JP3940137B2 - Differential load drive circuit - Google Patents

Description

  The present application relates to a differential load drive (driver) circuit, and more particularly to a differential load drive (driver) circuit that operates in both a linear mode for low current demands and a PWM mode for high current demands. .

  Due to its high efficiency, PWM (pulse width modulation) technology is frequently used in power electronics to drive large load currents. In comparison, linear currents are rarely used at high load currents due to their low efficiency. However, since the linear current source has no switching signal, there is no ripple in the output current. The load current driven by PWM inevitably suffers from some ripples, the amplitude of which depends on the cutoff frequency and the attenuation of the filter network.

  In order to drive a differential load, four power MOSFETs (metal oxide semiconductor field effect transistors) connected by an H-bridge are generally used. 1 and 2 show a typical H-bridge circuit used to drive a load. The H-bridge circuit shown in these figures is comprised of four switches (12, 14, 16 and 18) arranged as shown to drive a load 19, as is well known in the art. Is included.

  FIG. 1 shows the current flowing from left to right, defined here as “cooling”. FIG. 2 shows the current flowing from right to left, defined here as “heating”. 1 and 2 show the signals required to drive four H-bridge connected power MOSFETs to drive a resistive load in heating and cooling modes. For example, to drive the load in the cooling mode (FIG. 1), a PWM signal is applied to P1 and N1. On the other hand, P2 is impossible and N1 is fully turned on. This operation is similar to a buck converter, as is known in the art. The duty cycle of the PWM signal controls the current flowing through the resistive load. The filter elements L1, C1, L2, and C2 attenuate the ripple current that flows through the load. Each switch has an associated pre-driver circuit (not shown) that drives the switches at the appropriate level.

  Such a design encounters several problems when a small current is required to flow through the load. At small load currents, the PWM signal duty cycle is correspondingly small. However, the drive capability of the pre-driver circuit is limited by the duty cycle. Moreover, the gate capacitance of the power MOSFET is quite large. Therefore, it is impossible to drive the power MOSFET with a very small duty cycle, which prevents the system from outputting a small load current in either heating or cooling mode. Similarly, the proportion of ripple current increases considerably as the average DC value of the load current decreases.

  3 and 4 show another variation of FIGS. 1 and 2 in which one set of filter elements L2 and C2 has been removed. This generally results in cost savings and a smaller form factor. However, the circuits of FIGS. 3 and 4 still suffer from the same drawbacks as the circuits of FIGS. 1 and 2, ie, increased ripple at low current conditions.

  In one aspect, the invention comprises four power switches that form an H-bridge circuit that is selectively coupled to and supplies current to a load, and at least one current source, the circuit comprising: An H-bridge load drive circuit adapted to couple the power switch or the current source to the load as a function of load current.

  In another aspect, the present invention provides a plurality of power switches that are selectively coupled to a load to supply current to the load, and are operable to control a conduction state of the power switch, the plurality of power switches. A plurality of power switch drive circuits operable to selectively couple at least one of the power switches to the PWM signal and at least one current source, wherein the current source is in a low current state at the load The PWM signal is coupled to the load to provide current to the load, and the PWM signal is coupled to the load to provide current to the load during a high current condition at the load. provide.

  In yet another aspect, the present invention controls four power switches that form an H-bridge circuit that is selectively coupled to a load to supply current to the load and to control the conduction state of the power switch. A plurality of power switch drive circuits operable and selectively operable to selectively couple at least two of the plurality of power switches to a PWM signal; and at least one current source, the H-bridge The circuit includes a first mode in which the current source is coupled to the load to supply current to the load, and at least two of the power switches are coupled to the PWM signal to supply current to the load. And an H-bridge load driving circuit having a second mode.

  In yet another aspect, the present invention is a differential drive circuit for driving a thermoelectric cooler that is selectively coupled to a thermoelectric cooler load to supply current to the load. A plurality of power switch drive circuits operable to control a conduction state of the power switch and operable to selectively couple at least one of the plurality of power switches to a PWM signal; A first mode coupled to the load such that the current source supplies current to the load; and at least two of the power switches to supply current to the load. A differential drive circuit having a second mode coupled to the PWM signal is provided.

  Other features and advantages of the present invention will become apparent from the following description made with reference to the drawings. In the drawings, the same reference numerals indicate similar parts.

  In the following detailed description, the load 19 may include a thermoelectric cooler (TEC). Such devices can operate in heating and cooling modes depending on the direction of current flow. TEC is used as a heating / cooling element to control the exact temperature of the device, especially in optical communication devices. When a positive current passes through the TEC, the TEC heats the device with an accurate temperature requirement, and when a negative current passes through the TEC, the TEC cools the device. However, the present invention is not intended to be limited by such loads as well as to any type of load.

