DE1438565B2 - CIRCUIT ARRANGEMENT FOR WINNING A / A DC VOLTAGE - Google Patents

Description

Λ V

~ Äv7

40

is fulfilled, where AV the increase in the bias voltage (V), Δ V _r the decrease in the voltage (V _r ) on the capacitor (8), R ₁ the part of the resistor between the tap (13) and the capacitor (8) ( 9) and R _{2 represents} the other part of this resistor (9).

The invention relates to a circuit arrangement for obtaining a direct voltage from one of the series connection of a capacitor and a non-linear element supplied symmetrical first alternating voltage, the direct voltage at the capacitor being removable.

In known circuits, a DC voltage is usually through elements with asymmetrical Characteristic, e.g. B. Diodes, won. It is Z. B. known to generate one of the AC mains voltage independent DC voltage the AC voltage of the series connection of a Zener diode and a condenser (German Auslegeschrift 1 061 886). The amount of generated DC voltage depends exclusively on the Zener diode used in each case. It is also known an element with non-linear symmetrical current-voltage characteristic an asymmetrical, z. B. to supply pulsed voltage, whereby a direct voltage is obtained in the usual way, which also increases with the increasing amplitude of the supplied alternating voltage; such a Circuitry is used in U.S. Patent 2,628,326 in the line deflector portion of a television receiver.

The invention is based on the object of specifying a rectifier circuit that is as simple as possible, depending on the size of the AC input voltage and / or the dimensioning of the circuit as the AC input voltage increases, the DC output voltage either also increases or decreases or remains constant. In the case of a circuit arrangement, this task is carried out at the beginning mentioned type according to the invention achieved in that the element is at least approximately symmetrical Has characteristic curve and that the capacitor is connected to a bias voltage via a resistor, which the amplitude of the first AC voltage is proportional, and that the DC voltage between a Tap of the resistor and that connection of the capacitor is tapped, which is the connection point facing away from the capacitor and resistor.

An embodiment of the invention will be explained in more detail with reference to the drawing.

F i g. 1 shows a rectifier circuit for generating a DC voltage stabilized with respect to mains voltage fluctuations;

F i g. 2 shows voltages and currents in a diagram in which also the characteristic of the non-linear Element is shown;

F i g. 3 shows the output voltage V _{r of} the circuit according to FIG. 1 as a function of the mains voltage

In Fig. 1, a mains voltage V _{et is applied} to the primary winding of a transformer 1. A conventional rectifier circuit is connected to the secondary winding of this transformer, which consists of a diode 2 and a smoothing network, which is formed by a choke coil 3 and two smoothing capacitors 4 and 5. A bias voltage V therefore arises at the second capacitor 5, which due to the in FIG. 1 indicated connection of the diode 2 is a positive DC voltage. Of course, by reversing the diode 2, a negative DC voltage can be obtained across the capacitor 5.

With a tap 6 of the secondary winding of the transformer 1 is a second rectifier circuit connected, which consists of a voltage-dependent resistor 7 with a symmetrical characteristic, z. B. a VDR resistor, and a capacitor 8 consists. Usually such a VDR resistor will only be effective as a rectifier element if it receives an unbalanced AC voltage is fed.

According to the invention, an ohmic; Resistor 9 is applied to the VDR resistor 7, the bias voltage V , which also results in a rectifier effect here. The alternating voltage taken from the tap 6 to earth is, like that on the primary winding of the transformer 1, an exactly sinusoidal alternating voltage and is therefore symmetrical to earth potential. Through the to the

Bias voltage applied to the VDR resistor 7 enables rectification, so that the circuit according to FIG. 1 an initially increasing, then remaining constant and finally decreasing DC voltage can be taken as the line voltage V _{net increases.}

This can be explained as follows: Since almost no DC voltage drops across the part of the secondary winding of the transformer 1 between the tap 6 and earth, the bias voltage V is applied to the capacitor 5 in the series connection of the ohmic resistor 9 and the VDR resistor 7. The DC voltage at the VDR resistor 7 is referred to below as V _VDR . The bias voltage V increases in proportional relation to the mains voltage V _"el, whereas without AC voltage from the tap 6, the DC voltage V _VDR due to the nonlinear characteristic of the VDR resistor 7 _ne with increasing mains voltage V, would increase to always lesser extent.

In the foregoing, the bias voltage V is assumed to be positive, so that the connection point of VDR resistor 7 and capacitor 8 is positive compared to the connection point of VDR resistor 7 and tap 6, or in other words, tap 6 is negative compared to the connection point between that of VDR resistor 7 and capacitor 8. As mentioned above, no DC voltage occurs on that part of the secondary winding located between the tap 6 and earth, so that the DC voltage V _VDR is present at the capacitor 8 at the same time as a positive DC voltage V _r - V _VDR.

