DE3329437A1 - Circuit for controlling power switching transistors with galvanic separation - Google Patents

Abstract

For controlling a power switching transistor (MST), two non-ideal electric generators (Ig1, Ig2), three transformers (TR1, TR2, TR3), diodes and other necessary passive elements are used. The turning on or off of the power switching transistor depends on the signals (VH1, VH2, VH3) at the input of bipolar transistors (T1, T2, T3). If the bipolar transistors conduct alternately, electric generators (Ig1, Ig2) feed the transformers, which supply the current via galvanically separated windings for turning on the power switching transistor. For turning off the power switching transistor (MST), the third transistor (TR3) activates the third transformer, which forms a voltage with directly opposite polarity at the base of the power switching transistor and thereby turns it off. Diodes in the circuit of the third transformer prevent leaking away of the base current when the power switching transistor is turned on. <IMAGE>

Description

CIRCUIT FOR THE CONTROL OF POWER SWITCH TRANSISTORS

WITH GALVANIC SEPARATION The invention belongs to the field of electronic switching or the control of switching processes - H 03K 17/08.

The technical problem to be solved is the control of a power switching transistor with a feedback diode, which is discrete or already connected to the same monolithic circuit how the power transistor can be integrated, including galvanic isolation must be achieved.

The working states of the transistor are as follows: - uninterrupted Leading state; - uninterrupted blocking state; - all intermediate states with frequency of 100 kHz; - continuous operation as a diode; - the use of a low voltage bipolar transistor for controlling the power switching transistor.

Known solutions for controlling power switching transistors can be classified in some groups: 1 direct control of the Base current; 2. Direct control of the base current of larger ones in the Darlington pair located transistors; 3. Control of NPN switching transistors with a PNP transistor; 4 »Control of a PNP auxiliary switching transistor, 50 control a power switching transistor via transformers.-1. Under immediate control is meant the way in which the energy to feed the transistor base from a supply unit, which must be galvanically separated from the control electronics, is fed. The control signal is transmitted over an optical link.

These circuits are already being used by the manufacturers of power switching transistors and are used by them as test circuits. Besides that, too other circuits specified, the simpler and cheaper equivalents of the basic controller are. This could also be used to control the TransIstors with a single galvanic separate food level are counted. The examples are in the application book of Motorola Switchmode Application Manual, printed in Switzerland in 1980, listed in the last part of the book, the pages of which are not numbered.

Westinghouse also offers basic control solutions in her publication: Merle Morozovich: Tbhere, Why and How to Use the D60T Transistor, Westinhouse Semiconductor Division, Youngwood, PA 15697, 1979, p. 30, Figs. B and C.

With this type, the transistor is controlled as much as it is just necessary, He can be brought into the saturated state strongly. the Conducting losses can be reduced. This will reduce the switching losses increased and the shutdown extended. This can also be reduced in such a way that a circuit to prevent the supersaturation is incorporated. Any form of base current can be generated without difficulty. The main disadvantage is that for galvanic isolation two galvanic separate food units are necessary, one each for a positive and negative Base voltage. The feed unit for the positive base voltage must have the capability have the ability to deliver a sufficiently high current in the order of magnitude of several amperes, which is quite unfavorable at low voltage because of low efficiency. The transistors for opening the power switching transistor must be able to to deliver the entire base current. The capacity of the dining part compared to the Network and the bulk of the feed electronics exerts a negative influence on the behavior the circuit, especially at sometimes high frequencies. The problem becomes / with solved with an optocoupler, with which, however, the information transmission at high frequencies is disturbed.

2. In order to reduce the necessary base current, two or more Transistors connected in a Darlington circuit. This type is used in practice most widely used and therefore easiest to find in industrial products being found. The galvanic isolation is also optically connected galvanically separated power supply units realized.

The advantage in this regard lies primarily in the lower control current with the same collector current. Thereby the necessary power of the galvanic separate feed section for the positive base current is significantly reduced.

The transistors for this also need lower power dissipation Open the Darlington pair compared to the variant under point 1. The disadvantages are as follows: - higher voltage when the Transistor, which also causes higher losses; - because of the delay of the transistor for opening the power transistor are the switch-on and the switch-off times longer; - higher price because of the expensive opening transistor, the voltage U (sps) equal to that of the power switching transistor and the Have collector current I at least equal to that of the power switching transistor got to; - As with the variant under point 1, a galvanically isolated The power supply unit exists and the signal is transmitted via the optoisolator.

This type of control is used for transistorized devices Setting the speed for direct current servomotors from Siemens der Types: GRB 2012, GRB 2025, GRB 2030 and the servo device for setting the Speed FANUK used (documentation code A205-0089-0320 / 01).

