WO2012057692A1

WO2012057692A1 - A power durable current generator

Info

Publication number: WO2012057692A1
Application number: PCT/SE2011/051284
Authority: WO
Inventors: Yngve Linder
Original assignee: Yngve Linder
Priority date: 2010-10-29
Filing date: 2011-10-28
Publication date: 2012-05-03

Abstract

A power durable current generator comprises a first connection point (1), a second connection point (2), a transistor (T2), a current regulating resistor (R1), a potential generating circuit (30), a power durable circuit (12) and a potential maintaining circuit (16). A collector of the transistor (T2) is connected to the first connection point (1) and an emitter is connected via at least the current regulating resistor (R1) to the second connection point (2). The potential generating circuit (30) is connected to a base of the transistor (T2). The power durable circuit (12) comprises a current regulating arrangement (14) connected by a first end to the first connection point (1) and by a second end, in series via the potential maintaining circuit (16), to the emitter of the transistor (T2). The second end of the current regulating arrangement (14) is further connected to the potential generating circuit (30).

Description

A POWER DURABLE CURRENT GENERATOR

TECHNICAL FIELD

The present invention relates to a power durable current generator.

BACKGROUND

In current generators according to prior art it must be considered what power the included components can endure when dimensioning the current generator. This means that some components, e.g. transistors, must be dimensioned to endure a sufficiently high power which is connected to the rated voltage of the current generator, e.g. max 30 volts.

In the US patent 4,460,864, a transistor is connected with its base to a potential generating circuit and a current regulating resistor connected to the emitter. If a large voltage is applied over the transistor, the transistor may be damaged.

Since transistors with high power durability are more expensive than transistors with low power durability it is desirable to be able to use transistors with low power durability even when the generated power of the current generator, i.e. high rated voltage when a certain current is flowing through the connection.

The published US patent application US 2002/0140409 Al discloses a power supply unit. A resistor is connected in parallel to a transistor, between the emitter and collector. The resistor thereby takes a part of the current that otherwise would have passed through the transistor and makes thereby the circuit more power durable.

SUMMARY

One object of the present invention is to provide a current generator providing a constant current over a large voltage range and which is power durable. The above object is achieved by current generators according to the enclosed independent patent claim. Preferred embodiments are defined by the dependent patent claims. In general words, a power durable current generator comprises a first connection point, a second connection point, a first transistor, a first current regulating resistor, a potential generating circuit, a power durable circuit and a potential maintaining circuit. A collector of the first transistor is connected, at least indirectly, to the first connection point and an emitter of the first transistor is connected via at least the first current regulating resistor to the second connection point. The potential generating circuit is connected to a base of the first transistor. The power durable circuit comprises a current regulating arrangement. The current regulating arrangement of the power durable circuit is connected by a first end to the first connection point and by a second end, in series via the potential maintaining circuit, to the emitter of the first transistor. The second end of the current regulating arrangement of the power durable circuit is further connected to the potential generating circuit.

An advantage of the present invention is that a large portion of the current between the first connection point and the second connection point flows through the current regulating arrangement and the potential maintaining circuit, whereupon the transistor is relieved and the power generated in the transistor is reduced compared to prior art.

Further objects and advantages can be identified by a person skilled in the art from the detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with further objects and advantages thereof, may best be understood by making reference to the following description taken together with the accompanying drawings, in which:

Fig. 1 shows a current generator with a power resistor; Figs. 2-7 show embodiments of current generators with power resistors;

Fig. 8 illustrates a current generator as a combination of an upper and lower circuitry;

Figs 9-16 illustrate embodiments of upper circuitries of a current generator according to Fig. 8;

Figs 17-20 illustrate embodiments of lower circuitries of a current generator according to Fig. 8; and

Fig. 21 illustrates another embodiment of a current generator.

DETAILED DESCRIPTION

Figure 1 shows a current generator with a power resistor R3. In a test circuit of such a conventional current generator, the following components have been used; T2: BC547B and D l, D2: 1N4001

To generate a voltage reference for the base of transistor T2, point A is connected to a fixed voltage of 10V. If R20 is selected to 1 kO, a current of approx 10 mA is conducted through the diodes Dl and D2, but it is of course possible to use larger values for R20.

In order for a current of approx 18 mA to flow in at point C, Rl is set to approximately 33 Ω. If the highest voltage that point C can have is known, a resistor R3 is connected between the collector and emitter of transistor T2 to spare the transistor from unnecessary power dissipation whereby a transistor with lower current/ power durability can be used than what would have been required otherwise. At low voltage drops over the transistor, it is the transistor T2 that conducts the main part of the current through itself, but the more the voltage increases at point C, the more it is resistor R3 that conducts the current which also runs through the common resistor Rl .

