Motor Speed Control Circuit Using Clamp Circuits for Saturation Compensation
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Solution Overview
Problem
Existing motor speed control systems face inaccuracies in controlling motor speed due to variations in transistor saturation voltages, leading to incorrect acceleration or deceleration of fan motors, especially when stopping or running at full speed.
Innovation Solution
A motor speed control circuit that includes a reference voltage circuit, a speed voltage circuit, clamp circuits to limit voltage levels, and a comparator to generate a control signal for the drive coil, ensuring accurate speed control by comparing the reference and speed voltages within defined limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a complementary push-pull circuit is used in the operational amplifier output stage, then the output voltage range is extended, but the output voltage is reduced by the collector-to-emitter saturation voltage of the transistors
Solution Approach 1:
The patent changes the voltage level parameters by introducing clamp circuits that adjust the speed voltage levels. The clamp circuits raise the low-level speed voltage by a predetermined level and lower the high-level speed voltage by a predetermined level, compensating for the saturation voltage drops in the push-pull circuit and achieving accurate speed control despite the voltage reduction.
2Device complexity
If transistor saturation voltage variations are not compensated, then the circuit complexity is reduced, but the speed control accuracy deteriorates
Solution Approach 1:
The patent introduces clamp circuits as intermediary components between the speed voltage circuit and the comparator. These clamp circuits act as mediators that adjust the speed voltage levels by predetermined amounts, compensating for transistor saturation voltage variations without requiring complex control logic or additional sensing mechanisms.
3Ease of manufacture
If the speed voltage levels are not clamped, then the circuit simplicity is maintained, but the motor control accuracy worsens due to transistor voltage variations
Solution Approach 1:
The patent applies preliminary action by using clamp circuits to pre-adjust the speed voltage levels before they are compared with the reference voltage. The clamp circuits proactively compensate for expected saturation voltage drops by raising low levels and lowering high levels in advance, ensuring accurate speed control is achieved before the comparison and control decisions are made.
Data Source
AI summary
A motor speed control circuit which controls a rotational speed of a motor by controlling an amount of current flowing through a drive coil of the motor. The control circuit comprises a reference voltage circuit that generates a reference voltage corresponding to a speed-specifying signal inputted to specify the rotational speed of the motor; a speed voltage circuit that generates a speed voltage corresponding to an actual rotational speed of the motor; a clamp circuit that limits the level of the speed voltage generated by the speed voltage circuit; a comparator that has the reference voltage generated by the reference voltage circuit and the speed voltage limited in level by the clamp circuit applied thereto and compares the two; and a control signal generator that generates and outputs a control signal for controlling the amount of current flowing through the drive coil based on the comparing result of the comparator.