Discussion in 'General Electronics Chat' started by Omoshie, Mar 5, 2008.
Pls i need inverter circuit diagram for about 500W
Google has this - http://web.telia.com/~u85920178/power/invert1_00.htm.
Harry's inverter circuit has the multivibrator transistors operating from 12V.
Their emitter-base junctions break down in an avalanche breakdown when the multivibrator's supply voltage is more than about 7V. It is bad for them.
The output of his inverter is a square-wave but many electronic products need the higher peak voltage of a sine-wave or of a modified sine-wave.
Don't the base resistors drop most of that 12V?
Indeed. This is especially true of induction motors. I remember trying to run a drill motor from an inverter back in the early 80's. I got a whole 1/8 turn from it.
i was looking up 3phase inverters and saw a 500watt 3 phase for electric motors that used 60hz square waves to drive a motor.
would that inverter work well for a motor? i'm curious.
Three phase motors work a little differently from single phase induction motors. They're sort of like stepper motors. Sort of.
Compare this to the field in a single phase motor: http://www.allaboutcircuits.com/vol_2/chpt_13/9.html
Many campers, homesteaders, and other folk are wanting to run a blender in the wilderness. Many inverter designs therefore use PWM to emulate a sinusoidal output.
The capacitor charges to 11.3V. Then the other transistor conducts and tries to force this transistor's base down to -11.1V but the emitter-base junction breaks down at about -7V.
Are you sure? Looks like a common astable multivibrator circuit to me. http://www.falstad.com/circuit/ex-multivib.html
Am I missing something unique to Harry's circuit?
Yeah, I know this is an old thread but thought I would comment on the design.
First, Harry is using a toroidal style power transformer. Normally this style is fine except for the difficulty in manufacturing. But there is one other problem in push/pull inverter circuits.
If the timing sequences between the two switches differs by anything, and I do mean anything, over a period of cycles the operating point on the BH curve will walk up the curve or down the curve. It acts like a DC component. The result of curve walking is the transformer can/WILL saturate even if for olny a few cycles.
The result can be disastrous for the switches!!!
Yes, people do design things that get into production with similar problems and then one wonders why "gee, what caused that switch to fail!" Gapping the core can help. Gapping the core does not stop the problem but it greatly reduces it by "tilting" the BH curve. It also add to the magnetizing current which adds to the switch current along with other things and must be addressed during the design.
One of the worse situation I came across when I was a design engineer was so called simple circuits that popped up during engineering concept meetings along with the challenge "why won't this circuit work?" Many of those simple circuits did indeed work but it took many hours of engineering to establish the working boundary conditions to ensure it worked over the limits of component, voltage, current and temperature tolerances.