To determine the lowest value of R3, the highest voltage in point C minus the voltage drop over Rl is divided by the current that is desired to flow in at point C, as shown below in example 1. Example 1

Highest known voltage:

V

Desired inflowing current in point C: I_c=18 mA=0.018 A

Voltage drop over R1=0.018 A * 33 Ω=0.6 V

Voltage drop over the power resistor R3=30 V-0.6 V=29.4 V

This gives:

R3=29.4 V/0.018 A= 1633 Ω and a value of ^« 1.5 kO is selected

This yields a true current I_c through Rl of 30V/ 1533 Ω= 19.6 mA, which results in that the transistor is already fully cut off at Umax =30 V since the voltage drop over Rl=19.6 mA*33 Ω=0.64 V. If point C ends up on a potential which is higher than 27.59 V (i.e. 1533 Ω * 18 mA), then the circuit cannot regulate the current anymore. The voltage drop over Rl then becomes more than 0.6 V, the transistor is completely cut off and the circuit works (seen from point C) as a 1.5 kΩ resistor in series with a resistor of 33 Ω.

Even though the power consumption caused by the current I_A is low, a potential at point A has anyway to be provided in order to give a generated current.

Fig. 2 illustrates an embodiment of a power durable current generator according to the present invention. A transistor T2 is in this embodiment connected with its collector to a first connection point 1. An emitter of the transistor T2 is connected via a current regulating resistor Rl to a second connection point 2. A potential generating circuit 30 is connected to a base of the transistor T2. The potential generating circuit 30 comprises in this embodiment a resistor 20 and a potential generating component arrangement 18 connected between the base of the first transistor T2 and the second connection point 2. The power durable current generator further comprises a power durable circuit 12, in turn having a current regulating arrangement 14, and a potential maintaining circuit 16. In this embodiment, the current regulating arrangement 14 comprises a current regulating resistor R3, and the potential maintaining circuit 16 comprises two diodes D3, D4 connected in series with each other. The current regulating arrangement 14 of the power durable circuit 12 is connected by a first end to the first connection point 1. The current regulating arrangement 14 of the power durable circuit 12 is furthermore connected by a second end, in series via the potential maintaining circuit 16, to the emitter of the first transistor T2. The current regulating arrangement 14 and the potential maintaining circuit 16 thus become connected in parallel with the transistor T2 between the collector and the emitter. The second end of the current regulating arrangement 14 of the power durable circuit 12 is further connected to the potential generating circuit 30. In this embodiment, this means that the resistor 20 is connected between a connection point between on one side the current regulating arrangement 14 and the potential maintaining circuit 16 and on the other side the base of the transistor T2. In the present embodiment, the potential generating component arrangement 18 in the potential generating circuit 30 comprises a pair of diodes D l, D2. The diodes D 1 , D2 are connected in series with each other.

In a test circuit based on the above described embodiment, the following components have been used; T2: BC547B; Dl, D2, D3, D4: 1N4001. As will be discussed further below Rl = 33 Ω, R3 = 1.5 kO R20 = 330 Ω.

The connection of R3 in series with D3 and D4, and R3 in series with R20 results in that a relatively constant current will flow through R20. Moreover, the number of connection points is reduced to two; connection point 1 and connection point 2, instead of three connection points A-C as shown in Fig. 1. This results in that the voltage potential at the base of transistor T2 varies until the voltage over the circuit has reached a few volts.

In Fig. 2, the voltage over Rl becomes approximately the same as the voltage drop over D2 when a high enough voltage is applied over the circuit between connection point 1 and 2, which results in that the current through Rl becomes relatively constant. To give the base of transistor T2 a voltage reference, the diodes D 1 and D2 are used, and to generate the current which is required to create a voltage drop over D l and D2 the components D3, D4, R3 and R20 are used. Since the voltage drops over the base-emitter U_BE of transistor T2 and over D4 are relatively equal, the voltage drop over R20 will be relatively constant, which results in that an extra connection point to generate the voltage potential for the base of transistor T2 is not needed. The resistor R3 will, moreover, take care of the current when the voltage over the circuit increases and thereby a transistor with lower power durability can be used.

To get an approximate value for R3 in the test circuit, the current through Rl must be specified together with the largest possible voltage drop over the circuit, see below in example 2.

Example 2

Highest known voltage: U max- 30V

Desired current through Rl : IR1=18 mA=0.018 A

Desired current through R20 is about 1/ 10 of the current through Rl in this example: IR20=1.8 mA

Desired voltage drop over Rl and R20, respectively, UR1=UR20=0.6V

Voltage drop over D3 and D4, respectively, UD3=UD4^i¾0.6V

Voltage drop over the power resistor R3=U_max-UD3-UD4-URl=30-1.8=28.2V This gives:

R3=28.2 V/0.018 A=1567 Ω

R20O.6 V/0.0018 A=333 Ω

If the voltage over the circuit becomes too high (i.e. > 30V), the circuit cannot regulate the current I. The increased current through R3 results in that the voltage drop over Rl increases until the transistor T2 is completely cut off and the circuit in principle becomes completely resistive (and can be compared to R3 in series with R20 / / Rl). The connection according to the test connection according to Fig. 2 yields approx. 16-21 rtiA at approximately 5-30 volts between connection point 1 and connection point 2. In the embodiment presented above, the potential maintaining circuit 16 comprises a pair of diodes D3, D4. Also other components can have the same or similar properties and can be used instead. In a first alternative, a pair of components providing a diode action, connected in series with each other will also operate as a potential maintaining circuit 16. Such components providing a diode action can e.g. be an ordinary diode or a transistor connected in a diode coupling. In further alternative embodiments, the potential maintaining circuit 16 may also comprise a component providing a diode action connected in series with a resistor. As soon as a current is drawn through such an arrangement, a potential drop is present over the diode-like component and an additional potential drop is present over the resistor. In embodiments, where the current through the potential maintaining circuit 16 is kept essentially constant e.g. due to current mirror couplings, the potential maintaining circuit may even comprise a single resistor of appropriate size.

