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Relationship between Q factor and the coupling factor of two wireless coils – I am testing the data transfer between two wireless coils. The input sinusoidal signal of the primary coil is from the function generator, whose peak to peak level is 10V and frequency is adjustable between 1MHz to 5MHz. Read more

UC3845 won’t work after new replacement – I have managed to troubleshoot and confirm that the SMPS has a bad UC3845. I have noticed after powering the chip up using an external power supply that it will start working when VCC is 8.7Vdc. Now when I tested the start-up voltage I find it to be a 8.4Vdc. I don’t know what to do to push it up. Read more

Peltier element controller method, 20Amps bidirectional current – We wish to do a Peltier cooler for a Laser diode. The current will be up to 20 Amps, bidirectional, so we cannot use off-the-shelf switch mode Peltier controllers. We will also use two LTC6101 current monitors as per page 29 (datasheet) to get a current monitor signal which is unipolar but represents current flowing in either direction. Do you think our following method is the most lean? Read more

Zero detector for medium voltage line – I need a zero detector for a Medium-voltage line that has the capability of determining the polarity of following half-cycle. I am thinking of using AC optocoupler for zero detecting along with a simple circuit consist of (diode+DC Optocoupler+RC circuit at the other side of the optocoupler) which determine the polarity of the previous half cycle. Do you have any suggestion or better circuit in mind? Read more

AC to DC converter SMPS – I designed an SMPS which gives 5 Vdc output and 4A current. I  5Vdc output. The problem is when I connect the load output going to drop 3.2Vdc and load is 1 A. Can anyone suggest me what are the reasons for this? The overall circuit is designed on a general purpose PCB. Read more

Adjustable AC load 100W – I would like to build an adjustable AC load that will work from 10V up to say 250Vac, about 100W. Google search led to this lower power, lower voltage circuit. If I change the FETs to 600V, do you think it will work? Read more

Confusion about SMPS wire gauge – I am designing 12W SMPS using NCP1014AP06.

Input- 230VAC ± 15%, 50 Hz
Peak Input current through primary – 410 mA
Primary turns – 418
Primary inductance – 9.55 mH

Secondary turns – 38
Output – 24 V, 0.5 A
PWM frequency – 65 KHz
Duty cycle – 67%
Core selected – EE 19/8/5 (for small size)

Which wire size should I use? Read more

Grid tie inverter PLL control method – I’m designing a grid tie inverter. The important thing is it’s synchronized with grid sinusoidal waveshape both in phase and frequency. I was planning to use PLL4046B IC who will be given power from Vdd = 5 VDC.  When I designed the PLL circuit on the breadboard to check it, I saw that the output was in phase and the same frequency as the input sinusoidal. But instead of sinusoidal waveform, it is generating 50 Hz square wave of 5 V pk to pk amplitude at VCO output. Read more

Heat sink for a MOSFET – I would like to know whether it is compulsory to use heat sink for MOSFET or boost diode in PFC circuit. I have used UC3854 IC for switching the MOSFET in the boost converter. A 20Ω resistor was connected in series to the gate. 17 V Vcc was given to UC3854 IC. Is there any additional protection circuit needed? Read more

High current spikes during on and off – I am designing a PFC circuit (in boost configuration, inductor is CCM, switching frequency is 100kHz), and it has a high current spike during on and off of the MOSFET switch. I used a bulb as its load. I am not sure if these high spikes are results of the MOSFET parasitic noise or a common mode noise injected at the input of the PFC circuit? And how should I work out on the noise? Read more