FI60626B - STROEMKAELLA - Google Patents

Description

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JfägTfa ^ () UTLÄGGN I NGSSKRI FT 60626 C Patent granted 10 02 1932

Patent «seddelat ^ τ ^ (51) Kv.ik? /Int.ci.3 H 02 M 5 / 3Ί5ί 3/335 SUOMl-FINLAND (21) Pat« nttlhik «mut - PatancantSknlng 792517 (22) Hikemlipilv» —An » öknlog * d »g 1 ^ .08.79 '' (23) Alkupilvi — Glltlghetsdag ll» .08.79 (41) Tullut fulkiaektl - Bllvlt offantilg Qg g.

Patent and Registration Office .........

', (44) Date of issue | -

Patent- oeh registerstyrelsen Anaökan utiagd och uti. * Krift * n pubikend 30.10.8l (32) (33) (31) Requested priority — Begird prloritet (71) Salora Oy, Salorankatu 5-7, 21 + 100 Finland (FI) (72) Ismo Pyörre, Märynummi, Heikki Lehtinen, Turku, Finland-Finland (Fl) 7M Berggren Oy Ab (5 * 0 Power supply - Strömkälla

The present invention relates to a power supply comprising a transformer with primary and secondary windings, wherein the primary winding is connected in series with an electronic switch which is opened and closed at a certain frequency to provide a pulsating primary current, and at least one rectifier element is connected in series with the secondary winding.

For example, in a television set or other similar device having both an image display section and an audio power stage, the operating voltage of the audio power stage is often taken directly from the line power stage or the power supply of the line power stage for cost reasons. As a result, the load fluctuations of the audio power stage easily affect the size and / or brightness of the image.

Various means have been used to eliminate this disadvantage: 1. Class A sound power stage: The disadvantage is continuous power consumption.

2. Separate own power supply for the audio output stage: The disadvantage is the expensive construction.

3. Loose connection to the power supply of the video display section: The disadvantage is the high output impedance, which results in a low sound power.

2 60626 4. Image Resizing Compensation: Compensation circuits exhibit time constants that can even exacerbate image resizing with certain types of sound loads. In addition, compensating for a change in width often increases a change in brightness, and vice versa.

Other power supply connections with a switching element mentioned in the introduction, mainly a transistor or a thyristor, also have disadvantages. The disadvantage of using a transistor is mainly the losses at the time of switching, which occur as the transistor heats up, and when using a thyristor, it is difficult to obtain a sufficiently efficient switch-off current at high currents.

For example, in the circuits of U.S. Patent 4,017,784 and SE Patent 208,927, the primary switch is turned off by a resonant circuit on the primary side. At the same time, the pole voltage of the primary winding of the transformer differs from that of a rectangle and is thus not suitable for a circuit which in itself causes the current of the primary switch to commutate. During commutation, the current of the primary switch must not be reduced, so a circuit must be developed that loads the primary switch only during its positive half-cycle.

The object of the present invention is to solve these problems, and to achieve this the invention is characterized in that the secondary circuit is formed as a tuned rectifier by a capacitor connected to the secondary winding, the value of which is selected so that the secondary winding current is cut off at low current winding.

The invention will now be described in more detail by way of example with reference to the accompanying drawings, in which Figure 1 schematically shows the line termination of a television receiver with video and audio power sources, Figure 2 shows curves related to the description of Figure 1, Figure 3 shows a similar power supply with only one load circuit a similar case when the switching element is a transistor, and Fig. 5 shows a power supply connection with two switches operating in phase.

The circuit according to Figure 1 contains the following components: M = isolating transformer, = mains rectifier, = filter capacitor, SCR ^ -D2 = primary switch, = transformer primary winding, N2 = transformer secondary winding, from which the diode is rectified to capacitor C2 = filter choke, = filter capacitor.

FI-55278 discloses a connection of a television receiver in which the switch is implemented with a transistor. Figure 2 shows the current of the primary switch formed by SCR1-D2 without the sound coax and J1b the same current as the sound load in the circuit according to said patent 55278 when the switch is implemented with a transistor.

on eo. the switch voltage, U2 is the secondary voltage of the transformer, I2 is the current of the secondary winding N2 at the sound load and is the voltage of the capacitor C2.