  In the following, a detailed description will be given focusing on the power train of the differential load driver. Although the usual protective features associated with such applications, such as transient temperature and current, are described, this is considered to be within the spirit and scope of the present invention.

  The present invention is directed to a differential load driver circuit (eg, an H-bridge circuit) that operates in both a linear mode and a PWM mode. Linear mode operation is selected to reduce the ripple current associated with low current operation of the differential load driver. The switching point between linear and PWM operation is programmable and / or user configurable. This switching point may be selected based on, for example, the desired / allowed ripple current in the load, based on the capacitance of the switch in the H-bridge circuit, and / or based on other considerations. In other words, the differential load drive circuit of the present invention is operable between a linear current mode and a PWM current mode as a function of load current. Accordingly, the term “low” in connection with low current is to be interpreted broadly and may include any current flowing through the load. Similarly, the term “high” associated with a high current condition is relative to a low current (but higher than a low current) and is applied to a load that is greater than a predetermined low current applied to the load. It should be interpreted as an arbitrary current.

  Further, the following will be described in detail by describing various embodiments of the H-bridge differential load driving circuit. Since the operation of the H-bridge circuit is very well known, its description is omitted here.

First Embodiment FIGS. 5-8 illustrate a differential load driver (drive) circuit 50 according to a first exemplary embodiment of the present invention. In this exemplary embodiment, switch drive circuits 52, 54, 56 and 58 (respectively associated with each switch P1, P2, N1 and N2) are provided to control the operation of the power MOSFET switch. It has been. Current sources 60 and 62 are provided on each side of the H-bridge to provide a linear current to the load.

  Each of the switch driver circuits 52, 54, 56 and 58 includes a plurality of switches (as shown). The plurality of switches are selectively operated to couple the power MOSFET switch to a PWM signal or power supply (VCC) or to a PWM signal, power supply (VCC) or ground. Switches 64 and 66 are operated to couple current source 60 or 62 to the load, respectively. In this exemplary embodiment, three switches are included to couple the power MOSFET to the PWM signal, VCC and / or ground.

  The switches included in the switch drive circuits 52, 54, 56 and 58 are exemplary, and for the 52 and 54 cases, only one switch is required to couple to VCC. P-type switches P1 and P2 are coupled to VCC during linear mode operation, and n-type devices (N1 and N2) are coupled to VCC and ground in an alternating manner for both heating and cooling.

  FIG. 5 is an exemplary circuit diagram of an H-bridge load driver circuit 50 operating in a linear cooling mode, according to the first embodiment of the present invention. In this exemplary embodiment, during the low current conditions required by load 19, current source 60 is coupled to the load via switch 64. Current source 60 is generally defined as a linear current source, and the output current can be controlled via voltage or current feedback (not shown, but such feedback control is well known in the art) PMOS or NMOS Can be included. The power switches P1, P2 and N2 are disabled by the switch drive circuits 52, 54 and 58. Since there is no switching signal when operating in this mode, the present invention reduces and / or eliminates ripple current to the load. Also, the current source can be driven in all ways to zero load current. FIG. 7 shows the circuit 50 in a linear heating mode in which a current source 62 is coupled to the load 19 via a switch 66.

  However, current sources cannot drive very large load currents because power dissipation and efficiency will be a problem. When a large load current is required, the present invention switches to PWM mode operation as shown in FIG. 6 (cooling) and FIG. 8 (heating).

  During the transition from linear to PWM and during the transition from PWM to linear, the magnitude of the output current of the linear current sources 60, 62 must be comparable to the resulting current drive due to the start of PWM mode operation. It is desirable (but not essential) to reduce the difference in current discontinuity between PWM and linear modes. Such requirements can help avoid inherent vibration problems for the current source or the overall feedback system. FIG. 9 is a graph 90 showing the linear mode region I and the PWM mode region II. A crossover point 68 is also shown. As shown in the figure, it is desirable (but not essential) to ensure that the PWM mode start current is deliberately set slightly smaller than the linear mode current at the switching point. This is to ensure that all load current is encompassed by the current control. The current control can be voltage or current feedback information from the load.

