WO2011091497A2

WO2011091497A2 - Low voltage power supply

Info

Publication number: WO2011091497A2
Application number: PCT/BR2011/000021
Authority: WO
Inventors: Rodrigo Cezar De Mello Castaldo; Fernando Bastos DE MAGALHÃES; Neomar Giacomini
Original assignee: Whirpool S.A.
Priority date: 2010-01-27
Filing date: 2011-01-18
Publication date: 2011-08-04
Also published as: BRPI1000249A2; WO2011091497A3

Abstract

The present invention relates to a low voltage power supply (1 ) equipped with discrete components. The power supply comprises a timer circuit (4) able to establish a time basis variable in the shooting of a main switch (5), switching the electric conduction of the supply (1). Moreover, the supply (1) also includes two other components capable of interfering with the switching frequency of the supply, namely: current limiter (13) and output voltage limiter (12). When the current limiter (13) detects an overcurrent situation or when the output voltage limiter (12) detects an overvoltage situation, a latch (14) is actuated causing the timer circuit voltage (4) to be deviated from the main switch (5) to itself, thus causing the opening of the main switch (5).

Description

"LOW VOLTAGE POWER SUPPLY"

FIELD OF THE APPLICATION

The present invention relates to a low voltage power supply, especially a power supply composed of discrete electronic devices.

DISCLOSURE OF THE STATE OF THE ART

All types of electronic controlling circuits, whatever their applications, require an electric power supply that provides voltage and electric current within values and waveforms appropriate for their operation.

In the current state of the art, there are numerous types, brands and sizes of power supplies for several types of application. With respect to the field of home appliances, however, the options of power supplies for the controlling circuits, unfortunately, are not so cheap especially when it comes to products designed within a low cost philosophy, besides they do not present much flexibility with regard to power and the output voltage.

This is because these power supplies are provided in the form of a closed solution. Thus, in the topology of each manufacturer it is only possible to configure some specific components, in order to change the output voltage. Still, these circuits comprise as main component an integrated circuit responsible for, among other functions, controlling the switching characteristic of the power supplies applied in controlling systems.

Due to this type of construction that the power supplies of the prior art have, it becomes impossible to replace one component of a power supply from a manufacturer by another component of another power supply from another manufacturer. This problem is explained by the fact that each manufacturer develops its power supply to operate exclusively with your integrated circuit. Thus, it is virtually impossible to try to lower the costs of the power supply of a controlling system of a home applicance by means of the exchange of parts from different manufacturers.

In this sense, it is possible to note that the current context of power supplies for the controlling systems of home appliances needs a low cost solution, with flexibility, i.e. that can be assembled by similar components from different manufacturers and that also be flexible in the choice of power and output voltage.

OBJECTIVES OF THE INVENTION

It is therefore an object of this invention to provide a power supply of low cost and flexible in terms of power and output voltage and flexible in terms of the possibility of choice of components from different manufacturers.

SUMARY OF THE INVENTION

The objects of the present invention are achieved by means of a low voltage power supply comprising: a low voltage input stage comprising a rectifier; an output stage connected to a load; and this supply further comprises: a timer circuit which has its inputs connected to the DC bus of the supply and it is configured to have its time basis variable as the voltage change of said DC bus; a main switch comprising at least one actuation terminal and two conduction terminals, and the timer circuit output is connected to said actuation terminal; an electric energy storage device electrically connected to the first conduction terminal of the main switch and designed to supply an actuator. The actuator has its input electrically connected to the electric energy storage device and its output connected to the actuation terminal of the main switch. The actuator is also configured to perform fast discharges of energy in its output, an output voltage limiter being connected in parallel to the output stage of the supply, said limiter being further configured to actuate a latch through its output, a current limiter having its input electrically connected in series to the second conduction terminal of the main switch, said current limiter being configured to actuate a latch, an overcurrent protector having its input electrically connected in series with the load and its output electrically connected to the output voltage limiter circuit, and a latch having its input electrically connected to the output of the current limiter and the output voltage limiter and being still connected to the output of the timer circuit and to the actuation terminal (6) of the main switch, the latch being configured to receive the discharge of the timer circuit upon its actuation by current limiter and / or by the output voltage limiter.