Fig. 3 shows another embodiment of a simplified current generator with a power resistor R3 that resembles the connection that was described in connection with Fig. 2, but with the addition of a second transistor T4 and diode D5. The emitter of the second transistor T4 is connected to the collector of the first transistor T2. The diode D5 is connected between the bases of the transistors T2 and T4 and creates required voltage potential to the base of transistor T4.

Using T4: BC547B and D5: 1N4001, a test connection according to Fig. 3 yields approx. 16-20 mA at approx. 5-30 volts between connection point 1 and connection point 2. Fig. 4 shows a third embodiment of a simplified current generator with power resistor R3. The connection resembles the one described in conjunction with figure 2 except that the diodes D l and D2 have been replaced by a second transistor T4, where the base has been connected to the emitter of transistor T2. A collector of the second transistor T4 is connected to the base of the first transistor T2. The potential generating component arrangement 18 thereby comprises the second transistor T4. The current limitation of the connection comes into operation and transistor T4 starts to conduct when the voltage over Rl exceeds UB_E of T4, i.e. approximately 0.6V. The transistor T4 conducts current from the base of transistor T2 which results in that transistor T2 reduces the current when the voltage drop over Rl becomes too high. When transistor T2 conducts and when the voltage over Rl results in that T4 starts to conduct, the current is conducted away from the base of transistor T2 towards connection point 2. The potential at the collector of T4 is reduced and T2 limits the current. If the voltage over this connection becomes too high, transistor T4 will probably break. However, by connecting a resistor into the conductor that feeds the base of T4, the transistor T4 can be protected.

In a test coupling according to Fig. 4, T4 was selected as a BC547B transistor. In this connection, the connection principle and dimensioning of the power resistor R3 according to the principle described in connection with Figs. 2 and 3 can be used.

Fig. 5 shows yet another embodiment of a simplified current generator with power resistor R3. The connection resembles the one described in conjunction with Fig. 4 except that a diode D l is connected between the emitter of T4 and connection point 2 and the resistor Rl has been replaced by a resistor R4 which is twice as large as the resistor Rl in Fig. 4. This results in that the voltage drop over R4 is twice as large as the voltage drop over Rl in Fig. 4. In a test coupling R4 was selected to 66 Ω A connection according to Fig. 4 or Fig. 5 yields approximately 20-21 mA at an applied voltage of approx. 3-30 V between connection point 1 and connection point 2. The connections are stable and work very well.

Figures 2-5 thus show different embodiments of a simplified current generator with power resistor, where the connections of R3 in the respective circuit decreases the power dissipation in the transistors and thereby creates a more power durable current generator compared to current generators according to prior art.

Fig. 6 shows another embodiment of a current generator with two connection points that has a slightly more complex layout but that works according to the same principle as the previously shown current generators according to Figs. 2-5. The potential generating circuit 30 here comprises an operational amplifier Op. An output of the operational amplifier Op is connected to the base of the first transistor T2. A first supply voltage connection of the operational amplifier Op is connected to a point between the current regulating arrangement 14 and the potential maintaining circuit 16, as will be discussed further below. A second supply voltage connection of the operational amplifier Op is connected to the second connection point 2.

In the connection R3, D3 and D4 generate a voltage which is slightly higher than the potential at the base of transistor T2, since the voltage drop over D4 approximately corresponds to the voltage drop between base and emitter of transistor T2. This voltage is used to give an operating voltage/ supply voltage to an operational amplifier Op. Depending on which operational amplifier that is used, which current it is desired that the connection should yield and depending on the amplification (hFE) of transistor T2, the number of diodes may need to be adjusted. If a higher current through the connection is desired, it is possible to Darlington-connect two transistors and insert a diode in series with D3 and D4. That will however shift the voltage with approx. +0.6V that is needed for the circuit to start regulating. The potential generating circuit 30 further comprises resistor R5 and a Schottky diode Ds or other voltage reference component. The resistor R5 is connected with a first connection to the emitter of the first transistor T2 and with a second connection to the Schottky diode Ds. The Schottky diode Ds is connected between the first resistor R5 and the second connection point 2. The current generator further comprises a second resistor R2 connected in series with the current limiting resistor Rl between the emitter of the transistor T2 and the second connection point 2. A first input of the operational amplifier Op is connected to a point between the resistor R5 and the Schottky diode Ds, and a second input of the operational amplifier Op is connected to a point between the first current limiting resistor Rl and the resistor R2.