3. Often times, opening a power NPN transistor with a PNP Transistor used. Galvanic separation is required for the speed of the applications not necessary because it is at the low voltage level of the next transistor, the the PNP transistor opens, can be controlled. This solution will already be several Years from General Electric in the transistor servo controller HI-AK, which by U.S. Patent 3,883,786 is used. Basically the same solution the control of the power switching transistors can also be found in the US patents Find 3 652 913 and 3 560 829.

In many applications, such as bridge circuits, this type of control eliminates the need for galvanic isolation of the performance Switch -NPNTransi -stors bypassed.

In this way, a power transistor can be controlled well and thereby the losses are reduced during the conduction state.

The unfavorable side of this type becomes apparent at higher voltages, because they have a poor efficiency due to loss of power at the resistor for has the base current limitation by the PNP transistor. Big ones arise Shaft losses and long switch-off times.

4. For the control of a power switching PNP transistor exist multiple solutions. A characteristic example can be found in the book by Motorola Semiconductor Product Inc., Semiconductor Power Circults Handbook, Nov. 1968, pp. 6-29 will.

In this type, the power NPN transistor can be combined with an NPN transistor be opened or controlled. This darlington transistor can turn into a be brought to a higher state of saturation.

This causes losses due to the voltage drop across the transistor reduced if this leads. The following disadvantages are shown: - there are no commercial PNP transistors for high voltages and currents; - the opening transistor must have the same voltage UOE (SVS) as the power switching transistor and the collector current 1G must be of the order of magnitude of the base current of the power switching transistor which is why these transistors are expensive; - the switch-off times are not minimal, since the blocking is not done with negative current, and both transistors are uncontrolled in saturation; - here too there is an optoelectronic separation of the signal and a galvanically isolated supply unit for the base current is necessary.

5. The control of the base of the power switching transistor via the Transformers enables maximum utilization of the transistor in all operating states, so that it is used more and more.

a) There are many examples of such a galvanically isolated control principally the company Westinghouse in the publication: Nerle Norozovich: Where and How to Use the D60T Transistor, p. 30, Fig. A. This is detailed in Tech.Tips, 2-9, M. Norozovichtransistorized 50 kllz Popcorn Poppe; Westinghouse Power Semiconductor Division, Youngwood, PA 15 15967. Disadvantages are as follows: - It cannot operate at low frequency or even in a continuously conductive state Power transistor is working because of damage to the transformer core.

which is an interruption of the energy on the secondary side has the consequence. In order to be able to work at lower frequencies, with regard to all dimensions large transformers are used for the base current. Execution is no longer economical.

- You cannot work in an operating state in which the transistor is conductive for most of the period and because of DC bias of the ferromagnetic core is only blocked for a short time. Such can only be worked in an operating state in which the master state time 80 0% of the Total period or less.

b) The Motorola company, known as Switchmode, has similar solutions Application Manual, Switzerland, 1980. There are several possible types of blocking of the transistor used for which it can be determined that they are technically are clearer than those according to the literature cited above. Both are good and bad properties like that.

c) The solution according to the German patent application P 27 29 407 possesses The advantage of the above-mentioned solutions is that there are no diodes against oversaturation are necessary because the collector current itself also controls the transistor.

This achieves short storage times Primary side little energy needed for opening the transistor. This variant has similar disadvantages as in Example 5a.

d) A similar solution as in 5c is given in article by John Klimek: Reverse magnetic spike driver switching transistor efficiently, Pretoria, South Africa, Electronics, Dec. 29, 1981, p. 94, found.

The essence of this solution is that the transistor is next to one additional opening with the collector current also with that accumulated in the transformer Magnetic energy is blocked. With this solution also occurs the problem of low Frequencies in a working state at which the time of the conducting state much longer than the blocking period.

e) The solution that Helmut Y; noll deals with in his doctoral thesis, enables all working states of the transistor with minimal static and switching losses and maximum speed.

- Of all the solutions discussed, this is from a technical point of view the best, since the requirement for optimal control of the transistor is met.

Disadvantages occur mainly in the implementation and the price of the Total solution on, namely: - The power source is with a transistor and another necessary components and behaves with minor changes in the Impedance like a constant source. If there is a major change in the circuit impedance behaves during commutation. the Source like a thrush. When switching off, a short circuit must therefore be carried out and only then become the transistors for supplying the transformers are blocked. The short circuit must take all the time so that the power generator prepares for power supply is; in the interval in which the power switching transistor is blocked, wfrd therefore all the energy consumed by power generator.