BRIEF DESCRIPTION OF THE DRAWINGS

The figures show:

Figure 1 - A block diagram of the main components of the power supply of the present invention;

Figura 2 - The preferred embodiment of the power supply circuit of the present invention having highlighted the components of each block diagram of figure 1 ;

Figura 3 - The path traveled by the current during the beginning of the supply start cycle;

Figure 4 - The path traveled by the current when of the setting of the conduction of the main switch;

Figure 5 - The actuator subcircuit highlighted;

Figura 6 - The path traveled by the current in the actuator subcircuit when of the polarization of the actuator transistor;

Figure 7 - The graphs represent the voltages, over time, which act during switching of the main switch of the power supply of the present invention;

Figure 8 - The path traveled by the current when the main switch has just been opened;

Figure 9 - The path traveled by the current when of the polarization of the transistor of the output voltage limiter;

Figure 10 - The path traveled by the current when of the polarization of the latch transistors by the output voltage limiter;

Figure 11 - The current limiter highlighted; and

Figure 12 - The path traveled by the current when of the polarization of the latch transistors by the current limiter;

Figure 13 - The path traveled by the current when of the polarization of the protecting circuit of overcurrent and / or short circuit in the output of the power supply of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The low voltage power supply 1 of the present invention is preferably applied in home appliances and more preferably used to supply controlling systems for home appliances.

In addition, the power supply 1 of the present invention is a circuit preferably mounted in a printed circuit board, as the skilled in the art may well imagine.

Figure 1 schematically illustrates the power supply by means of a block diagram showing the main subcircuits that make up the supply circuit 1. From this figure 1 it is possible to note that the power supply 1 comprises an electric voltage input which is preferably represented by the electric energy grid 2 associated to an input stage 3. In the preferred embodiment of the present invention, the input stage 3 comprises a resistor and a rectifier. In Figures 1 to 6 and 8 to 13, the input stage 3 is represented by means of the resistor R1 and its rectifier is represented by two diodes D1 and D2.

The electric energy grid 2, as known by the skilled in the art, provides alternating electric voltage, and the electronic controls of the home appliances and much of the electronic equipments do not use the electric voltage such as it is provided by the grid 2, i.e. in alternate manner. Thus, the low voltage power supply 1 of the present invention comprises a rectifier formed by the two diodes D1 and D2 of the input stage 3 of electric voltage.

Considering that rectifiers and their applications in power supplies are elements already known by the skilled in the art, they will not be detailed here. In this regard, any types of rectifiers consistent with the characteristics of the power supply of the present invention can be employed.

Besides the input stage 3 of electric voltage, a power supply 1 of the present invention also includes other elements widely found in power supplies, such as: electromagnetic compatibility filter 17 (also known as EMC filter), the minimum voltage maintainer 18 in the busses 16 and the supply 1 and an overvoltage protector 19.

The electromagnetic compatibility filter 17 and the minimum voltage maintainer 18 in the busses 16 of the supply 1 are ilustrated in the figures 1 to 6 and 8 to 12 by means of the combination of two capacitors C1 and C2 with a resistor R2. Figure 2 more clearly illustrates the components that are part of the electromagnetic compatibility filter 17 and the minimum voltage maintainer 18.

The overvoltage protector 19, in turn, consists of a varistor Var1 electrically connected in parallel to the electric energy grid 2.

ELEMENTS OF THE STARTING CYCLE OF THE POWER SUPPLY

The low voltage power supply 1 of the present invention further comprises a timer circuit 4, which establishes a time basis for the beginning of the conduction of the main switch 5 of the power supply 1 of the present invention. More precisely, the timer circuit 4 is connected in parallel to the DC bus 16 of the power supply 1 and it is configured to have its time basis varying as said DC bus 16 varies its voltage, thus causing the main switch 5 to be actuated on a variable time base, i.e., it is actuated with variable switching frequency. From the figures, it can be seen, more precisely, the timer circuit 4 has its inputs connected to the DC bus 16 of the power supply 1 of the present invention.

As it can be seen from figure 14, preferably the timer circuit 4 is an RC circuit, in this case, formed by the resistors R3 and R19 and by the capacitor C3. Thus, when the capacitor C3 is charged, in a given moment, the potential difference on it is enough to start the conduction of the main switch 5 and consequently to start the conduction of electric current.

