This section covers all types of engines, from basic circuits needed to control a variable reluctance motor, the H-bridge circuit to control a permanent magnet motor pole. Each type of control circuit is illustrated with practical examples, but these examples are not intended as an exhaustive catalog of the control circuits commercially available, or the information contained herein is intended to replace the information found on the leaves manufacturer’s data components for the parties mentioned. This section covers only the control circuit of the most basic class for each engine. All these circuits assume that the power of the engine provides a control voltage does not exceed the rated motor voltage, which limits the performance of the engine. The next section, the control circuit current limited, practical circuits covers high performance training. controllers of variable reluctance motors typical reluctance stepper motors are variable variations on the contour of Figure 3. 3 Figure 1:. 1 In Figure 3. 1, boxes are used to represent the switches, a control unit, not shown, is responsible for providing control signals to open and close the switches at the right time to turn the motors. In many cases, the unit will control a computer or programmable interface controller, the software directly generating the outputs needed to control the switches, but in other cases, an additional control circuit is introduced, sometimes free! motor windings, solenoids and similar devices are all inductive loads. As such, the current through the motor windings can be switched on or off instantly without going through endless tension! When the switch controlling a motor winding is closed, allowing current to flow, the result of this is a slow rise in current. When the switch control of a motor winding is opened, the result is a voltage spike that can cause serious damage to the switch unless care is taken to appropriate care. There are two basic ways to cope with the peak voltage. The first is to bridge the motor winding with a diode, and the other is to bridge the motor winding with a capacitor. Figure 3. Figure 2 illustrates the two approaches: Figure 3. 2 The diode in Figure 3. 2 must be able to conduct electricity across the motor winding, but it did lead briefly each time the switch is off, as the current through the decays of liquidation. If diodes relatively slow, as the common family 1N400X are used with a switch quickly, it may be necessary to add a small capacitor in parallel with the diode. The capacitor in Figure 3. Poses two problems more complex design! When the switch is closed, the capacitor discharges through the ground, and the switch must be able to manage this short burst of discharge current. A resistor in series with the capacitor or in series with the power supply will limit the current. When the switch is opened, the stored energy in the motor winding will charge the capacitor to a voltage much higher than the supply voltage, and the switch must be able to tolerate this tension. To solve for the size of the capacitor, we equate the two formulas for the energy stored in a resonant circuit: P = C V2 / 2 P = I2 L / 2 where: P – stored energy in seconds or watt coulomb volt C – the capacity in farads V – voltage across capacitor L – inductance of the motor winding, in henrys I – current through the motor winding resolution for the minimum size of capacitor needed to prevent surges on the switch is easy enough: C> L I2 / (Vb – Vs) 2 Where: Vb – the breakdown voltage Vs of the switch – the power supply of variable reluctance motors have variable inductance which depends on the angle tree. Therefore, the design of the worst must be used to select the capacitor. In addition, the motor inductances are often poorly documented, if at all. The capacitor and the motor winding, in combination, form a resonant circuit. If the control system drives the motor at frequencies near the resonant frequency of this circuit, the motor current in the windings and, therefore, the torque exerted by the engine torque will be very different from the state equilibrium the nominal operating voltage! The resonant frequency is f = 1 / (2 (SC) 0. 5) Again, the frequency of electrical resonance for a variable reluctance motor depends on the angle tree! When a variable reluctance motor is used with interesting impulses near the resonance, the oscillating current in the motor winding leads to a magnetic field which tends to zero at twice the resonant frequency, which can significantly reduce the torque available! controllers unipolar permanent magnet and hybrid motors typical unipolar stepper motors are variations on the outline of Figure 3. 3: Figure 3. 3 in Figure 3. 3, as in Figure 3. 1, boxes are used to represent the switches, a control unit, not shown, is responsible for providing control signals to open and close the switches at the right time to turn the motors. The control unit is typically a computer or programmable interface controller, with the software directly generating the outputs needed to control the switches. As control circuit for variable reluctance motors, we must deal with the sudden inductive produced when each of these switches is turned off. Again, you can blow the inductive shunt using diodes, but now, four diodes are required, as shown in Figure 3. 