DE1438565A1 - Circuit arrangement for obtaining a direct voltage - Google Patents

Description

N 21 437 VIIIb / 21c Hamburg, February 22nd, 1968

NV Philips ¹ Gloeilampenfabrieken Ha-hh

My files: EI / P - 10 PH - 16

"Circuit arrangement for obtaining a direct voltage"

The invention relates to a circuit arrangement for obtaining a DC voltage, the value of which increases with Amplitude of a non-linear clement and a capacitor supplied symmetrical alternating voltage decreases.

In known circuits, a direct voltage is usually obtained by elements with an asymmetrical characteristic curve, e.g. diodes. It is also known to give an element with a non-linear symmetrical current-voltage characteristic an asymmetrical, e.g. to supply pulsed voltage, a DC voltage is obtained in the usual V / ice, which with increasing amplitude of the AC voltage also increases; such a circuit is disclosed in US Pat. No. 2,628,326 in the line deflection section of a television receiver.

A circuit arrangement of the type mentioned at the outset is obtained in which the desired relationship between the two is obtained in a simple manner supplied AC voltage and the withdrawn DC voltage is obtained if according to the invention the element has an at least approximately symmetrical current-voltage characteristic and a bias voltage is supplied to the element.

Possible embodiments of circuits according to the invention are explained in more detail with reference to the drawing.

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

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NfBUQ. Documents (Art 7, Section I, Paragraph 2, No. I, Clause 3 of the Amendment Act of 4.9.1967) ~ ² ~

Fig. 2 shows voltages and currents in a diagram in which. the characteristic curve of the non-linear element is also shown.

FIG. 2 shows the output voltage V _{10 of} the circuit according to FIG. 1 as a function of the chasing voltage V

In Fig. 1, the primary winding of a transformer 1 is connected to the Metz voltage V _nefc . A conventional rectifier circuit, 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, is connected to the secondary winding of this transformer. A direct voltage V therefore arises at the second capacitor 5, which is a positive direct voltage due to the connection of the diode 2 shown in FIG. Naturally, by reversing the diode 2, a negative DC voltage can be obtained on the capacitor 5.

With a tap 6 of the secondary winding of the transformer 1, a second rectifier circuit is connected, which from a voltage-dependent resistor 7 with a symmetrical characteristic curve, E.g. a VDR-VJi standing and a capacitor 8, consists. Usually such a voltage-dependent resistor can only be effective as a rectifier circuit if it has an unbalanced AC voltage is supplied.

According to the invention, a bias voltage is applied via an ohmic resistor 9, a voltage-dependent resistor 7, which also results in a rectifier effect. 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 therefore symmetrical to earth potential. The bias voltage applied to the resistor 7 enables rectification, so that the circuit according to FIG. can be taken.

This can be explained as follows.

Since the part of the lying between the tap 6 and earth

BATHROOM QRiSINAL

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-J-

Secondary winding of the transformer 1, there is almost no DC voltage drop, the DC voltage V at the capacitor 5 is connected to the series connection of the ohmic resistor 9 and the voltage-dependent resistor 7. The DC voltage at the voltage-dependent resistor 7 is referred to below as "Vy _DR . The total voltage V increases proportionally Ratio to V. To, while without AC voltage from the tap 6 the DC voltage V, _7rvD due to the non-linear

V i / n

Characteristic curve of the voltage-dependent resistor 7 with increasing mains voltage V. would increase to a lesser extent.

In the foregoing, the voltage V is assumed to be positive, so that the connection point between the voltage-dependent resistor 7 and the capacitor 8 is positive compared to the connection point between this voltage-dependent resistor 6 and the tap or with other V / orten, the tap 6 is negative compared to the connection point between the resistor 7 and the capacitor 8. As mentioned above, no DC voltage occurs on the part of the secondary winding lying between the tap 6 and earth, so that the DC voltage V _{VDR is} simultaneously a positive DC voltage V =

is on the capacitor 8.

The bias voltage V _V ~ _{R has the} effect that the alternating voltage at the voltage-dependent resistor 7 *, which is brought about by the alternating voltage taken from the tap, 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 example, first _{have assumed a positive voltage equal to the voltage V "~ R} , before the voltage V _vn " at the element 7 between the connection point of the capacitor 8 with the voltage-dependent resistor 7 and the tap 6 has a value equal to Receives zero.

