CN107783579A - circuit - Google Patents

Abstract

The present application provides a circuit comprising a current source intended to be connected in series with a load between two terminals of application of a first direct voltage. The element limits the voltage across the load and the circuit controls the value of the current in the current source with the current flowing in the element. By the method and the device, the power consumption of the current source for supplying power to the load can be optimized and realized, and meanwhile, the load to be supplied with power does not need to be modified.

Description

circuit

technical field

The present application relates to electronic circuits and, in particular embodiments, to circuits for powering a load from a variable DC voltage.

Background technique

When a load is to be powered at a fixed DC voltage, a voltage setting element is often used, typically a Zener diode connected in parallel with the load. A current source is then connected in series with this parallel combination and powers the assembly with a DC voltage. Zener diodes have the function of limiting (setting) the voltage across the load. The current source has the function of sinking the current flowing through the load as well as through the Zener diode.

For a fixed load (constant power dissipation), the current source is sized from this current to keep the Zener diode permanently in avalanche (acting as a voltage limiter).

However, for loads with variable power consumption, the current source must be sized according to the maximum power consumption of the load. This generates unnecessary power dissipation when the load is not drawing this maximum current.

Contents of the invention

One embodiment overcomes all or some of the problems of common circuits used to power a load.

Another embodiment optimizes the power consumption of the power supply circuit and more specifically reduces its losses.

One embodiment provides a solution that does not require modification of the load to be powered.

In order to achieve the above object, an embodiment of the present application provides a circuit, comprising: a current source configured to be connected in series with a load between two terminals of the application of a first DC voltage; coupled to limit the current across the load an element of voltage; and a control circuit configured to use the current flowing in the element to control the value of the current in the current source.

Preferably, said element comprises a Zener diode connected to a junction between said load and said current source.

Preferably, said circuit comprises a first MOS transistor configured as a diode and a current mirror on a second MOS transistor, said second transistor and a third transistor at said first DC voltage The terminals of the application are connected in series and the third transistor is assembled as a diode and a current mirror on a fourth transistor connected to the control terminal of the current source.

Preferably, said element comprises a Zener diode connected to a junction between said load and said current source.

Preferably, the Zener diode is connected in series with the first transistor.

Preferably, said element is internal to said load and controls said first transistor.

Preferably, said fourth transistor is connected in series with the resistive element between the two terminals of the application of the second direct voltage.

Preferably, said current source is formed by MOS transistors.

Preferably, the load includes a charge pump circuit.

Embodiments of the present application also provide another circuit, including: a first reference voltage terminal; a second reference voltage terminal; a load coupled between the first reference voltage terminal and the second reference voltage terminal; and a variable current source coupled in series with the load between the first reference voltage terminal and the second reference voltage terminal, the variable current source being configured to provide magnitude of the current.

Preferably, the first reference voltage terminal comprises a battery terminal, and the second reference voltage terminal comprises a ground terminal.

Preferably, an element coupled to said load to limit the voltage across said load is also included.

Preferably, said element comprises a Zener diode connected to a junction between said load and said current source.

Preferably said element is internal to said load.

Preferably, the variable current source includes:

a transistor with a current path coupled in series with the load between the first reference voltage terminal and the second reference voltage terminal; and a control circuit with a control output coupled to the control terminal of the transistor.

Preferably, the control circuit comprises a first MOS transistor, a second MOS transistor, a third MOS transistor and a fourth MOS transistor, the first MOS transistor being connected as a diode and a current mirror on the second MOS transistor , the second transistor is connected in series with the third transistor between the first reference voltage terminal and the second reference voltage terminal, and the third transistor is connected as a diode and across the fourth transistor The fourth transistor is coupled to the control terminal of the transistor.

Preferably, further comprising a voltage limiting element coupled between said first MOS transistor and a junction between said load and said current source.

Preferably, said voltage limiting element comprises a Zener diode.

Preferably, a resistive element coupled between said fourth transistor and a direct voltage terminal is also included.

Preferably, said first reference voltage terminal and said DC voltage terminal carry different voltages relative to said second reference voltage terminal.

Preferably, said current source is formed by MOS transistors.

Preferably, the load includes a charge pump circuit.

Embodiments of the present application also provide another circuit, including:

a first reference voltage terminal;

a second reference voltage terminal; an intermediate terminal;

a first P-channel transistor having a current path coupled between said first reference voltage terminal and said intermediate terminal, said first P-channel transistor being coupled as a diode; a voltage limiting element connected to said first The current path of a P-channel transistor is coupled in series between the first reference voltage terminal and the intermediate terminal; the current path of a second P-channel transistor is coupled between the first reference voltage terminal and the Between second reference voltage terminals, the second P-channel transistor has a control terminal coupled to the control terminal of the first P-channel transistor; the first N-channel transistor has a current path connected to the second The current path of a P-channel transistor is coupled in series between the first reference voltage terminal and the second reference voltage terminal, the first N-channel transistor is coupled as a diode; a second N-channel transistor, Its control terminal is coupled to the control terminal of said first N-channel transistor, said second N-channel transistor having a current coupled in series with a resistive element between said second reference voltage terminal and a third reference voltage terminal. and a current source transistor with a current path coupled between the intermediate terminal and the second reference voltage terminal, the current source transistor having a control terminal coupled to the second N-channel transistor.