Second Embodiment In use where only a small heating current is required, the embodiment of FIGS. 5-8 can reduce the number of reactive components by removing the LC set, as shown in circuit 100 of FIG. Can be changed to reduce FIG. 10 is an exemplary circuit diagram of an H-bridge load driver operating in a PWM heating mode according to a second embodiment of the present invention. The operation of circuit 100 in the low current linear heating mode is similar to that described above in FIGS. 5-8 and includes coupling current source 106 to load 19 (via switch 108). In this embodiment, the switch drive circuits 102 and 104 are similar to the switch drive circuits 52 and 56 of FIGS. The switch P2 includes a switch drive circuit 110. The current source in this case would be an external power PMOS P2 biased by the output of an OTA (output transconductance amplifier). Similar circuits can be constructed along these principles for application to small cooling currents.

  The switch drive circuit 110 is used as a bias circuit for the PMOS device P2, and may include an operational amplifier 112 and a current or voltage feedback signal 114. The operational amplifier is configured as a differential amplifier, and the feedback signal is compared with a reference voltage to generate a bias signal for controlling the conduction state of P2 so that P2 operates as a current source. Of course, those skilled in the art will recognize that many current sources can be configured, all of which can be considered equivalent in the present invention.

Third Embodiment In this embodiment of FIGS. 11-14, the set of LC filters has been removed. However, unlike the previous embodiment, this embodiment can provide large heating and cooling currents. FIG. 11 is an exemplary circuit diagram of an H-bridge driver circuit 200 operating in a cooling mode, according to a third embodiment of the present invention. In this embodiment, two current sources 210 and 212 are used. The current source 210 is a generation source, and the current source 212 operates to reduce the current. As shown in FIG. 11, when operating in linear, cooling mode, current source 210 is coupled to the load (via switch 214), N2 is fully turned on, and P2 is fully turned off. P1 and N1 are disabled. Switching circuits 202, 204, 206, and 208 couple the power MOSFET to the appropriate source (ie, PWM signal, VCC or ground) shown in FIGS.

  When operating in linear heating mode as shown in FIG. 13, current source 212 is coupled to the load, P2 is fully turned on, and N2 is fully turned off. P1 and N1 are disabled.

  12 and 14 show a circuit 200 operating in PWM cooling mode and heating mode, respectively. In these states, current sources 210 and 212 are disconnected from load 19 and P1 and N1 are driven by the PWM signal (via switch driver circuits 202 and 204). P2 and N2 are alternated between VCC and ground.

  Of course, those skilled in the art will appreciate that in the embodiments described herein, a controller such as that shown in FIG. 15 can be implemented to control the conduction state of the switch driver circuit and the current source switch. . The output of the controller 300 may include complementary PWM signals PWMP and PWMN for driving the PMOS and NMOS devices of the differential load drive circuit. The controller may also output switch control signals 302-308 to control the operation of the switches in the switch drive circuit (eg, 52, 54, 56 and 58 in FIGS. 5-8). The controller 300 may also generate switch control signals 312 and 314 to control switches associated with the current source (eg, 64 and 66 associated with the current sources 60 and 62 of FIGS. 5-8). The controller may use voltage and / or current feedback information, as is well known in the art, to control the power provided to the load in both linear and PWM operations. Of course, in some embodiments described herein, not all of the signals generated by the controller may be required, and therefore the controller can be modified to generate the appropriate signals. A low current detector circuit 310 may be included to control the switching point between the linear current mode and the PWM current mode. Such a detector may further include a user-configurable input threshold that sets a threshold between the low current mode and the PWM mode. Of course, the detector circuit 310 may be omitted instead of a predetermined input to the controller, in which case the predetermined input represents a crossover supply current (which may be determined by the user). The controller may be formed from application specific components and / or standard components available from inventory. Such PWM controllers are well understood in the art.

  There are many variations that will be apparent to those skilled in the art. For example, although the present invention implements a differential load driver circuit having a power MOSFET device, it uses other power switches known in the art, such as BJT devices and / or other switch mechanisms. Also good. All such modifications or additions are considered to be within the spirit and scope of the invention as defined by the appended claims.

  While the present invention has been described in detail with reference to preferred embodiments and methods of use, it will be understood by those skilled in the art that the present invention is not intended to be limited to these preferred embodiments and methods of use. Will be understood. Rather, the invention is in a broad scope intended only to be limited as set forth in the claims.

