JPH0284061A - Switching control type power circuit - Google Patents

Abstract

PURPOSE:To perform a stable constant-voltage operation over a wide range of AC input voltage by changing the maximum attainable value of a switching pulse duty ratio in a switching pulse duty ratio control circuit using a low voltage and a small current in such manner that the number of turns of a demagnetization winding is changed by a power converter part. CONSTITUTION:An input voltage discriminator 2 has a circuit for discriminating between AC input voltage from I1, I2 and also has its threshold between about 135V and 145V of the AC input voltage. When the AC input voltage to be applied is less than 145V, the transistor Tr2 of said input voltage discriminator 2 is OFF so that Tr5 is OFF and a voltage obtained by division of the output voltage of a terminal VR by R3 and R4 is applied to a terminal DT. When the AC input voltage exceeds 145V, the Tr2 is ON so that said Tr5 is also ON, the voltage applied to the terminal DT is higher than the voltage obtained by division of the output voltage of the terminal VR by R3 and R4, and the maximum duty ratio is so set as to be limited to a small value.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to switching control power supply circuits, particularly to switching the AC input range of forward-type switching control power supply circuits capable of inputting a wide range of AC voltages. It is.

[Conventional technology]

Conventional 1 For example, in the Middle East and developing countries, the voltage value of commercial AC power supplies varies depending on the region, such as 100V, 110V, 120V,
They are different like 200V, 220V, 240V, and in the US and Europe.

Unlike single-phase 115V and 220V, power supply circuits for devices used in such regions are required to have stable constant voltage operation over a very wide input voltage range. A switching control type power supply is an example of a power supply circuit that satisfies these requirements, but even this power supply circuit cannot operate stably when the upper limit of the input voltage is three times or more than the lower limit as mentioned above.
Particularly when the output capacity is large, it is currently difficult to achieve this even though the parts used are limited to ff1I.

First, regarding the difficulty of achieving the above-mentioned switching control type power supply circuit, Nikkei Electronics, July 24, 1978.
One of the circuits listed in the number is a forward switching control type power supply circuit that is simple and suitable for high power applications. The AC input voltage range of this power supply circuit is from 80V to 26V.
4V, DC voltage after rectification is 113V (80xσ) to 373V, output voltage ■. is 5V, and the DC voltage drop VD of the rectifier circuit on the output side is IV. Here, a Schottky diode is generally used as a rectifier for output side rectification to improve efficiency, and its practical reverse withstand voltage is limited to 30 to 35 V. The number of primary windings NP and the number of secondary windings N of the converter transformer.
Since the input voltage is 264v and the DC voltage V< applied to the primary winding of the transformer is 373v, it is limited by the value of equation (1), and the turns ratio N p / N s is 12 or more. This is the limit.

Nsy V i Terminal voltage V between secondary windings, ≦□・・・・・・・・・・・・(1
) Formula On the other hand, when the DC voltage applied to the primary winding of the transformer is 113V with an AC input voltage of 80V, the switching pulse duty ratio δ to ensure an output voltage of 5V is limited by Formula (2) and is approximately 0.64 or more. Is required.

Switching pulse duty ratio δ≧−Lβ and TsujiXm1−・・・・・・・・・・・・(2)
2N, ・V (Also, the condition for applying a voltage for a time of δ to the primary winding of the transformer and then restoring the magnetization direction of the transformer to its initial state in the demagnetizing winding is as follows, where the number of demagnetizing windings is Nu: Restricted by equation 3), when δ=0.64, Np/Nx needs to be about 1.8 or more.

δ Demagnetization condition N p/ N*≧(1-8)・・・・・・
...... Equation (3) Also, the voltage vT applied to the switching transistor during demagnetization is expressed by Equation (4), and when vt is 370V and the switching pulse duty ratio suddenly changes to 0.64, VT becomes A switching transistor with a withstand voltage of 1,300 V or more is required for practical use.

N, ・Vt” (1+) V4・・・・・・・・・・・・
・・・・・・(4) As a method to solve the difficulty of more than 2N cost, the conventional device uses a unidirectional thyristor and a bidirectional thyristor as described in Utility Model Publication No. 16315/1983. Use voltage double rectification for AC input from 100V to 120V, and voltage double rectification for AC input from 100V to 200V.
Up to 40V, the system switches to full-wave rectification and limits the voltage range applied to the transformer to approximately 226V to 370V DC.

In addition, in the device described in Utility Model Publication No. 63-21190, a tap is installed on the output side of the switching transformer, and when the AC input is from 100V to 120V, the turns ratio of the primary winding to the secondary winding is small, and AC manual power is applied. It was designed to increase the voltage from 200V to 240V.

