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**Calculation of input and output impedance** – Suppose any voltage current feedback network is implemented and we have calculated its Aβ (loop gain). Then how will I find its input/output impedance from this expression? Figure is given below for a reference

I have calculated Aβ as -gm1 ro1 {Rs gm / (1+ gm Rs)} Read more

**Voltage/current measurement: what am I doing wrong here?** – The schematic below shows part of a circuit that I am working on. I need to vary the current through the diodes using the series resistor R and take measurements. I have tried this in two ways:

a- using a scope current probe and

b- using two scope voltage probes to measure the voltage drop across the resistor and divide by resistance.

The problem is the measurements from these methods do not match:

a- The current probe measures 350mA on the pulse

b- Ch1 measures 2.23v and Ch2 10mv(see Captures 2,3 attached), with R = 2.5 ohm, the current should be I = 2.2/2.5 = 880 mA on the pulse

Why are these two results different?Am I doing something wrong here? Read more

**Isn’t a closed loop system with two poles at origin unstable?** – In a simple negative feedback system, you have transfer function:

G(s)/(1+G(s))

Gain Margin is the gain below unity when phase of G(s) is 180deg.

Phase Margin is the amount of phase needed to reach a total of 180 deg at unity gain. But if you have two poles at the origin, isn’t it stable from the start? Read more

**Resistor divider help needed** – I am trying to make the resistor divider below. I would like to figure out how to calculate the resistors for the different taps. The taps are going into op amps to turn on LEDs. Read more

**Oscillator not oscillating** – It’s designed to: 3.9Hz 50% duty 10v astable. Cannot figure this, the specification being obligatory to design. Read more

**How do you calculate** **power dissipated in a MOSFET?** – Rds(on) is < 0.18Ω MOSFET can handle 40A current? The MOSFET is STE40NK90ZD If 40A current is flowing through it with VBUS voltage 325V DC (H-bridge for Inverter) then what will be the power dessipated by Mosfet ? How to find out voltage drop across Drain and Source ? Read more

**Close loop gain and phase margin question** –

The above says at w0 loop gain is 0 dB. But I thought 0 dB should be way down and I marked as “what’s this point”. Can you explain? Read more

**How to choose the right amplifier?** – I’d like to clarify a few things about the choice of operational amplifiers. I borrowed the scheme published here on the forum. The author used the AD8620 amplifier. Unfortunately, pricing policy of European distributors (Farnel, Mouser, TME) makes it very expensive. The question is where would be cheaper to use other amplifiers without appreciable loss parameters. Read more

**ADC voltage current sensing** – I am trying to use MSP432 on chip 14-bit ADC to sense output from a current sensing op-amp. I am getting a large reading error from my ADC compare to the multimeter reading. My question is do I need to have a front end amplifier to buffer the input to ADC, or I can directly sense it? Read more

**3-level TRIAC AC dimmer** – I am designing a light dimmer with three levels of brightness. I am doing this strictly for educational purpose, so I constructed digital circuit with flip flops and nand gates, which outputs digital signal on each press of a button to four different outputs (one for each press). Now, I want to separate this circuit with optocouplers from triggering circuit with triac. Three levels of brightness will be implemented with string resistor ladder and capacitor. I need your help to calculate values of resistors and capacitor. At the first stage, I want about 120° firing angle, second stage about 60°, third stage about 0° and fourth stage 180°. I can’t find a useful article on the internet on how to calculate values of C and R. Read more

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