Buck regulator question
metron9
Posts: 1,100
I am putsin with buck regulators now making my own (attached circuit)
I am using a p-fet instead of the switch shown in the schematic. The gate of the pfet is connected to a 220 ohm resistor to the source and I use an N-fet to pull the p-fets gate to 0 to turn it on.
Everything works, I have a new 4001 pulse generator from global specialties I got from ebay for $49.00 using off times of 1 to 10 us and on times from 1us to 100ns I can vary the current through a single Luxeon LED from 5ma to 400mA or more.
Using 8V as an input for example from the bench supply and a current meter on the input of the LED I get the same or close to the same current on both the supply at 8V and the LED. The fet and inductor (4.7uh 3A) don't get very warm but they must be burning watts the same as if I used a resistor of the correct size to get 400mA from 8V.
I expect to see the bench supply read something like·180mA at 8V with an led forward voltage of 2.5 for example·with the LED current at 400mA.
My boost regulator works using 5V input at about 280mA I can run a 12V fan at about 100mA so that is working the way it should.
What am I doing wrong?
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!
Post Edited (metron9) : 9/23/2008 6:34:29 AM GMT
I am using a p-fet instead of the switch shown in the schematic. The gate of the pfet is connected to a 220 ohm resistor to the source and I use an N-fet to pull the p-fets gate to 0 to turn it on.
Everything works, I have a new 4001 pulse generator from global specialties I got from ebay for $49.00 using off times of 1 to 10 us and on times from 1us to 100ns I can vary the current through a single Luxeon LED from 5ma to 400mA or more.
Using 8V as an input for example from the bench supply and a current meter on the input of the LED I get the same or close to the same current on both the supply at 8V and the LED. The fet and inductor (4.7uh 3A) don't get very warm but they must be burning watts the same as if I used a resistor of the correct size to get 400mA from 8V.
I expect to see the bench supply read something like·180mA at 8V with an led forward voltage of 2.5 for example·with the LED current at 400mA.
My boost regulator works using 5V input at about 280mA I can run a 12V fan at about 100mA so that is working the way it should.
What am I doing wrong?
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Think Inside the box first and if that doesn't work..
Re-arrange what's inside the box then...
Think outside the BOX!
Post Edited (metron9) : 9/23/2008 6:34:29 AM GMT
492 x 226 - 5K