JPH0412665A - Switching power supply - Google Patents

Abstract

PURPOSE:To prevent a large current flow through a switching transistor by connecting a diode with such polarity as a reverse bias is applied to turn a FET OFF, upon throw-in of power supply, through utilization of a voltage induced in an auxiliary winding. CONSTITUTION:An auxiliary winding 12a and a diode 24 are arranged on the secondary of a transformer. When a power supply is thrown in to turn a switching transistor 3 ON for the first time, a voltage having such polarity as increasing the drain voltage of a FET 13 is induced in the secondary winding 12. Since the auxiliary winding 12a is wound such that the black mark point has positive polarity, the voltage induced in the auxiliary winding 12a causes to reverse bias the gate potential of the FET 13 through the diode 24. Consequently, turn ON operation of the FET is prevented thus preventing overcurrent flow through the switching transistor.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a switching power supply device that supplies DC stabilized voltage to industrial and consumer electronic equipment.

2. Description of the Related Art In recent years, with the development of various high-performance electronic devices, the power supplies used in the electronic devices are also required to have high functionality and high performance. Among these, various proposals have been made for improving power supply devices that perform electric power regeneration operation, which is characterized by high efficiency operation.

(For example, Japanese Patent Application No. 1-235035) Conventionally, this type of switching power supply device has a configuration as shown in FIG.

In Figure 2, 1 is a DC power supply, 2 is a resistor, 3 is a transistor as a switch means, 4 is a collector winding, 5 is a base winding, 6 is a resistor, 7 is a resistor, 8 is a capacitor, 9
is a diode, 10 is a transistor, 11 is a capacitor, 12 is a secondary winding, 13 is a field effect transistor, 1
4 is a parasitic diode of the field effect transistor 13, 1
5 is a smoothing capacitor, 16.16' is an output terminal, 17
The components are a reference power supply, 18 an error amplifier, 19 a pulse width converter, 20 a resistor, 21 a resistor, 22 a capacitor, 23 a diode, and 25 a transformer.

Next, the mutual relationship and operation of each component shown in FIG. 2 will be explained. When the DC power source 1 is connected, a starting current flows to the transistor 3 via the resistor 2, and the transistor 3 is turned on. As the transistor 3 turns on, the collector winding 4
A voltage is induced in the winding 5 which is electromagnetically coupled to the transistor 3, and a current flows to the transistor 3 via the resistor 6, so the transistor 3 continues to be turned on. On the other hand, when transistor 3 is on, capacitor 8 is charged via resistor 7, and when a predetermined voltage is reached, transistor 1 is charged via diode 9.
0 is turned on and transistor 3 is turned off. A portion of the energy stored in the transformer 25 while the transistor 3 is on is charged into the capacitor 11, suppressing the rise in collector voltage and reducing noise.
It is discharged from the next winding 12 through the parasitic diode 14 of the field effect transistor 13 to the smoothing capacitor 15, and is supplied to the load via the output terminal 16, 16'. The voltage between the output terminals 16 and 16' is the voltage between the reference power supply 17 and the error amplifier 1.
8 and is compared and amplified and applied to the pulse width converter 19. The pulse width converter 19 converts the input into a predetermined pulse width, and then applies the pulse width to the field effect transistor 13 via the resistor 20, thereby turning the field effect transistor 13 from on to off. If the voltage between the output terminals 16 and 16' is higher than the reference power supply 17, the field effect transistor 13 continues to be turned on even after all the energy from the secondary winding 12 is released to the smoothing capacitor 15, and the smoothing capacitor 15 continues to flow current to the secondary winding 12 through the field effect transistor 13.

When the field effect transistor 13 is turned off, the energy stored in the transformer 25 is regenerated from the collector winding 4 to the DC power supply 1 via the capacitor 11. At this time, capacitor 22. Since current flows through the base of transistor 10 for a time determined by resistor 21, transistor 3
is delayed for a predetermined period of time to prevent the energy stored in the capacitor 11 from being short-circuited by the transistor 3.

