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Diode Tester Limits Reverse Voltage And Forward Current To Protect Sensitive Junctions
Some diode manufacturers caution against using the diode tester function in ohmmeters because it could exceed the reverse-voltage and forward-current ratings of sensitive diodes. This is especially true in optical devices such as photodiodes and laser diodes. However, the circuit described here performs a simple go/no-go test on these diodes while limiting forward current and reverse voltage to safe levels (...
Achieve MPPT Control Without Power Calculation
A maximum power point tracking (MPPT) controller circuit is extremely useful in solar photovoltaic systems for boosting power usage efficiency. The traditional MPPT design, though, requires the use of a multiplier to calculate power from source voltage and current measurements. However, it’s possible to build an MPPT controller without this multiplication stage by measuring power on the load rather than using source parameters. If we aren’t in the presence of a...
Calculator Provides Quick Rectifier Ripple Approximation
The standard practice for calculating the ripple voltage of a simple rectifier circuit with a reservoir capacitor (Fig. 1) is to linearize the problem. A linear approximation of the voltage across the reservoir capacitor (Fig. 2) assumes that the discharge time is equal to the period of the input sine wave, which is only approximately true for...
Protect Current-Sense Amplifiers From Negative Overvoltage
A high-side current-sense amplifier typically amplifies the differential voltage across a sense resistor and provides an output voltage proportional to the current in that resistor. The amplifier rejects the common-mode voltage on which the sense-voltage rides. Such devices, therefore, can be used to detect overcurrent faults in a load or to make system power-management tradeoffs. Most high-side current-sense amplifiers are well suited for situations in which...
Turn A Compensated Current Sink Into A Common Emitter (CE) Amplifier
By adding only a few components, you can turn a temperature- and beta-compensated current sink into a common-emitter (CE) amplifier that maintains a stable biased operating point. This architecture is useful for building stable and device-tolerant BJT Class A amplifiers. The circuit in Figure 1 sinks a constant current (ICE3) through Q3’s collector and emitter. This design is balanced so changes in Q3’s...
Two Wires Carry Power And Data
At times, designers face a limited amount of wire and/or a limited cost to communicate with a remote device such as a sensor. Many devices allow communication over an ac or dc power line employing an AM or FM modulation scheme. However, they tend to be costly. This design is a simple, low-cost method for sending data across the same wire used to supply power. It’s based on modulating current from a remote device back to a host. A later example...
Two Wires Carry Power And Data: Backstory
This application is as useful today as it was when I described it in the Oct. 1, 1996 issue. The deployment of sensors has increased significantly, resulting in an increased demand for efficient interconnect techniques between sensors and a host system. The use of only two wires often is attractive from both a cost and reliability standpoint. Sensing applications are no different than others—power and size are being driven smaller while faster operation is desirable...
Backstory: Implement A Spark-Gap-Based Design For Low-Cost Energy Harvesting
The idea of using a spark-gap (SG) as the active element of a converter did not come as a sudden illumination. For a long time, I had been looking for an “acceptable” way of using high-voltage, low-current power-supply sources. For me, “acceptable” simply meant technically feasible without exotic technology and sufficiently efficient to be usable. As it was a selfimposed challenge, I had no definite specifications or deadline. When I had first reviewed the...
Create A Mixed-Mode Precision Rectifier With Second-Generation Current Conveyors
RECTIFIERS PERFORM AN IMPORTANT signal-processing function in many analog circuits. But conventional half-wave, full-wave, or bridge rectifiers employing diodes can’t be used with low-amplitude signals. The circuit described below is a mixed-mode precision rectifier that can handle both low-amplitude voltage and current signals. Many previously described precision rectifiers use voltage op amps, but conventional voltage op amps suffer from a...
High Power-Factor LED Driver Converts AC Input To Power Halogen Replacement
HIGH-BRIGHTNESS LEDS ARE AN inexpensive, robust, and green replacement for halogen light bulbs. LEDs offer a much longer lifetime and eliminate the safety hazards of the inert gas, the expense of the UV filter encasement, and the handling sensitivity of halogens. Since halogen bulbs typically are driven with 12 or 24 V due to their excellent efficacy at those voltages, buildings have been wired with 12- and 24-V ac transformers for halogen...
