JPH01318559A - Ac/dc converter circuit - Google Patents

Abstract

PURPOSE:To step down and convert a voltage through a simple circuit by providing an apparatus with a voltage and phase sensing circuits and by turning ON and OFF a switching element between an AC power source and a rectifying and smoothing circuit through the output of the sensing circuit. CONSTITUTION:A full-wave rectification and step-down circuit is composed of a AC power source 10, voltage and phase sensing circuits 21-22, Zener diodes D3-4, transistors TR1-2, field-effect transistors(FET) 23-24, and diodes D5-10 to supply a load resistor R5 with power. The voltage and phase sensing circuit 21 is composed of resistor R1 and R3, TR1, etc., to sense the negative half cycle of a voltage waveform of the AC power source 10. Also, the voltage and phase sensing circuit 22 is composed similarly to sense the positive half cycle of the voltage waveform in a like manner. Thus, the positive and negative voltage levels of AC input sensed by the sensing circuits 21, 22 are set at desired voltage levels, and FETs 23, 24 are turned ON simultaneously with AC input phase when the voltage levels are under the set values, to send AC input to the rectifying and smoothing circuit side.

Description

[Detailed Description of the Invention] Summary This invention relates to an AC/DC conversion circuit that converts AC power to DC power. In an AC/DC conversion circuit that rectifies and smoothes AC input from a power supply using a rectifier and smoothing circuit to obtain a DC output, a voltage/phase detection circuit that detects the voltage and phase of the AC input is provided, and the AC power supply and rectifier and smoothing circuit are also installed. A switching element is provided between the two, and the switching element is turned on and off according to the voltage level and phase of the AC input detected by the voltage/phase detection circuit, and the AC input is sent to the rectifying and smoothing circuit during the on period. Configure it as follows.

INDUSTRIAL APPLICATION FIELD The present invention relates to an AC/DC conversion circuit for converting AC power to DC power.

Electronic devices have a built-in power supply section that serves as a power source, and most of them use a DC power source. Most of these DC power sources use AC 100/200V of a commercial power source as a human power source, step down the voltage using a power transformer, etc., and rectify it using a bridge diode or the like to obtain DC power. Furthermore, a voltage stabilizing circuit is connected so that the voltage supplied to the electronic device does not fluctuate due to voltage fluctuations of the input source.

Under these circumstances, as electronic devices become smaller, there is a demand for smaller power supply units and higher efficiency.

BACKGROUND OF THE INVENTION FIG. 6 shows a circuit diagram of a conventional AC/DC conversion circuit.

T1 is a step-down transformer, D15 to D18 are rectifying diodes, C3 is a smoothing capacitor, and R5 is a load resistance. The diodes D15 to D18 constitute a bridge diode, which performs full-wave rectification of the AC power stepped down by the transformer T1. In this way, this circuit serves as an aftereffect rectification step-down circuit. When the AC input is a positive half cycle, diode D15 - resistor R5 - diode D1
In the negative half cycle, current flows in the order of diode D16, resistor R5, and diode D17. This allows AC input to be rectified and capacitor C
3 to obtain a DC output.

FIG. 7 shows another conventional circuit diagram.

The diodes D19 to D22 constitute a bridge diode, and the voltage due to the AC input is directly applied to this bridge diode. A constant voltage circuit 27 converts the input voltage into a desired voltage, and inputs a DC voltage smoothed by a smoothing capacitor C4.

The operation of diodes D19 to D22 and capacitor C4 is as follows:
Since it is the same as the conventional example shown in FIG. 6, its explanation will be omitted.

The voltage generated across the capacitor C4 is the constant voltage circuit 2.
7 to the desired voltage level.

In addition to the conventional examples shown in FIGS. 6 and 7, an AC/DC conversion circuit using half-wave rectification is also known.

Problems to be Solved by the Invention However, with the conventional AC/DC converter circuit as described above,
When using a transformer to step down the low frequency AC input (commercial frequency 50/60) (z), there is a problem that the shape of the transformer is large and heavy, which hinders the miniaturization and weight reduction of the power supply section. Ta.

Also, when stepping down the voltage with a constant voltage circuit without using a transformer,
There are two types of constant voltage circuits: series regulators and switching regulators.

When a series regulator is used, the power conversion efficiency is poor and the heat dissipation area is large, which hinders miniaturization.

When a switching regulator is used, there is a problem that the circuit configuration is complicated and the cost is not necessarily low.

The present invention has been made in view of these points, and its purpose is to provide an AC/DC conversion circuit that steps down and converts AC power into DC power using a simple circuit and without using a transformer. It is to provide.

Means for Solving the Problems FIG. 1 is a diagram showing the principle of the present invention, and (a) is a block diagram;
(b) shows a waveform diagram.