[Problem to be solved by the invention]

The conventional method of switching the rectification method described above requires a high withstand voltage and a large amount of electric power for the switching semiconductor, and has the disadvantage that an excessive charging current flows into the capacitor at the time of switching because the switching is performed in the preceding stage of the smoothing capacitor. In addition, in the case of a method that switches the tap of the secondary winding of the transformer, if the output current is large,
The switching element requires a large-capacity product, and the point that the voltage drop in the switching section is large and the efficiency decreases is not taken into account, and 2.
If an attempt is made to improve the switching frequency of the switching power supply, restrictions will be placed on the length of the wiring or board pattern of the next switching section. In addition, when a variety of output voltage types are required, the number of elements for switching the taps of the secondary winding of the transformer is required depending on the output type. There is no need for a large capacity switching element, regardless of the type of output voltage.
The object of the present invention is to provide a method that can perform stable constant voltage operation over a wide AC input voltage range.

[Means to solve the problem]

In order to achieve the above object, there are methods that reduce the power capacity of the switching means of the switching section in switching the circuit connections and their constants necessary to expand the AC input voltage range. That is, in order to perform stable constant voltage operation over a wide AC input voltage range, firstly, in the power conversion section, a demagnetized winding is used to flow a small current that is the same as the excitation current in a forward type transformer. The number of turns is changed to change the maximum value of the switching pulse duty ratio in a switching pulse duty ratio control circuit that uses low voltage and small current.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. This circuit can be roughly divided into a power supply circuit section 1, an input voltage discrimination section 2, and a reset winding switching circuit 3. The power supply circuit section 1, which consists of a maximum pulse duty ratio switching circuit 4, basically constitutes a forward type converter having a transformer that performs magnetization reversal using a well-known reset winding (demagnetization winding). Ori.

1, I is an AC input terminal, CB is a switch that serves both an overcurrent cutoff function and a power switch, and BDI is a bridge type rectifier ryJj1. c1 is a smoothing capacitor.

Tri is a switching transistor, TI is a converter transformer with a reset winding, and this reset winding is N
In this embodiment, one of the NR1 windings is divided into RI and NR2 windings, each end of which is drawn out and freely connected to other circuits. , the other is one of the NR2 windings and also the diode D2
is tangent to the cathode side of Further, the other of the turns of NR2 is connected to the cathode side of the diode D3.

DR is a driver circuit that drives the switching transistor Tri, and CN is a control circuit that controls the length of the on period of the switching transistor Tri, that is, the duty ratio, according to the fluctuation of the DC voltage between the output terminals 01 and 02. be. This control circuit can vary the maximum value of the duty ratio. I & large pulse duty ratio setting terminal D
The maximum pulse duty ratio (hereinafter referred to as the maximum duty ratio) can be determined according to the voltage applied thereto.In this embodiment, when 3V is applied to the terminal DT, the maximum duty ratio is 1.0 when applying O, OV
During this period, a control circuit having an internal mat configuration is used, in which the maximum duty ratio is determined at a substantially constant rate with respect to the applied voltage. Also, this control circuit CN has approximately DC5V.
It also has a terminal VR that can output the reference voltage.

The input voltage discriminator 2 has a circuit for discriminating the AC input voltage from I, , I, and in this embodiment has its discrimination position between about 135V and 145V of the AC input voltage. This operation is performed by stepping down the AC input using a transformer T2, converting it to DC using a rectifier circuit BD2, and discriminating the DC using a series circuit of a Zener diode ZD1 and resistors R1 and R2. The voltage is applied to the base of the transistor Tr2 to make it conductive, and at the same time, the conduction of Tr2 also makes the transistor Tr3 conductive, and then the AC input voltage becomes 1.
This is a circuit that keeps Tr2 in a conductive state even if the voltage drops below 40V, and sends the change in the collector of this transistor Tr2 as a signal to a reset winding switching circuit 3 and a maximum pulse duty ratio switching circuit 4, which will be described later, for switching. I have to. Further, the DC power converted into DC by the rectifier circuit BD2 is stabilized directly or by the stabilizing circuit VRI, and is sent as Vcc@M to each part of the power supply for use.

In this embodiment, the reset winding switching circuit 3 is composed of a relay Kl, its contact KIS, and its driving transistor Tr4.When Tr2 of the input voltage discriminator 2 is non-conductive, that is, when the applied AC input voltage is less than 145V, Tr4 is It becomes conductive and drives relay 1 to connect contacts 2 and 3 of KIS. Further, when the applied AC input voltage exceeds 145V, the Tr2 becomes conductive and the Tr4 becomes non-conductive.

K1 is not driven and contacts 1 and 3 of KIS are connected.

In the single circuit, relay contacts are used to connect 1 and 3, and 2 and 3, but it goes without saying that similar actions and effects can be achieved even if semiconductor elements are used for this purpose.

