RU2451384C1 - Transformerless dc power supply source - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: transformerless DC power supply source comprises two parallel connected half-wave circuits from serially connected diode and accumulating capacitor, operating in turns from positive and negative half-periods of AC network voltage, accumulating capacitors in which are connected with one pole of the filter capacitor via separating diodes, and with the other pole - via thyristors, control electrodes of which are connected to phase and zero conductors of the network, to which half-wave circuits are also connected via stabilitrons of alternate start-up of thyristors. An overvoltage protection stabilitron is connected in parallel to the low pass filter capacitor. Design simplification is related to exclusion of a step-down transformer from the low-voltage DC power supply source connected to the AC network. Accounting of power carried out with the help of an electric counter of active power will only show around 20% from the actually consumed power in the proposed circuit, since the latter is a complex load for an AC circuit with a dominant portion of a reactive component of a capacitance power.

EFFECT: design simplification and substantial reduction of an active component of consumed power.

2 dwg

Description

The invention relates to electrical engineering and can be used as a simple and economical source of low voltage direct current connected to an alternating current network.

In household appliances, low-voltage direct current sources connected to an alternating current network of 220 V 50 Hz are widely used. The main elements of such sources are step-down transformers, rectifier circuits and low-pass filters [1].

One of the disadvantages of such devices is the use of step-down transformers in them.

The specified disadvantage is eliminated in the claimed technical solution.

The aim of the invention is to simplify the design and a significant reduction in the active component of the energy consumed from the AC source compared with DC energy in an active load.

These goals are achieved in the inventive transformerless DC source containing half-wave rectifiers and a low-pass filter capacitor, characterized in that it includes two parallel half-wave circuits of series-connected diodes and a storage capacitor, operating alternately from the positive and negative half-periods of the alternating voltage of the network, storage capacitors in which they are connected to one pole of the filter capacitor through isolation diodes, and to the other the opposite pole — through thyristors, the control electrodes of which are connected to a network AC source — respectively to its phase and neutral conductors, to which the above half-wave circuits are also connected via zener diodes of alternating triggering of thyristors, in addition, a zener diode is connected in parallel to the low-pass filter capacitor overvoltage.

Achieving these goals is explained by the absence of a step-down transformer source in the circuit, as well as by the complex nature of the device for an AC voltage source in which the share of the reactive (capacitive) component is dominant.

The device diagram is shown in Fig. 1, and its effect is illustrated by the voltage diagrams presented in Fig. 2.

The source schema includes the following elements:

D ₁ - rectifying diode of the first charging circuit,

C ₁ - storage capacitor of the first charging circuit,

D ₂ - rectifying diode of the second charging circuit,

C ₂ - storage capacitor of the second charging circuit,

D ₃ - dividing diode of the second charging circuit,

D ₄ - dividing diode of the first charging circuit,

T ₁ - thyristor of the second charging circuit,

T ₂ - thyristor of the first charging circuit,

S ₁ is a zener diode of the thyristor T ₁ start _{of the} second charging circuit,

S ₂ is a zener diode of the thyristor T ₂ start _{of the} first charging circuit,

C ₃ - low-pass filter capacitor,

S ₃ - Zener diode on the capacitor C ₃ .

Consider the action of the claimed device.

An alternating voltage of the electric network (Fig. 2, a) with a period T and an amplitude U _{o is} applied through the triggering zener diodes S ₁ and S ₂ to parallel connected half-wave rectifier circuits from rectifier diodes D ₁ (D ₂ ) and storage capacitors C ₁ (C ₂ ) respectively. The latter are charged alternately from the positive and negative half-waves of the AC alternating voltage to the amplitude values of U _o during the time of a quarter of the T / 4 period, as can be seen from Fig. 2, b and 2, c. The discharge of these capacitors through the corresponding isolation diodes D ₄ (D ₃ ) and thyristors T ₂ (T ₁ ) to the low-pass filter capacitor C ₃ takes place alternately: when the charge of the storage capacitor C ₁ occurs in the first quarter of the positive half-wave of the mains voltage and then remains unchanged and equal to U _o until the time instant (T / 2) + Δt ₁ , as can be seen in Fig. 2b, from the indicated time instant, the storage capacitor C ₂ is discharged to the low-pass filter capacitor C ₃ , on the contrary, during charging from negative half IRS mains voltage storage capacitor C ₂ discharge occurs from the storage capacitor C ₁ to the low pass filter capacitor C _3. Moreover, the discharge of the storage capacitor C _{1 is} carried out at the opening of the thyristor T ₂ , and for the discharge of the storage capacitor C ₂ opens the thyristor T ₁ . These thyristors are alternately opened by control voltages generated on the trigger zener diodes S ₂ and S _1, respectively.

