JPH04351467A - Tertiary winding voltage detection type power supply circuit - Google Patents

Abstract

PURPOSE:To realize compactification without using a resistor for large power or a large radiator in a tertiary winding voltage detection type power supply circuit equipped with a control circuit for controlling a switch element by detecting the output front a tertiary winding of a transformer in order to obtain a constant voltage from the secondary winding side of the transformer by turning on and off with the switch element an input DC power supply applied to the transformer. CONSTITUTION:A switch circuit 3 is provided between an output terminal and a rectifier D2 on the secondary side, and a switch ON/OFF circuit 4 for monitoring the output voltage of a power supply circuit and for controlling the switch circuit 3 is provided. The switch ON/OFF circuit 4 is so formed that the switch circuit 3 is turned off when the output voltage exceeds a predetermined voltage and is turned on when it does not reach the predetermined voltage.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention turns on and off an input DC power supply supplied to a transformer using a switching element, and connects the tertiary winding of the transformer to obtain a constant voltage from the secondary winding of the transformer. The present invention relates to a tertiary winding voltage detection type power supply circuit equipped with a control circuit that detects the output of a switch element and controls a switch element.

[0002] In the tertiary winding voltage detection type power supply circuit, there is a problem that the voltage on the secondary side increases when the load on the output side becomes light, so in the past, a dummy circuit was provided to forcefully prevent the voltage from increasing. However, the power consumed by the dummy circuit increases in proportion to the current, and it was necessary to deal with the heat generated. It is desired to eliminate such inconveniences.

0003

2. Description of the Related Art FIG. 4 is a block diagram of a conventional example 1, FIG. 5 is a diagram showing output voltage characteristics of a tertiary winding voltage detection type power supply circuit, and FIG. 6 is a block diagram of a conventional example 2. In Figure 4, input terminal I0
, I1 and is applied to the primary winding N1 of the transformer 31, which has a tertiary winding N3. The control circuit 30 controls the current flowing through the primary winding N1 by outputting pulses with a constant period and turning on and off the switching transistor Tr using the output. transformer 31
The alternating current generated from the secondary winding N2 of
The DC voltage V0 is then rectified and smoothed by the capacitor C2 and supplied to the load from the output terminals O0 and O1.

In order to keep this DC voltage V0 constant against changes in current (changes in load), a method is often used in which the output voltage V0 is detected and the control circuit 30 is controlled. If the detection location is far from the location where the control circuit is installed, or if there is a possibility that noise may be mixed in from the external surge current in the path where the output voltage detection output is input to the control circuit, Figure 4
The function is realized by the output of the tertiary winding N3 of the transformer 31 as shown in FIG.

That is, a voltage obtained by rectifying and smoothing the detection output of the tertiary winding N3 by a diode D1 and a capacitor C1 is input to the control circuit 30. The control circuit 30 controls the pulse width output to the switching traffic Tr in accordance with the voltage value to adjust the current flowing through the primary winding N1.

The output voltage characteristics of this tertiary winding voltage detection type power supply circuit are shown in FIG. Since the voltage generated in the tertiary winding N3 is proportional to 1/n of the output voltage V0 as long as the output current I0 is above a certain level, the output voltage can be monitored equivalently. However, when the load on the secondary side becomes lighter, the current decreases and the output voltage V0 increases, but the current in the tertiary winding N3 decreases, so the control circuit 30 controls the pulse width to increase the current. This causes the problem that the output voltage increases during light loads.

That is, if the output current I0 (horizontal axis) shown in FIG. A phenomenon occurs in which the vertical axis) suddenly increases. In the configuration shown in Fig. 4, a resistor R is provided as a dummy load to prevent such a voltage increase, and when the output voltage increases, current is passed through this resistor R to cause a current of I1 or more to flow, thereby preventing the voltage increase. It's suppressed. However, as the output voltage increases, the power consumed by the resistor R increases in proportion to the increase, and the heat generated from the resistor increases, so a heat radiator is required to prevent this.

The configuration of conventional example 2 shown in FIG. 6 is an improved configuration of conventional example 1. The configuration of FIG. 6 is similar to that of FIG. 4 on the input side, but differs in that a rise prevention circuit 32 is provided on the secondary side in place of the resistor R in FIG. 4. To explain the operation of this rise prevention circuit 32, the current I in the characteristic diagram of FIG.
1 decreases and the voltage increases, the Zener diode ZD turns on. This turns on transistor Q, and resistors R1 and R2 connect to output terminals O0 and O1.
A connection is established between the two, and current begins to flow. Accordingly, only when the output voltage becomes a constant voltage, the resistor R1,
Since current flows through R2, wasteful power consumption (heat generation) can be prevented compared to when the resistor R is always energized as shown in FIG.

[0009]

[Problem to be Solved by the Invention] Also in the case of FIG. 6 of the conventional example 2, the higher the output voltage becomes, the more the rise prevention circuit 32
The problem is that it is difficult to miniaturize the tertiary winding voltage detection type power supply circuit because the power consumed by the tertiary winding voltage detection type power supply circuit is large, so resistors for high power (resistors R1 and R2) and large heat sinks for the transistors are required. was there.

SUMMARY OF THE INVENTION An object of the present invention is to provide a tertiary winding voltage detection type power supply circuit that can be miniaturized without requiring a large power resistor or a large heat sink.

