Portable power system using DC to DC converter

• US 6,087,815 A
• Filed: 11/07/1997
• Issued: 07/11/2000
• Est. Priority Date: 04/23/1997
• Status: Expired due to Fees

• Current Assignee: Altra Holdings Incorporated (Regal Rexnord Corp.)
• Original Assignee: Fiskars Corporation (Fiskars Oyj Abp)
• Inventors: Boda, James C., Hoerr, David M., Pfeifer, John Edward
• Primary Examiner(s): BERHANE, ADOLF D
• Application Number:
  US08/965,748
• Time in Patent Office: 977 Days
• Field of Search: 323/265, 323/268, 323/272, 323/282, 323/284, 323/350, 323/351, 323/283
• US Class Current: 323/282
• CPC Class Codes: B25F 5/00 Details or components of portable power-driven tools not particularly related to the operations performed and not otherwise provided for
• CPC Class Codes: H01M 10/46 Accumulators structurally combined with charging apparatus circuits for charging H02J7/00
• CPC Class Codes: H01M 50/247 specially adapted for portable devices, e.g. mobile phones, computers, hand tools or pacemakers
• CPC Class Codes: H01M 50/256 Carrying devices, e.g. belts
• CPC Class Codes: Y02E 60/10 Energy storage using batteries

Abstract

A portable power system for a hand tool employs a high-voltage transmission of power from a battery pack over a cord to a DC to DC converter, which steps the transmission voltage down to rated tool voltage. The system uses a switching transistor to transmit power according to a duty cycle which varies automatically according to tool current draw and voltage. The DC to DC converter employs synchronous rectification with an inductor-capacitor network to transform a duty cycle square wave into DC power. The startup voltage sense feature permits powering up the converter circuitry only when needed. The converter will shut down if no current has been drawn by the tool for a predetermined period of time or if the converter unit is in danger of overheating, as determined by a stored algorithm. The portable power system has safeguards to prevent fouling or shorting in wet environments, is adaptable to left or right handed users, and is physically configurable into a variety of carrying modes.

Claims

1. A DC to DC converter for a handheld electrical device, comprising:

a DC power input;

a power conversion circuit coupled to said input for receiving power at a first voltage and having an output, said conversion circuit selectively gating power at a desired second voltage different from the first voltage to the output, the output adaptable to be coupled to a power input of the handheld electrical device;

an output impedance element of the conversion circuit connected to the output, a logic circuit coupled to the output impedance element by a voltage sense line, a control path coupling the logic circuit to the conversion circuit, the logic circuit sensing a drop in voltage across the output impedance element as an indication that the handheld electrical device has been turned on by the user and that power is now required, the logic circuit, in response to sensing the drop in voltage, transmitting a control signal to the conversion circuit, the conversion circuit gating DC power at the second voltage responsive to receiving the control signal; and

a trickle current path from the input of the conversion circuit to the output of the conversion circuit to permit a sense voltage to reside across the output impedance element when the electrical device is not turned on.

2. The converter of claim 1, wherein the trickle current path includes a resistor having an impedance which is relatively large relative to an impedance between the input and the output.

3. The converter of claim 1, wherein the conversion circuit converts DC power appearing at the input with a first voltage to a second DC power with a second voltage.

4. The converter of claim 3, wherein the first DC power is at a voltage higher than the voltage of the second DC power.

8. The device of claim 1, wherein the conversion circuit is a DC to DC power conversion circuit.

9. The device of claim 8, wherein the conversion circuit is a zero crossing buck converter.

10. The device of claim 8, wherein the conversion circuit incorporates a pulse width modulating integrated circuit.

5. A handheld electrical device, comprising:

a remote power source supplying power at a first voltage;

a converter, a power conversion circuit of the converter having an input coupled to the remote power source by an electrical cord, the conversion circuit having an output, the conversion circuit selectively producing power at an output, the power produced at the output having a second voltage of a magnitude different from the first voltage, the output of the conversion circuit adaptable to be coupled to at least one functional electrical element of an electrical device by a power switch of the electrical device;

an output impedance element of the conversion circuit connected to the output, a logic circuit of the converter coupled to the output impedance element by a voltage sense line, a control path coupling the logic circuit to the conversion circuit, the logic circuit sensing a drop in voltage across the output impedance element when the switch is turned on, the logic circuit transmitting a control signal on the control path to the conversion circuit responsive to sensing the drop in voltage, the conversion circuit producing power at the output responsive to receiving the control signal; and

a trickle current path coupled between the input and the output of the power conversion circuit to permit a current to pass through the output impedance element, thereby creating a sense voltage across the output impedance element when the electrical device power switch is not turned on.

6. The device of claim 5, wherein the switch is manually actuated.

7. The device of claim 5, wherein the electrical device is a power tool.

11. A power supply system for a handheld electrical device, comprising:

a remote power source supplying power at a first voltage;

a converter, a power conversion circuit of the converter having an input coupled to the remote power source by an electrical cord, the conversion circuit having an output, the conversion circuit selectively producing power at an output, the power produced at the output having a second voltage of a magnitude different from the first voltage, the output of the conversion circuit adaptable to be coupled to at least one functional electrical element of an electrical device by a power switch of the electrical device;

at least one output impedance element of the conversion circuit connected to the output, a logic circuit of the converter coupled to the output impedance element by a voltage sense line, a control path coupling the logic circuit to the conversion circuit, the logic circuit sensing a drop in voltage across the output impedance element when the switch is turned on, the logic circuit transmitting a control signal on the control path to the conversion circuit responsive to sensing the drop in voltage, the conversion circuit producing power at the output responsive to receiving the control signal; and

a trickle current path coupled between the input and the output of the power conversion circuit to permit a current to pass through the output impedance element, thereby creating a sense voltage across the output impedance element when the electrical device power switch is not turned on.