Hi - I have a boost converter controlled by an AVR that is having some problems.
Specifically, it's running hot. Very hot (almost to the point of not being touchable). Both the FET and the inductor get toasty. Load is about 16ma @ 220V. I have not measured the input current (which is at 12V) but I imagine my efficiency is terrible. I will try to test this soon, however.
The output looks like a triangle waveform where the ramp up is very steep and the ramp down slope is maybe a 20th of the magnitude of the ramp up. Frequency is about 30Hz. Peak to peak is about 5V.
My PWM speed is 250KHz, my control loop speed is 2KHz and is trivially simple - if the measured output is too high it reduces the duty cycle by one step, and if it is too low it increases it by one step.
The problem is that the drain of my FET, once Vgs is brought low, often won't make it high enough to charge the output capacitors. Like there is a large delay from when the FET turns off to when the drain swings high, and by that time often the FET is already being turned on again so the drain falls down immediately. During the part of the output triangle wave where the output is dropping slowly, the drain *never* makes it high enough to charge the output capacitor. During the part of the triangle waveform where the output is increasing, the drain makes it high enough to charge the output capacitors about once every other cycle (so about at 125KHz).
The main parts are:
Switch: ST STD14NM50N
Inductor: Bourns SRR1280-271K (270uh)
Diode: Diodes Inc ES1G-13-F
Output capacitors: 1x Panasonic EEU-ED2E220 (22uf electrolytic)
2x TDK C3216X7T2W104K (100nf ceramic)
Gate is driven by a self designed FET gate driver, and rise and fall times are under 25ns.
Anybody have a clue as to what is going on here? I haven't had any good ideas yet.