JPS61227664A - Power converter - Google Patents

Abstract

PURPOSE:To prevent a switching semiconductor element from damaging due to the saturation of a transformer by connecting the output of a double voltage rectifying and smoothing circuit connected with the tertiary winding of the transformer with a load through a variable impedance circuit. CONSTITUTION:When operated in a normal state, a variable impedance circuit 8 is driven by a detection drive circuit 7, and an internal impedance in substantially zero. However, when the voltage of a capacitor c3, i.e., the output voltage V0 is remarkably low as compared with the normal state, the voltage VC3 of a capacitor C3 is detected by the circuit 7, the internal impedance of the circuit 8 is varied in response t the voltage to always maintain the VC3 to sufficiently avoid the saturation of a transformer T, thereby continuing the operation in the circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention connects a switching semiconductor element to the first winding of a transformer having at least six windings, and turns on and off the switching semiconductor element. The present invention relates to a power conversion device that supplies power to a load via a rectifying and smoothing circuit connected to the second winding of the transformer.

[Conventional technology]

Figures 2 and 3 are diagrams showing conventional power converters, and Figures 2 (CB) and 26 (CB) are diagrams showing the various parts of the circuits in Figures 2 (A) and 3 (IQ (A)), respectively. A diagram showing the waveform.

First, let us explain about Figure 2. In the figure, 1.2
is an input terminal, 3.4 is an output terminal, Ql is a switching semiconductor element such as a transistor, T is a first winding (input winding N1), a second winding (output winding MN2), and a third winding 5 is a transformer that shoulders the reset winding N3, diodes D1 and D2, and a choke coil L1.
2 is the load, V is the input voltage, 'Nl' vN2, vN are the winding Nl, N2, N2O voltages, vo is the output voltage, Tol is the collector of the transistor Qe, The emitter voltage is Ruru.

Next, operation 1 in FIG. 2 will be explained. When operating in a steady state, T is the period from when the transistor Q1 turns on at time t□ until it turns off at time t2. If N,
On period T. At N, the input voltage v1 is applied to the input winding N1, and the amount of change 1ΔB11 in the magnetic flux density of the transformer T is 1Δ"l l" -vI TON 1g (where, n is the number of turns of the transformer T, and S is the number of turns of the transformer T. (cross-sectional area of the iron core).

Then, during the reset period TR (TR≦T-ToN%, however, the input winding N1 is cut off during the periodic period, so a voltage is induced in the reset winding N, and the cough induced voltage increases to the input voltage V via the diode D3. , the magnetic flux density of the transformer T is changed 1ΔB21 by 1ja21 = -VI TR 3g.

Here, since lΔB11 = lΔB21, the transformer T is not saturated, and at time t4, the transistor Q1 is turned off again, and the above operation is repeated.

Next, the operation shown in FIG. 3 will be explained. When operating in steady state, the on-period T from time t to time t2. At N, the input voltage v1 is applied to the input winding N0, and the amount of change lΔB, l in the magnetic flux density of the transformer T becomes 1jB□l=VI TON 1g.

Next, the transistor Q from time t2 to time t3 t
1 during the reset period TB, the input winding N0 is cut off, so a voltage is induced in the reset winding N,
The induced voltage is passed through the diode i)4 to the output voltage v
0 is clamped at 0. At this time, the amount of change l in the magnetic flux density of the transformer T, 1, is 1 jB, I = -vOTR 1.

Here, since lΔB11 = lΔB21, the transformer T is not saturated, and at time t4, the transistor Q1 is turned off again, and the above operation is repeated.

[Problem that the invention seeks to solve]

By the way, power converters are generally controlled so that the input voltage is varied in inverse proportion to fluctuations, so that the voltage is controlled as follows.

However, in the conventional power conversion device, in the embodiment shown in FIG. 2, the reset period TR has the following relationship, and in the conventional example shown in FIG.
has the following relationship.

Therefore, the former? The bigger the person is, the more Hito For example, TR also becomes longer. The latter is T regardless of the valve.

It may be dull, but in that case, the maximum value of the collector-emitter voltage v91 of the transistor Q1 has to be reduced, and this means that the withstand voltage of the transistor Q1 will increase the permissible current capacitance. transistor Q
1 is disadvantageous in terms of selection.

As described above, in the conventional device, it is difficult to improve the utilization rate of the transistor Q1.

[Means for solving problems]

The present invention aims to eliminate the above-mentioned drawbacks by connecting a switch conductor element to the first winding of a transformer having at least 3 turns M, and turning the semiconductor switch conductor element on/off. In a power conversion device that is connected to the 20th winding of the transformer and supplies power to a load via a secondary rectifier circuit, a voltage doubler rectifier smoothing circuit is connected to the second winding of the transformer, and a voltage doubler rectifier smoothing circuit is connected to the second winding of the transformer. The present invention provides a power conversion device characterized in that the output of a voltage rectifying and smoothing circuit is connected to the load via a fully variable impedance/smoothing circuit.

[For production]

Since the present invention has the above-described configuration, the voltage applied to the switching semiconductor element during the reset period in a steady state is determined by the output voltage and the turns ratio between the first winding and the third winding. determined and remains constant against fluctuations in input voltage.

