(editor’s note: Intrigued by these power electronics problems? Have a question or another solution? Then click the “Read more” link and follow the conversation on EDAboard.com or log in to EDAboard and participate in the power electronics forum threads.)

Cheap mains conducted emissions tester? – Our direct drive, 100W offline, non-isolated LED driver failed EMC (screenshot). We need to re-test it ourselves. Do you know the cheapest LISN and spectrum analyzer that we can buy to repeat the test? It’s too expensive to keep going back to the test house. Read more

Current drawing circuit with no load – I built the attached circuit (it is a simple voltage doubler, Vou=2Vin). I used a ring oscillator to generate a 200kHz frequency (Phi1, Phi2 in the circuit). These two signals are non-overlapping. I got a perfect output voltage as expected. However, when I measure the input current, it seems my circuit is always drawing current and it keeps increasing when I increase the input voltage. Read more

 

 

 

 

Isolated probe for inverter measurements needed? I have a DSO TBS2072b from Tektronix (ground is not isolated). Will the DSO get damaged if I check the MOSFET output without using an isolated probe (using a normal probe)? Read more

Brushed DC motor control power stage design – I want to control the speed of my DC brushed motor. The ratings are:

voltage: 31 v
amperes: 3.8 amp
Watt: 80

Can you suggest driver circuits, switching modulation, and other considerations? I am following Microchip AN893 app notes. Read more

Inverter input and output – What will be the RMS output voltage of an inverter if the input is 240V DC? How much input is required in DC to get a 240V AC RMS output?  more

Level-shifting an MCU-generated PWM signal?– How would one use a µC-generated PWM signal to generate a PWM waveform spanning equal values above and below 0 V? Read more

Working with IR2104 for this application – I’m working on a solar battery charger and using an IR2104 MOSFET driver IC and two NMOS IRF540N ICs working only on the high side. I’m using a PWM with 20 kHz frequency, a Vcc 12 V, 10µf, and 63 V bootstrap capacitor. I want to switch the bulb which is used as a load between source and drain of high and low side of MOSFET to ground on and off.  But the load is on constantly and not switching. Read more

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

Transformer design for SMPS –  I need to get 5V@2A as output and using TNY266 as an offline switcher for SMPS regulation. Read more

Thermal considerations for 24V-27A DC motor drive – I need to drive a 24V/27A DC motor (650W). This motor must operate even when mains power is off, so a 24V lead-acid battery will be used. The transformer will be 1KW. My concern is the power dissipation on bridges, diodes, and MOSFETs when the motor is moving. The following components seem sufficient for the job.

http://export.farnell.com/multicomp/…3%3AKBPC5004FP
http://export.farnell.com/infineon/i…2-3/dp/2443434
http://export.farnell.com/on-semicon…rfnonsku=false

But the problem is the total power dissipation. For example, the diode will have a voltage drop of 0.3V, at 25A this will be 7.5W. The MOSFET will dissipate something less than 7W and the bridge more than 20W! Read more