Induction coil driver

• US 4,914,399 A
• Filed: 03/01/1989
• Issued: 04/03/1990
• Est. Priority Date: 03/01/1989
• Status: Expired due to Term

• Current Assignee: 3M Company
• Original Assignee: 3M Company
• Inventors: Doany, Ziyad H.
• Primary Examiner(s): MOTTOLA, STEVEN J
• Application Number:
  US07/317,820
• Time in Patent Office: 398 Days
• Field of Search: 324/67, 330/10, 330/51, 330/207 A, 330/251, 330/277, 330/306
• US Class Current: 330/10
• CPC Class Codes: H03F 3/2171 with field-effect devices H03F3/2173 - H03F3/2178 take precedence

Abstract

An amplifier which has special application as an induction coil driver. A multi-frequency signal is used to modulate the pulse width of a square wave, resulting in a pulse modulated signal. The pulse modulated signal is divided into two delay signals. The falling edge of each pulse is delayed in one of the delay signals, while the rising edge of each pulse is delayed in the other delay signal. This creates a "dead band" between the two signals for each pulse. The signals are used to drive two metal oxide semiconducting field-effect transistors, which are connected to positive and negative power supplies. The switching of the MOSFETs occurs during the dead band which, when combined with a novel inductor-diode circuit, results in high-efficiency power transfer. The amplified modulated signal is then subjected to a low-pass filter which cancels out the square wave carrier and switching noise. The amplified analog signal may then be applied to a non-tuned induction coil.

Claims

1. An apparatus for amplifying an analog signal, comprising:

means for generating a pulse modulated signal having pulse widths which are a function of the analog signal;

means for creating first and second delay signals from said pulse modulated signal, each of said delay signals having pulses therein corresponding to pulses in said pulse modulated signal, the falling edge of each said pulse in said first delay signal being delayed, and the rising edge of each said pulse in said second delay signal being delayed, thereby creating a dead band between said first and second delay signals for each said pulse;

a first switch having an output responsive to said first delay signal;

a second switch having an output responsive to said second delay signal;

power supply means connected to said outputs of said first and second switches; and

low-pass filter means connected to said outputs of said first and second switches.

2. The apparatus of claim 1 wherein:

said low-pass filter includes at least one inductor; and

said switching means further includes rectifier means for returning inductive energy in said inductor to said power supply means during said dead band.

3. The apparatus of claim 2 wherein said means for generating a pulse modulated signal comprises:

phase-locked loop circuit means responsive to the analog signal; and

means for providing a square wave as a primary input to said phase-locked loop circuit means.

4. The apparatus of claim 3 wherein said means for creating first and second delay signals comprises:

first and second delay networks connected in series with to the output of said phase-locked loop circuit means, said first delay network producing a ramped falling edge signal, and said second delay network producing a ramped rising edge signal; and

means for squaring off said ramped falling edge signal and said ramped rising edge signal.

5. The apparatus of claim 4 wherein:

said first switch is a p-type MOSFET whose source lead is connected to a positive rail of said power supply means; and

said second switch is an n-type MOSFET whose source lead is connected to a negative rail of said power supply means.

6. The apparatus of claim 1 wherein said means for generating a pulse modulated signal comprises:

phase-locked loop circuit means responsive to the analog signal; and

means for providing a square wave as a primary input to said phase-locked loop circuit means.

7. The apparatus of claim 1 wherein the output of said means for generating a pulse modulated signal is connected in series with to first and second delay networks, said first delay network producing a ramped falling edge signal, and said second delay network producing a ramped rising edge signal, and further comprising means for squaring off said ramped falling edge signal and said ramped rising edge signal.

8. The apparatus of claim 1 wherein:

said first switch is a p-type MOSFET whose source lead is connected to a positive rail of said power supply means; and

said second switch is an n-type MOSFET whose source lead is connected to a negative rail of said power supply means.

9. An apparatus for driving an induction coil, comprising:

means for producing an analog signal having one or more frequencies therein;

means for generating a pulse modulated signal having pulse widths which are a function of said analog signal;

means for creating first and second delay signals from said pulse modulated signal, each of said delay signals having pulses therein corresponding to pulses in said pulse modulated signal;

a first switch responsive to said first delay signal;

a second switch responsive to said second delay signal, the output of said first and second switches being combined to form an amplified modulated signal;

power supply means for regulating output of said first and second switches; and

low-pass filter means for converting said amplified modulated signal into an amplified analog signal, to be transmitted to the induction coil.