When a voltage is applied over the circuit between the first connection point 1 and the second connection point 2, a current starts to flow through R3. This current gives rise to, among other things, a voltage drop over the diodes D3 and D4, where the resulting voltage drop over D3 and D4 is used to give supply voltage to the operational amplifier Op. The operational amplifier Op which is connected as a "voltage comparator" compares the voltages in on its plus and minus inputs. Since a Schottky diode Ds is located at the "plus branch" of the inputs of the operational amplifier towards connection point 2, the plus input will be "high" before the minus input on startup. This results in that the output of the operational amplifier also will be "high". Since the supply voltage of the operational amplifier will be higher than UBE, i.e. >0.6V, of transistor T2, the transistor T2 will conduct a current.

Since the voltage drop over Ds is approximately 0.55 V with the selected component values, the output of the operational amplifier will be "high" until the voltage drop over Rl exceeds a voltage of approximately 0.55V. However, observe the following. By selecting an appropriate value for R5, the current through Ds will attain a value where the voltage drop over Ds is more or less insensitive to temperature changes, which means approx. 3-4 mA for the selected component BAT81, see further below. In this connection with the component values selected here further below, the voltages over Rl, R2, R5 and DS will be equal.

Figure 7 shows a sixth embodiment that basically resembles the one described in conjunction with Fig. 6. However, the resistor R5 has been connected to a point between D3 and R3 and the plus input of the operational amplifier. In other words, the first resistor R5 is connected with a first connection to a point between the current regulating arrangement 14 and the potential maintaining circuit 16. Note that the potential generating circuit 30 in this figure is illustrated as divided into two parts. In order to be able to generate a current of between 3-4 mA through the Schottky diode Ds see discussion above, the value of R5 must be selected approx. 3 times higher than above. Remaining component values are unchanged.

In test couplings of the embodiment of Fig. 6, the following components have been used; T2: BC547B, all diodes: 1N4001, D_s: Schottky diode BAT81. Another type of voltage reference is of course also possible to use. In the test coupling, the Op was a MCP6002 (1/2), and the resistors had the following values: Rl, R2 = 33 Ω, R3 = 1.5 kO, R5 = 150 Ω.

The function of the power resistor R3 is the same as in the previously described embodiments in Figs. 1-5. The connection yields with the used components 20 mA with a connection voltage of approx. 2.4 to 30V.

In the above described embodiments the resistor R3 is current limiting and is furthermore a part of a power durable circuit, where also the diodes D3 and D4 in preferred embodiments are included where applicable. Also the resistor Rl is current limiting. The NPN transistor T2 is controlled by a potential generating circuit which mainly consists of a resistor R20 connected to the base which furthermore is connected to connection point 2 via a potential generating component. This component may consist of at least two series connected diodes D l and D2 (see Figs. 1 and 2), or an additional NPN transistor T4 (see Fig. 4) or combinations thereof (see Fig. 3 with D l, D2, D5 and T4; or Fig. 5 with D l and T4).

It can be seen that when an applied voltage between a point between the current regulating arrangement 14 and the potential maintaining circuit 16 and the second connection point 2 becomes higher than a forward voltage drop between the base of the transistor T2 and the connection point 2, the potential generating circuit 30 is arranged to apply a base potential to the base of the first transistor. A potential difference between this base potential and a potential of the second connection point 2 is higher than a forward voltage drop between the base and the emitter of the transistor T2. A current is thus generated between the connection point 1 and the connection point 2. In all embodiments presented above, the current regulating arrangement 14 is furthermore arranged to apply the voltage between the point between said current regulating arrangement 14 and the potential maintaining circuit 16 and the second connection point 2 that is higher than a forward voltage drop between the base of the transistor T2 and the connection point 2 when a voltage between the first connection point 1 and the second connection point 2 exceeds a forward voltage drop between the base and the emitter of the first transistor T2. In other words, the connections start spontaneously when a sufficiently high voltage is applied between the first connection point 1 and the second connection point 2.

In many applications, it is requested that a current generator is constantly connected to a voltage source and that only the operation is switched on or off. This may be provided for in within the present ideas by supplying gates connected to the potential generating circuit 30 or current regulating arrangement 14. In the embodiments above the current regulating arrangement 14 comprises a current regulating resistor R3. In some embodiments presented below, the resistor R3 is kept, while in other embodiments it is removed. Due to the fact that there are numerous combinations thereof, the following embodiments will be described as a combination of two circuits, an "upper" and "lower". Any combination of these circuits will operate.

Fig. 8 shows a schematic drawing illustrating how an upper circuitry 10 (corresponding to the circuits shown in the figures 9- 16) is to be connected to a lower circuitry 20 (corresponding to the circuits in the figures 17-20) to accomplish a working constant current generator with gates.

The upper circuitry 10 has a first connection point 1 and a second gate S2, and two connections Al and Bl . The lower circuitry 10 has a second connection point 2 and a first gate SI, and two connections A2 and B2. Al is connected to A2 and B l is connected to B2 as shown with the dashed lines to get complete working circuits.

