Power supplies

• US 5,260,645 A
• Filed: 03/20/1992
• Issued: 11/09/1993
• Est. Priority Date: 04/17/1991
• Status: Expired due to Fees

• Current Assignee: Smiths Industries Public Limited Company
• Original Assignee: Smiths Industries Public Limited Company
• Inventors: Williams, Brian, Addison, David M.
• Primary Examiner(s): Ro, Bentsu
• Application Number:
  US07/856,590
• Time in Patent Office: 599 Days
• Field of Search: 318/138, 318/254, 318/439, 318/599, 323/299, 323/300, 323/301, 323/302, 323/303, 323/304, 307/57, 307/58
• US Class Current: 323/299
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators
• CPC Class Codes: H02P 6/06 Arrangements for speed regulation of a single motor wherein the motor speed is measured and compared with a given physical value so as to adjust the motor speed

Abstract

The power supply of a brushless d.c. motor has a trigger circuit that controls the frequency of a ramp generator which receives an output Vs from an unregulated voltage supply. The amplitude of the output V_R of the ramp generator is dependent on the amplitude of its input. A comparator receives the ramp output V_R at one input and a steady voltage V_D at the other input. The comparator produces a pulse output Vc, with each pulse being initiated and terminated at transitions of the ramp signal and the steady signal so that the width of each pulse increases when the unregulated voltage source decreases. The pulse output Vc is supplied to the control input of the motor'"'"'s commutation circuit. The commutation circuit switches the supply voltage Vs to the coils of the motor under control of the input Vc so that its mean d.c. output is independent of variation in the supply voltage.

Claims

1. A power supply including a switching circuit connected to receive a variable supply voltage, the power supply including a ramp generator that produces a ramp output whose amplitude alternates at a fixed frequency and increases gradually from a predetermined value to a second value that varies in response to variations in said variable supply voltage, a trigger circuit connected to control the frequency of the output of said ramp generator, the trigger circuit including a comparator and means supplying an alternating ramp input and a fixed input to said comparator, said comparator providing a trigger output to said ramp generator, the power supply further including a second comparator, means connecting the output of the ramp generator to one input of the second comparator, means supplying a steady signal to another input of the second comparator so that the second comparator provides a pulse output signal in which each pulse is initiated and terminated at transitions of the steady signal and the ramp output so that the pulse width varies in response to variations in said variable supply voltage, and means supplying the variable width pulse output of the second comparator to said switching circuit such that reduction in the supply voltage is compensated for by an increase in pulse width and such that an increase in the supply voltage is compensated for by a decrease in pulse width in such a way that the mean d.c. output of the power supply is substantially independent of variations in the variable supply voltage.

2. A power supply according to claim 1, wherein the ramp generator includes an integrator.