JPH0767276B2 - Full-bridge type switching regulator - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a full-bridge switching regulator, and more particularly to a full-bridge switching regulator bias prevention circuit suitable for a high input voltage and capable of obtaining a large capacity. It is a thing.

2. Description of the Related Art As a switching regulator suitable for a high input voltage and capable of obtaining a large capacity, a two-stone forward type and a full bridge type are widely known. The former method has the advantage that the conversion frequency can be increased to facilitate the downsizing of the device, but it has the disadvantage of inefficient use of the transformer, and the latter method is easier to achieve a larger capacity than the former method. On the other hand, there is a disadvantage that the transformer is likely to be demagnetized, and it is properly used as necessary.

Now, a conventional example of a full-bridge type switching regulator suitable for a high input voltage and capable of obtaining a large capacity will be described with reference to FIG. In FIG. 3, when an AC power supply is applied between the input terminals 1 and 1 ', it is rectified by the rectifier circuit 2, smoothed by the input smoothing capacitor 3, and connected to the main transistor 4 as an unstable DC power supply in series. Supplied to 5 and 6,7. Between the series connection points of the main transistors 4,5 and 6,7,
Primary winding 8-1 of transformer 8 and primary winding 9 of transformer 9
-1, the parallel circuit of the capacitor 10 and the resistor 11 is connected in series. On the other hand, in the secondary winding 8-2 of the transformer 8, the anodes of the rectifying diodes 12 and 13 are connected to the secondary winding 9 of the transformer 9.
-2 is connected to the anodes of the rectifier diodes 14 and 15, respectively, and the cathodes of the rectifier diodes are commonly connected to each other and connected to one output terminal 18. The center taps provided on the secondary windings 8-2 and 9-2 of the transformers 8 and 9 are commonly connected to each other and connected to the other output terminal 18 'through the output smoothing reactor 16. The smoothing reactor 16 constitutes a filter circuit together with the output smoothing capacitor 17.

The full-bridge type switching regulator configured as above is composed of main transistors 4, 7 and main transistors 5, 6.
Are turned on and off alternately and primary winding 8 of transformers 8 and 9-
1, 9-1 are excited in both polarities, but if the voltage-time products of the periods of being excited in the respective polarities are not equal, magnetic bias occurs. In order to prevent this magnetic bias, capacitor 10 and resistor 11
When a parallel circuit is connected to and the voltage-time product of a half cycle excited in one polarity causes a difference from the previous half cycle, charge is accumulated or remains in the capacitor 10, and the capacitor in the next half cycle is charged. Transformer only 8,9 between terminals
The voltage applied to the primary windings 8-1 and 9-1 becomes smaller or larger, and the voltage-time product is corrected.

However, as shown in FIG. 3, the primary winding 8− of the transformers 8 and 9−
When 1,9-1 are connected in series and the secondary windings 8-2,9-2 are connected in parallel, the difference in voltage induced in each secondary winding 8-2,9-2 Therefore, a difference may occur in the voltage shared by the primary windings 8-1 and 9-1. When the volt-second product due to this voltage difference has opposite polarities, no charge is accumulated in the capacitor 10, the action of correcting the volt-time product is not performed, and the magnetic bias increases and the main transistors 4,5,6,7 However, there is a problem that it is difficult to adapt to a high input voltage.

An object of the present invention is to solve the above-mentioned drawbacks. Each primary winding of a full-bridge type switching regulator in which the primary windings of two transformers are connected in series and the secondary windings are connected in parallel. It is an object of the present invention to prevent the eccentricity from expanding even if a difference in voltage-time product of opposite polarities is generated.

Configuration of the Invention The full-bridge type switching regulator of the present invention is
The input smoothing capacitor is composed of two capacitors connected in series, the primary windings of the two transformers are connected in series, and the series connection points are directly connected, and the primary winding of each transformer is connected. A parallel circuit of a capacitor and a resistor is inserted between the line and the series connection point of two sets of main transistors connected in series.

