Driver for low voltage motor control. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Electric motors
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If you are building an electrified radio-controlled toy, you will need a power circuit to control the motor with a reverse mode to change the direction of movement. All circuits presented in this article are controlled by logic levels from the output of the microcircuit. To smoothly adjust the engine speed, a PWM method is used, which allows the driver transistors to be used in switching mode and thereby increase the efficiency of the device.
The principle of PWM modulation is explained in Fig. 1.
With short positive pulses at one of the driver inputs, the engine speed is minimal. If you increase the pulse width over the same period, the engine speed also increases. The author considers the optimal period of PWM pulses to be 0,5... 1 ms.
The circuit shown in Fig. 2 is intended for motors with low current consumption of the order of 10...50 mA.
Due to the low gain of the transistors, the voltage drop on each of them reaches 0,8...0,9 V. Therefore, with log "G" at input 1 and log "0" at input 2, the VT1, VT4 switches are open and the real voltage on the engine with a 5-volt power supply it is 3,2...3,4 V. When reversing, log "1p" must be applied to input 0, and log "G" to input 2, the keys VT1 and VT4 will close, and VT2 and VT3 will open. If log."0" or log."G at two inputs, the "Stop" mode will be set.
The circuit shown in Fig. 3 has slightly improved characteristics and is designed for a current of 100...200 mA. It is not much different from the previous one. To increase the gain, the transistors are connected according to a Darlington circuit. The same results can be obtained if KT1 is used instead of transistors VT3, VT2 (Fig. 972), and KT2 is used instead of VT4-VT973.
The circuit shown in Fig. 4, in the opinion of the author, has the best characteristics. With load currents up to 1 A, the voltage drop across both switches is 0,6 V. At the output, when powered from 5 V, you can get 4,4 V.
In the "Stop" mode, log "0" is present at all inputs, transistor switches VT1, VT6 are closed. Transistors VT2-VT5 are also securely closed thanks to base resistors R2, R4, R5, R7. After applying log "1" to input 1, transistor VT1 opens, which, in turn, opens transistors VT2, VT3. When reversing, log “0” is first applied to input 1, and then after a few microseconds log “1” is applied to input 2, transistors VT1-VT3 will close, and VT4-VT6 will open. It is impossible to supply two log "1"s at the same time, since, unlike previous schemes, both switches will open and through currents will flow through the transistors. All circuits are equipped with protective diodes VD1-VD4, which reduce voltage surges when switching keys.
Author: S.M. Abramov
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