Micrel, Incorporated

Roel Van Ettinger

Paul Wilson

Christian Gater

An LED driver is disclosed that drives LEDs connected in parallel. Instead of applying current to all the parallel-connected LEDs at the same time, under control of a common PWM brightness control signal, the application of current to each parallel path is staggered by using staggered brightness control signals. The turning on of the LEDs in the different parallel paths will have the same duty cycle but will be out of phase. This reduces ripple in the power supply by reducing the magnitude of the instantaneous current sink. In one embodiment, a shift register contains a binary representation of the PWM duty cycle, and a clock shifts the bits along the shift register. The PWM brightness control signals for each parallel path of LEDs are tapped from different positions along the shift register so that the PWM brightness control signals are identical but staggered.

Driving multiple parallel LEDs with reduced power supply ripple

A low-dropout voltage (LDO) regulator that creates a zero in the open loop gain using a relatively small-sized current control element to divert part of the supplied load current through a 'zero' resistor before adding it to the output load. The main part of the output load is passed through a relatively large second current control element. A control signal generated by an error amplifier (e.g., an op-amp) is used to control the small current control element, but is passed through a boost zero compensating resistor before being applied to the large current control element. The voltage signal developed across the 'zero' resistor mimics the magnitude and phase of a zero in the loop. This voltage signal is added to the loop gain by, for instance, using a bypass capacitor, and the resulting feedback signal is supplied to the error amplifier.

Creating additional phase margin in the open loop gain of a negative feedback amplifier system using a boost zero compensating resistor

Evaluating an embedded EPROM in a host IC device involves using program circuitry to program/unprogram all of the floating-gate cells of the embedded EPROM, then simultaneously transmitting a predetermined test bias voltage to all of the programmed/unprogrammed floating-gate cells, and then evaluating the output terminals of all of the floating-gate cells using a logic (e.g., wired NOR or NAND) circuit, whereby successful operation of all of the embedded EPROM cells causes the wired logic circuit to generate a single positive test result signal, and the failure of one or more of the embedded EPROM cells causes the wired logic circuit to generate a single negative test signal. A reference cell is also evaluated using a bias testing circuit to determine that the reference voltage supplied during normal operation is at an acceptable voltage level.

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Bathgate, United Kingdom

Roel Van Ettinger