Control Current And Voltage Precisely For Regulators, Oscillators, And Amps
THE CURRENT REGULATOR IN Figure 1 boasts a very high current stability of around 1.7% within a temperature range that spans -40°C to 125°C. It can be used in precise current and voltage regulators, oscillators, and amplifiers. For its operation, the device utilizes a unique composition of thermal coefficients of bipolar transistors and Schottky diodes, which efficiently compensate for each ...
Buck Converter Powers 5-V Circuits From 12-V Solar-Cell Array
The circuit described here is a 12-V dc to 5-V dc (±5%) switched-mode power supply (SMPS). The supply uses a 12-V input from an array of four 3-V dc, 40-mA solar cells connected in series. (The cells are available for $3.75 each from www.Allelectronics.com.) At the array’s maximum output of 12 V dc, its maximum output power is 12 × 40 mA = 480 mW. The supply’s efficiency is 83% ±1%....
Create A Simple Crowbar To Protect Prototypes From Supply Overvoltage
Designers often test prototypes with a variable-voltage bench power supply. If they leave the bench for any length of time, someone may borrow the supply or otherwise change the voltage to a level that could damage components in the prototype. This problem can be prevented by using a variable-voltage “crowbar” circuit connected across the power-supply terminals along with the prototype under test (...
Low-Cost F-to-V Converter Delivers Robust, Accurate Performance
Although special-purpose frequency-to-voltage chips help you to create an F-to-V circuit block easily, they suffer from a major drawback. For given external components, their gainconstant, and hence voltage output, can vary more than ±5% from piece to piece (e.g, the LM331 and the LM2917). Their currentsource value also varies piece to piece by a similar amount, thus causing piece-to-piece variations in the maximum voltage-output beyond which F-to-V goes into...
Battery Simulators Check Out Chargers, Over-Discharged Batteries
The two battery-simulator circuits described here can help you quickly test a battery charger under a normal battery condition and an over-discharged battery condition. The circuits let you set any voltage to see how the device under test works. As shunt regulators, the circuits provide what is referred to, in expensive active power-supply loads, as constant voltage mode. Best of all, the regulators were thrown together with parts lying around my lab. The...
Add Simple Temperature Monitoring To Battery-Management Systems
Environmental concerns are spurring the development of clean transportation alternatives. Most popular are full electric and hybrid electric motor vehicles, which use stacks of lithium-ion battery cells as the electric power source. To ensure efficient operation and long battery life, the cells are continually monitored for the available charge, known as the state of charge (SOC). The temperature of the cells is an important factor for the SOC calculation. In...
Implement A Spark-Gap-Based Design For Low-Cost Energy Harvesting
Energy harvesting is the art of extracting useful power from energy sources normally deemed too weak, too dilute, or too impractical to be usable. I have already presented an example of such a â??harvesterâ?? (â??Trick A BJT-Based Converter Into Starting At Only 250 mV DC,â?? http://electronicdesign.com, ED Online ...
Logic-Level Signals Shifted To Dim -48-V LED Driver
The main source of power in a telecommunications system is -48 V. This source’s negative polarity and its large magnitude with respect to ground pose a challenge when designers want to use low-power ICs in the telecom system’s application circuits. Fortunately, the emergence of high-voltage ICs—with operating voltages of 75 V and higher—has enabled the use of simple biasing techniques in designing circuits for -48-V systems. The technique described here provides...
Seamless Power Switcher And Battery Charger Solution Targets Portable Devices
In today’s world, there are many applications for portable devices. These devices must have extremely low or no battery drain when turned off and need to charge their on-board batteries when connected to an external power supply, whether the device is turned on or not. This circuit provides seamless switching from batteries to external power and provides a simple charging solution. In addition, there are several output signals for a microcontroller (MCU). This...
Spice Model For An Ideal Transformer Allows Bi-directional Operation
This Idea For Design provides an alternative to an earlier IFD that noted that Spice does not have a device model for an ideal transformer (“A Spice Model For The Ideal Transformer”). The author explained, “Instead, Spice provides a coupled-inductor model in the K statement that includes self and mutual inductances.” The author’s proposed solution is a model that...
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