The main switch 5 comprises at least one actuation terminal 6 and two conduction terminals 7. As it can be seen from figure 1 , the output of the timer circuit 4 is connected to the actuation terminal 6 of the main switch 5. In the preferred embodiment, illustrated in Figure 2, the main switch 5 is a mosfet type transistor, thereby its actuation terminal 6 is the gate terminal ("gate") and its conduction terminals 7 are the drain terminals and "source". Obviously, other types of switches 5 can be used, or even other types of transistors can be employed in this invention, provided they meet the need for an operation of the supply of the present invention.

The main switch 5 has a first conduction terminal 7 connected to an electric energy storage device 8. Thus, when the main switch 5 is conducting current through its conduction terminals 7, the electric energy storage device 7 is loaded. In the preferred embodiment of the present invention, this electric energy storage device 7 is an inductor connected to the first conduction terminal 7 of the main switch 5, i.e., to the drain terminal of the main switch 5. However, other energy storage devices 8 may be employed within the scope of this invention.

The electric energy storage device 8 is also designed to polarize an actuator 9. The actuator 9 has its inputs electrically connected to the energy storage device 8 and its output electrically connected to the conduction terminal 6 of the main switch 5. In the preferred embodiment illustrated in Figure 2, the actuator 9 of the power supply 1 of the present invention is a transistorized subcircuit comprising a fast discharge capacitor C4 and at least one transistor Q3. Thus, when the electric voltage on the electric energy storage device 8 assumes a value that polarizes the transistor Q3 of the actuator 9, it occurs the conduction of electric current between the fast discharge capacitor C4 (connected to its emitter terminal) and the resistor R5 (connected to its collector terminal). Thus, since the resistor R5 of the actuator 9 is electrically connected to the actuation terminal 6 of the main switch 5, the electric current in this situation circulates through the terminal 6 of the main switch 5.

OPERATION OF THE SUPPLY IN THE START (OUTPUT VOLTAGE BELOW THE NOMINAL VOLTAGE)

The timer circuit 4, the energy storage device 8 and the actuator 9 are the components involved in the shooting of the main switch 5 of the power supply 1.

Thus, with regard specifically to the shooting of the main switch 5 of the low voltage power supply 1 , initially the voltage from the electric energy grid 2 is rectified and then supplies the timer circuit 4. The timer circuit 4, in turn, has its voltage increased over time, thus causing the conduction of the main switch 5. In continuation, by the effect of the electric current conduction through the main switch 5, the electric energy storage device 8 has its power increased over time. Thus, the actuator 9 is polarized by the electric energy storage device 8, which causes a fast discharge of electric current on the actuation terminal 6 of the main switch 6, which undergoes a large increase in tension, and then an abrupt drop to a value which tends to zero. This abrupt drop is caused by the latch circuit 14 that in this stage of operation of the power supply 1 is actuated by a current limiter circuit 13, as will be explained later.

In more details, as it can be seen from Figure 3, with the onset of the circuit supply of the supply 1 by the electric energy grid 2, the capacitor C3 of the timer circuit 4 begins to be loaded. So, it is established an electric voltage between the actuation terminal ("gate") and the second conduction terminal ("sorce") able to cause the main switch to conduct current through its conduction terminals 7. The voltage required to make the transistor used as main switch in this invention is of about 5 volts.

In Figure 3, it is highlighted the circuit traveled by the electric current just before the main switch 5 to enter into conduction. Figure 4, in turn, highlights the path traveled by the current flowing through the load 10 as soon it is established the conduction between the conduction terminals 7 of the main switch 5. In both figures, the load 10 is powered.

The electric energy storage device 8, from the moment it is established the conduction between the conduction terminals 7 of the main switch 5, begins to be loaded. As it can be noted, this storage device 8 is connected in parallel with the circuit input of the actuator 9, more precisely being connected with the basis terminals and emitter of the transistor Q3 of the actuator 9. Thus, when the voltage on the electric energy storage device 8 reaches a level sufficient to polarize the transistorized circuit of the actuator 9, the transistor Q3 of the actuator 9 enters into conduction mode. Thus, an electric current rapidly flows through the capacitor C4 and is directed to the actuation terminal 6 of the main switch 5. This causes a voltage peak in the actuation terminal 6 of the main switch 5, causing the main switch 5 to completely enter into conduction.