Timing diagrams of voltages at the storage capacitors u _C1 (t) and u _C2 (t) are presented in Fig. 2, b and 2, c. When the mains voltage reaches a certain small level corresponding to the breakdown voltage of the triggering zener diodes S ₁ for the positive half-cycle and the triggering zener diode S2 for the negative half-cycle, the thyristors T ₁ and T _2, respectively, open after a time interval Δt ₁ . The discharge of the storage capacitors C ₁ and C ₂ alternately and in the corresponding half-periods of the mains voltage to the low-pass filter capacitor C ₃ occurs quickly during the time Δt ₂ , as can be seen in Fig. 2, d. The frequency of the charges of the capacitor C ₃ is 2F = 2 / T.

It is important to note that the capacitance of the low-pass filter capacitor C _{3 is} chosen many times greater than the capacitance of the storage capacitors C ₁ and C ₂ , as follows from the relation C ₃ >> C ₁ = C ₂ . It is easy to understand that in this case, the voltage U _H on the capacitor of the low-pass filter C ₃ is significantly less than the amplitude of the mains voltage U _o . Indeed, the energy of the charged storage capacitor W ₁ is known, given by the expression W = C _{1 1} U _o ^2/2. In view of the inequality C ₁ >> C ₃ can assume that during the discharge of the storage capacitor in the lowpass filter capacitor practically all the energy W ₁ is transmitted to the capacitor lowpass filter, whose energy becomes approximately equal to W ₃ ≈C _F U _H ^2/2. This implies the value of the so-called voltage transformation coefficient in such a circuit, equal to k = U _H / U _o ≈ (C ₁ / C ₃ ) ^1/2 .

The value of the capacitance of the storage capacitors C ₁ and C ₂ determines the power of the DC source P = FC ₁ U _o ² ≈U _H ² / R _H , where R _H is the load resistance (Fig. 1). Average current in the load I = U _{H CP} / R _n (see Fig. 2).

When the load is disconnected, the voltage across the low-pass filter capacitor C ₃ will increase, and this low-voltage electrolytic type capacitor may fail due to breakdown. In order to prevent the risk of destruction of this capacitor, a zener diode S ₃ with a breakdown voltage (stabilization) somewhat higher than the rated voltage U _{H is} installed in parallel with it. Therefore, when the load R _H is connected, this zener diode does not work (it is non-conductive). The working current through the Zener diode S ₃ with the load off should be of the order of current I.

Consider an example implementation of the inventive device.

Let the device be connected to a network voltage of 220 V, while U _o = 310 V. If the capacitances of the storage capacitors are chosen equal to C ₁ = C ₂ = 30 μF with an operating voltage of 400 V, then to obtain the output voltage U _H = 12 V, the filter capacitor capacity low frequencies C ₃ should be chosen equal

C ₃ = C ₁ (U _o / U _n ) ² ≈20000 μF. The power of such a power source with a voltage of 12 V is equal to P≈144 W, dissipated in the load R _n = 1 Ohm (current in the load is 12 A).

The calculations showed that this circuit for an AC voltage source is a complex load, the active component of the energy consumed which is significantly less than the reactive (capacitive) with a ratio of approximately 1: 4 and, therefore, an active energy meter, usually installed in apartments and private houses of citizens, will show only 20% of the actually consumed energy from the AC network. Indeed, when the mains voltage reaches its maximum (U _o value), the current in the storage capacitor is zero, although it is maximum in the case of a purely active load. The correct accounting of the electric current energy consumed from the network is possible when installing an additional series-connected reactive energy meter. If electric motors with small cosφ operate in the same room together with the circuit under consideration, full or partial compensation of reactances (capacitive and inductive) is possible, and energy metering by an active energy meter will be more correct.

Additional electronic filtering of the output DC current is possible using well-known circuits.

The inventive device may find demand among developers of household electronic devices - televisions, computers, music centers, cordless phones, LED matrix lights, etc.

The claimed technical solution should be patented in major foreign countries for reasons of economic feasibility.

Literature

1. 750 practical electronic circuits. Reference Guide Ed. R. Phelps, per. from English V.A. Loginova, M., Mir, 1986, pp. 3-40.

Claims (1)

A transformerless DC source containing half-wave rectifiers and a low-pass filter capacitor, characterized in that it includes two parallel half-wave circuits of series-connected diodes and a storage capacitor, operating alternately from the positive and negative half-periods of the AC voltage, the storage capacitors in which are connected to one filter capacitor pole through isolation diodes, and with the other pole through thyristors controlling the electrodes of which are connected to the AC alternating current source, respectively, to its phase and neutral conductors, to which the above half-wave circuits are also connected via zener diodes of alternating triggering of thyristors, in addition, a surge protection diode is connected in parallel to the low-pass filter capacitor.

Images