Many electrical appliances in the home or shop are powered by electric motors. Most simple device has only one speed, rarely switching two or more preset speeds, usually solved simply by switching motor windings. In many cases it would be desirable steeples speed change.
For smooth speed control is most commonly used triac phase switching. According to the degree of opening of the triac, control engine speed. But this applies only without load. With increasing load speed decreases, until in extreme cases can also be stopping the engine. When load is increasing and a drop in speed will increase the current through the motor. If we observe the current load (motor), we can increase the burden on larger opening angle of the triac and thus adjust the speed to the present value. The whole process control triac and motor current monitoring can be implemented dedicated integrated circuit U2008B ATMEL in DIL08 housing. Description of involvement with this speed controller circuit is shown in the design manual.
The control circuit is inserted into the mains supply to the engine. The heart of the circuit is an integrated circuit U2008B, which contains all the functional blocks (voltage, current and limiting detector slow start, the phase control unit). The circuit is synchronized with the network through a limiting resistor R3 (330kΩ) to the input VSYNC (Pin 7). Power supply circuit is electrically connected to the network, the voltage drop ensures its own reactance foil capacitor C4 (220nF/CFAC) performed at 275V.
The engine speed is set by potentiometer P1 (50kΩ) in plastic (shaft). His runner is applied to the input control voltage CTR (pin 3) from U2008B. TY1 triac (BTA12-700) phase is controlled from the output OUT (pin 8). Load current is sensed as a voltage drop across the resistor R1 (0.05 Ω). Due to the currents flowing through the connected load and the two alternatives are available for resistor R1. Be arranged in parallel pairs design 5W resistors (0.1 Ω), or a small piece of resistance wire with a length of 1.7 cm (using two pieces of equal length, arranged in parallel). LC provides filtering against noise, C1 (100nF/CFAC) and L1 (2.2 mH). Inductor L1 is 2.2 mH inductance and should be rated for at least 3A current. Maximum engine power is limited to 600W.
The construction of the controller
Speed controller is constructed on one side printed circuit board measuring 50 x 47 mm. With the exception of the potentiometer P1 (50kΩ) for speed control does not have any involvement adjusters. With careful work, the regulator should work on the first try. The actual performance element TY1 (BTA12-700) can be placed on a small anodized heat sink type D02-BLK (13x9x19mm; 22K / W).
Because the controller circuit electrically connected to the network, it is necessary to ensure the revival of safety principles and work done by the controller built into the insulated (plastic) boxes. They should not have to touch any parts, except potentiometer P1.
Below schematic/project is updated and can regulate AC motor up to 2kW, we use powerfull triac BTA40/600B with continuous current of 25A.
• Full Wave Current Sensing
• Compensated Mains Supply Variations
• Variable Soft Start or Load-current Sensing
• Voltage and Current Synchronization
• Switchable Automatic Retriggering
• Triggering Pulse Typically 125mA
• Internal Supply-voltage Monitoring
• Current Requirement >3mA
• Low-cost Motor Control
• Domestic Appliance
The Atmel® U2008B is designed as a phase-control circuit in bipolar technology. It enables load current detection as well as mains-compensated phase control. Motor control with load-current feedback and overload protection are preferred applications.
Block Diagram with Typical Circuit: Load Current Sensing
U2008B Pin Description-Pin Symbol Function
Mains Supply, Pin 5
The Atmel® integrated circuit U2008B, which also contains voltage limiting, can be connected via D1 and R1 to the mains supply. Supply voltage, between pin 4 (pos., ⊥) and pin 5, is smoothed by C1. The series resistance R1 can be calculated as follows:
R1max = 0.85 x VM – VSmax / 2 × Itot
VM = Mains voltage
VSmax = Maximum supply voltage
Itot = ISmax + Ix = Total current compensation
ISmax = Maximum current consumption of the IC
Ix = Current consumption of the external components
Operation with externally stabilized DC voltage is not recommended.
When the voltage is built up, uncontrolled output pulses are avoided by internal voltage monitoring.
Apart from that, all latches of the circuit (phase control, load limit regulation) are reset and the soft start capacitor is short circuited. This guarantees a specified start-up behavior each time the supply voltage is switched on or after short interruptions of the mains supply. Soft start is initiated after the supply voltage has been built up. This behavior guarantees a gentle start-up for the motor and automatically ensures the optimum run-up time.
Phase Control, Pin 6
The function of the phase control is identical to that of the well-known Atmel® IC U211B. The phase angle of the trigger pulse is derived by comparing the ramp voltage V2 at pin 2 with the set value on the control input, pin 3. The slope of the ramp is determined by C3 and it’s charging current Iϕ.
The charging current can be regulated, changed or altered using R8 at pin 6. The maximum phase angle, αmax, (minimum current flow angle ϕmin) can also be adjusted by using R8.
When the potential on pin 2 reaches the set point level of pin 3, a trigger pulse is generated whose pulse width, tp, is determined from the value of C3 (tp = 9μs/nF). At the same time, a latch is set with the output pulse, as long as the automatic retriggering has not been activated, then no more pulses can be generated in that half cycle. Control input at pin 3 (with respect to pin 4) has an active range from –9V to –2V. When V3 = –9V the phase angle is at its maximum amax, i.e., the current flow angle is minimum. The minimum phase angle amin is set with V3 ≥ –1V.
The current-detector circuit monitors the state of the triac after triggering by measuring the voltage drop at the triac gate. A current flow through the triac is recognized when the voltage drop exceeds a threshold level of typically 40mV.
If the triac is quenched within the relevant half wave after triggering (for example owing to low load currents before or after the zero crossing of current wave, or for commutator motors, owing to brush lifters), the automatic retriggering circuit ensures immediate retriggering, if necessary with a high repetition rate, tpp/tp, until the triac remains reliably triggered.
Current Synchronization, Pin 8
Current synchronization fulfils two functions:
• Monitoring the current flow after triggering. In case the triac extinguishes again or it does not switch on, automatic triggering is activated as long as triggering is successful.
• Avoiding triggering due to inductive load. In the case of inductive load operation, the current synchronization ensures that in the new half wave no pulse is enabled as long as there is a current available from the previous half wave, which flows from the opposite polarity to the actual supply voltage.
A special feature of the IC is the realization of current synchronization. The device evaluates the voltage at the pulse output between the gate and reference electrode of the triac. This results in saving the separate current synchronization input with specified series resistance.
Voltage Synchronization with Mains Voltage Compensation, Pin 7
The voltage detector synchronizes the reference ramp with the mains supply voltage. At the same time, the mains-dependent input current at pin 7 is shaped and rectified internally. This current activates automatic retriggering and at the same time is available at pin 3. By suitable dimensioning, it is possible to attain the specified compensation effect.
Automatic retriggering and mains voltage compensation are not activated until | V7 - V4| increases to 8V. The resistance Rsync defines the width of the zero voltage cross-over pulse, synchronization current, and hence the mains supply voltage compensation current. If the mains voltage compensation and the automatic retriggering are not required, both functions can be suppressed by limiting |V7 – V4| < 7 V.
A further feature of the IC is the selection between soft start and load-current compensation.
Soft start is possible by connecting a capacitor between pin 1 and pin 4. In the case of load-current compensation, pin 1 is directly connected with resistance R6, which is used for sensing load current.
Load Current Detection, Pin 1
The circuit continuously measures the load current as a voltage drop at resistor R6. The evaluation and use of both half waves results in a quick reaction to load-current change. Due to voltage at resistor R6, there is an increase of input current at pin 1. This current increase controls the internal current source, whose positive current values are available at pin 3. The output current generated at pin 3 contains the difference from the load-current detection and the mains-voltage compensation.
The effective control voltage is the final current at pin 3 together with the desired value network. An increase of mains voltage causes an increase of the control angle α. An increase of load current results in a decrease of the control angle. This avoids a decrease in revolution by increasing the load as well as an increase of revolution by the increment of mains supply voltage.
The BTA40 600B is suitable for general purpose AC power switching. The BTA40/600B can be used as ON/OFF function in applications such as static relays, heating regulation, water heaters, induction motor starting circuits, welding equipment… or for phase control operation in high power motor speed controllers, soft start circuits… Thanks to his clip assembly technique, they provide a superior performance in surge current handling capabilities.
The circuit, which is conected directly to the mains, uses phase proportional control to eliminate current peaks at switch ON. Thease peaks are also suppressed to some extent by varistor S20K275V. Use 10A fast blow fuse.
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