Figure 5 highlights the subcircuit of the supply 1 that corresponds to the actuator 9. Figure 6, in turn, illustrates the path traveled by the electric current responsible for the peak voltage at the actuation terminal 6 of the main switch 5, when the transistor Q3 of the actuator 9 is polarized and enters into conduction.

The graphs illustrated in Figure 7 represent the voltages, over time, which act during the switching the main switch 5 of the power supply 1 of the present invention. The first curve represents the voltage on the capacitor C3 of the timer circuit 4. The second curve represents the voltage peak on the actuation terminal 6 of the main switch 5, as a result of the action of the actuator circuit 9. The third curve in Figure 7 represents the voltage measured between the "gate" terminals, or actuation terminal 6, and the "source" terminal of the main switch 5 that is, more precisely, the sum of the voltages represented in the first and second curves of Figure 7.

When the main switch 5 completely enters into conduction, the electric current begins to circulate (and to increase gradually) through a sensor element 20 of the current limiter circuit 13. In the preferred embodiment of the present invention, this sensor element 20 is a resistor that is represented in the figures by the reference R10 and it is part of the current limiter 13. The current limiter 13, in turn, has its input electrically connected in series to the second conduction terminal 7 of the main switch 5 and it is configured to actuate a latch circuit 14, as will be explained below. Moreover, it is worth mentioning that the current limiter 13 comprises, in addition to the current sensor element 20, a second resistor R9 and a capacitor C5, which form a low-pass filter, as shown in Figure 11.

In the preferred embodiment of the present invention, the latch 14 has its input electrically connected to the output of current limiter 13 and to the output of the output voltage limiter 12. Furtermore, the latch 14 is connected to the timer circuit output 4 and to the actuation terminal 6 of the main switch 5. Thus, the latch 14 is configured to receive the discharge of the timer circuit 4 through its actuation by the current limiter 13 and / or the by output voltage limiter 12.

Thus, the gradual current increase causes a gradual voltage increase to appear through the sensor element 20 (R10 in the figures) of the current limiter circuit 13. This voltage increases until the output of the current limiter circuit 13 have a voltage sufficient to actuate the latch circuit 14 illustrated in Figure 1. In turn, when actuated, the latch circuit 14 is responsible for reducing the voltage very quickly, until then present in the actuation terminal 6 of the main switch 5, to levels that tend to zero. This voltage level causes the main switch 5 to enter into cut, interrupting the flow of current through the same. When the latch 14 is actuated, the energy accumulated in the timer circuit 4 (more precisely in the capacitor C3) is discharged by the latch 14 itself. This operation is represented by figure 12.

When the main switch 5 interrupts the conduction, there is still electric energy accumulated in the electric energy storage device 8. Thus, this energy is discharged over an output stage 11 of the power supply, which maintains the load 10 until the energy of the storage device 8 is fully discharged or until the main switch 5 is again in conduction. Figure 8 illustrates the path traveled by the current when it occurs. As it can be seen, the energy storage device 8 (in which case, an inductor) is discharged on the output stage 11, represented by the subcircuit formed by the load 10, by a capacitor C6 of the output stage 11 and by a diode D8 of the output stage. It is important to note that in this situation of energy discharge, the storage device 8 has its polarity reversed, that is, the polarity of the storage device 8 has one configuration when it supplies the actuator 9 and one configuration inverted regarding the first when it discharges on the output stage 11. This inversion of polarity causes the main switch 5 to be in cut, part of the energy stored in the storage device 8 is discharged through the diode D5, the resistor R11 and the diode D4, all contained in the actuator 9. This current flow is also represented by figure 8. This process forces the cutting of the transistor Q3 of the actuator 9. After the electric energy storage device 8 is nearly or completely discharged, the cycle of shooting of the main switch 5 described here starts up again, causing the output voltage of the supply 1 to be increased by the passage of each cycle of shooting. When the output voltage of the supply 1 , after successive cycles of shooting, reachs the nominal value, the voltage supply 1 of the present invention has its operation modified by means of the intervention of other subcircuits.

