Common emitter non-symmetrical gain – I have simulated in LTspice a very simple CE amplifier. There is no AC capacitor at the emitter It is a  plain and simple CE emitter bias unbypassed with a gain of  Av = -Rc / RE = 4.07. It turns out that, as input is a perfect 1V sine at Vout, the negative swing reaches -3.82V and the positive swing goes to +4.11V. That is not so small as to be disregarded. Any ideas why negative swing doesn’t reach its full value? Read more

Multi-voltage power supply – I want to build a 3.3v, 5v DC power supply which will be fed by an AC-DC adaptor. I need 2A for 5V, 500mA for the 3.3V. Is there any one chip that can do that? I want to keep the supply compact. I am currently using MAX748A for 3.3v , and was thinking of adding a TPS5405DR from  Texas Instruments which is a 5v buck regulator. Read more

Simplest 10W mono audio amplifier – I would like to build a small monophonic audio amplifier that will take audio from the CD player and will be able to drive a transformer which, in turn, will AM modulate the anode of a small 8W transmitter. Since audio quality is not too important, I wonder if a class-C amplifier is ok, or does t have to be AB? I am looking for the simplest circuit that can do it. Read more

How to measure AC current – I need to measure the resistivity between two points using AC current. What kind of circuit would I need for this? Read more

Short circuit protection in H-bridge – I want to limit the circuit below to  3A. Can anyone provide me circuit for it? Read more

Do I need to make a DC path at the input of an op amp? – I’ve heard that a DC path is needed at the input of an op amp or the op amp won’t be functional because there is no path for the input bias current. But if I use MOSFETs to design the op amp, is there still input bias current (the gate of MOSFETs have no current)? Or do I still need to add R1 to make the op amp functional? Read more

Difference between single-stage and two-stage op amps – Can somebody explain the difference between single-stage and two-stage operational amplifiers? When do  we use single stage and when two stage and why? Read more

2-phase VFD design for conventional split air conditioner – I have studied a bit about the DC inverter air conditioner that promises a lot of energy saving. What I understand is that they require BLDC motor based compressors and dedicated electronic circuitry for operation. Our idea is that we run a permanent split capacitor motor without the capacitor. We build a 2-phase inverter that creates two voltages that have same frequency but different magnitude and phase (theoretically 90 degrees apart). The two voltages will be given to the main and auxiliary winding running the motor. I want to know what are the theoretical limitation in implementing it? Also, what practical challenges may be encountered such as component rating, filtering requirement etc.? Read more

Electronic sound of chirping canary circuit – Regarding the circuit below:  How do I know that my audio transformer is 1K : 8R? Is it by simply measure the DC resistance?

Aso, if  I wanted to use a ferrite core, how much should the number of turns for the primary and secondary coils, and will this core be simply a rod or one removed from a computer power supply? Finally, how does the above circuit operates? What I don’t know is the function of the two small caps 10n and 22n and why they have a very small capacitance related to the other two 100u caps. Read more

Using a thermistor for temperature reading – I bought a salinity probe from Oakton which is integrated with a temperature cable. I just learned from their engineers that they use an NTC 30K thermistor. If I look at the data sheet of this thermistor, I see large lookup tables between resistance and temperature. The temperature also has a degree gap in it. Anyone interfacing with this thermistor has to do a lookup into these large tables for every temperature reading, unlike the temperature chips such as  LM60 which has formulas that can be used to convert the read signal into temperature values with precision of 100 units. Why? Read more