Preferably, said voltage limiting element comprises a Zener diode.

Advantageously, further comprising a load coupled between said first reference voltage terminal and said intermediate terminal.

One advantage of the discussed embodiment is that it optimizes the power consumption of a current source powering a load.

Another advantage is that this adjustment does not require direct measurement of load power consumption or the output current of this load. Implementation of the described embodiments thus does not require modification of the load to be powered.

The foregoing and other features and advantages will be discussed in more detail in the following non-limiting description of specific embodiments in conjunction with the accompanying drawings.

Description of drawings

For a more complete understanding of the present application and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:

Figure 1 schematically shows a common example of a circuit for powering a load;

Figure 2 is a functional block diagram of an embodiment of a circuit for powering a load;

Figure 3 shows a circuit diagram for an embodiment for powering a load with a floating potential; and

Figure 4 shows an example of a load at floating potential.

Detailed ways

The same elements are labeled with the same reference numerals in different figures. For clarity, only those elements that are useful for understanding the described embodiments are shown and will be detailed. In particular, such embodiments are compatible with any type of load intended to be connected in series with a current source. An example of application of the embodiment to be described is directed to a load formed by a charge pump or a charge transfer circuit. In such circuits, the power consumption varies according to the power consumption of the components powered by the charge pump.

Similar problems generally arise whenever a load is to be supplied from a variable voltage and it is desired to set its supply voltage by means of Zener diodes or the like. In effect, the load is then connected in series with a current source which creates a node at floating potential. For example, this could be an amplification or comparison circuit referenced to a potential other than ground.

Fig. 1 shows a common example of a circuit for powering a load 1 (Q) with a DC voltage (for example, the voltage Vbat delivered by a battery) and with variable power consumption. The circuit to be powered, ie the load 1 , is connected in series with a constant current source 2 between two terminals 21 and 22 of the connection to a source (battery) providing a direct voltage. Zener diode 3 and the like are connected in parallel to load 1 . Zener diode 3 has an anode on the side of junction 23 of load and current source 2 .

Its operating principle is as follows. Usually, the size of the current source is determined according to the different power consumption of the load to sample the constant current Ibias to ensure the operation of the load. In the example of FIG. 1 , this consumption depends on the current Iout, which can be supplied by the load 1 . The current Ibias is chosen to be greater than the maximum value of the current Ic that can be drawn by the load 1 to ensure proper biasing of the Zener diode 3 . In the opposite case, Zener diode 3 is turned off and the supply voltage across load 1 , set by the threshold voltage of the Zener diode, drops.

In particular, such circuits are intended for applications in which there is a risk of variations in the direct voltage Vbat and in which the load must be supplied with an approximately constant voltage. This justifies the use of a Zener diode 3 or another component for setting the voltage threshold.

The problem with circuits of the type in Figure 1 is that the total power dissipation is independent of that of the load 1 . In practice, the constant current source 2 has to be sized with respect to the worst case of load power dissipation. This results in a maximum permanent power dissipation, even when the load does not require it, the excess current is then diverted by the zener diode.

FIG. 2 is a functional diagram of an embodiment of a circuit for powering a load 1 . As before, the load 1 is connected in series with the current source 4 between the two terminals 21 and 22 of the application of the direct voltage Vbat. However, the current source 4 is here an adjustable current source. The value of current I4 in current source 4 depends on control signal CTRL provided by circuit 5 , which compares the voltage at node 21 with the voltage at node 23 plus the threshold voltage of Zener diode 3 . In other words, the comparator 5 detects a change in the voltage across the load 1 with respect to the voltage set by the diode 3 .

Its purpose is to adjust the value of the current drawn by the current source 4 according to the power consumption of the load.

It may have been envisaged to use the measurement of the current lout provided by the load or the direct measurement of the current in the load 1 to assess its power consumption or to adjust the value of the current source. However, this will require modification of the actual load circuit. Furthermore, sampling data from the current drawn by the load at the load level may affect its characteristics.

Therefore, as shown in FIG. 2 , it is provided to control the current in the current source 4 using the current flowing through the Zener diode 3 . In fact, the current in the branch of the Zener diode tends to increase if the load power dissipation decreases, and the current in the branch of the Zener diode tends to decrease if the load power dissipation increases.

FIG. 3 shows a circuit diagram of an embodiment of a power circuit such as that shown in FIG. 2 .