4: Figure 3. The four diodes are needed because the motor’s two coils are not independent, there is a single center-tapped inductor with center tap at a fixed voltage. This acts as an auto! When one end of the motor winding is pulled down, the other end of fly, and vice versa. When a switch opens, the inductive kickback drive end of the motor winding to the positive supply, where it is clamped by the diode. The opposite end will fly down, and if it does not float to the voltage at the time, it will fall below the ground, reversing the voltage across the switch for this purpose. Some switches are immune to such reversals, but others may be seriously damaged. A capacitor can also be used to limit the voltage bounce, as shown in Figure 3. 5: Figure 3. 5 The rules for sizing the capacitor in Figure 3. 5 are the same as the rules for the dimensioning of the capacitor in Figure 3. 2, but the resonance effect is very different! With a permanent magnet motor, if the capacitor is driven at or near the resonant frequency, the couple will rise to as much as twice the torque at low speed! The resulting torque versus speed curve may be quite complex, as illustrated in Figure 3. 6: Figure 3. 6 Figure 3. Figure 6 shows a peak in the available torque to the frequency of electrical resonance, and a valley at the mechanical resonance frequency. If the frequency of electrical resonance is placed appropriately above what would be the threshold speed of the engine using a diode pilot basis, the effect may be a considerable increase of the effective cut-off speed. The mechanical resonance frequency depends on the couple, if the mechanical resonance frequency is anywhere near the electrical resonance, it will be moved by the electric resonance! In addition, the width of the mechanical resonance depends on local slope of torque versus speed curve, if the torque with speed, mechanical resonance will be crisp, while if the torque increases to a speed, will be broader or even split into several resonant frequencies. Practices unipolar and variable reluctance Drivers In circuits above, the details of necessary switches have been deliberately ignored. All the technology switching, toggle switches power MOSFET will work! Figure 3. 7 contains some suggestions for the implementation of each switch, with a motor winding and diode protection included for guidance: Figure 3. 7 Each of the switches in Figure 3. 7 is compatible with a TTL input. The 5-volt supply used for logic, including the 7407 open collector driver used in the figure should be well regulated. The engine power, typically between 5 and 24 volts, needs only minimal regulation. It should be noted that these power switching circuits are suitable for driving solenoids, DC motors and other inductive loads, and for driving stepper motors. Transistor SK3180 shown in Figure 3. 7 is a darlington power with a current gain over 1000, and the 10 milliamps passing through the resistance of 470 ohm bias is more than sufficient to allow the transistor to switch a few amps current in the windings. The buffer used to drive the 7407 Darlington can be replaced by a smart open-collector high voltage that can run at least 10 milliamperes. If the transistor fails, the driver high voltage open collector is used to protect the rest of the logic circuit of the motor. The IRC IRL540 shown in Figure 3. 7 is a transistor electric field effect. It can handle currents up to about 20 amps, and it goes down to 100 volts non-destructive, so the chip can absorb inductive spikes without protection diodes if it is attached to a heat sink big enough. This transistor has a very fast switching time, then protection diodes must be comparable or faster bypassed by small capacitors. This is especially important with the diodes used to protect the transistor against reverse bias! If the transistor fails, the zener diode and 100 ohm resistor protect TTL circuits. The resistance of 100 ohms also acts to slightly slow down the switching transistor. For applications in which each motor winding draws less than 500 milliamps, the family of tables ULN200x Darlington Allegro MicroSystems, also available as DS200x National Semiconductor and Motorola MC1413 Table Darlington lead several motor windings or other charges directly from inductive logic inputs. Figure 3. Figure 8 shows the pinout of the chip ULN2003 widely available, a Darlington transistor array 7 with TTL compatible inputs: Figure 3. 