- The power generator must have a control circuit, why it is costly.

- On transistors that supply the current through the transformers, high tensions occur during the mutation, as stated by the author in his article is not listed.

f) A technically even better solution was proposed by K, Boeheiniger and F. Bruger published in the article: Transformerless transistor pulse converters with output power up to 50 KVA, E and X, 1979, pp. 539-545.

The same solution is also given in the article: R. Würslin, Transistor converter operation on 380 V three-phase mains, 2nd Annual European Power Conversion Gonference, Sept. 3-5, 1980, Munich.

These solutions have no functional disadvantages, but because of them the high price of the MOS-FET transistors used, the price of the controlled Power bipoiartransistors, they are uneconomical. In this Case, the MOS-FET transistors work partly in an analog and partly in a switching mode of operation. Quite a lot of power is consumed in this process.

According to the invention the object (elimination of the disadvantages of the known yorrichtuagen.) solved with two-part power generators, each of which has its own Transformer feeds during a time in which the input transistors the Command to turn on the power transistor received. For blocking the power switching transistor a third input transistor is used, which also has a transformer in its branch and all other necessary components to ensure the desired switching characteristics having.

The invention is explained in more detail on the basis of the drawing.

These show: FIG. 1 a circuit diagram; Fig. 2 is a timing diagram.

The terminal of the input VH1 is connected to the base of the transistor T1, whereas the emitter with ground and the collector with the common point one Zener diode ZD1 and the primary winding 11 of the transformer TR1 are connected. The second connection of the winding iTN is connected to the current generator Igl. There is a series connection between the connections of the winding N1 Diode D9 and the Zener diode ZD1 and between the terminals of the winding N2 of the Transformer TR1 there is a series connection of resistors R1 and R2, whose connection point is connected to the base of a transistor T4, the Emitter connected to the common point of resistor R2 and winding N2 is. The collectors of the transistors T4 and T5 are together in a common Point with the connection of the winding N8 of the transformer TR3, the emitter of the Transistor MST and the diode DNsg connected. With the common point of resistance R1, winding N2 and winding N3 is the diode Dl and with the other connection the winding N3 is connected to the diode D2. The same is true of a transformer TR2 connected to one terminal of its secondary winding N5, the diode D4. the Diodes D2 and D4 are in a common point sit the collector of the Transistor MST and the diode DT connected. Between the connections of the secondary winding N6 of the transformer TR2, the resistors R3 and R4 are connected in series. you common point is with the base of transistor T5, the enitter with the common Point of winding N 6 and resistor R4 and the collector with the collector of the transistor T4 connected.

The common point of winding N6, winding N5 and the resistor R3 is connected to diode D3. The diode D2 and the diode D4 are together with connected to the collector of the transistor MST.

The terminal of the input VH2 is connected to the base of the transistor T2, where the emitter with ground and the collector with the common point of the Zener diode ZD2 and the connection of the primary winding N4 of the transformer TR2 is connected. The second connection of the winding N4 is connected to the current generator Ig2. Between A series connection of the diode D10 is located at the connections of the winding N4 and the Zener diode ZD2.

The terminal of the input VH3 is connected to the base of the transistor T3, the collector with the common point of connection of the winding N7 of the transformer TR3 and the Zener diode ZD3 is connected. Between the terminals of the winding 7, a series circuit of the diode D11 and the Zener diode ZD3 is connected. The common point of the diode D11 and the connection of the winding 7 is with the Terminal + V connected. Between the connection of winding N8 of transformer TR3 and the base of the transistor ItST, the diodes D8, D7, D6 and D5 are connected in series.

In parallel with the collector and the emitter of the transistor EST is the Diode DgET switched; these two points also form the output terminals IZ1 and IZ2 of the circuit as shown in FIG.

When the command for conducting or switching through the power switching transistor MST is obtained, the transistor T1 or T2 is turned on.

