IT202100003965A1 - “CIRCUIT TO REDUCE HEATING AND INCREASE THE EFFICIENCY OF SEMICONDUCTOR RECTIFIERS” - Google Patents

Description

DESCRIPTION of the invention with TITLE:

?Circuit for reducing heating and increasing the efficiency of semiconductor rectifiers?,

a) Field of technique

The invention described below relates to the field of semiconductor alternating voltage rectifiers. The circuit object of the present invention replaces the traditional diode. Some notable uses of this invention are, among others, the rectification of the single-wave and double-half-wave mains voltage.

b) State of the art

The semiconductor rectifiers are constituent elements of the rectifier circuits, which are of great importance since? they allow to transform electrical power from alternating mains voltage into direct voltage power, for multiple uses ranging from power supplies for electronic devices, to computers, to recharging systems for electric vehicles. Typically, the sinusoidal voltage of the single-phase type, but the same is true for three-phase systems with the known extensions, at the rectifier input, is processed so that the output voltage assumes only positive values. The circuits that follow the rectifier circuit, and which will not be discussed? furthermore, as they are known, they are responsible for leveling and making the electric voltage as constant as possible, ready for the end user

One of the main problems of a rectifier circuit? that the voltage applied at the input undergoes, before being taken at the output, a drop equal to the value of the threshold voltage of the rectifying element. Typically, the rectifier element? a semiconductor diode or, especially in integrated circuits, a diode-connected bipolar transistor. Because of said voltage drop, part of the electric power that passes through the rectifier device is transformed into heat, equal to the product of the value of the current passing through the circuit by the value of the overall potential drop on the diode, or on more? diodes in series, for example in the case of a diode bridge rectifier. Therefore, part of the useful power ? dissipated in the form of thermal power. The entity? The dissipated power ranges from a few milliwatts in rectifier circuits for small devices to hundreds or thousands of watts in circuits for high or very high power applications.

In the pre-existing technique there is therefore a triple unsolved problem connected to the electric rectification process: 1) the rectifying devices must be cooled to avoid irreversible damage, with cooling fins in the air and possibly with the addition of fans, or even with suitable circuits with refrigerant fluid, with a high cost; 2) the power dissipated in the rectifying elements (for example semiconductor diodes) ? subtracted from the useful power and therefore the energy efficiency of the rectification process? lowered; 3) each operating cycle of heating and subsequent cooling of each rectifying element leads to a decrease in its operating life time.

Lot of work ? been done on diodes and transistors, especially in high and very high power applications, to design, mathematically model and create structures suitable for the dissipation in air or in a suitable refrigerant liquid of the heat developed by the undesired conversion of electric power into thermal power inside a a device.

Semiconductor rectifiers made with BJT are known in the art. In GB2163306A ? shown is a bridge rectifier made with 8 p-n-p and n-p-n transistors for powering telephone equipment, with low powers. This patent for? it does not contain any information regarding the reduction of overheating of the grinding elements.

Patent US6563725B2 shows a circuit comprising BJTs used for rectification, with the advantage of higher speed? and reliability? and possibility? of monolithic integration with respect to the prior art, but not ? aimed at solving the problems of overheating of the rectifying elements.

Apparatuses for preventing heating or for cooling BJT transistors are known in the art. Techniques strictly related to the present invention are not known, but a series of patents on cooling fin arrangements (see for example US8912577B2 and EP0384301A2), use of gas or liquid cooling circuits (see for example US6829081B2 and WO2011065245A1), or particular semiconductor integrated configurations exploiting the Peltier effect, such as in US8344359B2. This last patent teaches to reduce the overheating of the BJT during its operation through the use of a geometric structure and an arrangement of materials of the BJT different from those of the prior art, and therefore specially made for cooling, but its content differs from the present invention that, on the contrary, ? a circuit arrangement of standard elements, as described below.

The circuit object of the present invention partially solves the problems of dissipating heat, increasing efficiency and lengthening the operating life of the rectifying element in a completely different and innovative way.

c) Description of the circuit to reduce heating and increase the efficiency of semiconductor rectifiers

The circuit object of the present invention ? consisting of a bipolar transistor (bipolar junction transistor, BJT) and an electric load connected between the base and collector of the aforementioned BJT. In this arrangement, the entire circuit between the base and emitter terminals acts electrically like a current rectifier, i.e. it behaves like a semiconductor diode. In particular, the actual grinding function ? performed by the low-emitter junction of the BJT. By appropriately dimensioning the electric load in relation to the voltage applied between the base and the emitter and to the intensity? of current flowing between the collector and the emitter, the BJT ? driven to work in its direct saturation region. In this working point, the voltage between collector and emitter ? much smaller than that between the base and the emitter. Since the BJT is in direct saturation, almost all the voltage falls on the load, which ? applied between the base and the emitter and the load ? crossed by almost all the current that passes through the BJT from the collector to the emitter. In particular, almost all the base-emitter voltage of the transistor falls on the load, this being approximately equal to the working voltage of a diode in direct conduction, from which the saturation voltage between the collector and emitter must be subtracted, which for? ? much lower than the base-emitter voltage.

