Sine wave inverter voltage clipping – I’m in the process of building a sine wave inverter (MOSFET full-bridge and a low frequency transformer). I can’t manage to tune up the output filter (a series inductor in the transformer primary circuit and a capacitor across the secondary transformer). I have tried different inductor cores (E shape ferrite, ferromagnetic toroid) but the output voltage isn’t perfect (there are some perturbations around the middle point of every half wave – between the zero crossing and peak voltage).
This is happening at no load or with a small resistive load (60W bulb lamp).When I connect an AC fan (150W), the output is clipping harder (the waveform has almost a trapezoid shape) and the transformer starts humming. What could be the problem? What’s the effect of a bigger/smaller filter inductance or capacitor? Read more
Ripple in rail voltage of H-bridge – I have a 12V full bridge operating at 100KHz, driving a transformer. The transformer output is rectified and filtered with a capacitor and then connected to a resistive load. The 12V input to the bridge comes from a pair of 1.5 meter long copper cable, 4mm in diameter. The rail voltage is very unstable. The pk-pk ripple is roughly 5V at 40A current, with 50uF ceramic capacitors connected across the rails. Connecting additional 7000uF aluminium capacitor lowers the ripple to 3V pk-pk. The capacitor begins to heat up. Adding another 14000uF lowers the ripple only by 0.5V. It appears that the value of ripple is more dependent on the number of capacitors in parallel rather than the value of the capacitors. Read more
Identifying component inside power supply – I am stumped and need help identifying a component inside this power supply. This is the 2nd psu I have gone through with this company and now this one has failed. The first one I originally purchased lasted less than 24 hours. This one made it almost 3 1/2 weeks before blowing the same exact component. I am hoping someone can point me in the right direction so that I’m able to purchase a new component (possibly maybe recommend one that is better than the one it’s designed with). Read more
Open circuit protection 3 phase AC – I am looking for open circuit protection in a 3-phase AC system. I would like to have an interrupt when one of the phases is disconnecteded at the output of my inverter. Is there any simple way to implement this? Read more
Flyback snubber not working – I’m trying to replicate and understand an offline flyback converter the circuit I’m trying to replicate is this one. It uses the NCP1216 controller. I’m using a variac to soft-start my line voltage so I can identify problems before components blow. The secondary has no-load, just the capacitors+bleed resistor. When I’m ramping the voltage up to ~120VDC (minimum mains) the controller is going flat-out, i.e. 50% duty (because the FB pin is still high), the primary current gets quite high, and the voltage across the snubber capacitor greatly exceeds what one would expect (>1kV). Once the voltage ramping has reached ~120VDC the primary current falls to nothing and the voltage across the snubber falls to normal levels (~150V). Why is the RCD snubber not clamping properly? Does this circuit really work?Read more
Variable power supply 0 – 80V 50A high initial current – I’m trying to build a charger with variable output of 0-80V and 0-50A. Now I’m stuck with high currents to charge up the large capacitor that I have on the output. Below are the simple schematics of what I’m having right now. I’m controlling the output voltage by a potentiometer from the controller circuit that controls the firing angle of the SCR (Silicon Controlled Rectifier). I have tried to insert a 2K 5W resistor in series before the rectifier but it charges correctly the first DC bus but it gets too hot when I attach the output capacitor of 10.000uf 400V. I’m aware that the circuit needs a transformer and output coil but I would like to make it work without and then make an step further. Perhaps I’m wrong and it won’t work without the transformer and the output coil. Any recomendations to follow up and make this circuit more stable? Read more
Preventing MOSFET from blowing on motor controller – Need advice on how to prevent the MOSFET from blowing up on a motor controller. This is for a scooter with 250watt motor and the controller is a Chinese cheap stuff with variable throttle from a hall effect sensor. The controller is supposed to be current limiting to ~10amps (250watt and 24v) but I suspect the motor was drawing too much current on uphill and the current limiting feature did not work. Is there anything I can add/solder to this board that would prevent the MOSFET from blowing because of the high current? Read more
2.5 kW Full bridge boost converter – I have 42 V input from a battery source and 500 V DC output is required. The switching frequency is 100 kHz. Full bridge with MOSFETs on the primary side and full bridge diode rectifier on the secondary side. I need help with the transformer design and the feedback control implementation. Read more
BTL Class D filter with high impedance load – I am designing a high-current BTL filter with a high impedance load. In normal designs, you would expect a low impedance of ay 6Ω I am looking at an impedance level of 3333Ω. My issue is that to give the filter a decent Q the inductor would have to be massive in size say 150mH. I cannot use something that large because of size constraints. The filter I have at the moment to give acceptable losses is severely under-damped (as per picture). Is there any way to reduce this peak (Q factor), or given the constraints of the design is this something I will have to live with? Read more
Controlling a current of a large inductor -If I wanted to control the current of an unknown and potentially very large inductance how do I approach that? Or more generally, how can you control any system with unknown and potentially large inertia (like a voltage source and large C). Read more
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