When energy continues to be regenerated from the collector winding 4 to the DC power source 1 and the voltage across the capacitor 11 decreases to reverse polarity, the diode 23 becomes conductive and clamps the voltage across the capacitor 11. Thereafter, the transistor 10 is turned off again, the transistor 3 is turned on, and the operation of causing current to flow from the DC power supply 1 through the collector winding 4 again and storing energy in the transformer 25 is repeated.

If the voltage between the output terminals 16 and 16' decreases, the output of the pulse width converter 19 is output to turn off the field effect transistor 13, so that it is smoothed from the secondary winding 12 via the parasitic diode 14. When the energy release to the capacitor 15 is completed, no current flows from the smoothing capacitor 15 through the secondary winding 12, so the energy regeneration is not performed and the voltage between the output terminals 16 and 16' increases.

Further, if the voltage between the output terminals 16 and 16' increases, the operation is reversed to the above operation to keep the voltage between the output terminals 16 and 16' constant.

Problems to be Solved by the Invention In such conventional technology, when the DC power supply (1) is connected and the transistor 3 is turned on for the first time, a voltage is applied to the double of the field effect transistor 13 via the secondary winding 12. However, since no charge is stored in the smoothing capacitor 15 and the operation of the pulse width converter 19 remains stopped, the field effect transistor 13 attempts to turn off. However, since the field effect transistor 13 has a parasitic capacitance 26 between its gate and drain as shown in FIG. applied.

If the value of the parasitic capacitance 26 is 1500PF and the rate of increase of the voltage applied to the drain is 200V/μS, then the parasitic capacitance 2
The current flowing through 6 reaches as much as 0.45 A. Since the value of the resistor 20 is usually selected to be between 20 and 50 Ω, for this reason +11 A voltage of 9 to 22.5 V is applied to , and the field effect transistor 13 is turned on. Therefore, when the transistor 3 is on, the field effect transistor 13 is also on, so the inductance of the collector winding 4 disappears, and an excessive current flows through the transistor 3, causing the transistor 3 to burn out in the worst case. It will end up being put away. Especially in the case of switching power supplies used in plasma dischargers, the output terminals 16.16'
Since the voltage between them is selected to be 150 to 200 V at the rated time, it is not uncommon for the rate of increase in the voltage applied to the drain of the field effect transistor 13 to reach 2000 V/μS, and in this case, a current of 3 A flows. As a result, it was not very usable.

(2) On the other hand, if the size of the transistor 3 is increased in order to prevent the above problem, the price of the entire device will increase.

(3) Also, if the field effect transistor 13 is replaced with a bipolar transistor and a diode connected in parallel, this problem will not occur, but the bipolar transistor has a slow operating speed and requires a base current, so switching loss and Drive losses increase,
Since high frequency operation is not possible, the transformer and heat sink become larger, the drive circuit becomes more complex, and internal losses increase.
This resulted in larger devices, higher prices, lower efficiency, and lower reliability.

The present invention takes the above-mentioned problems into consideration, and has stable operation even when the power is turned on, is small in size, low in price, and has high reliability.

The aim is to provide a highly efficient switching power supply.

Means for Solving the Problems In order to achieve the above objects, the present invention has the following features: a transformer having second and third windings; a parallel circuit of a first switching means connected to one end of the first winding; and a first capacitor; a power supply connected between the other ends of the wire; a series circuit of a second capacitor and a field effect transistor connected to both ends of the second winding; and one end of the third winding and the field effect transistor. a rectifying element connected between the gates of the field-effect transistor in a direction in which a reverse bias is applied to the field-effect transistor; The configuration includes a control means and a second control means that detects the voltage across the second capacitor, turns on and off the field effect transistor, and maintains the voltage between the ends constant, and the control means switches the first switching means. The energy stored by passing current through the first winding of the transformer is transferred to the second winding by switching the field effect transistors through the second winding.
discharge into the capacitor.

Further, when the second capacitor reaches a predetermined voltage, the field effect transistor remains on and energy is recovered from the first capacitor to the power supply via the first winding. In this way, the second control means controls the on-period of the field effect transistor, and is controlled to keep the voltage of the second capacitor, which is a smoothing capacitor, constant.