SUPPLY OPERATION AFTER ITS OUTPUT REACHES THE NOMINAL VOLTAGE

The starting cycle from the power supply 1 , described above, as already stated, in- creases the output voltage over time. Thus, to prevent the output voltage to exceed the nominal value and cause damage to its load (controlling system of a home appliance), the present invention comprises the output voltage limiter subcircuit 12.

As it can be seen from figure 1 , the output voltage limiter 12 is connected in parallel with the output stage 11 and with the load 10 of the power supply 1 of the present invention. Due to this connection in parallel, the output voltage limiter 12 uses the output voltage of the supply 1 to check if the voltage is above the nominal value. In the preferred embodiment of the present invention, the output voltage limiter 12 comprises at least one transistor Q2 able to be polarized by an overvoltage applied to the output stage 1 , being said transistor Q2 of the output voltage limiter 12 connected to the latch 14 by means of a resistor R15. Thus, if the output voltage is above the nominal value, the output voltage limiter 12 actuates the latch 14, electrically connected to the actuation terminal 6 of the main switch 5.

Just as in the previous operating mode, when actuated, the latch circuit 14 is responsible for rapidly reducing the voltage so far present at the actuation terminal 6 of the main switch 5 to level tending to zero. This voltage level causes the main switch 5 to enter into cut, interrupting the flow of current through the same.

The capacitor C6 of the output stage 11 of the supply 1 is connected in parallel with the output voltage limiter 12. Thus, the output voltage is directly applied on the output voltage limiter 12, which makes the action of the limiter 12 immediate, in the case of overvoltage.

The output voltage limiter subcircuit 12 is designed to actuate the latch 14 from the polarization of a transistor Q2. Thus, if the output voltage is such that enables the polarization of this transistor, it occurs the conduction of electric current through this device to the input of the latch 14, causing the latch 14 to be actuated. Figure 9 shows the path traveled by the current when of the polarization of the latch transistor 14 by the output voltage limiter.

The latch 14 comprises a capacitor that is directly charged by the output voltage limiter subcircuit 12. This capacitor C5 of the latch 14 is designed to have a short load time, so that it can quickly polarize the transistors Q4 and Q5 composing the subcircuit of the latch 14. Once these transistors Q4 and Q5 composing the subcircuit of the latch 14 are polarized, the capacitor C3 of the timer circuit 4 discharges on the components of the latch 14. This situation can be best viewed by means of figure 10, which highlights the path traveled by the current in this situation.

Parallel to the controlling of overvoltage, the present invention also controls situations of overcurrent and / or short circuit in the output of the power supply 1. The subcircuit responsible for detecting and actuating this protection is the overcurrent protective subcircuit 15. The output of this overcurrent protective subcircuit is connected to the output voltage limiter 12, to take advantage of this connection with the latch 14. In the preferred embodiment of the present invention, so as to take advantage of the conection of the same with the latch 14. In the preferred embodiment of the present invention, the overcurrent protector 15 has its input electrically connected in series with the load 10 and its output electrically connected to the output voltage limiter circuit 12.

In this sense, when an overcurrent and / or short circuit situation occurs, the overcurrent protector 15 actuates the latch 14 through the action of one part of the output voltage limiter circuit 12. More precisely, when this situation occurs, the overcurrent protector 15 can polarize the transistor Q2 of the output voltage limiter circuit 12. In turn, the polarization (conduction) of Q2 results in the actuation of the latch 14, thus causing the main switch 5 to prematurely enter into cut, protecting the circuit of the power supply 1.

In both cases wherein the overcurrent and / or short circuit protective subcircuit 15 or the output voltage limiter 12 operate, the supply 1 interrupts the conduction, once the main switch 5 is opened, and the load 10 is still supplied by means of the discharge of the electric energy storage device 8 on the subcircuit of the output stage 11 of the supply 1.

Therefore, as it can be seen, the present invention uses discrete components, which are widely found in the market, besides having a lower price compared to the solutions provided with an integrated circuit. Additionally, due to the components being quite simple, there is no dependence on a single manufacturer, being this the reason for which the designer of the power supply 1 uses components from different manufacturers in the circuit described herein.