10. The apparatus of claim 9 wherein said means for creating first and second delay signals comprises:

first and second delay networks connected in series with to the output of said means for producing a pulse modulated signal, said first delay network producing a ramped falling edge signal, and said second delay network producing a ramped rising edge signal; and

means for squaring off said ramped falling edge signal and said ramped rising edge signal whereby the falling edge of each said pulse in said first delay signal is delayed, and the rising edge of each said pulse in said second delay signal is delayed, thereby creating a dead band between said first and second delay signals for each said pulse.

11. The apparatus of claim 10 wherein:

said low-pass filter includes at least one inductor; and

said first and second switches are connected, respectively, to first and second rectifier means for returning inductive energy in said inductor to said power supply means during said dead band.

12. The apparatus of claim 11 wherein said means for generating a pulse modulated signal comprises:

a phase-locked loop circuit responsive to said analog signal; and

a square wave source connected to the primary input of said phase-locked loop circuit.

13. The apparatus of claim 12 wherein:

said first switch is a p-type MOSFET whose source lead is connected to a positive rail of said power supply means; and

said second switch is an n-type MOSFET whose source lead is connected to a negative rail of said power supply means, the drains of each said MOSFET being connected, resulting in said amplified modulated signal.

14. An inductive transmitter comprising:

a signal source for producing an analog signal having one or more frequencies therein;

a square wave generator;

a pulse width modulator connected to said signal source and said square wave generator for generating a pulse modulated signal having pulse widths which are a function of said analog signal;

first and second delay networks connected in series with the output of said pulse width modulator, said first delay network producing a ramped falling edge signal, and said second delay network producing a ramped rising edge signal;

means for squaring off said ramped falling edge signal and said ramped rising edge signal, forming first and second delay signals, the falling edge of each pulse in said first delay signal being delayed, and the rising edge of each pulse in said second delay signal being delayed, thereby creating a dead band between said first and second delay signals for each said pulse;

a power supply having positive and negative rails;

a first switch responsive to said first delay signal, the input of said first switch being connected to said positive rail of said power supply;

a second witch responsive to said second delay signal, the input of said second switch being connected to said negative rail of said power supply, and the output of said first and second switches being combined to form an amplified modulated signal;

a low-pass filter connected to said combined output of said first and second switches for converting said amplified modulated signal into an amplified analog signal, said low-pass filter having at least one inductor;

first rectifier means connected to said first switch;

second rectifier means connected to said second switch, each of said rectifier means alternately returning inductive energy in said inductor to said power supply during successive dead bands; and

induction coil means connected to the output of said low-pass filter.

15. The inductive transmitter of claim 14 wherein:

said pulse width modulator comprises a phase-locked loop circuit;

said means for squaring off said ramped falling edge signal and said ramped rising edge signal comprises first and second Schmitt triggers, said first Schmitt trigger being connected to said first delay network, and said second Schmitt trigger being connected to said second delay network;

said first switch is a p-type MOSFET whose source lead is connected to said positive rail of said power supply; and

said second switch is an n-type MOSFET whose source lead is connected to said negative rail of said power supply, the drains of each said MOSFET being connected together to form said combined output.

16. The inductive transmitter of claim 14 wherein:

said one or more frequencies in said analog signal lie in the range of approximately 50 kHz to 200 kHz;

said square wave generator generates a square wave having a frequency of approximately 500 kHz; and

said pulses in said first and second delay signals each have a delay time of approximately 25 nanoseconds.

17. A method of amplifying an analog signal comprising the steps of:

modulating a square wave to produce a pulse modulated signal having pulse widths which are a function of the analog signal;

creating first and second delay signals from said pulse modulated signal, each of said delay signals having pulses therein corresponding to pulses in said pulse modulated signal, the falling edge of each said pulse in said first delay signal being delayed, and the rising edge of each said pulse in said second delay signal being delayed, thereby creating a dead band between said first and second delay signals for each said pulse;

utilizing said first and second delay signals to regulate first and second switches, respectively, the input of said first switch being connected to a positive voltage supply, the input of said second switch being connected to a negative voltage supply, and the outputs of each of said switches being combined to produce an amplified modulated signal; and

passing said amplified modulated signal through a low-pass filter, thereby generating an amplified analog signal.

18. The method of claim 17 further comprising the step of applying said amplified analog signal to induction coil means.