This is illustrated in more detail in Fig. 2, in which the curve 10 the represents known non-linear current-voltage characteristic of the voltage-dependent resistor 7. In the absence of a preload at the voltage-dependent resistor 7 the alternating

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voltage around the vertical axis in Fig. 2, ie around ground potential, fluctuate. The mean value of the current through the capacitor 8 (the capacitance value of the capacitor 8 is selected so large that at the frequency of the alternating voltage used, the impedance of this capacitor is small compared to any possible resistance value of the voltage-dependent resistor 7, so that almost no alternating voltage occurs on the capacitor 8 ), is then equal to zero, so that on average no charge is fed to the capacitor 8 from the alternating current. There can therefore be no question of a rectifier effect in this case.

If, according to the invention, a bias voltage is applied to the voltage-dependent resistor 7, the alternating voltage no longer fluctuates around Srdpotential, but around the potential caused by the bias voltage. As explained above, the voltage at the tap negative with respect to the connection point of the resistor 7 and the capacitor 8, since ke the capacitor 8, ine alternating voltage occurs, l ^ st the bias voltage Vy _DR as the negative bias voltage for the voltage-dependent resistor 7 to be considered.

So it is assumed in Fig. 2 that with an alternating voltage at the voltage-dependent resistor 7 with an amplitude V, a bias voltage V _VDR = V _Q due to the direct voltage V is present. The alternating voltage with the amplitude ν therefore initially fluctuates around a value V _{Q represented} by the line 11 . As a result of the bias voltage V _n alone, a current I _{n would} flow. As a result of the applied alternating voltage V, however, there is also an alternating current, which is represented by the curve I- in FIG. Compared to the values corresponding to the zero crossings of the applied voltage ν, this alternating current I »has a mean value shifted in the negative direction; this means that the capacitor 8 is supplied with a negative charge. Due to the application of the bias voltage is thus obtained for the AC voltage from the tap 6 * a rectifying action by which a more negative voltage is given to the capacitor 8 _•? and the positive DC voltage V originally present at the capacitor is thus reduced. The bias voltage for element 7 is correspondingly reduced to a value V ₀ ^1.

80 98 0 5 / OA36 * ~ ⁵ ~ '

1438566

set so that the alternating voltage finally occurs in the position shown in dashed lines in FIG.

That the portion caused by the rectified AC voltage actually has to be subtracted from the voltage V, can also be viewed as follows. When the tap 6 is positive to earth, the alternating current tends to move away from the tap 6 to flow through the resistance element 7 and the capacitor 8 to earth. This is a positive going stream which supplies the capacitor 8 as it were positive charge.

The current I _Q as a result of the DC voltage V is directed from the choke coil j5 through the ohmic resistor 9> the voltage-dependent resistor 7 and the tap 6 to earth. The current I _Q told the positive part of the alternating current I are thus directed in opposite directions in the voltage-dependent resistor 7 and counteract one another.

If the tap 6 is negative to earth, the alternating current and the current I ₀ in the voltage-dependent resistor 7 are rectified, and Iq and the negative part of the alternating current I support each other. half-wave induced current than caused by the positive half-wave current so that a negative current flows in the means of ³ relative to the by the bias voltage V related alone, having the same direction in the element 7 current has a higher value substantially greater. the capacitor 8 charge is therefore withdrawn until equilibrium is restored at a lower capacitor voltage V.

It follows from the foregoing that the effect remains unchanged if the capacitor 8 and the voltage-dependent resistor 7 are interchanged. In this case the positive part of the alternating current through the series connection of the capacitor 8 and the resistance element 7 is predominant, but this fi will again have the tendency to reduce the charge brought about by the bias voltage V.

^r 'BAD ORIGINAL

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-β-

As long as the voltage V is low, with increasing DC voltage V, the voltage V „ _DR at the voltage-dependent resistor J will increase to a greater extent than the voltage V - V _VDR at the ohmic resistor 9. It follows that if the voltage V increases slightly, the bias voltage V _V _. _R and therefore also the positive voltage V on the capacitor 8 increases faster than the negative voltage part, which is created by rectifying the AC voltage "between the tap 6 and earth with the help of the voltage-dependent resistor 7 and the capacitor 8] there must first be a certain bias" Vy _{DR be} constructed before rectification by means of the last-mentioned part of the circuit can be discussed.

With a further increase in V, however, V _VDR and therefore V increase to a lesser extent and the rectified voltage component has a more pronounced effect.

_{In the embodiment} on which FIG. 2 is based, the voltage at the voltage-dependent resistor J was given by V, mi5 = CI

-ß

where ß = 0.2 and σ = 200 volt amp. The resistor 9 had a value of 100 kOhm. Point 6 was a center tap so that the amplitude of the alternating voltage at this point was half the amplitude of the alternating voltage across the entire secondary winding of transformer 1. With ₁ 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 the tap β was 12.5 volts. _{The current I Q} caused by the direct voltage alone was -0.02 mA, with a voltage of 25.0 volts on the capacitor 8. As a result of the rectification of the supplied alternating voltage, the current was shifted towards larger negative values, the voltage V on the capacitor 8 being reduced.