8 The base resistance on each Darlington transistor corresponds to the standard bipolar TTL outputs. NPN Darlington Each is wired with its emitter connected to pin 8, designed as a grounding prong, each transistor in the package is protected by two diodes, a short-circuit the emitter to the collector, protection against reverse polarity to through the transistor, and connecting the collector to pin 9, if pin 9 is connected to the motor power supply positive, the diode to protect the transistor against inductive spikes. The ULN2803 chip is essentially the same as the ULN2003 chip described above, except that it is in a 18-pin package, and contains 8 Darlingtons, allowing a chip to be used to drive a pair of common unipolar permanent magnet or variable reluctance motors. For motors drawing less than 600 milliamps per winding, the pilot quad UDN2547B authority made by Allegro Microsystems will manage all four windings of stepper motors unipolar common. For motors drawing less than 300 milliamps per winding, Texas Instruments SN7541, 7542 and 7543 dual power drivers are a good choice, both options include some logic to the pilot power. Motors bipolar H-Bridges and activities are more complex permanent magnet bipolar stepper motors because they have no center taps of their windings. Therefore, to reverse the direction of the field produced by a motor winding, we need to reverse the current in the coil. We could use a solid double pole switch electromechanical To do this, the electronic equivalent of such a change is called an H-bridge and is described in Figure 3. 9 As with unipolar control circuits mentioned above, the switches used in the H-bridge must be protected against voltage spikes caused by switching off a motor winding. This is usually done with diodes, as shown in Figure 3. 9. It should be noted that H-bridges are not only the control of bipolar stepper motors, but also for the control of DC motors, solenoids, push-pull (those divers with permanent magnet) and many other applications. With 4 switches, the basic H-bridge has 16 possible operating modes, including seven short-circuiting the power! The following operating modes are interesting mode of delivery, switches A and D closed. Reverse mode, switch B and C are closed. These are the usual modes of operation, allowing current to flow from the supply through the motor windings and beyond the earth. Figure 3. 10 illustrates the preliminary mode: Figure 3. 10 decay mode or fast mode freewheeling, open all switches. Any current flowing in the motor windings will work against the full supply voltage plus two diode drops, so current decay rapidly. This mode provides dynamic braking effect is little or no motor rotor, so that the rotor side freely if all motor windings are energized in this mode. Figure 3. 11 illustrates the current flow immediately after the passage of the attacker runs a fast decay mode. Figure 3. 11 modes decay slowly or dynamic braking mode. In these modes, the current can flow through the motor winding with minimal resistance. Therefore, if current flows in a coil of the motor when one of these modes is entered, the current will slowly decay, and if the motor rotor rotates, it induces a current which will act as a brake on the rotor . Figure 3. 12 illustrates one of many useful slow decay modes, D with the switch closed if the motor winding has recently been in fashion forward, the state of the switch B may be open or closed: Figure 3. Most of the 12 H-bridges are designed so that the logic necessary to avoid a short circuit is included at a very low level in the design. Figure 3. 13 illustrates what is probably the best arrangement: Figure 3. 13 Here, the following operating modes are available: XY decay mode ABCD 00 0000 1001 01 Fast forward 10 11 0101 0110 Reverse slow decay The advantage of this arrangement is that all the relevant modes are retained, and they are encoded with a minimum number of bits, it is important when using a microcontroller or a computer system to drive the H-bridge because many of these systems have limited the number of bits available for parallel output. Sadly, few chip H-bridge integrated on the market of such a system of simplified control. Practice Bipolar Drive Circuits There are a number of H-bridge driver integrated market, but it is always useful to consider the implementations of discrete components to understand how an H-bridge Antonio Raposo (RDA @ Cybill. INESC. Pt) suggested the H-bridge circuit in Figure 3. 14; Figure 3. 14 The X and Y to the inputs of this circuit can be driven by open collector TTL outputs as in the control circuit unipolar Darlington basis of Figure 3. 7. The motor winding will be energized if exactly one of X and Y inputs is high and one of them is low. If both are low, both transistors will drop off. If both are high, both transistors of pull-up will be off. Consequently, this simple circuit is the engine braking mode dynamics in both the 11 and 00 states, and does not offer a freewheeling mode. The circuit in Figure 3. 14 consists of two identical halves, each of which can be properly described as a push-pull driver. The half life of H-bridge is sometimes applied to these circuits! It is also interesting to note that half H-bridge circuit is quite similar to the output control circuit used in TTL logic. In fact, the TTL line driver tri-state actors such as the 74LS244 74LS125A and can be used as a half-H bridge for small loads, as shown in Figure 3. 