected. 3. A MOSFET in which a bias circuit and a delay circuit are connected to a gate electrode and a resistor are connected to an AC input wiring or a power wiring immediately before a smoothing capacitor of a primary rectifier circuit. Inrush power prevention circuit. 4. A voltage clamp circuit wherein a resonance voltage generating point and a capacitor having an appropriate capacitance are connected by a MOSFET having a gate electrode connected to a fixed bias point.