The voltage V _{VDR has the} effect that the alternating voltage at the VDR resistor 7, which is brought about by the alternating voltage taken from the tap 6, will not fluctuate symmetrically about earth potential, as would be the case without a bias voltage. The AC voltage at the tap 6 must, for. B. have initially assumed a positive voltage equal to the voltage V _VDR before the voltage V _VDR at the element 7 between the connection point of the capacitor 8 with the VDR resistor 7 and the tap 6 has a value equal to zero.

This is shown in FIG. 2 clarifies in more detail, in which the curve 10 shows the known non-linear current-voltage characteristic of the VDR resistor 7 represents. In the absence of a bias on the VDR resistor 7 would be the AC voltage about the vertical axis in FIG. H. around earth potential. The mean value of the current through the capacitor 8 (the capacitance value of the capacitor 8 is so large chosen that the impedance of this capacitor at the frequency of the AC voltage used is small compared to every possible resistance value of the VDR resistor 7, so that almost none AC voltage occurs across the capacitor 8) is then equal to zero, so that the capacitor 8 on average no charge is supplied from the alternating current. A rectifier effect can therefore in this case be out of the question.

If, according to the invention, a bias voltage is applied to the VDR resistor 7, the alternating voltage no longer fluctuates around earth potential, but around the potential caused by the bias voltage. As explained above, the voltage at the tap 6 is negative compared to the connection point of the VDR resistor 7 and the capacitor 8. Since there is no AC voltage at the capacitor 8, the voltage V _{VDR is to be} regarded as a negative DC voltage for the voltage-dependent resistor 7. Thus, in FIG. 2, provided that with an alternating voltage across the VDR resistor 7 with an amplitude V, a bias voltage V _VDR = V ₀ caused by the direct voltage V is present. The alternating voltage with the amplitude V therefore initially fluctuates around a value V _{0 represented} by the line 11. As a result of the bias voltage F ₀ alone, a current I _{0 would} flow. As a result of the applied alternating voltage V , however, there is also an alternating current which is indicated by the curve I ₁ in FIG. 2 is shown. This alternating current Z ₁ has a mean value shifted in the negative direction compared to the values which correspond to the zero crossings of the applied voltage V; this means that the capacitor 8 is supplied with a negative charge.

As a result of the application of the bias voltage, a rectifier effect results for the alternating voltage from the tap 6, by means of which the capacitor 8 is given a more negative voltage, and the positive direct voltage V _r originally present on the capacitor is thus reduced. Correspondingly, the bias voltage for the VDR resistor 7 is also reduced to a value V ₀ , so that the alternating voltage is finally in the range shown in FIG. 2 position shown by dashed lines occurs.

That the portion caused by the rectified AC voltage actually has to be subtracted from the voltage V _r can also be seen as follows:

When the tap 6 is positive to earth, the alternating current flows from the tap 6 via the VDR resistor 7 and the capacitor 8 to earth. This is a positively directed current which, as it were, supplies the capacitor 8 with a positive charge. The current / ₀ as a result of the bias voltage V is directed from the choke coil 3 via the ohmic resistor 9, the VDR resistor 7 and the tap 6 to earth. The current / ₀ and the positive part of the alternating current / are thus directed in opposite directions in the VDR resistor 7 and counteract one another. If the tap 6 is negative to earth, the alternating current and the current / ₀ in the VDR resistor 7 are rectified, and I ₀ and the negative part of the alternating current / support each other. Because of the non-linear characteristic of the VDR resistor 7, the current caused by the negative alternating voltage half-wave is significantly greater than the current caused by the positive half-wave, so that on average a negative current flows, which compared to that caused by the bias voltage V alone, in VDR resistor 7 the current pointing in the same direction has a higher value. Charge is therefore withdrawn from the capacitor 8 until equilibrium is again established at a lower capacitor voltage V _r.

It follows from the foregoing that the effect remains unchanged if the capacitor 8 and the VDR resistor 7 are interchanged. In this case the positive part of the alternating current through the series connection of the capacitor 8 and the VDR resistor 7 is predominant, but this will again reduce the charge brought about by the direct voltage V _r. As long as the bias voltage V is low, at

increasing bias voltage V, the voltage V at the _VDR VDR resistor 7 to a greater extent to increase as the voltage V- V _VDR across ohmic resistor 9. It follows that, with little increasing bias voltage, the DC voltage V _VDR and, therefore, the positive voltage V _VDR = V _r at the capacitor 8 increases faster than the negative voltage part which is produced by rectification of the alternating voltage between the tap 6 and earth with the aid of the VDR resistor 7 and capacitor 8, on further increase the bias Kaber takes therefore V _VDR and V _r always to a lesser extent, and the rectified voltage component has a more pronounced effect.