If the transistor T1 turns on, flows through the primary winding N1 of the transformer TR1 a current which is determined by the current generator Ig1. on a secondary current must flow on the secondary side of the transformer TR1, as this how a current transformer works. In the first month a current flows through the Resistor R1 and the base of transistor T4 and therefore the transistor switches T4 through Now the current begins through the diode D1 into the base of the transistor MST to flow, which therefore switches through. When the transistor MST conducts, the Base current IBMST smaller, since the secondary current of the transformer DR1 is about the diode D2 and the collector of the transistor MST begins to complete. then The load current and part of the secondary current flows through the collector of the transistor MST of the transformer, it depends on the load current 1B how much of the secondary current IS2 through the base of transistor MST and how much of that current through the collector will flow. The larger the load current 1B, the larger the saturation voltage becomes UGE and the less current is through the collector of the transistor and the more Current drain through the base of the transistor MST. This will increase the tension The UBE of the transistor MST will increase and therefore the current through the base will also increase of transistor T4 higher. As the base current 1B4 will increase, the voltage becomes UCE4 will decrease and accordingly the voltage on the secondary winding will increase of the transformer TR1 do not change significantly. The number of turns of the elongated Windings N3 and 5 are attached to the secondary windings of transformers TR1 and Tß2 depends on which saturation voltage UGE should appear at the transistor rED. The higher the number of turns will be N3 and N5, the higher the saturation voltage becomes; it ranges between N2 / 2 or N4 / 2 and zero. Zero occurs mainly in power Darlington transistors on.

Since the core of the transformer TRl would come into saturation, if the transistor T1 were open too long, the transistor T1 must be blocked and already controls transistor T2 a little earlier. In the time when both transistors T1 and T2 conduct, the commutation is carried out. Because of the inductance of the lines and the leakage inductance of the transformer of the current in its full Value cannot flow and it cannot fall to zero for the same reason, can be achieved with a correctly selected time of overlap (commutation) be that the base current of the transistor MST will be without current indentations (5. Fig. 2).

This means that during the commutation the base current is not under will drop the necessary value. Usually the commutation is around as much prolongs that the sum of the two currents during commutation is greater than that is normal base current that flows to the base of transistor MST, if only one Transistor conducts (T1 or T2). Above all, it is important to have two power generators can be used (Ig1, Ig2), as this reduces the mutual influence between the two Branches is eliminated. When the transistor T2 conducts and the transistor Tl still is locked, the identical functional sequence is repeated as in the case, if only the transistor T1 conducts.

During the conduction state of the transistor MST, a 1 $ sequence the conductive state of the transistors T1 and T2 changed, with constant overlap is carried out.

Also important is the role of the Zener diodes ZD1 and ZD2, which are the primary windings Nl and N4 of the transformers TR1 and TR2 are connected in parallel. The diodes 9 and D10 prevent the current through the Zener diodes ZD1 and ZD2 when the transistors T1 and T2 are in the charging state. When the transistors T1 and T2 are blocked, a voltage with opposite polarity is induced on the primary sides of the transformers and with a height that is limited by the threshold of the Zener diodes ZD1 and 2D2.

The energy used in the past is now used at the Zener diodes in transformers TR1 and TR2 while transistors T1 and T2 are conducting was saved.

The voltage of the Zener diodes ZD1 and ZD2 must be high enough so that during the pause, i.e. during the time in which the transistor T1 and T2 is locked, all magnetic energy is consumed. This will ensured that the core in the following periods because of DC bias will come into saturation.

The blocking of the transistor MST takes place in such a way that both transistors T1 and T2 are blocked and transistor T3 is turned on for a short time2 This ensures rapid blocking of the transistor MST, since it is with a negative voltage between the base and the emitter of the transistor MET is blocked will. How long this voltage will last depends on the transformer TR3. It exists a similar problem as with transformers TRl and TR2. The diodes D5, D6, D7 and D8 prevent current flow through transformer TR3 when the transistor is MST is conductive.

The role of transistors T4 and T5 is as follows: The transistor MST with the diode DT connected in parallel can also only work as a diode. if the transistor ItST is used with an integrated reverse voltage diode DMST, this has a voltage drop of up to 5 V in the forward direction, which is a lot is more than with discrete diodes and the same current.

Because of the voltage drop across the DItST diode, the current would also through the two secondary windings of the Trarsformatoren TR1 and TR2 as well as the Leave diodes D2 and D4 off.

Since this conduction state of the diode DMST is arbitrarily long, what above all depends on the type of use of the power switching transistor, get the Cores of the transformers TR1 and TR2 in the saturation state. The resistance value of the secondary windings of the transformers TR1 and TR2 is very small. Because of this the voltage drop across diode D2 and D4 is higher. Because these diodes run discreetly and cause a small voltage drop, flows through the diode D2 and D4 a large current, which is otherwise normally through the diode DMST and the transistor J-LEiT would flow and thermally destroy them both If the Transistors T4 and T5 could be used, but could in such operation (Activity of the DMS diode) the transistors T1 and T2 and accordingly also the transistors T4 and T5 are blocked. Now the impedance in the circuit is high and the whole Current flows through the diode DMST.

Even if the circuit is working for opening the transistor MST, i.e. that the transistors T1 and T2 commutate, the.

