Analog Top Talks in May 2019 on EDABoard.com

Peer-to-peer, engineer-to-engineer questions and answers from the EDABoard.com engineering community around analog ICs and analog design. Click the “Read more” link and follow the entire conversation and maybe add your two cents by logging in to EDAboard.com.

Mains setpoint monitoring basic circuit – I need to monitor the mains with setpoint and I need an isolation too. I need a digital signal as output. When the mains is above the setpoint, I get a ‘1’ and when below the setpoint I get a ‘0’. I am using opamp (with hysteresis) for the monitoring. Read more

1VAC to 1VDC converter using opamp – Need help in making 1VAC to 1VDC converter. I tried to simulate on PROTEUS different OP-AMP circuits available on net. But not working. it always give high voltage(supply voltage) at output when input is given 1VAC. Read more

SCR speed brushed DC 180V motor control – Why is my schematic not working for a speed control brushed 180v Dc motor. I used BT 150 and used PWM to trigger gate of SCR. Read more

Simple op-amp current sink question – I’m working on a battery charger using an LTC4020 controller and one of the inputs allows scaling of the charging current. Read more

How does feedback loop control the duty cycle of buck regulator – While going through internal structure of a buck regulator, there was a feedback loop connected from the voltage divider circuit therein connected to a comparator and the input fed to the SR flipflop R end. How does this feedback control the duty cycle? Read more

Help for my Collpits oscillator circuit – I designed a local oscillator with a frequency of 380 MHz. But I have a problem with implementation on the PCB. I tested my circuit using a spectrum analyzer signal hound 4 GHz, but it didn’t show output. I need an explanation about my oscillator circuit scheme and its implementation on the PCB. Read more

Differential pair question – So I was asked this question during an analog design interview and I got it wrong. The picture of the diff. pair is linked above. VG1 is at Vdd/2 while VG2 is swept from 0 to VDD. The question was to plot Vout and to talk about the operating modes of the M1 and M2. From simulation, it seems to depend on the drain of M5? If the minimum value across it is Vov of 5, is there any relationship between this and VG1, VG2? Read more

Offset correction of current to voltage amp configuration – I have a classic I/V setup with 1 megohm feedback using an ADA4177.  Normally the non-inverting is to ground but I would like to inject my offset bias into this input. Is this an ok approach or is there a better method for this configuration. Read more

Frequency divider circuit issue – I am trying to implement a divide-by-two circuit quoted from the book “Low power CMOS circuits technology logic design and CAD tools” by Christian Piguet Could anyone advise about the spice error “timestep too small” ? Read more

Designing a variable current source – I want to design a variable current source, voltage controlled – from 0.1mA to 2.5A. Do you have any tips, circuits, etc? Read more