DE3912849A1 - Electrical power supply unit - Google Patents

Abstract

An electrical power supply unit having at least one output has a transformer (10) to whose primary winding (11) a voltage is applied, which voltage is pulsed by means of a controllable switch (13). Two outputs (16, 17) are connected to the secondary winding (15), the transformer (10) being operated as an isolating transformer (flyback converter) for the voltage at the first output and as a forward converter for the voltage at the second output. The discharge time of the transformer (10) can be varied in order to control the isolating transformer output voltage. <IMAGE>

Description

The invention relates to a power supply device according to the preamble of claim 1.

For power supplies, i.e. for devices for power supply ins special from electronic consumers, Trans formers used with a galvanic door Entry and exit can be achieved. The trans formers are generally used in flyback or used in forward converter operation. In both cases Operating modes are in the primary circuit of the transformer lying electronic switch, which in general is a transistor, at a certain clock frequency on and off, causing the input direct current clocked is interrupted. In flow converter operation is the secondary winding of the transformer poled so that the transistor over during its conducting phase the transformer is loaded with the consumer.  

If the transformer can be operated as a flyback converter there is a diode on the secondary side, the one with the appropriately polarized secondary winding so acts that during the turn-on time of the transistor the consumer is not supplied with electricity, so that during this switch-on time in the core of the transformer magnetic energy is stored, which is in the off switching state of the transistor via the consumer ent can load, see Macek, switching power supplies, motor control genes and their special components, Dr. Alfred Hüthig, Hüthig-Verlag Heidelberg, 1982, pages 27 and ff.

There is the possibility to go to the secondary side Formation of a so-called multi-output converter several outputs ge to connect. Different voltages removed at the exits, e.g. 5 V and 12 V. The Regulation of these output voltages is only common possible.

Due to regulations regarding tolerances for the voltage or power supply of certain But consumers are still required to start to regulate voltages individually. Such regulations are not known.

The object of the invention is therefore a power supplier to create equipment of the type mentioned at which have two outputs, both separated are controllable from each other.

This object is inventively characterized by nenden features of claim 1 solved.  

Further advantageous embodiments of the invention are can be found in the subclaims.

With non-regulated output for flyback converter operation and Neglecting losses is the stress time area on the primary side equal to the voltage time area the secondary side. The following applies:

A _prim = A _sek (1)

Furthermore:

A _sek = U _Fly × t _Fly (2)

Here mean:

A _prim = primary voltage time area
A _sek = secondary voltage time area
U _Fly = fly back voltage
t _Fly = fly back time.

From equation (2) it follows:

U _Fly = A _sek / t _Fly . (3)

From equation (3) it can be seen that the voltage U _{Fly can be} changed or controlled by changing the time T _Fly . There are two ways to do this:

It is possible on the secondary side in the flyback converter powered working output an electronic switch insert that connects the output to ground so that the transformer can discharge to ground.  

There is also the option of discharging the energy stored in the magnetic core on the primary side. For this purpose, two transistors are switched on in the primary circuit in such a way that one transistor is provided in front of and the other transistor behind the primary winding of the transformer. Both transistors are switched on or off at the same time for clocking, and one of the two transistors is switched on to control the output voltage U _Fly or the time t _Fly , while the other transistor remains in the switched-off position. As a result, the magnetic energy stored in the core can discharge on the primary side via the switched-on transistor.

Starting from the voltage U _Fly , the short circuits of the secondary or primary winding effecting transistors are then practically controlled, whereby the amount of voltage U _Fly can be regulated by the switch-on duration or the start of the switch-on time.

Using the drawing, in which some embodiments of the invention are intended to be the invention as well as further advantageous refinements and improvements stations of the invention explained and described in more detail will.

It shows:

Figs. 1 to 3 each shows a circuit arrangement in which the invention is implemented, and

Fig. 4 four voltage-time diagrams, with a voltage-time diagram ( Fig. 4a) shows the unregulated state.

Reference is made to FIG. 1.

The circuit arrangement has a transformer 10 , the primary winding 11 of which is in a circuit which holds a rectifier diode 12 and a transistor 13 , which is controlled by a suitable controller 14 . At the junction of the diode 12 with the secondary winding 11 of the transformer 10 , a smoothing capacitor 15 is connected, one connection of which is connected to the cathode of the diode 12 and the other connection to ground.

