JPS58182475A - Switching control type power supply circuit - Google Patents

Abstract

PURPOSE:To improve load currents to output characteristics by overlapping voltage generated in a transformer to detecting voltage for the ON-period of a switching transistor and controlling switching timing. CONSTITUTION:Voltage is generated in detecting winding Nc for the ON-period of the switching transistor TR4, the negative DC voltage of magnitude corresponding to input voltage Vi appears at a mid-point D of resistors R17, R18, and negative voltage at the point D is synthesized with positive voltage appearing in the collector of a transistor TR1 for detecting errors. The switching timing of the switching transistor TR4 is controlled in response to voltage after the addition. Accordingly, load currents to output voltage characteristics can be made constant at all times regardless of the variation of input voltage Vi.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a switching @-type power supply circuit, and particularly aims to improve its load current versus output voltage characteristics.

Switching control type power supply circuits are classified into various types, one of which uses a switching transistor and a converter transformer to generate gross oscillation. The power supply circuit was proposed first.

Therefore, first, the circuit shown in FIG. 1 will be explained, and the problem am to be solved by the present invention will be presented.

The power supply circuit in Figure 1 can be roughly divided into an input rectifier (1),
Blocking oscillator (2) and converter transformer (3)
), an error detection section (4), a control circuit section (5), and an output rectification section (6).The blocking oscillation section (2) is composed of a The input winding (N1) of the converter transformer (3) and the collector-emitter of the switching transistor (TR4) are connected in series with the emitter feedback resistor (Rw4) and the current detection resistor (R++). Return Volume 1i (N
-# (C) of B) to the lower end of the feedback resistor (Rw4) and the other end (d) of positive feedback to the flow limiting circuit W! I(SK)
This configuration is connected to the base of the switching transistor (TR4) via. Next, the error detection section (4)
Fluctuations in the DC voltage between the lines (Ll) (Ll) are detected using an error detection transistor (TR+) and a Zener diode (D
5), and the above line (Li
) (Ll) is the voltage generated in the feedback winding (NB) and detection winding (Nc) of the transformer (3) during the off-period of the switching transistor (TRY), which is connected to the diode (D7) and the capacitor (C5). ) and diode (
D6) and a capacitor (Cs) for rectification and smoothing.

Furthermore, the control circuit section (5) includes a switching transistor (
A pair of control transistors (TR2) whose collectors and emitters are connected between the base of TR4) and the aforementioned line (Ll) via resistors (Rw) (Rwo), respectively.
TR5), the base of one of which (TRt) is Rri
connected to point B on the output side of the error detection unit (4), and
This point B is connected to point A on the upper end side of the current detection resistor (Rth) through a capacitor (C7) and a resistor (Rw6). Further, the output 91 waterfall portion (6) is connected to the transformer (3) when the switching transistor (TR4) is turned off.
The voltage generated in the output winding (N2) of the diode (D9
) and a capacitor (C9) for rectification and smoothing.

The circuit shown in Fig. 1 is configured as described above, and basically, when the power switch (SW) is turned on, the generated #J current Is is passed through the resistor (R2) to the switching transistor (TR4).
) to start a blocking oscillation and start #
In the steady state after J, the switching transistor (TR
4) to control the turn-off timing.

That is, when the switching transistor (TR4) is on, the current Ii passing between its collector and emitter
(Figure 2 (b)) causes a negative voltage (based on Li) that increases over time between both ends of the current detection resistor (R11), and this voltage is applied from point A to the resistor (Rw6) and capacitor (C7). It is guided to point B through . At that time, this point B has a positive potential (Ll is the reference) according to the DC voltage between the lines (Ll) (Ll), so the potential of point B is as shown in Figure 2 (F). It's going to change. At this time, the emitter (0 point) of the control transistor (TR2), that is, the base of the switching transistor (TR4) is connected to the feedback winding (N
Since the positive feedback voltage (Fig. 2 (c)) from a) is applied and has a constant positive potential, the potential of the previous point B is this 0
When the voltage is lower than the potential at the point, the control transistor (TR2) is turned on and (TRi, ) is also turned on.

