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COMBINATION VIBRATOR AND ELECTRICAL INDUCTOR DC TO DC/AC CONVERTER

IP.com Disclosure Number: IPCOM000007538D
Original Publication Date: 1995-Nov-01
Included in the Prior Art Database: 2002-Apr-04
Document File: 2 page(s) / 115K

Publishing Venue

Motorola

Related People

Bob Stengel: AUTHOR [+2]

Abstract

The vibrator or silent alert used in pagers is a DC motor with a weight distribution that is unbal- anced about the axis of rotation. When a message is received the motor is connected to the battery and the unbalanced weight results in the entire pager vibrating, silently alerting the user ofa message recep- tion. Since the motor is idle almost all ofthe operat- ing time, it seems like a very good candidate for utilization of its elements for other functions within the product. There are typically three inductors associated with the armature of the motor, which is designed to have one connected between the two motor terminals at all rotation angles. In addition, the inductance value and losses are consistent with those used in DC to DC or AC converter applica- tions. This paper discusses the application of the motor inductance for a DC to AC voltage multiplier for a piezo alert tone element, and a DC voltage multiplier for an LED indicator or back lighting. These functions are compatible with the intended vibrator function and could be utilized at the same time ifdesired, see Figure 1.

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MO7VROLA Technical Developments

8

COMBINATION VIBRATOR AND ELECTRICAL INDUCTOR DC TO DC/AC CONVERTER

by Bob Stengel and Clifford L. Anderson

  The vibrator or silent alert used in pagers is a DC motor with a weight distribution that is unbal- anced about the axis of rotation. When a message is received the motor is connected to the battery and the unbalanced weight results in the entire pager vibrating, silently alerting the user ofa message recep- tion. Since the motor is idle almost all ofthe operat- ing time, it seems like a very good candidate for utilization of its elements for other functions within the product. There are typically three inductors associated with the armature of the motor, which is designed to have one connected between the two motor terminals at all rotation angles. In addition, the inductance value and losses are consistent with those used in DC to DC or AC converter applica- tions. This paper discusses the application of the motor inductance for a DC to AC voltage multiplier for a piezo alert tone element, and a DC voltage multiplier for an LED indicator or back lighting. These functions are compatible with the intended vibrator function and could be utilized at the same time ifdesired, see Figure 1.

  The challenge of the design was to achieve the DC to AC or DC function without the motor arma- ture turning. This was accomplished by pulsing the inductor at a high frequency and transferring the stored energy out before the torque develops enough force to result in any rotation. For the DC to AC application two clocks were used. The first clock is for pulsing the inductor and transferring the inductor magnetic stored energy (Ei = 1/2Li*) to the capaci- tive load of the piezo tone element as a stored elec- tric energy (EC = nxE,). This energy is accumulated over many pulses (n) resulting in a voltage increase for each pulse across the piezo element. The second clock provides a means for discharging the stored energy across the piezo element to ground resulting in an AC signal at the second clock rate.

  The power available from a DC to DC converter is limited by the energy available per unit of time from the energy storage capacitor or inductor. For a step up DC to DC converter using an inductor, the energy available per pulse cycle is I$ = 1/2Li2, where i is the current in the inductor at the point in time when it is disconnected from the battery or source. This current is determined from the relation i(t) = Vdd/R(l-e-(R'L)'), where Vdd iS t...