At the secondary winding 15 a , a first output 16 and a second output 17 are connected, of which the output 16 is connected to one end of the secondary winding. A diode 18 and a choke 19 are connected to this end of the secondary winding; at the connection point of the diode 18 with the choke 19 there is another diode 20 which is connected to ground in the reverse direction. At the Ver connection point of the output terminal 16 with the choke 19 , a smoothing capacitor 21 is connected to ground.

The other end of the secondary winding 15 a is connected via a diode 22 in the reverse direction to a short-circuit transistor 23 ; the anode-cathode path of a diode 25 with the output terminal 17 is connected to a tap 24 of the secondary winding 15 ; between the cathode of the diode 25 and the output terminal 17 there is a smoothing capacitor 26 which is connected to ground.

Both at the output 16 , at which the transformer 10 is operated in flow mode, as well as at the output 17 , at which the transformer 10 is operated in flyback mode, a supply voltage can be removed, whereby the voltages can be regulated individually. It is to be added that a tap 26 a is provided approximately in the middle between the tap 24 and the connection connected to the output terminal 16 from the secondary winding , which is switched to ground ge.

When the short-circuit transistor 23 is switched off, the circuit operates as follows:

The Durchflußwandlerbetrieb is unproblematic extent table, as at power up of the transistor 13, the Tran sistor 13 is charged with an input connected to the terminal 16 consumers. This results in the voltage U ₁ at terminal 16 .

During this switch-on time of the transistor 13 , electromagnetic energy is stored in the core of the transformer 10 , which can discharge in the switched-off state of the transistor 13 via the connecting terminal 17 . The energy flows through the diode 25 into the capacitor 26 serving as a buffer, and thus the voltage at the connecting terminal 17 can be removed in flyback converter mode. This case is shown in Fig. 4a. It can be seen in the on state of the transistor 13, the voltage time area A ₁ (flow converter operation) and in the off state of the transistor 13, the voltage time area A ₂ (flyback mode). The voltage time area A ₂ determines the voltage U ₂ , with the duration t _Fly , based on the relationship U ₁∼ A ₁ and U ₂∼ A ₂ / t _Fly .

When the transistor 23 is turned on, part of the magnetic energy stored in the core of the transformer 10 can be discharged via the diode 22 and the transistor 23 in the on state from the time t _x , so that, as shown in FIG. 4d it is obvious that the voltage U _{2 is} increased with the same voltage time area A ₂ . The voltage level U ₂ is changed depending on the time t _x . Thus, if t _{Fly is made} smaller, U ₂ becomes higher, and vice versa.

The embodiment of FIG. 2 is similar to that of FIG. 1. The essential difference is that the Tran sistor 23 is connected to the connection point of the diode 25 to the terminal 17, so that the discharge of the stored in the transformer 10 power over the capacitor 26 is carried to earth, whereby the voltage U _Fly according to FIG. 4b is again achieved.

At point 24 , the secondary winding 15 a is divided under. It is assumed for explanation that the entire secondary winding has 15 turns, whereas the tap takes place at 12 turns, where 12 volts are removed. This data can of course be changed by suitable dimensioning of the secondary winding and the tap point and is therefore only an example.

If the transistor 23 is switched off, then only the 12-turn circuit is active and accordingly only 12 volts can be drawn off at the terminal 17 . If the 15-turn circuit 15 b is switched to 12 volts when the transistor 23 is switched on, this leads to the fact that the output of the 12-turn circuit leads 9 volts accordingly to the turn ratio. So that he keeps a gradation of the voltage time area A ₂ when switching on the transistor 23 ; this increases U ₂ and because of the peak value formation by the capacitor 26 , this voltage remains practically constant even over the stepped gap. The current flows practically during the entire freewheeling phase, once from the 12-turn circuit and once from the 15-turn circuit. The current flow time in the capacitor 26 is thus lengthened, whereby the effective current, which loads the capacitor 26 , is reduced. This has no influence on the level of the voltage. Thus, by changing the time t _x at which the transistor 23 is switched on, the voltage U _{2 is} increased or decreased, ie because it is also regulated.