With this, Conden! 7' (Cs), a reverse bias current Id flows between the base and emitter of the switching transistor CTR4) through the illustrated path, turning on this switching transistor.

When the DC voltage obtained from the output rectifier (6) increases during the prayer operation, the DC bias potential at the previous point B (10 in Fig. 2 (v)) decreases accordingly, so the switching transistor The turn-off timing of (TR4) becomes earlier and the on period becomes shorter. Therefore, the energy stored in the input winding (N1) during the ON period of the switching transistor (TRa) decreases, thereby lowering the DC output voltage. Furthermore, when the DC output voltage decreases, constant voltage control is performed by the completely opposite operation.

Note that the switching transistor (T
Turn-on of R4) is achieved by reversing the resonant current due to the inductance and distributed capacitance of the input winding (N1) in the direction of the aforementioned current Ii during the off period (second
See the resonance period in the figure. In addition, the positive feedback current If during the off period of the switching transistor (TRa) is designed to flow along the thread shown in the figure.
Consider the case where the load current taken out from the output rectifier (6) is increased.

That is, the power (load power) extracted from the output rectifier (6) is proportional to the energy accumulated in the input winding (N1) by the current 11 during the ON period of the switching transistor CTRa, so the load current By increasing , the peak value 1 cp of the type fiIi (see FIG. 2 (b)) is controlled in the direction of increasing.

That is, in this case, the DC voltage between the lines (Ll) and (L2) decreases, which causes the DC bias potential at point B (to in Figure 2) to rise, causing the control transistor (
This is to delay the turn-off of the switching transistor (TR4) and lengthen the on period of the switching transistor (TR4), thereby increasing the peak current value Icp. Therefore, the maximum load current (average value) that can be collected from the output rectifier (6) is caused by the error detection transistor (TRY) being completely turned off and the ON period of the switching transistor (TRa) being fixed at the maximum length. This corresponds to the state in which

By the way, the peak current value Icp is expressed as: Vl is the voltage to the DC between both ends of the input rectifier unit (11 smoothing capacitors (C2));
, where the length of the on period of the switching transistor (TR4) is T1, is given by the following equation.

1 Icp = -0T+ 1 Therefore, the maximum load current mentioned above is longer than the on-period T1
) as well as the input voltage (Vi), and a larger load current can be extracted from the output rectifier (6) when Vi is high than when Vi is low. Figure 7 (a) shows the load current vs. output voltage characteristics.
When the input voltage (Vi) is low as shown in (dashed line)
, the case of the rated value (actual number 41), and the case of the high value (dotted chain line) are different.

In this way, in the conventional switching control type power supply circuit as shown in Fig. 1, the maximum load current that can be supplied changes depending on the input voltage (Vi). Not suitable for television receivers, etc. This is because in a television receiver, the load 11 current changes greatly depending on the brightness of the screen, etc., so the characteristics of the power supply circuit that change depending on the input voltage (Vi) (Figure 7 (1)) are taken into account. and each circuit in the device! &:, l'
1'-shi, and therefore its design becomes very difficult.

Therefore, the present invention proposes a switching control type power supply circuit that can vary the load current vs. output voltage characteristic according to the input voltage.
Let me explain.

Fig. 5 shows an embodiment of the power supply circuit of the present invention, and parts corresponding to those in Fig. 1 are given the same symbols, but the features are as follows. It is a diode (D+o) and a capacitor (between both ends (e) (C1) of the detection winding (Nc).
Coo) is connected as shown in the figure, thereby causing the detection winding (CTR4) to be connected during the ON period of the switching transistor CTR4).
The voltage generated at Nc) is rectified and smoothed to obtain a voltage of the polarity shown in the capacitor (Coo), and the negative voltage (L2 is the reference), which is the difference between this voltage and the voltage of the capacitor (C5), is applied to the resistor (R+z). The voltage is divided by (R+8) and guided to point B in the error detection section (4) by the resistor (R+9).

