B
Bill Bowden
I'm building a small Boost regulator using an inductor, transistor
switch, diode and filter cap, but I cannot get enough current into the
inductor before the transistor starts dropping a large portion of the
supply voltage. I don't think the problem is related to the transistor
gain or base drive since the circuit will draw a couple amps with just
a DC input on the transistor base resistor, and all I need from the
inductor is about 500mA peak.
I have the thing connected to a square wave generator and scope and it
works well at about 73% efficiency on small loads. But as I reduce the
frequency to increase the ramp time and peak current, and power output,
the voltage across the transistor (while it is on) starts to increase
dramatically around 400mA of current, and I need more than that.
It looked like the inductor might be saturating, so I reduced the
number of turns and ran it at a higher frequency, but that didn't solve
the problem. It still runs out of gas around 400mA.
I'm going to try a larger core to see if that helps, but I thought
using fewer turns at a higher frequency would allow more current?
-Bill
switch, diode and filter cap, but I cannot get enough current into the
inductor before the transistor starts dropping a large portion of the
supply voltage. I don't think the problem is related to the transistor
gain or base drive since the circuit will draw a couple amps with just
a DC input on the transistor base resistor, and all I need from the
inductor is about 500mA peak.
I have the thing connected to a square wave generator and scope and it
works well at about 73% efficiency on small loads. But as I reduce the
frequency to increase the ramp time and peak current, and power output,
the voltage across the transistor (while it is on) starts to increase
dramatically around 400mA of current, and I need more than that.
It looked like the inductor might be saturating, so I reduced the
number of turns and ran it at a higher frequency, but that didn't solve
the problem. It still runs out of gas around 400mA.
I'm going to try a larger core to see if that helps, but I thought
using fewer turns at a higher frequency would allow more current?
-Bill