The other possibility, as shown in FIG. 4c, is to let the transistor 23 first be switched on, whereby a corresponding gradation of the voltage time area is generated. When the transistor is turned off at t _x 23, then increases the upper value of the voltage U ₂ at the time t _x, and thus can be used in a corresponding manner (peak value) when removed, to the terminal 17 voltage U ₂ to be regulated.

The voltage time areas A ₁ and A ₂ are the same and constant.

Fig. 3 shows a further embodiment of the inven tion.

The diode 12 and the smoothing capacitor 15 are located on the primary side of the transformer 10 . On both sides of the primary winding 11 , a transistor 30 and 31 are connected, of which the transistor 31 connects the primary winding 11 to earth. Furthermore, freewheeling diodes 32 are provided for the transistor 30 and 33 for the transistor 31 , the task of which is explained below. One end of the secondary winding 15 a of the transformer 10 is connected to an output terminal 34 , while the other end of the secondary winding 15 a is connected via a reverse-connected diode 35 and a choke 36 to earth 37 . between the connection point of the diode 35 with the inductor 36 on the one hand and to the terminal 34 on the other hand, a Zener diode 38 is switched to keep the voltage taken off at the terminal 34 constant. At the connection point of the diode 35 with the corresponding end of the secondary winding 15 a branches off to the terminal 39 leading conductor branch 40 , in which a diode 41 is switched on; a smoothing capacitor 42 is connected between the connection point of the diode 41 with the connecting terminal 39 on the one hand and the connecting terminal 34 on the other hand; another smoothing capacitor 43 between terminal 34 and ground 37 is in series with capacitor 42 .

The mode of operation of the circuit arrangement according to FIG. 3 is as follows:

First, the two transistors 30 and 31 are closed. As well as the transistors 31 and 30 go into the conductive state, a voltage is supplied to the load or to the consumer via the inductor 36 , the diode 35 and the secondary winding, the flow converter operation being given in this moment. If the two transistors 30 and 31 are in the off position, that is to say in the blocking state, then the electromagnetic energy stored in the transformer 10 is discharged via the cable 40 to the terminal 39 , so that the voltage removed there corresponds to the so-called return voltage U _Fly ; in this case the power supply is operated in flyback mode. This is the case in FIG. 4a.

There is now the possibility of regulating the voltage at the terminal 39 by bringing either the transistor 31 or the transistor 30 into a conductive state during flyback converter operation. In this case, the energy stored in the magnetic core is discharged via the freewheeling diode 33 when the transistor 31 is in the conductive state or is discharged via the diode 32 when the transistor 30 is brought into the conductive state. Fig. 4d shows this embodiment: After switching off the two Transisto ren 30 and 31 , the transistor 31 is turned on at time t _x and in this way the electromagnetic energy discharges to the ground and accordingly the time t _{Fly is} shortened and the voltage U ₂ enlarged.

The activation times of the transistors 23 and 31 can be adjusted to a constant value via a suitable circuit dependent on the voltage U ₂ ; this regulation is known per se and as such is of little importance for the invention.

Claims (5)

1. Power supply device with at least one output, with a transformer, on the primary winding of which a clocked voltage can be applied by means of a controllable switch, preferably a transistor, since characterized in that two outputs are connected to the secondary winding, the voltage at the first Output of the transformer as flyback converter and for the voltage at the second output of the transformer is operated as a forward converter, and that the discharge time of the transformer can be changed to control the flyback converter output voltage. 2. Power supply device according to claim 1, characterized characterized that parallel to the exit for the lock converter operation Means to achieve a short circuit are switched. 3. Power supply device according to claim 2, characterized in that the blocking magnetic transducer output ( 17 ) on a tap ( 24 ) of the secondary winding ( 15 ) is switched and that the winding area between the tap and the winding end can be bridged and by means of the controllable switch ( 23 ) Mass can be derived. 4. Power supply device according to claim 1, characterized in that a controllable switch (Transi stor 30, 31 ) are provided in series with the primary winding at the two ends thereof, one of which can be switched to the conductive state during the closing time of the other during lockout of the other . 5. Power supply device according to claim 4, characterized in that in each case a free-wheeling diode ( 32 , 33 ) is connected in parallel to a series connection of the primary winding ( 11 ) with one of the transistors ( 30 , 31 ).