15: Figure 3. 15 This circuit is effective for driving motors with a maximum at about 50 ohms per winding voltages up to about 4. 5 volts with a supply of 5 volts. Each buffer three states in the LS244 can run about twice today and you can source and internal resistance of buffer is sufficient, when the supply current to be divided equally between the current drivers that are executed in parallel. This device allows all relevant States obtained by the driver in Figure 3. 13, but these states are not coded as efficiently: XYE Fashion – 1000 fast decay slow disintegration advance 100,010,110 reverse slow decay The second dynamic braking mode, XYE = 110, gives a slightly lower than the first braking due to the fact that the LS244 drivers can fall more power than they can source. The microprocessor (formerly Telcom Semiconductor) TC4467 Quad CMOS driver is another example of a general purpose driver that can be used as four independent H Half-bridges. Unlike the old drivers, the data sheet for this driver even suggested using it for motor control applications with supply voltages up to 18 volts and 250 milliamps per winding engine. One problem with the intensification of chips available on the market of motor control is that many of them have relatively short life of the contract. For example, Seagate Series IPxMxx chip dual H-bridge (by IP1M10 IP3M12) were very well thought out, but unfortunately it appears that Seagate does this when they used stepper motors for positioning in the minds of readers Seagate disk. The Toshiba TA7279 dual H-bridge would be another choice of another great engines of less than 1 amp, but again he seems to have been made for internal use. SGS-Thompson (and others) L293 dual H-bridge is a direct competitor for the chips above, but unlike them it does not include protection diodes. The L293D chip, introduced later, is pin-compatible and includes these diodes. If the previous L293 is used, each motor winding must be resolved through a bridge rectifier (1N4001 equivalent). The use of LEDs allows a series resistor to be placed in the recirculation current to accelerate the decomposition of the current in a motor winding when turned off, which may be desirable in certain applications. The family L293 offers an excellent choice for driving small bipolar stepper development of one ampere per motor winding up to 36 volts. Figure 3. 16 shows the pinout common L293B L293D and chips: Figure 3. 16 This chip can be considered independent 4-H Half bridges, has allowed two or two-H bridges complete. This is a power DIP package with pins 4, 5, 12 and 13 for conducting heat from the PC card or an external heat sink. SGS-Thompson (and others) L298 dual H-bridge is quite similar to the above, but is able to handle up to 2-A per channel and is packaged as a component of power, as with the LS244, the is sure the two bridges over M-298 Packaged in a 4-Amp H-bridge (the data sheet for this chip provides specific advice on how to do). A warning is appropriate for the 298, the chip switches very fast, fast enough that the current protection diodes (equivalent 1N400X) does not work. Instead, use a diode as the BYV27. The National Semiconductor LMD18200 H-bridge is another good example, which can handle up to 3 amps and has full protection diodes. Although integrated H-bridges are not available for very high currents or very high voltages, there are many on the market designed components to simplify construction of bridges from H-discrete switches. For example, International Rectifier sells a line of half H-bridge drivers, two of these chips over four MOSFET switching transistor is sufficient to construct an H-bridge The IR2101, IR2102 IR2103 and are based half H-bridge drivers. Each chip has two digital inputs to directly control the two switching transistors on a leg of an H-bridge The IR2104 and IR2111 same logic side output switches to control a H-bridge, but they also understand the logic input side, in some applications, may reduce the need for external logic. In particular, the 2104 includes an enable input, while in April 2104 more chips switching transistor 8 can replace L293 without requiring additional logic. The data sheet of the chip (formerly Telcom Semiconductor) TC4467 Quad CMOS family of drivers includes information on how to use the drivers of this family to lead the Power MOSFET H-bridges running up 15 volts. A number of chip makers are complex H-bridge circuits that include current limit, it is the subject of the next section. It is also interesting to note that there are a number of 3-phase bridge drivers on the market, suitable for driving the Y or triangle configured three-phase permanent magnet steppers. Few of these engines are available, and these chips have been developed with steppers in mind. However, the Toshiba TA7288P, the GL7438, the TA8400 and TA8405 are own creations, and two such chips, with one of six half-bridges ignored, will properly monitor a 5-winding 10 steps per motor revolution.
