I have built a small and very simple flyback SMPS based on NE555N IC. The circuit
exactly I did built from is shown below:
It works nicely for small loads.
However I have some issues with it:
- Despite NE555N datasheet says output (pin 3) voltage is only about 2 volts lower than Vcc, I have only +6.3v on pin 3. Is it a digital multimeter misreading?
- The MOSFET used there is IRF3205, but currents beyond 6-7A force it to heat up, and 10A (with 100-110 Watts on secondary) even more (heatsink is ready to boil water)
- Some answers here and some sources on the web (and this circuit) recommend using logic level mosfets. Can I avoid using them (probably until I get some of them)? Will logic
level mosfets work perfectly compared to regular ones I using now if their properties (Vdss, Id, Rds(on), Qg) will be relatively same?
Impulse transformer was salvaged from old dead 200W ATX SMPS, its sizes are (WxHxD) 36x42x16 mm. Its main problem that it's cracked (but still works without noises).
Primary has 8 turns of 1mm wire, secondary has 160 turns of 0.3mm wire; another secondary has 3 turns for 5 volts source (also 1mm wire).
Heatsink sizes are 32x39x14 mm probably aluminum (also from old hardware). Larger heatsink is avoidable because of limited space where circuit will be stored.
Supply is 12V 19Ah Lead-acid battery pack.
I strive to minimize thermal losses on this circuit, so I am seeking ways to minimize power losses on MOSFET.
Does MOSFET overheat due to undervoltage on gate (hence not fully opened) or cracked transformer core? Do I need some other enhancements for this circuit?