[0011]

[Means for Solving the Problems] FIG. 1 is a basic configuration diagram of the present invention. In Figure 1, 1 is a control circuit, 2 is a transformer,
3 is a switch circuit, and 4 is a switch opening/closing circuit. In addition, Tr is a switching transistor, C1 and C2 are capacitors, and D1 and D2 are rectifier elements (diodes).
This is the same as the conventional example.

Conventionally, the voltage was suppressed by consuming the energy generated on the secondary side with a resistor, etc., but in the present invention, when the output voltage is about to rise, the switch circuit is controlled to suppress the voltage on the secondary side. This is to suppress the occurrence of such problems.

[0013]

[Operation] In Fig. 1, a switching transistor Tr is provided on the primary side of the transformer 2, and the voltage is detected by the tertiary winding, and the pulse width supplied from the control circuit 1 to the switching transistor Tr is adjusted to control the current of the primary winding. The configuration for controlling is similar to the conventional example. The output of the secondary winding N2 is converted into direct current via a rectifier D2 and input to the switch circuit 3. The output of the switch circuit 3 is supplied to the load from output terminals O0 and O1 via a smoothing capacitor C2. The output voltage on the output terminal side is monitored by the switch circuit 4, and when it is detected that the output voltage exceeds a certain level (the voltage level corresponding to the current I1 in Fig. 4), the switch circuit 4 turns off the switch circuit 3. If the voltage level does not reach the predetermined level, a control signal is generated to turn on the switch circuit 3 and transmit the rectified output of the secondary winding N2 to the output terminal.

By doing so, it is possible to prevent the output voltage from increasing even if the load connected to the output terminal becomes lighter, and it is possible to eliminate the need for an energy absorbing resistor.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 is a configuration diagram of an embodiment of the main part of the present invention, and FIG. 3 is a diagram showing operational waveforms of the embodiment. In Figure 2, 2 is the same transformer as in Figure 1 (only the secondary winding N2 is shown), Q1
The FET transistors, resistors R1, R2, R3, R4, transistors Q2, and differential amplifier AMP, which correspond to the switch circuit 3 in FIG. 1, correspond to the switch opening/closing circuit 4 in FIG.

The operation of FIG. 2 will be explained with reference to FIG. Assuming that the output voltage of the secondary winding N2 of the transformer 2 is V1, an intermittent waveform output is generated as shown in the first part of ▪ in FIG. 3. At this time, transistor Q1 is on (conducting)
In this state, the smoothed output voltage V0 generated at the output terminals O0 and O1 is approximately constant as shown in the first part of the black square in FIG.

That is, in this state, the differential amplifier AM
P is monitored by comparing a constant reference voltage E with the output voltage V0, which is the rectified output of the diode D2.
When the output voltage V0 does not reach a certain level (the voltage corresponding to the current I1 in Figure 5), its output becomes "L" and the transistor Q2 turns off, so the collector voltage of the transistor Q2 becomes close to the output voltage V0. The gate voltage of FET transistor Q1 becomes "H" and this voltage turns on this FET transistor Q1 (
conduction) state.

On the other hand, when the level of the output voltage V0 exceeds the above-mentioned certain level, the output of the differential amplifier AMP becomes "H" and the transistor Q2 is turned on. This short-circuits the gate and source of the FET transistor Q1, resulting in an off (non-conducting) state. When it becomes non-conductive, the output current to the load side is turned off (power supply is stopped), so the output of the secondary winding N2 has a shorter current flow time, as shown in the second half of ■ in Figure 3. becomes smaller by that amount. Therefore, even if the output voltage V0 rises once, it falls as shown in the second half of ◯ in FIG. After falling, when the voltage falls below a certain level, the differential amplifier AMP is inverted again and the FET transistor Q1 is turned on again.

3 in FIG. 3 is an FET that operates as described above.
Voltage V2 between source and drain of transistor Q1
, and the voltage V2 during the on (conducting) state is approximately 0
(When a low resistance element is used) However, when in the off (non-conducting) state, a voltage waveform of a constant level appears as shown in the figure.

[0020]

[Effects of the Invention] According to the present invention, in a tertiary winding voltage detection type power supply circuit, the heat generated can be reduced by converting the circuit that prevents the output voltage of a light load into a switch circuit without using a dummy load. This eliminates the need for large heatsinks required in conventional circuits, making it possible to downsize and enable high-density mounting.

[Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram of the present invention.

FIG. 2 is a configuration diagram of an embodiment of the main part of the present invention.

FIG. 3 is a diagram showing operational waveforms of the embodiment.

FIG. 4 is a configuration diagram of conventional example 1.

FIG. 5 is a diagram showing output voltage characteristics of a tertiary winding voltage detection type power supply circuit.

FIG. 6 is a configuration diagram of conventional example 2.

[Explanation of symbols]

1 Control circuit 2 Transformer 3 Switch circuit 4 Switch opening/closing circuit Tr Switching transistor C1, C
2 Capacitor

Claims (1)

[Claims] [Claim 1] The input DC power supply supplied to the transformer is turned on and off by a switching element, and the output of the tertiary winding of the transformer is detected in order to obtain a constant voltage from the secondary winding side of the transformer. In a tertiary winding voltage detection type power supply circuit that is equipped with a control circuit that controls the switching element using A tertiary winding voltage detection type power supply circuit is provided with a switch opening/closing circuit for controlling the output voltage, and the switch opening/closing circuit turns off the switch circuit when the output voltage exceeds a predetermined voltage, and turns on the switch circuit when the output voltage does not reach the predetermined voltage. .