In an AC/DC converter circuit that obtains a DC output by rectifying and smoothing an AC input from an AC power supply 10 in a rectifying and smoothing circuit 11, a voltage/phase detection circuit 12 for detecting the voltage and phase of the AC input is provided. 10 and rectifier smoothing circuit 11
A switching element 13 is provided between them. And the voltage
The switching element 13 is turned on and off according to the voltage level and phase of the AC input detected by the phase detection circuit 12, and the AC input is sent to the rectifying and smoothing circuit 11 during the ON period.

Function According to the present invention, when converting an AC input into DC by full-wave rectification, the positive and negative voltage levels of the AC input detected by the voltage/phase detection circuit 12 are set to desired voltage levels. As shown in FIG. 1(b), when the voltage in the positive and negative half cycles of the AC input is less than the set voltage, the switching element 13 is turned on in synchronization with the phase of the AC input, and the rectification is performed. An AC input is sent to the smoothing circuit 11 side. and,
The DC output output from the rectifying and smoothing circuit 11 is supplied to the resistor R5.

When converting AC input to DC using half-wave rectification, the voltage level of the AC input detected by the voltage/phase detection circuit 12 is similarly set to the desired voltage level, and the voltage in the positive half cycle of the AC input is set to the desired voltage level. When is below the set voltage, the switching element 13 is turned on in synchronization with the phase, and an AC input is sent to the rectifying and smoothing circuit 11. Thereby, the voltage of the output power can be set according to the voltage detection level in the voltage/phase detection circuit 12, so that rectification and step-down of the AC input can be easily performed.

Embodiments The present invention will be explained in detail below based on embodiments shown in the drawings.

FIG. 2 shows a circuit diagram of an embodiment of the AC/DC conversion circuit according to the present invention, which is a full-wave rectification step-down circuit.

10 is an AC power supply, 21.22 is a voltage/phase detection circuit, D
3. D4 is a Zener diode, Dl, D2, D5~
DIO is a diode, R1-R5 are resistors, TRI, TR
2 is a transistor, 23.24 is a field effect transistor (FET), and C1 is a capacitor. Diode D5 is an internal diode of FET 23, diode D6 is an internal diode of FET 24, and resistor R5 is a load resistance.

The voltage/phase detection circuit 21 includes resistors R1, R3, a diode DI, a Zener diode D3, and a transistor TR.
1, and detects the negative half cycle of the voltage waveform of the AC power supply 10. Voltage/phase detection circuit 22
is composed of resistors R2 and R4, a diode D2, a Zener diode D4, and a transistor TR2, and detects the positive half cycle of the voltage waveform of the AC power supply 10. Resistors R1 and R2 are Zener diodes D3,
The current limiting resistor of D4, resistors R3 and R4 are FET23,
Gate current limiting resistance of FET24, diodes D1, D
2 is for preventing backflow when polarity is reversed. Zener diodes D3 and D4 are reference voltage sources for setting the DC output voltage. The transistors TRI and TR2 turn on and off the FET23 and FET24 in synchronization with the phase of the AC input.

The operation of the FET 23 is controlled by the voltage/phase detection circuit 21, and the operation of the FET 24 is controlled by the voltage/phase detection circuit 22.
controlled by. Diodes D7 to DIO constitute a bridge diode, and FET23 and FET
The AC input sent out through 24 is full-wave rectified.

Capacitor C1 smoothes the pulsating output from the bridge diode.

FIG. 3 shows an operational waveform diagram of the circuit of FIG. 2.

Set voltage of diode D4 is x (V), diode D3
Let y (V) be the set voltage of
Since diode D4 is off, transistor TR2
is off. As a result, FET24 is in an on state, and diode D5 - diode D7 - capacitor C1
A current flows through the resistor R5, the diode Di0, and the FET24 in this order. When the input terminal e reaches the voltage at the point A, the Zener diode D4 is turned on and the transistor TR2 is turned on, so the FET 24 is turned off and a voltage higher than the voltage at the point A is not applied to the resistor R5.

When the voltage in the positive half cycle passes its peak and becomes lower than the voltage at point a' (=xV), Zener diode D4 and transistor TR2 are turned off, so FET24 is turned on again, and diode D5- Current flows in the order of diode D7-capacitor 01 and resistor R5-diode DIO-FET24. Furthermore, FET
During the period when 24 is off (point a to a'), the capacitor CI
The charges accumulated in the resistor R5 are discharged to the resistor R5.

Furthermore, when the phase of the input terminal advances and becomes a negative half cycle, the voltage/phase detection circuit 22 and FET 24 become reverse biased, and the voltage/phase detection circuit 21 and FET 2
3 is a forward bias. The input voltage changes from O' to point b voltage (
-yV), the Zener diode D3 and the transistor TRI are off, so the FET 23 is turned on. Therefore, current flows in the order of diode D6 - diode D9 - capacitor CI and resistor R5 - diode D8 - FET 23, and the voltage of AC power supply 10 is applied to the resistor R5 side.

When the input voltage e reaches the voltage at point b, the Zener diode D3 and the transistor TRI turn on, so the FET
23 is turned off, and the voltage of the AC chamber 110 is not applied to the resistor R5.