In test circuits of the different embodiments, the following components are used: Tl, T3: BC557B, T2, T4: BC547B, Dl, D2, D3, D4: 1N4001, D_s = Schottky diode BAT81. Another type of voltage reference is of course also possible to use. Op = MCP6002 (1/2), Rl, R2 = 33 Ω, R3 = 1.5 kO, R5 = 150 Ω, R6 = 10 kO, R7, R9 = 2.7 kO, R8 = 56 Ω, R10-R15 = 68 Ω, R16 = 68 Ω (alternatively 10 kΩ) and R20 = 330 Ω.

R10-R16 are resistors that are dimensioned in the upper circuitry to obtain suitable currents through the connections Al and Bl . The function of R4x (e.g. R44, R400, etc.) is to prevent that the connections start by mistake, for instance when the voltage over the circuit increases rapidly between connection point 1 and connection point 2, by mechanisms that are related to rapid voltage changes and the built-in capacitances of components, by leaking components or by interference.

Most of the connections shown in the figures 9-16 in combination with the connections shown in the figures 17-20 can easily be made to start by themselves by removing the R4x-resistors and create controlled leakages with resistors. These leakages give rise to a potential or current at the base of one of the transistors, where the current can be amplified and thereby cause the circuit to start. In most connections it is easy to create these currents with one or more resistors. For instance, resistors can be placed over the collector and emitter of T2. In the figures 9-16, resistors can be placed over the collector and emitter of Tl . In all connections these "leakage resistors" can also be connected between the connections A and B.

In the embodiments of Figs. 8-20 the current generators are started and stopped with gates provided that a certain voltage over a determined level is applied over the circuit between connection point 1 and connection point 2.

The advantages with the connections according to this description are, among other things, that it is possible to control them with gates or choose to allow them to start themselves. The choice of these properties can be decided by e.g. allowing a switch to connect and/ or disconnect the resistors with the denomination "R4x" (where x represents any number) which prevent the circuits to start easily by themselves/ in an unwanted fashion, or connect and/ or disconnect resistors which create controlled "leakage currents" as previously mentioned.

The circuits with gates are "self-sustaining", and in order for the circuits with gates to work like such, the upper circuitry that are illustrated in the figures 9-16 and the lower circuitry that are illustrated in the figures 17-20 need to have certain properties. These properties are for the upper circuitry that current must not flow from connection point 1 to connection Bl unless current flows between connection point 1 and connection Al . For the lower circuitry applies that current must not flow from connection A2 to connection point 2 unless current flows from connection B2 to connection point 2.

The current generator in these embodiments thus comprises a gate S2 in the upper circuitry. The current regulating arrangement 14 comprises a transistor Tl . An emitter of the transistor Tl is connected to the first connection point 1, possibly via a resistor, e,g. resistors Rl l, R13, R14 or R15. A collector of the transistor Tl is connected to the point between the current regulating arrangement 14 and the potential maintaining circuit 16,

1. e. the connection Bl, possibly via a current regulating resistor R3. A base of the transistor Tl is connected to the gate S2. This arrangement thus enabling start and stop of the current generator by an external voltage applied at the gate S2.

The current generator in these embodiments comprises in the lower circuitry a gate SI. This gate SI is either connected to a point between the current regulating arrangement 14 and the potential maintaining circuit 16, i.e. the connection Bl, or to the base of the first transistor T2. This arrangement enables start and stop of the current generator by an external voltage applied at the gate S 1.

In a combination between an upper circuitry and a lower circuitry, one of the gates S I and S2 may be omitted, since both gates can be used both for starting and stopping the current generation of the total circuit.

To start the circuits with gate S I, provided that a high enough voltage is applied between connection point 1 and connection point 2, the gate SI is brought to a potential which is higher than the potential at connection point

2. From a current perspective it is like driving a current into the gate SI which makes transistor T2 to start conducting current. When a current starts flowing through T2 the upper circuitry will make a current to start flowing also down via connection B2 and that results in that the connection enters regulated self-sustainment. The sum of the currents via A2 and B2 are determined/ limited by the lower circuitry, Figs. 17-20, and the proportions between the currents via Al and Bl are determined by the upper circuitry. The proportions may be different for different types of upper circuitry, Figs. 9- 16. Furthermore, in some embodiments the currents look different for different voltages over the circuits between connection point 1 and connection point 2. Any components provided between Al and A2 or Bl and B2, respectively, may also influence the proportions.

Furthermore, when the circuit has "started", a certain minimum current must always flow through the branches A1-A2 and B2-B2. If not, the self- sustainment will "fall".

To stop the circuits, the gate S 1 is brought to a potential which is so low that the current out from the gate is larger than the one brought to the point at the gate via connection B2. This will make transistor T2 to stop conducting current and the self-sustainment of the connection falls.

Start via the gate S2 occurs by bringing the gate S2 to a potential slightly lower than the potential at connection point 1, which results in that a current starts flowing down via connection B2 and the connection enters self-sustainment. To stop the currents with gate S2, the gate S2 is brought up to a potential which yields a current into the gate that is larger than the one running down via connection A2, which results in that no current can flow out from the base of transistor Tl which is connected to the gate S2 and thereby the transistor stops conducting current down via B2 and the self- sustainment falls.