Examples Hereinafter, examples will be described. FIG. 1 is a circuit diagram of a full-bridge type switching regulator of the present invention, and the same parts as those in FIG. 3 are designated by the same reference numerals. The feature of the present invention is that, as shown in FIG. 1, an input smoothing capacitor is composed of two capacitors 3-1 and 3-2 connected in series, and the primary windings of two transformers 8 and 9 are used. The lines 8-1 and 9-1 are connected in series to directly connect between the series connection points, and the transformers are connected.
Between the primary windings 8-1, 9-1 of 8, 9 and the main transistors 4,5 and 6, 7 connected in series, a parallel circuit of a capacitor 10-1 and a resistor 11-1 and a capacitor 10 are provided. -2 and resistance
It is a parallel circuit connected to 11-2.

Next, the operation of the circuit of the present invention described above will be described. Now, the primary winding 8-1 of the transformer 8 and the primary winding 9-1 of the transformer 9
Due to the voltage difference shared by the
If the upper end of 1 is positively polarized and the lower end of the primary winding 9-1 of the transformer 9 is positively polarized, the capacitors 10-1, 10-2
In each case, the charge is accumulated so that the left side becomes positive, so the voltage applied to the primary windings 8-1 and 9-1 of the transformers 8 and 9 by the voltage between the capacitor terminals in the next cycle Becomes smaller or larger, and the voltage-time product is corrected.

FIG. 2 is a diagram showing another embodiment of the present invention, in which the output smoothing reactor 16 is divided into 16-1 and 16-2. If there is a difference in storage time between the main transistors 4, 7 or 5, 6 that are turned on and off at the same time, this circuit delays the turn-off of the main transistor with a long storage time and a snubber circuit (not shown) This prevents a large peak current from flowing through. For example, when the main transistor 4 is turned off later than the main transistor 7, the main transistor 7 is turned off first, so that the current flowing in the primary winding 9-1 of the transformer 9 is input smoothing capacitor 3-2. To be bypassed. Therefore, a voltage having a positive polarity at the lower end is induced in the primary winding 9-1 of the transformer 9, but the secondary winding 8-2 of the transformer 8 and
The center taps of the secondary winding 9-2 and the center tap of the transformer 9 are connected in common via smoothing reactors 16-1 and 16-2, respectively.
The peak current does not flow through the main transistor 4 via the snubber circuit (not shown), and the energy is stored in the output smoothing reactor 16-2. Therefore the main transistor 4,7
Alternatively, the peak current does not flow even if there is a difference in storage time between 5 and 6, and it is not necessary to use a main transistor having a large allowable current.

EFFECTS OF THE INVENTION As described in detail in the embodiments, the full-bridge type switching regulator of the present invention does not cause transformer bias magnetization and can be easily adapted to a high input voltage. Further, even if there is a difference in the storage time of the main transistor, a large peak current does not flow in the main transistor delayed off, and it is easy to achieve a high frequency.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of a full bridge type switching regulator of the present invention, FIG. 2 is a circuit diagram of another embodiment of the present invention, and FIG. 3 is a circuit of a conventional full bridge type switching regulator. It is a figure. 1,1 '... Input terminal, 2 ... Rectifier circuit 3,3-1,3-2 ... Input smoothing capacitor 4,5,6,7 ... Main transistor 10,10-1,10-2 ... Capacitor 11,11 -1,11-2 ... Resistance 16,16-1,16-2 ... Output smoothing reactor 18,18 '... Output terminal

Claims (2)

[Claims] 1. An unstable DC power supply is supplied to two sets of main transistors connected in series, and the primary windings of two transformers are connected in series between the series connection points, and each secondary winding is connected. Are connected in parallel via a rectifying diode, and a stable DC power supply is used in a full-bridge switching regulator that obtains a stabilized DC power supply between output terminals via a filter circuit consisting of an output smoothing reactor and an output smoothing capacitor. The smoothing input smoothing capacitor is composed of two capacitors connected in series.
A direct connection between the series connection point of the secondary winding and a parallel circuit of a capacitor and a resistor inserted between the other end of each primary winding and the series connection point of the main transistor. Bridge type switching regulator. 2. A full bridge type according to claim 1, wherein two output smoothing reactors are provided and inserted between each secondary winding of the two transformers and the output terminal. Switching regulator.