Peer-to-peer, engineer-to-engineer questions and answers from the EDABoard.com engineering community around power electronics. Click the “Read more” link and follow the entire conversation and maybe add your two cents by logging in to EDAboard.com

AC motor speed control – In my project I have to control the speed of AC230V,50HZ, 4A, single phase motor. I tried TRIAC BT136 with optocoupler 3041 but it is switching on when the PWM is high, but in low pulse, it’s not working…..Then removed the optocoupler it working fine.
Then used IRF540 but it always in ON condition. Read more

MOSFET is not turning off perfectly – I am currently trying to build a circuit for load switching with power MOSFET. But at high frequencies, I am getting irregular waveform. Read more

 

The non-isolated 30W offline LED driver and common mode noise filtering – We are doing a non-isolated, offline, 30W PFC Boost-Buck LED driver. In order to get better filtering of common mode emissions, would you say it is preferable for us to take an earth wire to the PCB? Read more

Noise current limit for household appliances – What’s the figure for the conducted emissions noise current limit at 100kHz for household appliances? I’m making an SMPS for a home appliance. Read more

Continuous charging and uncharging a large capacitor – I need to charge and uncharge a capacitor continuously with 20 mF (application industry aggregate). The amplitude is 400Vpp (400V <-> 0 or +200V <->-200V). The signal should be rectangular. Let’s say with a max. Rise and fall time of about 10 ms. The frequency should increase by 10 Hz -the> period of 100 ms. How would you realize this problem? Read more

Double LLC resonant converter – I am designing a bidirectional DC-DC converter comprising of two resonant tanks. My topology is like two H bridge giving two square wave output to two LLC resonant tanks. I am employing PFM to maintain constant output voltage. I have designed a single core dual primary dual secondary HF transformer using PQ50/50 core with an equal turn ratio of 4.2. The magnetizing inductance is around 570uH. The total resonant inductance is 136 uH, and resonant capacitance is 111.86 nF. However, the two square wave input from the H bridge are not identical. Read more

IR2110 low side problem – How much better improvement would you expect to get in common mode emissions in a 30W offline flyback by connecting the ferrite core to primary circuit ground? Read more

Flyback converter design for 250V – I m developing on physiotherapy stimulator which works on AC. and output will be high voltage DC
input: 230V 50Hz
Output Voltage : 250V / 80mA . <0.5% of ripples
Switching frequency: 100kHz
SMPS transformer selected: EF20( suitable for 20W and above
To achieve the above spec, I thought to design a fly-back converter of 20W (250V*0.08mA). I have referred a PI application note to design it. Here are some problems:
1. Designing snubber circuit. : The reflected voltage will so high that it can easily destroy the MOSFET
2. Designing SMPS transformer: finding difficulty to select core /bobbin for such a high voltage
Can anybody suggest which is right topology I have to use? Read more

SMPS transformer windings – I am looking at the schematic of an SMPS for some audio system and I can’t figure out, how the heck does that high frequency transformer work… I don’t understand the winding for supplying IC3 (PWM controller). Is this primary or secondary winding and how can voltage be induced on it? Read more

Using 18650 li-on battery to boost 5v – I am trying to boost 18650 battery voltage to 5v in order to charge a mobile phone. I used mc34063. When I connected to cell phone it shows charging but there is no current flow. I connected the circuit to dc load but output voltage drops to 2.5 V.I just tried to get 200ma but it drops to 2.5v. When I increase the current voltage decreases more. Below is the graph of current voltage at output. Read more