Therefore, almost all the power applied from the outside to the circuit object of the present invention is dissipated on the load, and almost equal to the product of the base-emitter voltage and the collector current. Consequently, due to the law of conservation of energy, only a small fraction of the total power applied to the circuit is dissipated inside the BJT. As a result, the load, for example a resistor, experiences a temperature rise instead of the BJT. Therefore, in this circuit configuration, the BJT experiences reduced thermal stress. Furthermore, the load can be positioned at a considerable distance from the BJT, thus avoiding heating the BJT by transmission or radiation of thermal energy. The present invention therefore considerably reduces the problem of the thermal stress of the semiconductor rectifying elements. Furthermore, with the present invention , the overall efficiency of the rectification process considerably increased by placing a payload in place of the resistor between the base and collector of the BJT.

The electronic circuit 100 object of the present invention ? shown in Figure 1a. The BJT 101 transistor? connected to a load R 102, for example a resistor, through the base terminals B 103 and emitter E 104. The circuit 100 ? accessible only from terminals A 105 and B 106, and between them can? be viewed as a whole as a two-pole which behaves electrically like a diode having anode at the A terminal 105 and cathode at the B terminal 106, respectively.

Consider the circuit 100 forming part of the circuit 107 of Figure 1b. The variable voltage VG ? supplied by the voltage generator G 108 and the BJT n-p-n transistor 101 ? connected to generator G 108 via base terminals B 103 and emitter E 104. Load R 102 connects base terminals B 103 and collector C 106 of the BJT 101.

The following considerations for n-p-n transistors also apply to p-n-p transistors, taking into account the correct polarity? of voltages and direction of currents.

Let us consider below the circuit 107 shown in Figure 1b. The purpose of the circuit? that of rectifying the current flowing in it, thus behaving at the external terminals like a semiconductor diode.

In it, the task of rectifying the current flowing following the application of the variable voltage VG supplied by the voltage generator G 108 ? performed by the n-p-n BJT transistor 101 connected to the generator G 108 via the base terminals B 103 and emitter E 104, which therefore act towards the generator G 108 like the terminals of a semiconductor rectifying diode.

When the VG voltage exceeds the BJT 101 transistor VBE<ON> voltage, the base-emitter junction conducts. By suitably sizing the impedance value of the load R 102, the BJT transistor 101 works in its so-called direct saturation operating region 200. A typical direct saturation operating region 200 ? shown in Figure 2 for an n-p-n type transistor. In this region we have:

VBE = VBE<SAT>, (1) which assumes a typical value slightly higher than VBE<ON>. Furthermore we have:

IC = bSATIB, (2) with bSAT > 1, where the current gain bSAT ? typically lower than the bF of the forward active region. In Figure 2 ? shown as an example the working point Q = (VCE<*>, IC<*>) 201, in correspondence of which bSAT ? much greater than 1.

At the operating point Q 201, does the current IC<* >and the collector-emitter voltage VCE<* > flow in the BJT 101? equal to or lower than VCE<SAT>, which for example assumes values in the approximate range 0.01-0.2 V in the case of a BJT made in silicon.

So, can you? write for the base-collector voltage:

VBC<* >= VBE<*>- VCE<*>? VBE<* >= VBE<SAT>. (3) The power supplied to the circuit 107 by the voltage generator G 108 of value VG ?:

PG = VGIG, (4) where:

IG = IB<* >+ IC<*>. (5) The power dissipated in the load R 102 ?:

PR = VRIR = VBC<* >IC<* >? VBE<*>bSATIB<*>. (6) On the other hand, by the law of conservation of energy, we have:

PBJT = PG - PR = VGIG - VBE<*>bSATIB<* >= VG (IB<* >+ IC<*>) - VBE<*>bSATIB<* >=

= VBE<*>(IB<* >+ bSATIB<*>) - VBE<*>bSATIB<* >= VBE<*>IB<*>. (7) Therefore, using (3) and (6), we can? write:

PBJT < VBE<*>bSATIB<* >? VBC<*>bSATIB<* >= PR, (8) place bSAT > 1.

(8) shows that PBJT < PR, all the more? how much bSAT ? greater than 1.

By suitably choosing the value of the load R 102, almost all the power transferred to the circuit 100 by the generator G 108 PG ? dissipated on load R 102.

The load R 102 therefore has the function of dissipating almost all the power which would otherwise be dissipated on the semiconductor device in charge of the rectifying action.