It is a figure which shows the conventional H-bridge load drive circuit in the operation | movement of cooling mode. It is a figure which shows the conventional H-bridge load drive circuit in the operation | movement of a heating mode. FIG. 6 is a diagram illustrating another conventional H-bridge load drive circuit in cooling mode operation. FIG. 6 is a diagram illustrating another conventional H-bridge load drive circuit in heating mode operation. 1 is an exemplary circuit diagram of an H-bridge load drive circuit operating in a linear cooling mode, according to a first embodiment of the present invention. FIG. FIG. 3 is another exemplary circuit diagram of an H-bridge load drive circuit operating in PWM cooling mode according to the first embodiment of the present invention. 3 is another exemplary circuit diagram of an H-bridge load drive circuit operating in a linear heating mode, according to a first embodiment of the present invention. FIG. FIG. 3 is another exemplary circuit diagram of an H-bridge load drive circuit operating in PWM heating mode according to the first embodiment of the present invention. 4 is an exemplary graph showing a relationship between a PWM mode and a linear current mode of the present invention. FIG. 4 is an exemplary circuit diagram of an H-bridge load driving circuit operating in a PWM heating mode according to a second embodiment of the present invention. FIG. 6 is an exemplary circuit diagram of an H-bridge load driving circuit operating in a linear cooling mode according to a third embodiment of the present invention. FIG. 6 is another exemplary circuit diagram of an H-bridge load drive circuit operating in PWM cooling mode according to a third embodiment of the present invention. FIG. 6 is another exemplary circuit diagram of an H-bridge load drive circuit operating in a linear heating mode according to a third embodiment of the present invention. FIG. 6 is another exemplary circuit diagram of an H-bridge load drive circuit operating in a PWM heating mode according to a third embodiment of the present invention. FIG. 3 is a block diagram illustrating an exemplary controller for controlling the operation of a load driver circuit according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 19 ... Load, 50 ... Differential load drive circuit, P1, P2, N1 and N2 ... Switch, 52, 54, 56 and 58 ... Switch drive circuit, 60 and 62 ... Current source.

Claims (16)

A plurality of power switches that are selectively coupled to the load to supply current to the load;
A plurality of power switch drive circuits operable to control a conduction state of the power switch and operable to selectively couple at least one of the plurality of power switches to a PWM signal;
At least one current source;
The current source is coupled to the load to provide current to the load during a low current condition at the load, and the PWM signal provides current to the load during a high current condition at the load. A differential load drive circuit coupled to the load to provide.   The differential load drive circuit of claim 1, wherein the plurality of power switches form an H-bridge differential load drive circuit.   Further comprising two current sources, one of the current sources is coupled to the load during a first low current period and the other of the current sources is coupled to the load during a second low current period. The differential load drive circuit according to claim 1. Four power switches forming an H-bridge circuit selectively coupled to the load to supply current to the load;
A plurality of power switch drive circuits operable to control a conduction state of the power switch and operable to selectively couple at least two of the plurality of power switches to a PWM signal;
At least one current source;
The H-bridge circuit includes: a first mode coupled to the load such that the current source supplies current to the load; and at least two of the power switches to supply current to the load. An H-bridge load drive circuit having a second mode coupled to the PWM signal.   The H-bridge load driving circuit according to claim 4, wherein the first mode is a low current mode, and the current source supplies a linear current to the load.   5. The H-bridge load driving circuit according to claim 4, wherein the second mode is a high current mode. Four power switches forming an H-bridge circuit selectively coupled to the load to supply current to the load;
At least one current source;
The H-bridge circuit is configured to operate in a linear mode using the current source and a PWM mode in which the switch is controlled by a PWM signal.   And further comprising a plurality of power switch drive circuits operable to control a conduction state of the power switch and operable to selectively couple at least two of the plurality of power switches to a PWM signal. Item 8. The H-bridge load drive circuit according to Item 7.   8. The H-bridge load drive circuit of claim 7, further comprising at least one filter circuit coupled between at least two of the four power switches and the load.   The H-bridge load driving circuit according to claim 7, wherein the load includes a thermoelectric cooler. A differential drive circuit for driving a thermoelectric cooler,
A plurality of power switches selectively coupled to the thermoelectric cooler load to supply current to the load;
A plurality of power switch drive circuits operable to control a conduction state of the power switch and operable to selectively couple at least one of the plurality of power switches to a PWM signal;
At least one current source;
A first mode in which the current source is coupled to the load to supply current to the load; and at least two of the power switches are coupled to the PWM signal to supply current to the load. A differential drive circuit having a second mode.   The differential drive circuit of claim 11, wherein the plurality of power switches form an H-bridge differential load drive circuit.   The differential drive circuit according to claim 11, wherein the first mode is a low current mode in which a direction of a current flowing through the load limits a cooling mode.   The differential drive circuit according to claim 11, wherein the first mode is a low current mode in which a direction of a current flowing through the load limits a heating mode.   The differential drive circuit according to claim 11, wherein the first mode is a high current mode in which a direction of a current flowing through the load limits a cooling mode. The differential drive circuit according to claim 11, wherein the second mode is a high current mode in which a direction of a current flowing through the load limits a heating mode.

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