A MOS transistor P1 configured as a diode (here with a P-channel) is inserted between the cathode of the Zener diode 3 and the terminal 21 . Transistor P1 is configured as a current mirror on a P-channel MOS transistor P2 connected in series with an N-channel MOS transistor N2 between terminals 21 and 22 . Transistor N2 is configured as a diode and current mirror on N-channel MOS transistor N1. Transistor N1 and current-to-voltage converting resistive element R are connected in series between terminal 21' of application of direct voltage (Vcc) and ground 22. The voltage Vcc applied to the terminal 21' is not necessarily the same as the voltage applied to the terminal 21. In practice, the voltage Vcc applied to the terminal 21' is usually a lower voltage. The junction 51 of the resistor R and the transistor N1 is connected to the gate of the N-channel MOS transistor N4 forming the current source 4 .

Assuming that the load power dissipation increases, the current in transistor P1 and thus in Zener diode 3 tends to decrease. The current reduction reproduced in transistor P2 and subsequently in transistor N1 (current mirrors N1 , N2 ) is functionally equivalent to modifying the value of the resistive bridge formed by element R and the on-state resistance of transistor N1 . This results in an increase in the voltage at node 51 and thus an increase in the current drawn by transistor N4.

Conversely, if the load power consumption increases, the current increase in transistor P1 is reflected in the current in transistor N1, which causes a decrease in the gate voltage CTRL of transistor N4, whereby the current drawn by transistor N4 decreases.

In dimensioning the circuit of FIG. 3 , the fact that the supply voltage of the load 1 is now set by the threshold voltage of the Zener diode plus the threshold voltage of the diode-fitted transistor P1 will of course be taken into account.

One advantage of the discussed embodiment is that it optimizes the power consumption of the current source 4 powering the load 1 . Another advantage is that the adjustment does not require direct measurement of the load power consumption or the output current lout of this load. The implementation of the described embodiment thus requires no modification of the load 1 to be powered.

As a specific example, the voltage Vbat is a voltage of tens of volts. Load 1 is a charge pump circuit designed to power the application circuit. The voltage Vcc is of the order of a few volts.

FIG. 4 illustrates an example of a charge pump circuit capable of forming the load 1 of the circuits of FIGS. 2 and 3 . This circuit itself is common.

A clock generator 11 (CK Gen) is powered between terminals 21 and 23 and provides the input signal of the first inverter 12 in series with the second inverter 13 . Outputs of the inverters 12 and 13 are each connected to first electrodes of the capacitive elements 14 and 15, respectively. Three diodes 16, 17 and 18 are connected in series between terminal 21 and terminal 19 which supplies current lout. Finally, the second corresponding electrodes of capacitors 14 and 15 are connected between diodes 16 and 17, between diodes 17 and 18, respectively. The operation of this circuit is known.

Various embodiments have been described. Various alterations, modifications and improvements will occur to those skilled in the art. In particular, although the embodiments have been described with respect to a load 1 connected on the positive voltage side, the described circuit is easily transformed into a load connected in series with a current source, which is on the positive voltage side. Furthermore, although an embodiment is described in which current limitation in the load is ensured by an external limiting element connected across the load, it is also possible to use a reference voltage (eg internal to the load) to control the gate of transistor P1. This change is specifically intended for use where the load has such a reference voltage. Ultimately, it is within the ability of a person skilled in the art to size the circuit components based on the functional indications provided above, the maximum required power consumption of the load, and by using electronic circuit sizing tools common per se.

Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the application. Accordingly, the foregoing description is by way of example only and is not intended to be limiting. This application is limited only by the claims and their equivalents.

While this application has been described with reference to exemplary embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the exemplary embodiments, as well as other embodiments of the application, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims cover any such modifications and embodiments.

Claims (9)

1. A kind of 1. circuit, it is characterised in that including：Current source, it is configured as and is supported on the two of the application of the first DC voltage It is connected in series between individual terminal；It is coupled to element of the limitation across the voltage of the load；And control circuit, it is configured as profit The electric current flowed in the element controls the value of the electric current in the current source.
2. 2. circuit according to claim 1, it is characterised in that the element includes being connected in the load and the electricity The Zener diode at the abutment between stream source.
3. 3. circuit according to claim 1, it is characterised in that the circuit includes the first MOS transistor, and described first MOS transistor fitted to be diode and the current mirror on the second MOS transistor, the second transistor and third transistor Connected between the terminal of the application of first DC voltage, and the third transistor fitted to be diode and Current mirror on the 4th transistor of the control terminal of the current source is connected to.
4. 4. circuit according to claim 3, it is characterised in that the element includes being connected in the load and the electricity The Zener diode at the abutment between stream source.
5. 5. circuit according to claim 4, it is characterised in that the Zener diode is connected with the first transistor.
6. 6. circuit according to claim 3, it is characterised in that the element is inside the load and controls described One transistor.
7. 7. circuit according to claim 3, it is characterised in that the 4th transistor AND gate resistive element is in the second direct current Connected between two terminals of the application of pressure.
8. 8. circuit according to claim 1, it is characterised in that the current source is formed by MOS transistor.
9. 9. circuit according to claim 1, it is characterised in that the load includes charge pump circuit.