In particular, in one of the possible embodiments of the present invention, the load ? a resistor R 102 e is: i) made with materials resistant to temperatures much higher than those bearable by any semiconductor material (for example tungsten wire or other suitable material, resistant to sufficiently high temperatures) ii) placed in a position conveniently distant from the BJT 101 to prevent the heat developed in resistor R 102 from heating up the BJT 101 itself.

With reference to Figure 1c , an alternative configuration 111 of the present invention uses a payload R 102 so that power PR is not wasted. There? ? done directly or by interposing between the base B 103 and the collector C 106 a suitable power conversion circuit 109, for example realized with switching technology. In this configuration 111, the power otherwise lost due to thermal dissipation on the resistor R 102 ? instead recovered and used by payload ZLOAD 110, increasing cos? the overall efficiency of the rectification process considerably. The power converter 109 is also in charge of varying the impedance seen by the BJT 101 between the base B 103 and the collector C 106 so as to maximize the overall efficiency for each operating condition.

The news? absolute of the invention lies at least in the following elements:

1) the circuit 100 reduces the heating of the BJT 101 by power dissipation by shifting the dissipation mainly in the load, for example a resistor, R 102, preserving the rectifying function performed by the BJT 101, and behaves like a semiconductor rectifying diode at the terminals A 105 and B 106;

2) power dissipation ? largely shifted from BJT 101 to R 102 cargo due to entirely original exploitation of BJT 101 operation in its direct saturation region 200;

3) in an alternative embodiment 111 of the circuit, the efficiency of the rectification process ? considerably increased recovering on payload ZLOAD 110, connected instead of R 102, the otherwise dissipated power.

4) the entity? of the benefit described in 1), 2) and 3) depends on the value of R 102 and on the value actually achieved by bSAT, also taking into account the specific BJT 101 used and the other boundary conditions;

5) as stated in points 1), 2) and 3), the object of this invention differs from all other devices and systems in order to reduce the effects of heating due to power dissipation and to raise the conversion efficiency of power in semiconductor rectifiers. In fact, the power to be dissipated is moved from the BJT 101 to the load R 102 and not removed from the BJT 101 with thermal measures.

d) Description of the drawings

Figure 1

Figure 1a

Figure 1a illustrates the elements constituting the circuit 100 object of the present invention and their interconnection, exemplifying the case of use of a BJT 101 of the n-p-n type.

In particular, the following elements are shown:

- a bipolar junction transistor BJT 101;

- an electrical load R 102;

- a terminal A;

- a B clamp.

The BJT 101 has the base B 103 and the collector C 106 connected via the load R 102.

The circuit 100 replaces the traditional diode in all its applications, by connecting terminal A 105 in place of the anode of the diode and terminal B 106 in place of the cathode of the diode. Figure 1b

Figure 1b shows the connection of the circuit 100 object of the present invention with a voltage source VG 108, supporting the description of equations (1) to (8).

In particular, the following elements are shown:

- a bipolar junction transistor BJT 101;

- an electrical load R 102;

- a G 108 variable voltage generator of VG value.

Figure 1c

Figure 1c shows the alternative configuration 111 of the invention in which the power, which in the configuration of Figure 1a is dissipated on the R load 102, is instead transferred via the power converter (POWER CONVERTER) 109 to the ZLOAD payload 110.

In particular, the following elements are shown:

- a bipolar junction transistor BJT 101;

- a power converter (POWER CONVERTER) 109;

- a ZLOAD 110 payload.

- a clamp A;

- a B clamp.

Figure 2

Figure 2 shows the graph of the VCE-IC output characteristics of a typical n-p-n type BJT transistor. The graph shows that, within the forward saturation region (FORWARD SATURATION REGION) 200, for example in the working point Q 201, the collector current IC ? much greater than the base current IB, and at the same time the collector-emitter voltage VCE ? much smaller than the VBE<ON>.

In particular, the following elements are shown:

- a graph of the output characteristics in the VCE-IC plane typical of a BJT bipolar junction transistor;

- an operating point Q 201 of the BJT transistor;

- the forward saturation region (FORWARD SATURATION REGION) 200.

Figure 3

Figure 3a

Figure 3a shows the prior art, i.e. the traditional single half-wave rectifier circuit made with diode 301.

In particular, the following elements are shown:

- a variable voltage generator of value VG 108;

- a diode 301;

- a load resistor Rload 300.

Figure 3b

Figure 3b shows a single half-wave rectifier circuit, example of application of the circuit 100 object of the present invention, in which R 102 ? a resistor. The single half-wave rectifier circuit? realized in an innovative way by replacing the diode 301 with the circuit 100 object of the present invention. It behaves in the same way as the circuit of Figure 3a with respect to the load resistor 300.