Transistor MS- with the diode DMST used in the function of a diode will. This time, because of the current through the diode DMST, the collector current is des Transistor MST equal to zero; therefore a base emitter voltage is also the same Zero necessary.

Since the secondary current is imposed, it flows through the resistor R1 and the base of the transistor T4 in the first period (see FIG. 1) and the resistor R3 and the base of the transistor T5 in the second period of the switching of the transformers TR1 and TR2 only have such a current that the collector current of transistors T4 and T5 represents all of the remaining secondary current. That part of the tension that creates the Difference between the voltage drops across diodes D2 and D4 and the diode D «ST now appears on transistors T4 and T5.

Two transistors are used because one transistor, which could functionally replace two, not a larger one during commissioning Electricity is completed.

fian maste namely dimension a transistor for maximum current, which is why it is better to take two for lower currents as they are very accurate can be dimensioned.

The galvanic separation with the power switching transistor and the Control electronics can have insulation between the primary and secondary windings the transformers TR1, TR2 and TR3 can be achieved.

The proposed solution enables a power transistor to be controlled in very demanding working conditions with a use of inexpensive Components, which also significantly cheaper the whole device. Are muted before all the Transistors T1, T2 and T3, the low voltage bipolar switching transistors are. This circuit offers the greatest advantage when for the power switching transistor ItST uses a power darlington transistor with an integrated diode will. These transistors have a slightly higher saturation voltage and the same Amplification like discrete transistors.

By using the proposed circuit, these can be used in all Working conditions are used, but at the same time the efficiency improves of the devices because of lower power darlington transistor losses.

Blank page

Claims (1)

CIRCUIT FOR THE CONTROL OF POWER SWITCHING TRANSISTORS WITH GALVANIC SEPARATION OF THE PATENT CLAIM: Circuit for controlling power switching transistors, with galvanic separation, which means that a first Input terminal (VH1) is connected to the base of a transistor (T1) whose Emitter to ground and its collector to the common point of a Zener diode (ZD1) and a first connection of a primary winding (N1) of a first transformer (TR1) is connected, a second connection of one of these winding (N1) with a current generator (Ig1) and a connection of a diode (D9) and its second Terminal connected to the Zener diode (ZD1) that between the terminals the secondary winding (N2) of the first transformer (TR1) two resistors (R1, R2) are connected in series, with the common point of these resistors (R1, R2) the base and to the common point of the connection of the winding (N2) and the resistor (R2) of the emitter of a transistor (T4) are connected, that the collector of this transistor (T4) and a second transistor (T5) together with one connection of a secondary winding (N8) of a third transformer (TR3) with an output terminal (IZ2) and with the emitter of a transistor (MST) to which one connection of a diode (DMST) is also provided, tied together are that at the common point of the resistor (R1) and the connection of the Secondary winding (N2) of the first transformer of one connection of another Secondary winding (N3) and one terminal of a diode (D1) are connected, its other connection to one connection of a diode (D3) to the base of the transistor (MST) and connected to one terminal of a series connection of diodes (D5, D6, D7, D8) is that the other connection of this series connection with the other connection of the Secondary winding (N8) of the third transformer is connected between that Connections of the secondary winding (N6) of a second transformer (TR2) two resistors (R3, R4) are connected in series, with these resistors at the common point (R3, R4) the base and to the common point of the connection of the winding (N6) and the resistor (R4) connected to the emitter of the second transistor (T5) are that at the common point of the resistor (R3) and the connection of the Secondary winding (N6) of the second transformer of one connection of another Secondary winding (N5) and one terminal of the diode (D3) are connected that the other terminal of the secondary winding (W3) of the first transformer (TR1) a diode (D2) and the other terminal of the winding (N5) of the second transformer (TR2) via a diode (D4) to the collector of the transistor (MST), to which also the other terminal of the diode (DMST) is connected, as well as with another Output terminal (in1) are connected that a second input terminal (VH2) with the Base of a transistor (T2) is connected, its emitter to ground and its collector to the common point of a Zener diode (ZD2) and the first connection of the Primary winding (N4) of the second transformer (TR2) is connected, the second connection of this winding (N4) with a current generator (Ig2) and a connection the diode (D10) and its second terminal connected to a Zener diode (ZD2) are that a third input terminal (VH3) to the base of a transistor (T3) is connected, its emitter to ground and its collector to the common Point of a Zener diode (ZD3) and the first connection of the primary winding (N7) of the third transformer (TR3) are connected, the second connection of this Winding (N7) with the terminal (+ V) of a voltage supply and a connection of a Diode (D11) and its second terminal are connected to the Zener diode (ZD3).