The lower circuitries

By looking at the lower circuitries, Figs. 17-20, it can be seen that the current through the B branch drives the lower regulator. A part of the current in the B branch is branched off (R20, D2, D l) and generates the reference voltages for T2 in Fig. 17. A part of the current in the B branch is branched off and provides driving current to T2, T4 (R2, T2_be T4_be) in Fig. 18. A small part of the current in the B branch is branched off and provides driving voltage for the OP in the Figs. 19 and 20. Preventive resistors R40-R43, R400, R401 are as discussed further above connected between the second connection point 2 and/ or connected in parallel to the potential maintaining circuit 16.

The lower circuitries can then, by the aid of the above mentioned driving voltages/ currents, regulate the currents through the branches A and B. The currents from point A2 running through T2 and the currents from point B2 running through D3 and D4 are added and run jointly through Rl . The lower circuitries then compare the voltages over Rl with a reference voltage. This reference voltage has been generated by the aid of a small part of the current through the B branch according to the above explanation in the Figs. 17 and 18. In the Figs. 19 and 20, the reference voltage is however generated by the currents running through both branches. Alternatively, if a reference is connected as a separate branch between connection B2 and connection point 2, the reference voltage is generated by a small part of the current through branch B.

If the voltage over Rl is too high, i.e. higher than the reference voltage, U.D1+D2 in Fig. 17, U e of transistor T4 in Fig. 18 and UDS or other V_ref in the Figs. 19 and 20, the lower circuitries will "cut off the current through T2. If T2 completely cuts off the current through the A branch, the upper circuitries, Figs. 9-16, will completely cut off the current through the B branch. The relationship between the sizes of the currents through the two branches is determined by the upper circuitries.

A very precise current generator, which is relatively temperature stable, is acquired in Fig. 19. An operation amplifier Op is driven by the "internal currents" and a reference voltage (D_s/V_ref) is driven and established by "internal currents".

In Fig. 20, reference voltages to Op are generated by making a branch from connection B2 down to connection point 2. This branch constitutes a resistor R5 and a diode D_s or some other voltage reference in series in the mentioned order from connection B2 to connection point 2. From a point between these components the +input of the Op is connected. A disadvantage of this connection, if a Schottky diode is used, is that the voltage drop over and current through the resistor R5 and the diode D_s would vary more when the temperature in and current through D3 and D4 is changed compared to the connection shown in Fig. 19.

The upper circuitries

As discussed further above, preventive resistors R44-R48 can be connected between the first connection point 1 and the gate S2. In order for the circuitry to work it is required that current runs through both the upper and the lower circuitry, to get self-sustainment. This can be solved in different manners. It is possible to choose to allow a part of the total current to pass a power resistor at higher voltages over the circuit between connection point 1 and 2 in order to be able to use transistors with lower power durability as in Figs. 9 and 10.

Alternatively, it is possible to allow the currents be relatively equal in both branches as in Fig. 12 and 13. This is the case if RIO and Rl 1, and R12 and R13 are made equally large.

It is possible to allow the current in branch A be much smaller than the one in branch B, or the opposite way, as in Figs. 14-16. Since a certain minimum current must run through each branch one may need to choose to use a lower value for R48 and R49 than the ones that are used in the test connections in order to make the connections work well.

In Fig. 11, the voltage drop over R8 is allowed to be approximately 0.6 V at the moment when the currents through the branches are equal. That the currents are of equal size is determined by the total voltage drop over the circuit and IR9*Tl(hfe) when UR9 is approximately 0.6 V. The upper circuitries can be made in other variants. It is also possible to connect other components between the points Al and A2, and Bl and B2.

In Fig. 21 another set of embodiments of current generators are illustrated. The basic embodiment is drawn with full lines, while a few of the possible alternatives are indicated by broken lines. In the basic embodiment of Fig. 21, the current regulating arrangement 14 comprises two PNP transistors Tl and T3, connected by their emitters via a respective resistor R22 and R21, respectively, to the first connection point 1. In a preferred embodiment, if one selects the resistor R21 with a resistance twice the size of the resistance of resistor R22, the current I from connection point 1 divides in two parts I_A and IB, where IB is twice the size of .

In an alternative embodiment, the resistor R22 and the transistor Tl can be exchanged for the circuit illustrated in the broken insert at the upper right part of Fig. 21. By using two parallel flows, identical resistors and transistors can be used for R21 and T1/T3. This has the advantage that the currents through all six transistors becomes equal. The size of the R21 and R22 resistors can be from 0 Ω and upwards, depending on the degree of matching between the transistors. In this example, the value of R21 has been selected to be 165 Ω.

Different types of Darlington and/ or cascode coupled transistors can generally be used in all current regulating arrangements.