The maximum pulse duty ratio switching circuit 4 is connected to the control circuit C.
Firstly, the VR terminal voltage of N is divided by resistor R1°R2 and applied to the maximum pulse duty ratio setting terminal DT, and secondly, capacitor C3 is tangentially connected in parallel to resistor R1 to divide VR
When the terminal voltage rises, the voltage is directly applied to the terminal DT and then gradually lowered to the voltage divided by R1 and VH2. Thirdly, the transistor Tr is connected in parallel to the resistor R1.
5 and a resistor R5, and changes the voltage applied to the terminal DT by making the transistor Tr5 conductive or non-conductive. To explain the operation of this circuit in relation to the AC input voltage application state, first, the application of AC input voltage is 1
When the voltage is less than 45 V, the transistor Tr2 of the input voltage discriminator 2 is non-conductive, so the Tr5 is non-conductive, and a voltage obtained by dividing the output voltage of the terminal VR by the R3 and R4 is applied to the terminal DT. Furthermore, when the AC input voltage reaches 145V, the Tr2 becomes conductive, so the Tr5 also becomes conductive to the terminal D.
The voltage applied to T is set to be larger than the voltage obtained by dividing the output voltage of terminal VR by R3 and R4, and the maximum duty ratio is set to a small value.

Next, we will specifically explain what voltages and currents each part generates. First 11. The AC input voltage range between I and 80v to maximum 264v, and the rectifier circuit BDI (7) output V< is DC112V, to DC370V, 01.02 (
7) The output voltage is DC5V for constant voltage operation, and D3. D4. The DC drop VD up to Ll and 01 and 02 is.

Schottky diodes with a practical reverse breakdown voltage of 35V are used for D3 and D4 to 1V, converter transformer T1 N, number of turns is 24 turns, number of Nj turns is 2 turns, number of NR1 turns is 12 turns, NR2 turns. The number of wires is 15 turns, the inductance of the Np winding is at least 2 mH, the maximum voltage for discrimination against the input voltage of input voltage discriminator 2 is 145 V, Vj is DC 205 V, and the maximum pulse duty ratio δ is the operation of Tr2 of input voltage discriminator 2. The AC input voltage is 145V.
The constants of the maximum pulse duty ratio switching circuit 4 are set so that when the AC input voltage is less than (V<=205V DC), the constant is o, 65, and when the AC input voltage is 145V or more, the constant is 0.4. Also,
The repetition frequency of the on period of the transistor Tri is 100
At KH, the period from one on period to the next on period is 10 μs. In the circuit set up as shown above,
First, the maximum value of the voltage across the N1 winding, which can also be the reverse voltage applied to D3 and D4, is the value of (5) from equation (1) above, which is the value of diode D3. The value is 9) compared to 0 and 88, which is less than the practical reverse breakdown voltage of D4, and magnetization reversal of the converter transformer is possible, and magnetization saturation does not occur.

Next, the pulse duty ratio δ for ensuring the output voltage from 01 and 02 at 5V is the value of (6) when V< at the minimum value of the AC input voltage is 112V from the above formula (2), and the AC input voltage When Vj is 145V and 205V, it becomes the value (7), and a constant voltage output of 5V is possible below the maximum pulse duty ratio limit set above.Next, the demagnetization condition of the converter transformer is as above ( From formula 3), when V< is less than 205V, magnetization is reversed by the NR1 winding, so Np/Ni=Next, the maximum value VT of the voltage applied to the emitter and collector after the on-period of the switching transistor Tri ends is , V< is 20
When the maximum pulse duty ratio is less than 5V, that is, the maximum pulse duty ratio increases to 0.6, and magnetization reversal is performed with the NR1 winding, (1
0), when V< is 205v or more, that is, the maximum pulse duty ratio increases to 0.4, the magnetization reversal is set to NR.
When the first winding and the NR2 winding are connected in series, the value (11) is obtained, and the practical withstand voltage of the transistor Tri is 900 V, which is easily available.

In addition, when V< is 205 V or more, the NR1 winding and NR2 winding are connected in series to perform magnetization reversal. The same current as the excitation current flows, and its maximum value becomes the value (12), which is the ratio switching circuit used in the reset winding switching circuit 3.

Small capacity relays or semiconductor elements can be used.

370 (V)x4 (u “) = o, 74 A,
, , , , <12) 2 (mH) [Effects of the Invention] Since the present invention is configured as described above, it has the following effects.

By switching the number of demagnetized windings and the maximum pulse duty ratio, stable constant voltage operation can be performed over a wide AC input voltage range and over a wide Ti current input range. In addition, the above switching has the advantage of being able to use low-power components, and can be realized using switching transistors with relatively low withstand voltages. Even in 'am's having an output converter transformer, there is an advantage that no additional parts are required.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing one embodiment of the present invention.

Claims (1)

[Scope of Claims] 1. A conversion circuit that inputs an AC voltage and converts the output converted into DC by a rectifier circuit to AC, and inputs the AC output to a primary coil and generates a voltage from both ends of the secondary coil. a converter transformer that derives the output and has a demagnetizing winding, an output-side rectifier circuit that inputs the derived output, and a control circuit that detects the output level of the rectifier circuit and changes the output duty ratio of the conversion circuit. In a switching control type power supply circuit, the demagnetizing winding of the converter transformer is divided into at least two or more parts, and one or more of the divided demagnetizing windings is demagnetized. A switching control type power supply circuit comprising a switching circuit used as a winding and a switching circuit for switching a maximum limit value of an output duty ratio of the conversion circuit.