The operation is as follows: When the primary switch SCR ^ conducts, there is a rectified DC voltage from the network of C ^ in the windings. In this case, the N2 terminals have a voltage according to the N1-N2 conversion ratio, so that the anode of D1 has a positive voltage. If U2 is greater than U ^ r the diode will start to conduct. In this case, C2 is connected via N2 to the node of N2. Since there is always a coupling coefficient of some magnitude between N 1 and N 2, which is O., it sees the coupling of the stray inductance formed by the coupling coefficient and the capacitance of C2 reduced by the conversion ratio in series. In this case, a step voltage is applied to the series-connected L-C circuit, whereby a Blue current is formed in this circuit, I2 · Since the connection takes place via a diode, the circuit is only able to oscillate for one half cycle, ie energy is transferred from the primary to capacitor C2.

Then the pole voltage of the capacitor C2 increases according to the curve of Fig. 2 with time t - ^ - t ^ · This "ripple" of U ^ is filtered with low pass L1C3 ·

In Figure 2, curve I. _ shows the conductive time t.-t_, la ± 3 of the primary switch, after which the current is transferred to the parallel diode D2 for time t ^ -t ^, after which at time t ^ the primary switch opens. Since the primary switch here is a thyristor, its current must be switched off for the release time required by the thyristor.

This is time t ^ -t ^. In order for the operation to continue undisturbed, the current of the sound coil N2 must be switched off at the moment t ^ · This can easily be achieved by selecting C2 of a suitable size, i.e. by forming a secondary circuit tuned by N2 and C2 so that I? break at the moment t? or before.

4,60626

Since the energy of the image load also occurs when the primary switch conducts to the stray inductance between N 1 -N 2, this charge remains constant if the primary terminal voltage remains constant. The primary terminal voltage depends on the mains voltage, the loss of resistance and the base voltage of the SCR.

The mains voltage remains essentially unchanged despite the variations in sound load in question. The voltage drop of the N 2 resistor has to be kept small just to prevent heat generation, so it is irrelevant. The grounding voltage of SCR ^ is constant because it is a thyristor. Thus, the current of N2 can vary between t ^ -t3 without changing the image size.

In practice, values have been measured in which the sound load has varied between zero and twice the image load values without interfering with the image.

The solution according to the invention can also be applied to a power supply other than a television audio output stage.

In the case described above, the winding induces the commutation current of the thyristor SCR1 in the primary of the transformer. If there is only one load circuit, as shown in Fig. 3, a separate commutation circuit is constructed in a known manner, which in the figure consists of a second thyristor SCR2 and an inductance L2 and a capacitor. Again, the tuned rectifier according to the invention offers the considerable advantage that the thyristor can be switched off at low current values, which makes the commutation circuit simple and inexpensive.

Figure 4 shows a corresponding situation when the switch is a controlled transistor T1, i.e. it is a so-called, switch current source. Switching losses can now be minimized by re-tuning the switching moment to occur at low transistor currents. If desired, the switching moment can be determined, for example, by feedback taken from the secondary circuit by means of logic, so that the current of the transistor is substantially zero at the moment of switching.

Finally, Figure 5 shows an alternating current power supply for higher powers, for example a welding power supply. The connection is the same as above,

Claims (6)

A power supply comprising a transformer (M) with a primary and a secondary winding (N 1, N 2, N 2), the primary winding (N 2) being connected in series with an electronic switch (SCR 2; T) which is opened and is closed at a certain frequency to produce a pulsating primary current, and at least one rectifier element (D1) is connected in series with the secondary winding (N2) to generate a rectified output voltage (U1), characterized in that the secondary circuit is the value of which is selected so that the current of the secondary winding (N2) is cut off by the rectifier element (D1) at the moment when the current of the primary winding (N2) is small. 2. The power supply according to claim 1, wherein the primary-side switch has taken a thyristor (SCR ^), characterized in that the secondary-side capacitor (C2) is selected such that the secondary coil (N2) of the current goes to zero slightly before the thyristor has the commutation. A power supply for a television receiver according to claim 2, wherein said transformer (M) is formed by a line transformer, characterized in that the receiver's image load and sound load are connected to two different secondary windings (N2, N3) of the line transformer and the tuned rectifier is N2). 4. The power supply according to claim 1, wherein the primary-side switch is implemented by a transistor (T), characterized in that the secondary circuit of the transistor is taken from feedback control to open at a time when the secondary coil (N2) of the current is zero or close to zero. Power supply according to one of the preceding claims, the primary circuit of which comprises two alternating electronic switches 660626 (SCR 1, SCR 2) / characterized in that the respective two secondary circuits of the transformer are formed as tuned rectifiers and their rectified outputs are connected together. 5 60626 but on the primary side there are two alternately controlled thyristors SCR ^ and SCR ^ and on the secondary side there are respectively two tuned rectifiers with a common resonant frequency determining capacitor C2 · Power supply according to Claim 5, characterized in that the excitation capacitor (C2) of the secondary circuit is common to both secondary windings.