When using a cascode coupling in the lower part of the circuit, an additional transistor may be connected in series with transistor T2, connected with the collector to the point A2 and the emitter connected to the collector of transistor T2. A base potential for the additional transistor is preferably achieved by introducing a potential generating component in the conductor connecting the resistor R26 with the connection point between the resistor R26, the base of transistor T2 and the conductor that via an additional branch is connected to the base and collector of the transistor T4. The base of the additional transistor is thus connected to a point between the resistor R26 and the introduced potential generating component. When introducing such an additional transistor in a circuit according to Fig. 21, the potential generating component can be a resistor of a suitable value or some type of diode. If a cascode connection is used, the potential at the branching of the currents Ic and ID, i.e. at the point B2, has to be increased with an amount corresponding to the voltage drop over the potential generating component of the additional transistor. In order to increase the potential at the branching of the currents Ic and ID a same potential generating component can be introduced between the branching point of the currents Ic and ID and the emitter of the transistor T2 in series with the components in the potential maintaining circuit 16. In this example, resistors of suitable and the same resistances can be used in both branches. It is possible to use resistors of a same value since the currents Ic and ID in both branches in the example are equal. Resistors with a value of e.g. about 270 Ω would be operable. Alternatively, diode connected transistors of a same type and with a same connection as the transistor T4 would be possible to use.

A cascode coupling of the upper part of the circuit can be achieved in a similar way.

The cascode coupling results in that the current regulating transistor T2 operates under constant voltage conditions U_CE- This results in, among other things, that the power dissipation from and the temperature of the transistor T2 becomes constant even if the voltage over the connection varies. This leads to that the current regulation becomes less sensitive for voltage variations over the connection.

In another alternative embodiment, a start resistor Rs can be provided over the transistor Tl . This ensures that the circuit starts to conduct when a voltage is provided between connection points 1 and 2. Alternatively, a gate S2 can be provided, which enables a controlled start and stop of the circuit by applying appropriate voltages according to the ideas presented further above. In such embodiments, it is also in some applications of benefit to have so-called snubbers, exemplified by the three alternatives CI, R471 and C2+R472. These snubbers prohibit the circuit to start if the voltage over the connections are changed rapidly or due to outer disturbances.

In the main embodiment of Fig. 21, the potential maintaining circuit 16 comprises a Schottky diode DS2, e.g. a BAT 81, connected in series with a diode connected transistor T6. As discussed further above, there are also other alternative potential maintaining components that can be utilized in a similar way. The potential generating circuit 30 here comprises a resistor R26 in series with a diode connected transistor T4 and resistor 24. The base of transistor T2 is connected to the collector and base of the transistor T4. In the preferred embodiment discussed further above, each of the resistances of resistors R26 and R24 could be selected to be twice the resistance of resistor R23. In a test coupling, R24 and R26 were set to 165 Ω, while R23 was selected to be 82.5 Ω. The current in the B branch will then be divided into two equal parts Ic and ID. This means that the same current pass through all three transistors T2, T4 and T6, and the circuit thereby becomes very temperature stable.

In alternative embodiments, a start resistor Rs can be provided over the transistor T2. This ensures in an analogue manner to what was discussed above that the circuit starts to conduct when a voltage is provided between connection points 1 and 2. Alternatively, a gate S I can be provided, connected in two alternative points, which enables a controlled start and stop of the circuit by applying appropriate voltages according to the ideas presented further above. In such embodiments, it is also of benefit in some applications to have so-called snubbers, exemplified by the three alternatives C3, R473 and C4+R474. These snubbers may prohibit the circuit to start spontaneously if disturbances or rapid voltage changes are applied to the circuit. In further alternatives, the resistor R24 can be exchanged for a Schottky diode DS 1 (or any other component with diode-like properties) . The current IE then becomes defined by the voltage drop over the Schottky diode DS 1. The current regulating arrangement 14 gives a certain proportion between the currents in the two branches A and B. In such a case, the Schottky diode DS2 in the potential maintaining circuit 16 could be exchanged for a resistor R25. In the present particular example, with the values of the components as given here above, the currents IA, Ic and ID becomes equal if the value of the resistor R25 is set equal to the value of resistor R26.

The embodiments described above are to be understood as a few illustrative examples of the present invention. It will be understood by those skilled in the art that various modifications, combinations and changes may be made to the embodiments without departing from the scope of the present invention. In particular, different part solutions in the different embodiments can be combined in other configurations, where technically possible. The scope of the present invention is, however, defined by the appended claims.

Claims

1. A power durable current generator comprising:

a first connection point (1);

a first transistor (T2);

a first current regulating resistor (Rl, R4, R23);

a potential generating circuit (30); and

a second connection point (2);

a collector of said first transistor is connected, at least indirectly, to said first connection point (1) and an emitter of said first transistor is connected via at least said first current regulating resistor (Rl, R4, R23) to said second connection point (2);

said potential generating circuit (30) is connected to a base of said first transistor (T2),

characterized by

a power durable circuit (12), comprising a current regulating arrangement (14); and

a potential maintaining circuit (16);

said current regulating arrangement (14) of said power durable circuit (12) is connected by a first end to said first connection point (1);

said current regulating arrangement (14) of said power durable circuit (12) is connected by a second end, in series via said potential maintaining circuit (16), to said emitter of said first transistor (T2); and

said second end of said current regulating arrangement (14) of said power durable circuit (12) is further connected to said potential generating circuit (30).

