Simple Energy-Tripped Circuit Breaker DesignPosted Sep 07th 2011A circuit breaker protects sensitive load circuits fromexcessive current flow by opening the power supply whenthe current reaches a predetermined level. The simplestcircuit breaker is a fuse, but blown fuses require physicalreplacement. An electronic circuit breaker provides thesame measure of circuit protection as a fuse without thesingle-use problem. Nevertheless, an electronic circuitbreaker with a fixed trip current threshold, while effectivefor protection, can become a nuisance if tripped by shortduration current transients—even if the circuit breaker self-resets.
One way to minimize nuisance breaks is to employ a slow-blow technique, which allows relatively high levels ofcurrent for short intervals of time without tripping thebreaker. Ideally, the breaker’s trip threshold would be afunction of total transient energy, instead of just current.This article describes an electronic circuit breaker,combining current sensing with timing to create anenergytripped breaker, which protects sensitive circuitswhile minimizing nuisance trips.Low Noise Varactor Biasing with Switching RegulatorPosted Sep 01st 2011Telecommunication, satellite links and set-top boxes allrequire tuning a high frequency oscillator. The actualtuning element is a varactor diode, a 2-terminal device thatchanges capacitance as a function of reverse bias voltage.
The oscillator is part of a frequency synthesizing loop, asdetailed in Figure 1. A phase locked loop (PLL) comparesa divided down representation of the oscillator with afrequency reference. The PLL’s output is level shifted toprovide the high voltage necessary to bias the varactor,which closes a feedback loop by voltage tuning theoscillator. This loop forces the voltage controlled oscillator(VCO) to operate at a frequency determined by thefrequency reference and the divider’s divisionDesigning Linear Circuits for 5V Single SupplyOperationPosted Aug 24th 2011In predominantly digital systems it is often necessary toinclude linear circuit functions. Traditionally, separatepower supplies have been used to run the linearcomponents.
Recently, there has been increasing interest in poweringlinear circuits directly from the 5V logic rail. The logic rail isa difficult place for analog components to function. Thehigh amplitude broadband current and voltage noisegenerated by logic clocking makes analog circuit operationdifficult.Generally speaking, analog circuitry which must achievevery high performance levels should be driven fromdedicated supplies. The difficulties encountered inmaintaining the lowest possible levels of noise and drift inan analog system are challenging enough withoutcontending with a digitally corrupted power supply.Many analog applications, however, can be successfullyimplemented using the logic supply. Combiningcomponents intended to provide high performance fromthe logic rail with good design can give excellent results.The examples which follow show this in a variety ofprecision measurement and control circuits which functionfrom a 5V supply