This document describes a simple energy-tripped circuit breaker design that protects sensitive load circuits from excessive current flow. The circuit breaker opens the power supply when the current reaches a predetermined level, similar to a fuse, but without needing physical replacement like blown fuses. To minimize nuisance trips, the breaker employs a slow-blow technique that allows relatively high current levels for short intervals without tripping. Ideally, the trip threshold would be a function of total transient energy rather than just current. The described circuit breaker combines current sensing with timing to create an energy-tripped breaker that protects circuits while minimizing nuisance trips.

1. Simple Energy-Tripped Circuit Breaker Design
Posted Sep 07th 2011
A circuit breaker protects sensitive load circuits from
excessive current flow by opening the power supply when
the current reaches a predetermined level. The simplest
circuit breaker is a fuse, but blown fuses require physical
replacement. An electronic circuit breaker provides the
same measure of circuit protection as a fuse without the
single-use problem. Nevertheless, an electronic circuit
breaker with a fixed trip current threshold, while effective
for protection, can become a nuisance if tripped by short
duration current transients—even if the circuit breaker self-
resets.

2. One way to minimize nuisance breaks is to employ a slow-
blow technique, which allows relatively high levels of
current for short intervals of time without tripping the
breaker. Ideally, the breaker’s trip threshold would be a
function of total transient energy, instead of just current.
This article describes an electronic circuit breaker,
combining current sensing with timing to create an
energytripped breaker, which protects sensitive circuits
while minimizing nuisance trips.
Low Noise Varactor Biasing with Switching Regulator
Posted Sep 01st 2011
Telecommunication, satellite links and set-top boxes all
require tuning a high frequency oscillator. The actual
tuning element is a varactor diode, a 2-terminal device that
changes capacitance as a function of reverse bias voltage.

3. The oscillator is part of a frequency synthesizing loop, as
detailed in Figure 1. A phase locked loop (PLL) compares
a divided down representation of the oscillator with a
frequency reference. The PLL’s output is level shifted to
provide the high voltage necessary to bias the varactor,
which closes a feedback loop by voltage tuning the
oscillator. This loop forces the voltage controlled oscillator
(VCO) to operate at a frequency determined by the
frequency reference and the divider’s division
Designing Linear Circuits for 5V Single Supply
Operation
Posted Aug 24th 2011
In predominantly digital systems it is often necessary to
include linear circuit functions. Traditionally, separate
power supplies have been used to run the linear
components.

4. Recently, there has been increasing interest in powering
linear circuits directly from the 5V logic rail. The logic rail is
a difficult place for analog components to function. The
high amplitude broadband current and voltage noise
generated by logic clocking makes analog circuit operation
difficult.
Generally speaking, analog circuitry which must achieve
very high performance levels should be driven from
dedicated supplies. The difficulties encountered in
maintaining the lowest possible levels of noise and drift in
an analog system are challenging enough without
contending with a digitally corrupted power supply.
Many analog applications, however, can be successfully
implemented using the logic supply. Combining
components intended to provide high performance from
the logic rail with good design can give excellent results.
The examples which follow show this in a variety of
precision measurement and control circuits which function
from a 5V supply