When the voltage in the negative half cycle passes its peak and becomes lower than the voltage at point b' (=yV), Zener diode D3 and transistor TR1 are turned off, so FET23 is turned on again, and diode D6- Current flows in the order of diode D9-capacitor C1 and resistor R5-diode D3-FET23. Furthermore, FET2
3 is off (points b to b'), the charge accumulated in the capacitor C1 is discharged to the resistor R5.

By repeating such operations, a DC voltage with less ripple due to full-wave rectification can be obtained at both ends of the resistor R5.

FIG. 4 shows a circuit diagram of another embodiment of the AC/DC conversion circuit according to the present invention, which is a half-wave rectification step-down circuit.

The resistor R5 is a load resistance, the capacitor C2 is an output smoothing capacitor, the diode D14 is an output rectifying diode, and the diode D13 is an internal diode of the FET 26.

The voltage/phase detection circuit 25 includes resistors R6 and R7, a transistor TR3, a diode Dll, and a Zener diode D.
I2. Resistor R7 is the gate current limiting resistor of FET26, and resistor R6 is the Zener diode D.
The current limiting resistor 12 and the diode Dll are reverse current prevention diodes when the input terminal has reverse polarity, and the transistor TR
3 drives the FET 26 on and off in synchronization with the phase of the input voltage.

FIG. 5 shows an operating waveform diagram of the circuit of FIG. 4.

Assuming that the set voltage of the Zener diode D12 is X (V), when the input voltage e from the AC power supply 10 is from 0 to less than the point a voltage (=xV), the Zener diode D12 and the transistor TR3 are off, so the FET 26 is It's on. As a result, current flows in the order of AC power supply 10, capacitor C2, resistor R5, diode D14, and FET26.

When input terminal e reaches point a, Zener diode D
Since I2 and transistor TR3 are turned on and FET 26 is turned off, input voltage e from AC power supply 10 is not applied to resistor R5.

After passing the voltage peak in the positive half cycle and becoming lower than the voltage at point a' (=xV), the diode D12,
Since the transistor TR3 is turned off, the FET26 is turned on again, and current flows in the order of the AC power supply 10, the capacitor C2, the resistor R5, the diode D14, and the FET26. In addition, during the period when the FET 26 is off (point a to point a'),
The charge accumulated in capacitor C2 is discharged to resistor R5.

Furthermore, when the phase of the input voltage e advances to a negative half cycle, the input terminal e is blocked by the diode 014. By repeating such operations, a DC voltage with less ripple due to half-wave rectification can be obtained at both ends of the resistor R5.

Effects of the Invention Since the present invention is configured as detailed above, it is possible to provide an AC/DC conversion circuit with a small number of circuit components without using a transformer, etc., and the power supply section can be made smaller, lighter, and lower in price. become. Furthermore, since AC power exceeding the voltage set by the voltage/phase detection circuit is not sent to the rectifying and smoothing circuit, a stable voltage can be supplied to electronic equipment even if the input terminal fluctuates.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the principle of the present invention, (a) is a block diagram, (b)
) is a waveform diagram, Figure 2 is a circuit diagram of an embodiment of the AC/DC conversion circuit according to the present invention, Figure 3 is an operational waveform diagram of the circuit shown in Figure 2, and Figure 4 is a diagram of the AC/DC conversion circuit according to the present invention. Other Example Circuit Diagrams: FIG. 5 shows an operating waveform diagram of the circuit shown in FIG. 4, FIG. 6 shows a circuit diagram of a conventional AC/DC conversion circuit, and FIG. 7 shows another conventional example circuit diagram. 10... AC power supply, 11... Rectifier smoothing circuit,
12.21.22.25...Voltage/phase detection circuit, 1
3... Switching element, 23.24.26... FET, 27... Constant voltage circuit, R1-R7... Resistor, T1
...Transformer, Dl, D2, D5~Dll...Diode, D3, D
4, Dl2... Zener diode, TRI~TR
3...Transistor, C1-C4...Capacitor. (bl Moto Kiri ≦ 11! Moon's 11th day figure 1, $21+: Koishi Kanki's Shimogata figure 3 figure 5 θ Moon 1: Koshiroi er Tsume) ri b I row of hills Rometo figure Figure 4 Group 4+: J71I? hard work

Claims (1)

[Claims] AC input from an AC power source (10) is rectified and smoothed by a rectifying and smoothing circuit (11).
) In an AC/DC converter circuit that obtains DC output by rectifying and smoothing it, a voltage/phase detection circuit (
12), and furthermore, a switching element (13) is provided between the AC power supply (10) and the rectifying and smoothing circuit (11), and a switching element (13) is provided between the AC power source (10) and the rectifying and smoothing circuit (11), and a switching element (13) is provided between the AC power source (10) and the rectifying and smoothing circuit (11). An AC/DC conversion circuit characterized in that a switching element (13) is turned on and off by a switch, and an AC input is sent to a rectifying and smoothing circuit (11) during the on period.