That is, in this embodiment, during the ON period of the switching transistor (TR4), a running voltage is generated in the detection winding (Nc) by increasing the turn ratio of 41 (N+) (Nc) to the input voltage (Vi). Therefore, in the end, the resistance 01+r)C
M+a) I) Midpoint (DIK is the input voltage (vt)) A negative DC voltage of a magnitude corresponding to K appears, and this negative voltage at point D is applied to the collector of the error detection transistor (TRY) at point B. It is combined with the positive voltage that appears.

As a result, the DC bias potential at point B with line (L2) as the reference potential becomes a positive potential that is low when the input voltage (vl) is high and becomes high when tracing, and this bias potential is connected to the resistor ( R+4) and the negative voltage led by the capacitor (C7) are superimposed.

Therefore, the Kuhn-on of the control transistor (TR2) or the turn-off of the switching transistor (TR4) Vi
, when the input voltage (Vi) is high, it is fast, and when it is low, it is slow. This is an error detection transistor (TRY
) is completely turned off when the maximum load current is supplied. Therefore, the resistance (Rs) (Ry) and (
If the values of R+y)(R+a)(R+w) are appropriately selected, even if the input voltage (Vi) fluctuates, the switching transistor (
TRJ) turn-off timing can be changed. Therefore, regardless of the fluctuation of the input voltage (Vi),
This means that the load current vs. output voltage characteristic can always be kept constant as shown in 4N7 diagram (b).

Next, FIG. 4 shows another embodiment of the present invention, in which the same components are given the same symbols, but the differences from FIG. 3 are as follows. .

It connects the voltage generated in the feedback winding (NB) during the ON period of the switching transistor (TR4) to the diode (D2).
0) and the capacitor (C20), and the voltage obtained from this K to the above capacitor (C2o) and the capacitor (
The positive voltage that is the sum of the voltages of Cs) is connected to the resistor (Rz7) (R2
g) (R2w) leads to point B as in the case of FIG.

That is, in this embodiment, the DC bias potential at point B is always higher than in the case of FIG. 1 by the voltage of the capacitor 'NCzo).
The turn-off timing of the switching transistor (TR4), which corresponds to the time when TRY) is turned off, is always delayed from the case shown in FIG.

Therefore, the load current that can be supplied for a given input voltage (Vi) is larger than in the case of FIG. However, in this embodiment, the DC bias potential at point B is the input voltage (V
i) becomes higher when it is high than when it is low, so the load current vs. output voltage characteristic changes as shown in Figure 7(a) with respect to changes in input voltage (Vi), as shown in Figure 7(c). It will change even more than that. Therefore, this embodiment is suitable for devices that require relatively small fluctuations in power input and as large a load current as possible.

Figure 5 shows yet another embodiment of the present invention.

Similar to the circuit shown in Fig. 3, this embodiment has a constant load current vs. output voltage characteristic regardless of the input voltage (Vi) (Fig. 7 f).
b)), but the error detection section (4) and -
The configuration of the j control circuit section (5) differs from that in FIG. 3 as follows. That is, the resistor (Rib) and capacitor (C7) connected between the B points of the error detection transistor (TRY) are removed, and instead, the upper end of the turn-off capacitor (Cs) is AAK-connected. Then, a diode (DSO), a capacitor (Cso), and a resistor (Rs
) (Rss) (Rsv) are connected as shown.

Therefore, in this example, the line (L+) (L2)
Nine error detection transistors proportional to the dark DC voltage (
The negative voltage (L+ is the reference) at the collector of TRY) and the positive voltage across the capacitor (Cso) proportional to the input voltage (Vi) at point D are combined at point B, and the potential at point B becomes the line ( It is a negative potential with reference to Ll). In this state, when the switching transistor (TR4) is turned on, the negative voltage at point A (L+ is the reference) that decreases over time is superimposed on the voltage across the turn-off capacitor (Ci), and the emitter of the control transistor (TRz), that is, E Therefore, the negative potential at point E is lower than the negative potential at point B, and at time 9 (see Figure 6), the control transistor (TRz) is turned on and (TRs) is It turns on, and as a result, a reverse bias current 1d flows through the illustrated path and the switching transistor (TR4) is turned off. Therefore, this embodiment also performs constant voltage control using the same operating principle as the circuit shown in FIG.
At this time, the potential at point B is low when the input voltage (Vi) is high and high when it is low, so as in the case of FIG. 6, when the input voltage (Vi) is high, the switching transistor ( When the turn-off timing of TRa) is not flat or low, it is controlled to be delayed. Therefore, the load current vs. output voltage characteristic in this case is also constant with respect to the input voltage (Vi) as shown in FIG. 7(b).