Finally, it should also be noted that the power supply 1 of the present invention comprises a variable switching frequency, since besides the fact that there is a time basis, or switching frequency given by the timer circuit 4, there is also the cutting time of the main switch 5 caused by the interference of the output voltage limiter 12 and the current limiter 13. This variation in the switching frequency given by the variation of the DC voltage in the bus 16 of the power supply 1 and also by the variation of the load 10 at the output of the supply 1 causes a spectrum spread of the harmonics energy that the power supply 1 injects in the eletric grid 2. In the state of the art, the switching frequency is almost constant, whereby all energy is concentrated in certain well-defined harmonics (multiples of the constant frequency), causing the amplitude of these harmonics to be significantly higher with respect to the circuit topology presented by the present invention, which uses variable switching frequency. Thus, the performance in relation to the interference and the EMC / EMI electromagnetic compatibility of the present invention tends to be higher in relation to the power supplies that use topologies with constant switching frequency.

Claims

1. Low voltage power supply (1) comprising:

the input stage (3) of electric voltage that comprises a rectifier;

an output stage (11) connected to a load (10),

said load being characterized by the fact that it comprises:

a timer circuit which (4) having its inputs connected to the DC bus (16) of the supply (1) being configured to have its time basis variable as the voltage change of said DC bus (16);

a main switch (5) comprising at least one actuation terminal (6) and two conduction terminals (7), the timer circuit output (4) is connected to said actuation terminal (6);

an electric energy storage device (8) electrically connected to the first conduction terminal (7) of the main switch (5) and designed to supply an actuator (9);

the actuator (9) having its input electrically connected to the electric energy storage device (8) and having its output connected to the actuation terminal (6) of the main switch, the actuator (9) being further configured to perform fast discharges of energy in its output; an output voltage limiter (12) being connected in parallel to the output stage (11) of the supply (1), said limiter (12) being further configured to actuate a latch (14) through its output;

a current limiter (13) having its input electrically connected in series to the second conduction terminal (7) of the main switch (5) and said current limiter (13) being configured to actuate a latch (14);

an overcurrent protector (15) having its input electrically connected in series with the load (10) and its output electrically connected to the output voltage limiter circuit (12); and a latch (14) having its input electrically connected to the output of the current limiter (13) and to the output voltage limiter (12) and being also connected to the output of the timer circuit (4) and to the actuation terminal (6) of the main switch (5), the latch (14) being configured to receive the discharge of the timer circuit (4) upon its actuation by current limiter (13) and / or by the output voltage limiter (12).

2. Low voltage power supply according to claim 1 , characterized by the fact that the timer circuit (4) comprises a circuit composed of two resistors (R3 and R19) and a capacitor

(C3).

3. Low voltage power supply according to claim 1 , characterized by the fact that the main switch (5) is a transistor.

4. Low voltage power supply according to claim 1 , characterized by the fact that the the electric energy storage device (8) is an inductor.

5. Low voltage power supply according to claim 1 , characterized by the fact that the the actuator (9) is a subcircuit of the supply 1 provided with at least one transistor (Q3) capable of establishing the conduction of electric current between a capacitor (C4). It is electrically connected to the emitter terminal of said transistor (Q3), and a resistor (R5), connected to the collector terminal of said transistor (Q3), being said resistor (R5) of the actuator (9) electrically connected to the actuation terminal (6) of the main switch (5).

6. Low voltage power supply according to claim 1 , characterized by the fact that the output voltage limiter (12) comprises at least one transistor (Q2) capable of being polarized by means of an overvoltage applied on the output stage (11), being said transistor (Q2) of the output voltage limiter (12) connected to the latch (14) by means of a resistor (R15).

7. Low voltage power supply according to claim 1 , characterized by the fact that the current limiter (13) comprises a current sensor element (20) and a second resistor (R9) that, together with a capacitor (C5) of the latch (14), form a low-pass filter.

8. Low voltage power supply according to claim 1 , characterized by the fact that the latch (14) comprises a capacitor (C5) associated to a resistor (R15) of the output voltage limiter (12) that is connected to the collector of the transistor (Q3) of said output voltage lim- iter (12) and, at the same time, to the second resistor (R9) of the current limiter (13), the latch (14) also comprising two transistors (Q5, Q4) capable of being polarized by the voltage applied on the capacitor (C5) of the latch (14), from the loading of the capacitor (C5) by the current limiter (13) and / or by the output voltage limiter (12).