In particular, the following elements are shown:

- a variable voltage generator of value VG 108;

- a circuit 100 object of the present invention;

- a load resistor Rload 300.

Figure 3c

Figure 3c shows the prior art, i.e. the diode bridge circuit made in the traditional way with four diodes 301.

In particular, the following elements are shown:

- a variable voltage generator of value VG 108;

- four diodes 301 bridged;

- a load resistor Rload 300.

Figure 3d

Figure 3d shows a bridge circuit, example of application of the circuit 100 object of the present invention, in which R 102 ? a resistor. The bridge circuit? made in an innovative way by replacing each of the four diodes 301 of the traditional bridge with the circuit 100. The exemplary load ? consisting of the resistor Rload 300. It behaves in the same way as the circuit of Figure 3c with respect to the load resistor 300.

In particular, the following elements are shown:

- a variable voltage generator of value VG 108;

- four circuits 100 object of the present invention connected as a bridge;

- a load resistor Rload 300.

e) Implementation method of the invention

The invention? implemented by realizing, with all the precautions known in the art, the circuit 100 with a BJT 101 and a load R 102, interconnected as indicated in Figure 1a, or, as shown in the circuit 111 in Figure 1c, by interposing between the base B 103 and the manifold C 106 a power converter so as to transfer power, which would otherwise be dissipated on R 102, to the ZLOAD payload 110 with the desired voltage or current level. The circuit 100 forms part of the single and double half-wave rectifiers, as shown in Figures 3b and 3d, to be considered examples but not limited to these.

f) Industrial use of the invention

The object of the present invention 100 ? used by replacing the traditional diode of the pre-existing technique in each electrical circuit where ? It is possible to take significant advantage of the lower heating of the BJT 101 compared to the traditional diode. In medium and high power applications, the configuration 111 shown in Figure 1c provides a significant increase in overall efficiency, through the transfer to a ZLOAD payload 110 of the power that instead in the configuration of Figure 1a ? dissipated on load R 102.

Two typical applications of circuit 100 are shown in Figure 3. In Figure 3a ? shown is a traditional diode single half-wave rectifier 301 and in Figure 3b ? shown is the innovative circuit created by replacing the traditional diode with the circuit 100 object of this invention. The circuit of Figure 3b performs the same function as the circuit of Figure 3a with respect to the load resistor Rload 300.

The approximate value of R 102 which brings the BJT 101 into saturation, for each value of Rload and VG, ? obtained through the following formula, in the case where R 102 is a resistor of value:

R? VBE<SAT >Rload/(VG - VBE<SAT>), (9)

where the approximation ? as much better as bSAT ? greater than 1.

In Figure 3c ? shown a double half-wave rectifier composed of four traditional diodes; the Figure shows 3d the innovative circuit realized by replacing each of the four diodes of the traditional bridge with the circuit 100 object of this invention. The circuit of Figure 3d performs the same function as the circuit of Figure 3c with respect to the load resistor Rload 300.

Finally, it is clear that modifications and variations can be made to what is described and illustrated herein without thereby departing from the scope of protection of the present invention, as defined in the attached claims.

Claims (5)

CLAIMS of the invention entitled: ?Circuit for reducing heating and increasing the efficiency of semiconductor rectifiers?, Claims 1) A circuit 100 for reducing heating and increasing the efficiency of semiconductor rectifiers; said circuit 100 comprises at least the following elements: a - a bipolar transistor BJT 101; b - an electrical load R 102; said circuit 100 ? characterized by the fact that the electric load R 102 ? connected between the base terminal B 103 and the collector terminal C 106 of the BJT 101. 2) A circuit according to claim 1, in which said circuit 100 the electric load R 102 ? consisting of a resistor. 3) A circuit according to claim 1, in which said circuit 100 the electric load connected between base B 103 and collector C 106 of the BJT 101 ? consisting of the input port of a two-port network 109 which constitutes a power converter circuit (POWER CONVERTER) 109, which power converter 109 supplies the ZLOAD payload 110 connected to its output port with the desired electrical regime. 4) A circuit according to claim 2, in which said circuit 100 the resistance value of the resistor R 102 ? chosen so as to fix the working point Q 201 of the BJT 101 in its direct saturation region 200 in relation to the electrical load Rload 300 considered, according to the approximate formula R ? VBE<SAT >Rload/(VG - VBE<SAT>), where VBE<SAT >? the base-emitter saturation voltage of the BJT 101. 5) A circuit according to claim 3, in which said circuit 100 the value of the input impedance ZIN of the two-gate network 109 ? chosen so as to fix the working point Q 201 of the BJT 101 in its direct saturation region 200 in relation to the electrical load Rload 300 considered, according to the approximate formula ZIN ? VBE<SAT >Rload/(VG - VBE<SAT>), where VBE<SAT >? the base-emitter saturation voltage of the BJT 101.