2. Current generator according to claim 1, characterized in that said potential maintaining circuit (16) comprises one of:

a first pair of components providing a diode action, connected in series with each other; and

a component providing a diode action connected in series with a resistor.

3. Current generator according to claim 2, characterized in that said component or components providing a diode action is/ are selected from the group of:

a diode; and

a transistor connected in a diode coupling.

4. Current generator according to claim 1, characterized in that said potential maintaining circuit (16) comprises a resistor and in that said current regulating arrangement (14) is arranged to provide a constant current to said potential maintaining circuit (16).

5. Current generator according to any of the claims 1 to 4, characterized in that said potential generating circuit (30) comprises:

a resistor (R20, R26), connected with a first connection to a point between said current regulating arrangement (14) and said potential maintaining circuit (16), and with a second connection to said base of said first transistor (T2); and

a potential generating component arrangement connected between said base of said first transistor (T2) and said second connection point (2).

6. Current generator according to claim 5, characterized in that said potential generating component arrangement comprises a second transistor (T4); a base of said second transistor (T4) is connected to said emitter of said first transistor (T2); a collector of said second transistor (T4) is connected to said base of said first transistor (T2) .

7. Current generator according to claim 5, characterized in that said potential generating component arrangement comprises a second pair of diodes (D l, D2), the diodes (D l, D2) of said second pair of diodes are connected in series with each other.

8. The current generator according to any of the claims 1 to 4, characterized in that said potential generating circuit (30) comprises:

an operational amplifier (Op);

an output of said operational amplifier (Op) is connected to said base of said first transistor (T2);

a first supply voltage connection of said operational amplifier (Op) is connected to a point between said current regulating arrangement (14) and said potential maintaining circuit (16), and a second supply voltage connection of said operational amplifier (Op) is connected to said second connection point (2).

9. The current generator according to claim 8, characterized in that said potential generating circuit (30) further comprises:

a first resistor (R5) ; and

a Schottky diode (Ds) or other voltage reference component;

said first resistor (R5) is connected with a first connection to one of: said emitter of said first transistor (T2) and

a point between the current regulating arrangement (14) and the potential maintaining circuit (16);

said first resistor (R5) is connected with a second connection to said Schottky diode (Ds);

said Schottky diode (Ds) is connected between said first resistor (R5) and said second connection point (2);

said current generator further comprises a second resistor (R2) connected in series with said first current limiting resistor (Rl, R4, R23) between said emitter of the first transistor (T2) and said second connection point (2);

a first input of said operational amplifier (Op) is connected to a point between said first resistor (R5) and said Schottky diode (Ds), and a second input of said operational amplifier (Op) is connected to a point between said first current limiting resistor (Rl, R4, R23) and said second resistor (R2).

10. The current generator according to any of the claims 1 to 9, characterized in that said potential generating circuit (30) is arranged to apply a base potential to the base of the first transistor when a voltage between a point between said current regulating arrangement (14) and said potential maintaining circuit (16) and said second connection point (2) higher than a forward voltage drop between said base of said first transistor and said connection point (2) required for said first transistor (T2) to conduct is applied, a potential difference between said base potential and a potential of said second connection point (2) being higher than a forward voltage drop between said base and said emitter of said first transistor (T2) required for said first transistor (T2) to conduct.

11. The current generator according to claim 10, characterized in that said current regulating arrangement (14) is arranged to apply said voltage between a point between said current regulating arrangement (14) and said potential maintaining circuit (16) and said second connection point (2) higher than a forward voltage drop between said base of said first transistor and said connection point (2) required for said first transistor (T2) to conduct when a voltage between said first connection point (1) and said second connection point (2) exceeds a forward voltage drop between said base and said emitter of said first transistor (T2) required for said first transistor (T2) to conduct.

12. The current generator according to any of the claims 1 to 11, characterized in that said current regulating arrangement (14) comprises a second current regulating resistor (R3).

13. The current generator according to claim 10, characterized by a first gate (SI) connected to one of:

said point between said current regulating arrangement (14) and said potential maintaining circuit (16); and

said base of said first transistor (T2), thereby enabling start and stop of the current generator by an external voltage applied at said first gate (S I).

14. The current generator according to claim 13, characterized by a preventive resistor (R40-R43, R400, R401) connected between said second connection point (2) and/ or connected in parallel to said potential maintaining circuit (16).

15. The current generator according to claim 13 or 14, characterized by a second gate (S2);

said current regulating arrangement (14) comprises a transistor (Tl); a collector of said transistor (Tl) is connected to said first connection point (1), possibly via a resistor;

an emitter of said transistor (Tl) is connected to said point between said current regulating arrangement (14) and said potential maintaining circuit (16), possibly via a second current regulating resistor (R3);

a base of said transistor (Tl) is connected to said second gate (S2), thereby enabling start and stop of the current generator by an external voltage applied at said second gate (S2).

16. The current generator according to claim 15, characterized by a preventive resistor (R44-R48) connected between said first connection point (1) and said stop gate (S2).