Rechargeable 30 LED burns up on AC – I have some emergency rechargeable lights. As soon as I connect them to a 220V AC outlet 220v they burn up. I opened one of them and saw that two resistors are black. It has a three-state switch. Can anyone find out if the circuit is faulty? Read more

How do I reduce noise from this amplifier? – I have made a  speaker unit that can listen to three channels simultaneously or by demand. I want to reduce the “background” noise from the amplifier. There is way too much noise when all three channels are active at same time. What is the best way? Read more

Will an LM317 for SIM900 work? – I am planning to use an LM317 as power supply for SIM900 to get 4.2 regulated output voltage. Will this work? Read more

Paralleling CMOS inverters  -I need to use a CMOS gate (NOT) to invert the output signal of an optocoupler. One single inverter gate could be enough (the output current requirement is low) but I’ll use a 74ACT14 chip which contains six inverters. Is there any problem (signal transition glitches or something) if I put all of them in parallel? Read more

70MHz peak detector/amplitude detector – I have a sine wave between 60-70MHz and I want to measure the amplitude of the signal. I thought that the best way is to build a peak detector but after 10MHz, the circuit has a hard time detecting the peak. Any suggestions? Read more

Switch capacitors – What is a switch capacitor in analog circuit design?  Read more

What is the purpose of this op amp circuit? -I was reviewing some circuits and this circuit got my attention. I was wondering what is the operation and its function? It seems some sort of pulse generating circuit between 27V & 15V. What will be the Time duration between the pulses? Read more

Test bench for amplifiers and comparators – I designed a comparator and would like to test it for features such as aol, gain, overdrive, offset, slew rate, and more. Is the test bench for amplifiers also good for comparators? Read more

Phase-margin in a control loop with an inductive load – I am trying to make an AC current stabilisation and I am having some phase margin troubles when I add the LC filter necessary for a PWM stage output. Here is the LTSpice simulation: Read more

LM2576-5.0V power supply problem – I have an LM2576-5.0V fixed 5V output IC both SMD and through hole. When I use through-hole IC, the circuit works fine. When I give 12V 2A adapter input, it gives me 5V 2A output and I can charge my 10400mAH powerbank. But when I use the SMD IC, it doesn’t give me output. What is my mistake? Read more