In the embodiment shown in FIG. 5, the turn-off capacitor (C5) is charged by the switching transistor (TR
This is done by the current Ir flowing through the path shown in the figure during the off-state of a).

As explained above, the present invention provides a power supply circuit of the type that detects fluctuations in the voltage generated in the converter transformer during the off period of the switching transistor and controls the switching timing of the transistor according to the detected voltage. Since the switching timing is controlled by superimposing the voltage obtained by rectifying and smoothing the voltage generated in the transformer during the ON period of the switching transistor on the detection voltage, the load current vs. output voltage characteristics of the power supply circuit can be input. Although there is an advantage that the voltage can be set arbitrarily, the first point in solving the problem to be solved by the present invention is
Although the power supply circuit shown in the figure has been described, the present invention is applicable to other switching control type power supply circuits, and is therefore not limited to the illustrated embodiment.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a power supply circuit previously proposed by Honda-Hinto, and FIG. 2 is a diagram showing voltage and current waveforms at various parts thereof. FIG. 5, FIG. 4, and FIG. 5 are diagrams showing different embodiments of the power supply circuit of the present invention, respectively, and FIG. 6 and FIG. 7 are diagrams for explaining the operation thereof. (1)...Input rectification section, (2)...Blocking oscillation section, (3)...Converter transformer, (4)...
Error detection section, (5) - control circuit section, (6)... output rectification section, (TRJ Ray switching transistor, (
N1)...Input winding (first winding), (NB)...
・Feedback winding (second winding), (Nr)...detection section va
(Third winding)) Figure 2 # 7 Figure 7 0 JIL Wa 1 liter 2 liters (C) Procedural amendment (Voluntary) Commissioner of the Japan Patent Office 1, Indication of the case 1982 Patent Application No. 65590 No. 2 Title of the invention Switching control type power supply circuit 6 Person making the amendment Patent applicant Address 2-18 Keihan Hondori, Moriguchi City Name (188) Sanyo Electric Co., Ltd. Representative Kaoru Iue 4, Agent address Keihan Hon, Moriguchi City Dori 2-chome 18-5, Kami iE's subject specification row υ, "Detailed explanation of the invention" column 6, Yuzu IF's details LM] page 5, line 19 - funeral page 14, line '1, as shown in T1 Kamasa - "Ru. gself [4C, therefore, the European position of point E is higher than the negative position of point B" M4-Tora/Jista (TR2J (/J bass emitter song'+t) J: At the moment when (VBIC) is low F (condolence number 6), this TR2 is turned on and r (Tsute R3 is also turned on.)

Claims (1)

[Claims] (11 For DC input, the first winding of the converter transformer and the collector-emitter of the switching transistor are connected in series; In the power supply circuit, an error detection section detects fluctuations in a DC voltage obtained by rectifying and smoothing a voltage generated in the switching transistor, and controls the switching timing of the switching transistor according to the output of the detection section. A DC voltage proportional to the voltage generated in the second winding or the fifth winding during the ON period of the transistor is added to the output voltage of the error detection section, and the switching timing is determined according to the voltage after the addition. A switching control type power supply circuit characterized in that the switching transistor controls a blocking oscillation circuit with the first winding and the second winding (or the fifth winding). The switching IIJ type power supply circuit according to claim 1, wherein the circuit for controlling the switching timing is configured to control the turn-off timing of the switching transistor.