JPS62181577A - Power unit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a power supply device, particularly a control method in a flyback type power supply device.

[Prior art]

Conventionally, it is well known that in this type of high voltage generation circuit using the flyback method, a flyback voltage is generated at a resonance period determined by the flyback transformer (horizontal deflection output transformer) and its peripheral components. . Therefore, in order to operate the above circuit efficiently, it is necessary to determine the resonant period T, use that value as a reference, determine the off time T OFF of the semiconductor switching element according to the following relationship, and design the circuit.

T/2≦TOFF<T However, even if the above-mentioned design is carried out, the above-mentioned resonance period T will vary due to, for example, changes in ambient temperature and load, as well as variations in characteristics such as the inductance of the flyback transformer. , during the on period of TOFF<T/2, as shown in Figure 1 (collector voltage waveform diagram a and collector current waveform diagram b of the switching (element) transistor), the switching element is turned on at the wave width part of the resonance waveform. (dotted line), and during the off period when TOFF>T, the wave width of the second waveform diagram is generated (dotted line) as shown in Figure 2 (switching transistor collector voltage waveform diagram and collector current waveform diagram b). ) often occurred.

In such a case, if the waveform is passed as is (turned on), the generated voltage becomes an extremely low impedance source, resulting in serious damage to the switching transistor.

〔the purpose〕

The present invention has been made in view of the problems of the conventional examples as described above, and it solves the drawbacks such as damage to semiconductor switching elements, and also allows designers to avoid being constrained by variations in characteristics and types of flyback transformers. The purpose of the present invention is to provide a power supply circuit that allows circuit design without any problems and standardization of this type of circuit, which has been extremely difficult in the past.

〔Example〕

The present invention will be explained below based on examples. Figure 3 shows
1 is a block diagram of an example circuit according to the present invention. FIG. 1 is a flyback transformer, 2 is a switching transistor connected to the primary winding side of the flyback transformer 1, and 3 is a switching transistor connected to the primary winding side of the flyback transformer 1.
4 is a damper diode connected to the collector side of the switching transistor, 5 is an output current setting value, and 6 is an output detection circuit using this setting value input and an output current detection resistor 8. The error amplifier 7 compares and amplifies the error output signal level, and the timer circuit A generates an on time corresponding to the error output signal level.
A low potential (zero level) detection circuit 10 connected to the switching transistor 2 and used to detect the zero cross timing of the flyback voltage waveform is set (S) in response to the low potential detection signal, and the timer circuit Bll is set (S). This is a (R) flip-flop circuit set by the output. Further, 12 is an OR gate circuit, 13 is an amplifier circuit, 1
4 is a drive power supply, and 15 is an output terminal of this power supply circuit.

Next, the operation of the circuit of this embodiment will be explained. FIG. 4 shows the operation waveform diagram of each part. When voltage is supplied from the drive power supply 14,
Since the initial detected output current value is zero (Fig. 4g),
The error output level with respect to the set value 5 is the maximum. Therefore, the maximum on-time width of timer A7 is sent out (Fig. 4b).
), the switching transistor 2 is made conductive via the amplifier circuit 13, and turned off after a certain period of time. The collector voltage/current waveform diagrams of the switching transistor 2 at this time are shown in FIGS. 4e and 4f.

- After the conduction of the switching transistor 2 is turned off, the collector voltage waveform e starts to oscillate with a natural period determined by the primary-side equivalent inductance of the flyback transformer 1 and the resonance capacitor 3, and as shown in FIG. A zero level is detected (FIG. 4c), and the flip-flop circuit 10 is set. Here, the flip-flop circuit lO output d and the timer Bll output a are the trigger input of the timer A7 via the OR gate 12.
The timer Bll is configured to time out and trigger the timer A7 when the power supply voltage rises or when zero level detection of the waveform is not performed due to a load abnormality or the like.

Therefore, the output d of the flip-flop circuit 10 is triggered by the timer A7 to send out an on-time pulse corresponding to the error signal. Note that since the output of the timer A7 serves as a trigger for the timer Bll and a reset signal (R) for the flip-flop 10, the flip-flop circuit 10 is initialized immediately after the timer A7 is activated.

Through the above series of repeated operations, the output current rapidly reaches the set value 5. Furthermore, since the switching transistor 2 is turned on at the node of the flyback waveform, the flyback transformer l and the resonant capacitor 3 automatically reach the optimum point.

In the above embodiment, the converter output current is controlled, but the same effect can be obtained by detecting voltage instead of current and controlling the output voltage.

〔effect〕

As described above, according to the present invention, the low potential point of the waveform of the flyback voltage during the OFF period of the semiconductor switching element in the flyback type power supply device is detected, and the switching element is turned on using the detection signal. Because I configured it to .

It is possible to standardize circuits without being constrained by ambient temperature, load fluctuations, variations in characteristics of flyback transformers, etc., and it is also possible to supply a highly reliable power source without the risk of damaging the switching elements. It became.

[Brief explanation of drawings]

1 and 2 are respective waveform diagrams of the collector voltage/current of a switching element in a conventional circuit, FIG. 3 is a block diagram of an embodiment of the circuit according to the present invention, and FIG. 4 is a diagram of various parts of the same embodiment. It is an operation waveform diagram. 1...Flyback transformer? ... Semiconductor switching element (transistor) 3 ... Resonance capacitor 5 ... Output current setting value 9 ... Low potential (zero level) detection circuit 15 ...
...Output terminal Figure 1 Figure 2 Whistle 3 Wa

Claims (1)

[Claims] A detection means for detecting a low potential point of a flyback voltage waveform during an off period of a semiconductor switching element connected to the primary winding side of the flyback transformer, and a detection signal from the detection means turns on the semiconductor switching element. A power supply device comprising: a control means for controlling the power source;