JPH0287966A - Forward dc/dc converter - Google Patents

Abstract

PURPOSE:To improve the power conversion efficiency of a high frequency transformer by taking out the exciting energy for the high frequency transformer at the secondary output. CONSTITUTION:A pulse signal subjected to pulse width control corresponding to the variation of an output voltage E0 is applied onto the base of a switching transistor 10. When the switching transistor 10 is turned OFF, no energy is transmitted from the primary to the secondary and reverse voltage is induced in the windings 11a, 11b, 16 by the exciting energy of a high frequency transformer 11. At this time, current loop through the primary winding 11a is blocked by a transistor 10 while current loop through the secondary winding 11b is blocked by a diode D2, but a current loop is formed through the winding 16 and a diode 17. Consequently, exciting energy for the high frequency transformer 11 flows, in the form of de-energizing current i1, through the current loop of the winding 16 in the direction of an arrow shown on the drawing and transmitted as an output energy to the output terminals 15a, 15b.

Description

[Detailed Description of the Invention] [Summary] Regarding a forward type DC-DC converter for a power supply device in which the output voltage is stabilized by pulse width control, the purpose is to improve the power conversion efficiency of a high frequency transformer, and the switching is performed by a pulse signal. a switching element that converts the pulsed voltage into a pulsed voltage, a high-frequency transformer that applies the pulsed voltage to the primary side and converts it into high-frequency AC power and outputs it to a secondary output circuit; Excitation energy output means is provided on the next side and extracts the excitation energy of the high frequency transformer as output energy.

[Industrial Application Field] The present invention relates to a forward type DC-DC converter, and particularly to a forward type DC-DC converter for a power supply device stabilized by pulse width control.

[Conventional technology]

2. Description of the Related Art A switching regulator is generally known as a stabilized power supply device that controls the amount of current supplied by detecting fluctuations in DC output voltage. Various DC-DC converter circuit types are used in this switching regulator, but among these, the forward type DC-DC converter has a relatively simple circuit configuration as a -type converter, and it is easy to increase the frequency. Therefore, it is often used in medium capacity switching regulators.

FIG. 4 is a circuit diagram of a stabilized power supply equipped with a conventional forward type DC-DC converter.

In the figure, 1 is a DC input power supply, 2 is a switching transistor whose pulse width is controlled, and 3 is a high-frequency transformer for high-frequency power conversion. Connected to power supply 1. The high-frequency transformer 3 also has a feedback winding 3b on the primary side, the end of which is connected to the start end of the primary winding, and the start end of the feedback winding 3b is connected to the input power source via a feedback diode D1. It is connected to the negative electrode of 1.

A choke commutating diode D3 is connected in parallel to both ends of the secondary winding yA3C of the high frequency transformer 3 via a rectifying diode D2, and a smoothing capacitor C is connected in parallel to both ends of the commutating diode D3 via a choke coil L. It is connected to the. Further, a load 4 is connected to output terminals T, , T2 connected to both ends of the capacitor C.

FIG. 5 is a diagram of voltage and current waveforms at various parts.

In the stabilized power supply device having the above configuration, when a pulse signal as shown in FIG. 5(a) whose pulse width is controlled according to the variation in the output voltage E0 is supplied to the base of the switching transistor 2, the transistor 2 is turned on. , and the input voltage E is applied to the primary winding 3a of the high frequency transformer 3.

Accordingly, a pulse current i1 (see FIG. 5) flows, which is a DC current corresponding to the load and an excitation current of the high frequency transformer superimposed.

During the ON period of the transistor 2, a voltage is generated at both ends of the secondary winding 3C, with the winding start end being positive and the winding end being negative, and this voltage excites the choke coil L and supplies energy to the load. do. When the transistor 2 is turned off, the energy transmitted from the negative side to the secondary side disappears, and the excitation energy of the high frequency transformer 3 is fed back to the input power source 1.

That is, due to the excitation energy of the transformer, a reverse voltage is generated at both ends of the feedback winding 3b, with the end of the winding being positive and the beginning of the winding being negative. A current i (see FIG. 5C) flows through the feedback loop of line 3b, and the reverse voltage generated in feedback winding 3b is clamped to the human power supply voltage and fed back. Note that FIG. 5(d) shows the collector of transistor 2.
Voltage vCEr applied between the emitters (e) of the same figure shows the voltage E generated across the -order winding 3a.

On the other hand, the excitation of the secondary choke coil L is performed by the secondary winding 3C.
The reverse voltage generated by the choke coil L is clamped to the output voltage E0 in the loop of choke coil L→capacitor C→diode D3→choke coil L.

[Problem to be solved by the invention]

In the forward type inverter as described above, the excitation energy of the high frequency transformer 3 is transferred to the feedback winding 3b provided on the negative side.
Since the feedback diode D1 is used to feed back to the input type s1 on the primary side, the power conversion rate (power transfer rate) of the high frequency transformer is low and the transformer tends to be large.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a forward type DC-DC converter that can increase the power conversion rate of a high-frequency transformer and can be downsized.

[Means to solve the problem]

FIG. 1 is a diagram showing the principle of the forward type inverter of the present invention.

In the figure, a switching element 10 switches in response to a pulse signal and converts it into a pulsed voltage.