In the FIG. 2 embodiment, underlying the voltage at the VDR resistor 7 was given by V = CI _VDR, with β = 0.2 and C = 200 Volt Amp. ~ ^{Were>. The resistor 9 had a value of 100 k ohms. Point 6 was a center tap, so that the amplitude of the first alternating voltage at this point was half the amplitude of the second alternating voltage across the entire secondary winding of transformer 1. With peak rectification by means of diode 2 and the associated smoothing network, the direct voltage V had a value of 25 volts, while V at tap 6 was 12.5 Volts. If the tap 6 were not in the middle of the winding, but at its lower end, so that the AC voltage at the VDR resistor 7 would be zero, then the bias voltage of V = 25 volts alone _{would result in a current J 0} of -0.02 mA caused and a voltage of 23 volts occur across the capacitor 8. By rectifying the alternating voltage of 12.5 volts supplied from the center tap, the current was shifted towards larger negative values, the voltage V _r on the capacitor 8 being reduced.

The resulting voltage V _r on the capacitor 8 as a function of the mains voltage V _ne on the primary side of the transformer 1 finally results in that in FIG. 3 curve 12. In the vicinity of the capacitor voltage V _n , this curve shows a falling course.

A final DC output voltage V— can now be taken from the tap 13 at the resistor 9. When the various elements of the circuit of FIG. 1 can be selected in such a way that the nominal network voltage V _{om is associated with} a voltage V _n which is on the sloping branch of curve 12 in FIG. 2, it is evident that, given the correct position of the tap 13, the DC output voltage V- remains constant when the mains voltage V "_e"changes; because an increase in the bias voltage V then leads to an equally large decrease in the voltage V _r and vice versa.

The correct position of the tap 13 can be calculated as follows: If the part of the resistor 9 between the tap 13 and the capacitor 8 has a resistance value of R ₁ ohm and the other part has a resistance value of R ₂ ohm, then for the drawn direct voltage V. - be written:

V = =

VR ^ V _n R ₂ R ₁ + R ₂

If the voltage V increases by an amount ΔV , the voltage V _rl decreases by an amount - AV _n . For the change Δ V- can therefore be written:

R ₁ AV-R ₂ AV _n

AV ₌ =

R ₁ + R ₂

It follows that AV = = 0 when R ₁ AV RV id

= R ₂ I V _n

is or

W _ __ ^ _
AV _n ~ R ₁

R ₇

By such a choice of the resistor 9, that its ohmic value is small compared to the value of the VDR resistor 7 at relatively small bias voltage, however, is large compared to this value when a relatively large bias voltage V, _et at varying supply voltage V "of the sloping Branch of curve 12 over a large area

straight line. The relationship

Δ V

is therefore in

this range is to be regarded as almost constant, so that the condition found in expression (1) in this area can be met.

Therefore, the ratio between the resistance part R _{1 of} the resistor 9 between the tap 13 and the capacitor 8 and the resistance part R ₂ between the tap 13 and the choke coil 3 is equal to the ratio between the voltage change AV of the bias voltage V and the voltage change AV _{n of} the voltage V _n , then A V- = 0 in the range mentioned. In other words, in this case the DC voltage K_ taken is constant in the range mentioned.

The tap 13 can also be selected in such a way that the DC output voltage K_ with increasing Mains voltage decreases (tap 13 closer to the connection point of resistor 9 and the capacitor 8) or increases with increasing mains voltage (tap 13 closer to the connection point of the resistor 9 and the inductor 3).

It is evident that, by reversing the diode 2, a resulting negative voltage V _r with a profile similar to that shown by the curve 12 can be achieved.

The resistance element 7 with a non-linear current-voltage characteristic does not need a voltage-dependent one Resistance, e.g. to be a VDR resistor. So would a resistance element too can be used with a strongly negative temperature coefficient. However, the frequency must be the one used AC voltage are so low that the resistors with a negative temperature coefficient, which are mostly sluggish and can follow the alternating voltage.

1 sheet of drawings

Claims (5)

Patent claims: 1. Circuit arrangement for obtaining a DC voltage from a symmetrical first AC voltage supplied to the series connection of a capacitor and a nonlinear element, the DC voltage being removable at the capacitor, characterized in that the element (7) has an at least approximately symmetrical characteristic curve and that the capacitor ( 8) via a resistor (9) to a bias voltage (V) which is proportional to the amplitude of the first alternating voltage, and that the direct voltage is tapped between a tap of the resistor (9) and that terminal of the capacitor (8), which is the The connection point of the capacitor (8) and resistor (9) faces away. 2. Circuit arrangement according to claim 1, characterized in that the element (7) is a VDR resistor is provided. 3. Circuit arrangement according to claim 1, characterized in that the bias voltage (V) is achieved by rectifying a second alternating voltage, the amplitude of which is proportional to the amplitude of the first alternating voltage. 4. Circuit arrangement according to claim 3, characterized in that the bias voltage (V) is greater than the amplitude of the first alternating voltage, preferably twice as large. 5. Circuit arrangement according to one of claims 1 to 4 for generating one of the Amplitudes of the two alternating voltages independent direct voltage, characterized in that that the tap (13) of the resistor (9) is chosen so that the relationship