Furthermore, when the output voltage is significantly lower than in the steady state, the internal impedance of the variable impedance circuit is changed to prevent saturation of the transformer.

〔Example〕

FIG. 1 is a diagram showing an embodiment of the present invention, and FIG.
) is a diagram showing waveforms of various parts of the circuit of FIG. 1(A).

In the same figure, 6 is a voltage doubler rectifier and smoothing circuit consisting of diodes D5, D6 and capacitor C21C3, 7 is a resistor R,
, R, , is a circuit that detects the voltage of the capacitor C3 and drives the variable impedance circuit 8. The circuit 08 detects the voltage of the capacitor C3 and drives the variable impedance circuit 8 according to the voltage of the capacitor C1. This is a variable impedance circuit whose internal impedance is changed by being driven by r7, and is made up of, for example, a transistor Q2.

Next, the operation shown in FIG. 1 will be explained.

(jL) When operating in a steady state When operating in a steady state, the variable impedance circuit 8 is driven by the detection drive circuit 7, and the internal impedance is approximately zero. Also, the capacitor C1 is charged with the difference voltage between the input voltage Ve and the voltage vc2 of the capacitor C2.
ON period T. In N, input volume l! An input voltage is applied to MN1, and the amount of change in magnetic flux density of transformer T is 1 nois, 11
ΔB, I = VI TON becomes 8.

Next, transistor Q1 from time t2 to time t31
During the reset period T8, the input winding N is cut off, so a voltage is induced in the reset winding N3, and the induced voltage is passed through the diode D6 to the voltage vc3 of the capacitor C1, that is, the output voltage V.

and the voltage v02 of the capacitor C2, the difference voltage V, -V.

The amount of change 1ΔB2I in the magnetic flux density of the magnetic flux T is as follows.

Here, since 1ΔB and I = lΔB21, the transformer T is not saturated, and at time t, the transistor Q0 is turned on again and the above operation is repeated.

Friend, the voltage v applied to the transistor Q1.

In the reset period TR, l is v9□ = v1 - Tsu - vN,
= is determined by the output voltage V and the turns ratio and is constant with respect to variations in the n1 input terminal.

This is higher than the conventional example shown in FIGS. 2 and 3 because the required collector-e-emitter voltage v of transistor Q1 is
The maximum value of Q□ can be lowered. From this,
If the maximum value of vQl is set to the same value as in the conventional example, the allowable current value of the transistor Q1 can be reduced, and the utilization of heavy metals can be improved.

(b) When the output voltage v0 is noticeably lower than in the steady state. Therefore, when the output voltage v0 is extremely low, v0
Since the value of 3 may drop significantly or become negative in steady state, the transformer T may become saturated.Therefore, the voltage of the capacitor C1 is detected by the detection drive circuit 7, and the voltage By changing the internal impedance of the variable impedance circuit 8 according to
However, v(J is nl) Transistor Q is a variable innovidance circuit.

This circuit can continue to operate by always maintaining the relationship between the voltage applied to the main current path of the transformer T (cs f) sufficient to avoid saturation of the transformer T.

〔Effect of the invention〕

As described above, the present invention connects a switching semiconductor element to the tenth winding of a transformer having at least three windings, and turns the semiconductor switching element on/off to connect p1 to the second winding of the transformer. In a power converter that supplies power to a load via a rectifier and smoothing circuit connected to the transformer, when a voltage doubler rectifier and smoother is connected to the third winding of the transformer, the This power converter is characterized in that it is connected to the load through a variable impedance circuit. Since the present invention has such characteristics, it is possible to increase the duty ratio without requiring the switching semiconductor element to have a large withstand voltage, and it is particularly suitable for power converters with large input tolerances. High output can be obtained without increasing the withstand voltage and current tolerance of the element. In addition, the excitation energy of the transformer can be taken out as output without loss at a steady output voltage, so high efficiency of the power conversion device can be achieved. In addition, the transformer can be reset even when the output voltage is low, such as when starting up or when an output short-circuit occurs69, which prevents damage to switching semiconductor devices due to transformer saturation.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, and FIGS. 2 and 6 are diagrams showing a conventional power conversion device. 1.2...Input terminal 3.4...Output terminal 5.
... Rectification and smoothing circuit W & 6 ... Voltage doubler rectification and smoothing circuit 7...
・Detection drive circuit # & 8...Variable impedance circuit Q
l,! ...Transistor T...Transformer N,...
...First winding M N, ... Second winding N3.
...26 windings M D, ~D6...Diode Z
D...Zener diode Ll...Choke coil C~C3...Capacitor R1e R2...Resistor 2...Load Patent applicant Origin Electric Co., Ltd. (A) Fig. 3

Claims (1)

[Claims] A switching semiconductor element is connected to a first winding of a transformer having at least three windings, and by turning on and off the switching semiconductor element, a rectifying and smoothing circuit is connected to a second winding of the transformer. In a power conversion device that supplies power to a load, a voltage doubler rectifier and smoothing circuit is connected to the third winding of the transformer, and an output of the voltage doubler rectifier and smoother circuit is connected to the load via a variable impedance circuit. A power conversion device characterized in that: