Stabilized DC motor speed controller. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Electric motors

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The circuit is designed to regulate and maintain a stable speed of a low-voltage motor with power from a few watts to 1000 watts at a supply voltage of not more than 20 V.

The sensor of the electronic ignition system of a VAZ car is used as a speed sensor. This sensor is made on the basis of a Hall sensor and is a round magnetic screen fixed on an axis with slots that, during rotation, pass into the slots of the Hall sensor. As a result, pulses are generated at the output of the sensor, the frequency of which is directly proportional to the rotational speed of the shaft on which the magnetic screen is fixed.

Refinement of the electric motor consists in installing the above-mentioned sensor of the ignition system on its shaft, which needs to be improved, associated with the through passage of the motor shaft through it

During the rotation of the motor shaft, the Hall sensor F1 generates pulses that are fed to the input of the Schmitt trigger D1.1. A shaper is assembled on triggers D1.2 and D1.3, which makes the duration of these pulses constant, independent of the speed.

The duration of the pulses is set by the R6-C3 circuit, and does not change over a wide range of rotation speeds. Thus, at the output of element D1.4 there will be pulses with a constant amplitude and duration, the duty cycle of which will vary depending on the speed of the motor shaft.

These pulses are fed to the integrator on the diode VD2, resistor R7 and capacitor C4. high-level pulses charge capacitor C4, diode VD2 prevents the capacitor from discharging through output D1.4 during a low logic level. At this time, discharging is only possible through R7 and input resistance A1.

As a result, a constant voltage is formed on C4, which is directly dependent on the speed of the motor shaft. This voltage is supplied to the inverting input of the operational amplifier A1, which is turned on by the comparator.

An exemplary voltage is supplied to the direct input A1, the value of which can be adjusted by a variable resistor R2. As soon as the voltage at the inverting output is greater than the voltage at the direct one, the output powerful field effect transistor VT1 closes, and when the voltage at C4 becomes lower than the voltage at the direct input A1, the field effect transistor VT1 opens. There are no circuits for hysteresis or response delay in the circuit of this comparator, it is not necessary here. As a result of the operation of the circuit, there is not some kind of constant voltage at the output of the comparator, but mainly pulses, the duty cycle and frequency of which constantly changes in such a way as to maintain the speed motor constant, regardless of the load on the shaft.

A powerful switching field-effect transistor of the IRF3205 type is installed at the output of the circuit.

It accepts a maximum current of 98A, has an on-state resistance of only 8mΩ, and a maximum source-to-drain voltage of 55V. This transistor is commonly used in various automotive circuits. Despite the large maximum current, the transistor can work very well with a low load current, so this circuit can be successfully used both to adjust the speed of a powerful engine and a low-power one.

Of course, if the circuit is planned to be used only with a low-power motor, then the output stage can be made on a less powerful transistor, as well as a lighter sensor can be used, for example, based on a slot optocoupler from an old "ball" computer mouse and a light perforated wheel for interrupting light flow between the LED and the phototransistor of the slotted optocoupler. The circuit used fixed resistors MLT, according to the power marked on the circuit.

Non-polar type capacitors. K73-17. Polar capacitors - imported analogues of domestic K50-35. The D814V zener diode can be replaced with any 10 V zener diode. The KR1561TL1 microcircuit can be replaced with a K561TL1 or an imported analogue can be selected.

The field-effect transistor IRF3205 can be replaced with IRF460, IRF470, IRF350-IRF362, or you can choose another suitable analogue from the reference book.

When operating on a load that consumes a current of more than 10 A, the transistor must be installed on a radiator. As a radiator, and as the basis of the housing for the entire assembly, you can use the housing from a faulty automotive ignition switch for carburetor cars of the Volga or UAZ brand, and perform the entire installation on the dismantled board of this switch.

Author: Tarasenko V.I.

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