The resulting voltage V on the capacitor 8 as a puncture of the 'mains voltage V. On the primary side of the transformer 1, the curve 12 shown in Pig »J> finally results. In the vicinity of the capacitor voltage V- this curve shows a decreasing course.

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You can now see the final output voltage V_ of the tap 13 on the resistor 9. When the various elements of the * circuit according to Pig. 1 can be selected such that the nominal mains voltage V _nom includes a voltage V _rl which lies on the sloping branch of curve 12, so it is evident that with the correct position of the tap 13, the voltage V_ is constant when the mains voltage V changes remain; because an increase in voltage V then leads to an equally large decrease in voltage V 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, ohms and the other part has a resistance value of R ₂ ohms, then V can be written for the drawn direct voltage:

VR ₁ + V _rl

R ₁ 4

If the voltage V increases by an amount AV, the voltage V _rl decreases by an amount - Δν _Γΐ . The following can therefore be written for the change AV ₌ the drawn voltage V_:

R ₁ AV - R ₂

R ₁₊ R ₂

It follows from this that Δν_ = 0 when R ₁ AV = R ₂ AV ■, or

By choosing the resistor 9 in such a way that its ohmic value is small compared to the value of the resistor element 7 at relatively lower DC voltage V, but is large compared to that Value at a relatively high DC voltage V, so is

-8th-

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143866 &.

in the case of a changing line voltage V _{net of} the falling type of curve 12, a straight line over a large area. The ratio V is therefore to be considered to be almost constant in this area.

so that the condition found in expression (l) is in this Area can be met.

Therefore, the ratio between the resistance part (R,) of the resistor 9 is between the tap Ij5 and the capacitor 8 and the Uiderstandteil (Rg) between the tap IjJ and the Choke coil 3 equal to the ratio between the voltage change V of the voltage V and the change in voltage V- of the voltage V ,, then V_ = 0 in the range mentioned. In other words, in In this case, the drawn DC voltage V_ is constant in the range mentioned.

The tap 13 can also be selected so that the voltage V_ decreases with increasing mains voltage (tap 13 closer to the connection point of resistor 9 and capacitor 8) or increases with increasing mains voltage (tap IJ> closer to the connection point of resistor 9 and the choke coil 3) ·

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

The resistance element 7 with a non-linear current-voltage characteristic does not always have to be designed as a voltage-dependent resistor. So would a resistor element with a! strongly negative temperature coefficients can be used for this purpose. However, the frequency of the alternating voltage used must then be so low that the resistors with a negative temperature coefficient, which are usually inert, can follow the alternating voltage. The element ¹ J can also be designed as a diode, the anode of which is connected to the capacitor 8 and the cathode of which is connected to the tap. -.

Patent claims:

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Claims (5)

Claim 1. Circuit arrangement for obtaining a DC voltage, the value of which becomes a non-linear one with increasing amplitude Element and a capacitor supplied symmetrical alternating voltage decreases, characterized in that the Element (7) has an at least approximately symmetrical current-voltage characteristic and that the element is biased is fed. 2. Circuit arrangement according to claim 1, characterized in that the connection point between the non-linear element (7) and the capacitor (8) via an ohmic resistor (9) is connected to a direct voltage (V) which is applied to the Series connection of the ohmic resistor (9) and the resistance element (7) is located. 3 circuit arrangement according to claim 2, characterized in that that the direct voltage (V) is obtained by rectifying an alternating voltage, the amplitude of which is proportional to the The amplitude of the alternating voltage is generated by the series connection of the nonlinear element (7) and the capacitor (8) is fed. 4. Circuit arrangement according to claim ^, characterized in that that the direct voltage is greater, preferably double, compared to the amplitude of the alternating voltage. 5. Circuit arrangement according to claim 4, characterized in that that the DC voltage obtained is taken from a tap of the resistor (9), through which this is connected to the part (R.) connected to the capacitor (8) and divided into a part (Rp) connected to the direct voltage (V), and that when the supplied alternating voltage changes in a range around the nominal value, i V = 8098dT5 / 04 ^ 6 [nterlagen {Art. 7 & I Aba. 2 No. I sentence 3 of the Amendment Act. v. 4.9.196 Γ) where V is the increase in direct voltage - (V) and V is the decrease in voltage V across the capacitor (8), so that the direct voltage (V_) taken from the tap is constant in the range mentioned. 809805/0436