Varnum Smith Holland

52065405, Apr 27, 1993

May 9, 1991

7/697895

Claudio de Sa e Silva - Lynnwood WA
Jeffrey D. Putsch - Milford NH
Varnum S. Holland - Amherst NH
Wilburn M. Miller - Wilton NH

Unitrode Corporation - Billerica MA

H03K 5135
H03K 17284
G05F 156

307127

A transformer isolated circuit for driving a semiconductor power switch includes a transformer which is driven with a high frequency Pulse Width Modulated (PWM) signal in such a way that the constantly present PWM carrier supplies the power needed for high gate current pulses, while different duty cycles determine the "on" or "off" state of the power device under control. Transformer saturation is prevented by sensing primary current and returning it to zero once per PWM cycle. Because of the high PWM carrier frequency used, the average transformer power is low, yet the secondary side is able to deliver high pulse currents for fast "on-off" switching of the gate of even the largest N- or P-channel device, without need for auxiliary power supplies. Also included are provisions for extremely fast output current limiting, for use where short circuit protection is necessary. Discussion of a monolithic implementation is included.

46137670, Sep 23, 1986

Oct 31, 1983

6/546983

Varnum S. Holland - Amherst NH

Unitrode Corporation - Lexington MA

H03K 1772
H03K 326

307288

An SCR having a reduced forward-voltage drop comprising an independently powered latch circuit driving an output transistor in combination with an additional turn-off transistor. The SCR provides saturated operation of the output transistor and self-commutation which allows for the SCR to turn-off. The present invention is particularly suitable for use in integrated circuit structures having additional circuit functions thereon.

47942770, Dec 27, 1988

Aug 10, 1987

7/085297

Varnum S. Holland - Amherst NH

Unitrode Corporation - Lexington MA

G05F 318
H01L 2972
H01L 2704
H03K 1716

307296R

A low voltage lockout circuit preferably of integrated circuit form to provide a lockout signal when an internally generated reference voltage is insufficient. According to the present invention, a reference voltage is produced by passing a constant current through a reference voltage element, such as a zener diode. Insufficient reference voltage caused by a low power supply input voltage is detected by sensing the saturation of the constant current source. The present invention indicates the precise point of saturation of the constant current source and produces a lockout signal for use by other portions of the integrated circuit, or external devices. The lockout signal also indicates the minimum usable power supply input voltage. The constant current source and the saturation detection element are combined and implemented within a single semiconductor structure. The semiconductor structure includes a transistor having a second collector, wherein the minority carriers are re-emitted from the first collector upon saturation of the first collector, and received by the second collector; the resulting current produces the lockout signal.

45917787, May 27, 1986

Aug 22, 1984

6/643299

Varnum S. Holland - Amherst NH

Solid State Chargers Research & Development - Lutherville MD

H02J 704

320 39

A direct current pulse producing circuit, which can be connected in series with a battery or battery pack to be charged or recharged, or in series with a smoothing circuit of a D. C. power supply, includes Darlington configured transistors forming part of a current amplifier. The pulse producing circuit can be directly connected in series with the battery or battery pack, or the smoothing circuit across a conventional A. C. 117 volt, 60 Hz. voltage source. The direct current pulse producing circuit may be realized as monolithic integrated circuit, and includes a rectifying diode, one electrode of the rectifying diode being formed by at least part of a substrate upon which the circuit is formed. Circuit components are formed in the monolithic circuit which effect the cancelling of undesired current caused by parasitic transistor action resulting from use of the substrate or a portion thereof as an electrode of a rectifying diode. The undesired current is in effect cancelled by a mirror current of substantially equal magnitude and opposite direction with respect to the undesired current.