The high frequency transformer 11 converts a pulsed high frequency voltage applied to its negative side into a desired voltage and supplies it to the secondary side rectifying and smoothing circuit 12 .

The excitation energy output means 13 is provided on the secondary side of the high frequency transformer 11 and extracts the excitation energy of the high frequency transformer 11 as output energy.

[Function] In the forward type DC-DC converter having the above configuration, when the switching element 10 is turned off, the high frequency transformer 11
The excitation energy flows to the excitation energy output means 12 as a demagnetizing current, and is thereby taken out to the output side as output energy.

Therefore, according to the present invention, the power conversion efficiency of the high frequency transformer can be improved.

〔Example〕

Hereinafter, embodiments of the forward type DC-DC converter according to the present invention will be described in detail with reference to the drawings.

FIG. 2 is a configuration diagram of a stabilized power supply device equipped with a forward type DC-DC converter according to the present invention.

In the figures, the same or equivalent parts as in FIG. 1 are designated by the same reference numerals. Both ends of the primary winding 11a of the power conversion high-frequency transformer 11 are connected to a DC input power source 14 via the collector-emitter of the switching transistor 10.

A choke commutating diode D3 is connected in parallel to both ends of the secondary winding 11b of the high frequency transformer 11 via a rectifying diode D2 as a rectifying and smoothing circuit, and a choke coil L is connected to both ends of the commutating diode D3. Smoothing capacitor C is connected in parallel, and capacitor C
A load 16 is connected to the output terminals 15a and 15b connected to both ends of the
is connected.

Further, on the secondary side of the high frequency transformer 11, there is provided an energy extraction winding 16 whose winding start end is connected to the winding end of the secondary winding 11b, and the winding end of this energy extraction winding 16 is connected to a diode. Choke coil L via 17
and the smoothing capacitor C. Note that the winding 16 and diode 17 correspond to the excitation energy output means 13 in FIG. 1.

Next, the operation of this embodiment configured as described above will be explained.

The third pulse width is controlled according to the variation of the output voltage EO.
When a pulse signal as shown in FIG. 1A is applied to the base of the switching transistor 10, the transistor 10 is turned on and off, and the input voltage E is applied to the primary winding 11a of the high frequency transformer 11.

Along with this, the pulsed primary current iI (third
(see figure) flows and is supplied to the secondary winding via the high frequency transformer 11. During the ON period of the transistor 10, a voltage is generated across the secondary winding 11b, with the starting end being positive and the ending end being negative, and this voltage causes the output voltage to be smoothed by the choke coil L and the capacitor C. E0 is supplied to the load 16. At this time, start winding with the end facing straight.
Since the current loop caused by the voltage generated in the winding 16 with the end of the winding being negative is blocked by the diode 17, its energy is not transmitted to the output side.

When the switching transistor 10 is turned off, the energy transmitted from the negative side to the secondary side disappears, and the excitation energy of the high frequency transformer 11 causes each winding 11a to
, llb and 16. At this time, the current loop of the primary winding 11a due to the reverse voltage is caused by the transistor 10
Although the current loop in the secondary winding 11b due to the reverse voltage is blocked by the diode D2, a current loop is formed through the diode 17 in the loop of the winding 16. Accordingly, the excitation energy of the high-frequency transformer 11 flows as a demagnetized current in the current loop of the winding 16 as shown by the arrow in FIG. 2, and as a result, the excitation energy is transmitted as output energy to the output terminals 15a and 15b. That will happen.

The waveform of the current i at this time is as shown in Figure 3 (C),
Further, the waveform of the voltage VCH applied between the collector and emitter of the transistor 10 is as shown in FIG. become.

Therefore, in this embodiment as described above, the excitation energy of the transformer is transmitted to the secondary output, so that the power transfer rate of the high frequency transformer is improved and the conversion efficiency of the DC-DC converter can be increased.

Note that the excitation energy output means in the present invention is not limited to the circuit system shown in the above embodiment.

〔Effect of the invention〕

As described above, according to the present invention, the excitation energy of the high-frequency transformer is taken out to the secondary output, so the power conversion efficiency of the high-frequency transformer can be increased, which is extremely useful as it allows the high-frequency transformer to be miniaturized. It is something.

FIG. 3 is an operating waveform diagram of each part in this embodiment, FIG. 4 is a block diagram of a stabilized power supply device using a conventional forward type inverter, and FIG. 5 is an operating waveform diagram thereof.

In the figure, 10 is a switching element; ll is a high frequency transformer, 12 is a secondary side rectifying and smoothing circuit; 13 is excitation energy output means; 14 is a DC input power source.

[Brief explanation of drawings]

Fig. 1 is a principle diagram of the forward type inverter of the present invention. Fig. 2 is a block diagram showing an embodiment of the forward type inverter according to the present invention applied to a stabilized power supply device. Fig. Fig. Fig. 8. Conventional groove Fig. Fig. Fig. 8. Part C broken shape diagram

Claims (1)

[Claims] (1) A switching element (10) that switches in response to a pulse signal and converts it into a pulsed voltage, and a secondary side output circuit (12) that converts the pulsed voltage into high-frequency AC power by applying it to the primary side. ); and excitation energy output means (11) provided on the secondary side of the high frequency transformer (11) for extracting the excitation energy of the high frequency transformer (11) as output energy.
13) and a forward type DC-DC converter.