Here, when the first switching means is turned on when no charge is stored in the first capacitor, the energy is applied to the field effect transistor via the second winding. In this case, either it is turned off by the second control means or there is a parasitic capacitance between the drain and gate of the field effect transistor, so the voltage generated at the drain is applied to the gate and acts to turn on the field effect transistor. .

When it is turned on, there is no charge stored in the second capacitor, so
This means that the second winding is short-circuited, and a large current flows through the first switching means. To prevent this, the voltage generated in the same way is used in the third winding, and the field effect transistor is connected with a polarity that is reverse biased to turn off the field effect transistor through the rectifier. When the gate of the field effect transistor is reverse biased and the first switching means is on, the field effect transistor is not turned on.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to FIG. In FIG. 1, the same parts as in the conventional example shown in FIG. What has been added to FIG. 2 is an auxiliary winding 12a, which is a third winding provided on the secondary side of the transformer, and a diode 24.

Next, the related operations of the above components will be explained.

First, when the transistor 3, which is the first switching means, is turned on by the first control means, a second switch is generated in the secondary winding 12, which is the second winding.

A voltage with a polarity that increases the drain voltage of the field effect transistor 13, which is the switching means, is induced. In addition, a voltage is induced in the auxiliary winding 12a, and since it is wound so that its polarity is positive, as shown in the black dot in FIG. By biasing, the current flowing through the parasitic capacitance 26 shown in FIG. 3 explained in the conventional example is absorbed, and the rise in voltage between the gate and source is suppressed. As a result, the field effect transistor 13 is turned on and continues to be turned off without causing a large current to flow through the transistor 3. After a predetermined period of time has elapsed, if the polarities of the voltages in the secondary winding 12 and the auxiliary winding 12a are reversed, energy is discharged from the secondary winding 12 to the smoothing capacitor 15 via the parasitic diode 14. If the above operation is repeated and the voltage between the output voltages 16 and 16' increases, the second control means consisting of the error amplifier 18, reference power supply 17, and pulse width converter 19 to keep the output voltage constant is activated. A signal to turn on and off the field effect transistor 13 is applied to the gate of the field effect transistor via the resistor 20, but when the field effect transistor 13 must be turned on, the diode 24
Since it is reverse biased by the output voltage of the auxiliary winding 12a, it does not interfere with the operation of the pulse width converter 19.

Although the above description has been made for the case where an N-channel field effect transistor is used, it is clear that the polarity of the diode 24 will be different if a P-channel field effect transistor is used.

Effects of the Invention As is clear from the above explanation, according to the present invention, while the drain voltage of the field effect transistor is applied, the diode connected to the gate is conductive, and the field effect transistor is reverse biased. Since it can be turned off reliably, it is possible to prevent the field effect transistor from turning on, which occurs when the switching transistor is turned on for the first time. This prevents excessive current from flowing through the switching transistor, and allows the use of small and inexpensive components in the transistor. Since burnout of the switching transistor can also be prevented, a highly reliable, compact, inexpensive, and highly efficient switching power supply can be realized.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of a switching power supply device according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing the configuration of a switching power supply device according to the conventional technology, and FIG. 3 is an internal equivalent of a field effect transistor. It is a circuit diagram. 1...DC power supply, 3...Transistor (first switching means), 4...Collector winding (first winding) 11... Capacitor (1st
capacitor), 12... Secondary winding (second winding), 12a... Auxiliary winding (third winding), 1
3... Field effect transistor (second switching), 14... Parasitic diode, 15...
... Smoothing capacitor (second capacitor), 17.
...Reference power supply, 18...Error amplifier, 1
9... Pulse width converter, 24... Diode, 25... Transformer.

Claims (1)

[Claims] a transformer having first, second, and third windings; a parallel circuit including a first switching means connected to one end of the first winding; and a first capacitor; a power supply connected between the other end of the first winding;
a series circuit of a second capacitor connected to both ends of the winding and a field effect transistor serving as a second switching means; and a field effect between one end of the third winding and the gate of the field effect transistor. and a rectifying element connected in a direction in which a reverse bias is applied to the type transistor,
a first control means for controlling the first switching means to cause a current to flow through the first winding; and a first control means for controlling the second switching means and keeping the voltage across the second capacitor constant. A switching power supply device having two control means.