JPS6232701B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ringing converter as a DC-DC converter.

A conventional ringing chain converter is constructed as shown in FIG. 1, 1' are input terminals, 2, 2' are output terminals, R1 is a starting resistor,
R2 is a base resistance of the switching transistor Q1, D1 is a rectifying diode, C1 is a smoothing capacitor, and T is a converter transformer.
Then, the output information obtained by the resistor R0 that detects the output voltage V _OUT and the output detection circuit 3 is added to the control circuit 4, and the control circuit 4 controls the switching operation of the transistor Q1, thereby increasing the output. It has stabilized. Since this circuit performs feedback control to stabilize the output, the oscillation frequency changes in inverse proportion to the amount of output load.

The reason why the oscillation frequency changes in inverse proportion to the output load is that the input DC voltage V _IN is constant, and the output DC voltage V _OU
Assuming that _T : constant, the output capacitance P _OUT of the ringing-choke converter is expressed by the following equation. However, it is assumed that there is no loss.

P _OUT = (V _IN · δ) ² /2 · L _P · f ... (1) θ: Duty ratio, L _P : Self-inductance of the primary winding of converter transformer T, f: Frequency.

This is equal to the product of the output voltage V _OUT and the output current I _OUT , so (V _IN・δ) ² /2・L _P・f=V _OUT・I _OUT
...(2) Also, the duty ratio δ is δ=1/(1+N _S /N _P・V _IN /V _OUT
)...(3) N _P : Number of primary windings of converter transformer T,
N _S : Number of secondary windings.

Here, if V _IN : constant and V _OUT : constant as mentioned above, equation (3) becomes constant, and from equation (2), the relationship 1/L _P・f∝I _OUT ...(4) can be obtained. . When L _P is constant, equation (4) becomes 1/f∝I _OUT (5), and the oscillation frequency f changes in inverse proportion to the output voltage V _OUT , that is, the amount of output load.

Therefore, when there is no load or a light load, the oscillation frequency increases from several times to more than ten times the oscillation frequency at the rated load, so the transistor Q1 and control circuit 4 cannot catch up with that frequency, making it easy to cause intermittent oscillation. This causes problems such as deviation from the safe operating area of the transistor, generation of audible noise, and increase in ripple.Also, since the frequency shifts to a high frequency, the core loss of the converter transformer T and the transistor Q
A problem arises in which the switching loss of 1 increases.

Therefore, the frequency at rated load is determined by taking into consideration the transition to high frequencies at no load, but the frequency at rated load cannot be set too high, and the design of the converter/transformer T is difficult. This tends to be uneconomical, and it is also inefficient because some percentage of the rated load is consumed by the dummy load in order to alleviate the shift to high frequencies when there is no load.

The present invention has been made in view of the above points, and its purpose is to improve the converter transformer and reduce the shift of the oscillation frequency to high frequencies during no-load and light-load conditions. An object of the present invention is to provide a ringing chiyoke converter that solves these problems.

Hereinafter, the present invention will be explained with reference to Examples. Second
The figure is a circuit diagram of one embodiment. Two converter transformers T1 and T2 are used, and the primary windings N _P1 and N _P2 of the transformers T1 and T2 are connected in series to connect the input terminal 1 and the switching terminal. Transistor Q1
and the base winding N _B1 , N
_B2 is connected in parallel with the same polarity via diodes D3 and D4 and connected between the base resistor R2 and input terminal 1', and the secondary windings N _S1 and N _S2 are connected to the diodes D1 and
Connect capacitor C in parallel with the same polarity via D2.
Connected to 1. The output detection circuit 3 includes a resistor R3
and an error amplifier 5 that compares the voltage corresponding to the output voltage V _OUT obtained at the midpoint of R4 with the reference voltage V _ref .
and a photocoupler PC that transmits the output of the error amplifier 5 to the control circuit 4 via a resistor R5.

Inductances L P1 and L _P2 of the primary windings N _P1 and N _P2 of the converter transformers T1 and _T2 mentioned above.
is designed to exhibit the characteristics shown in FIG. 3a with respect to the ratio of output current to the rated value. Specifically, the inductance value of the curve is designed to be relatively low and difficult to saturate, and the inductance value of the curve is designed to be larger than that of the curve, and the saturation point is smaller than that of the curve.

The primary windings N _P1 and N _P2 are connected in series as described above, so the combined inductance (L _P1 +L _P2 ) shown in the curve is the equivalent inductance on the primary side. The inductance value of the curve has a large value when the output is no load or light load, and a small value when the output is rated.

From equation (5) above, looking at the curve (converter characteristics of a general ringing-choke converter) and the oscillation frequency at the time of the curve, the frequency change rate (f/fo) (where fo is the oscillation frequency at the rated time)
becomes as shown in FIG. 3b. ' curve, the inductance value L _P1 is constant, so the output current and oscillation frequency are inversely proportional, and when the output current decreases and reaches 1/10 of the rated value, it will increase to 10 times the rated value. . In contrast, in the case of the 'curve', the inductance changes and increases when the load is light, reducing the frequency shift to high frequencies.
The output is 1/10 of the rated output, which is slightly less than three times the rated output.

As described above, according to the present invention, the inductance on the primary side of the converter transformer at no load and light load is larger than that at rated load, so the shift of the oscillation frequency to a high range is reduced, which solves the conventional problem. It is characterized by being able to improve problems such as intermittent oscillation and deterioration of efficiency. The present invention is suitable for small capacity switching regulators, high voltage output stabilized power supplies, etc.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional ringing choke converter. FIG. 2 is a circuit diagram of a ringing choke converter according to an embodiment of the present invention. FIGS. 3a and 3b are characteristic diagrams for explaining the operation of the ringing-choke converter of this embodiment. 1, 1'...Input terminal; 2, 2'...Output terminal;
3... Output detection circuit; 4... Control circuit; 5... Error amplifier; T, T1, T2... Converter transformer; PC... Photo coupler.

Claims (1)

[Claims] 1 In a ringing choke converter that feeds back output information to control the switching state and stabilize the output, the first inverter transformer includes a primary winding that has a large inductance and is easily saturated, and the first inverter transformer that has a small inductance and is easily saturated. The primary windings of both inverter transformers are connected in series, and the secondary windings and base windings are connected in parallel to form a second inverter transformer including a primary winding that is difficult to connect. 1. A ringing choke converter, which functions equivalently as one inverter transformer, and has a primary winding inductance larger at no load and light load than at rated output.