KreAture
Apr 23, 2004, 07:30 AM
I finally got it to work, but ended up with something a bit different than the topic I started with. So I decided to repost it here with a better thread-name.
Basically it's a regulator using a LM circuit (linear regulator) as a stabelizer instead of as the actual regulator. It basically does the job of a zener voltage reference and error amplifier/fet-driving circuitry with feedback filter. In essence it thus reduces partscount to 7.
The schematic looks like this:
(see attached image)
Depending on if one needs more current, or low input voltage capability one can use a lov threashold FET or a high current capable bipolar transistor.
There are now two different layouts. One for non-passthrough and another for passthrough of the RXchannel. You'll see wich is wich.
The two green pads are for the coil wich is mounted on the back of the board.
Parts-list is as follows:
Part Value
C1 47u (30v capable)
C2 470u (minimum 5v capable)
D1 SM6T30A (30 V capable transient diode)
FET1 IRF7404 (0.7v threshold 20v capable. This limits max V-in to 20v.)
L1 Coil. Preferably toroid, atleast 5-600 uH, mounted on back of board.
R1 30 to 100 Ohm, 0805 size
REG LM340MP-5,0 (Or any pin-compatible 5v linear reg.)
I will be posting the PCB mask when I get home.
Some tests I've done with this setup include 750 mA continous load with both FET and bipolar transistor. The FET only resulted in 60-65% eff possibly due to the fact that it has max eff at a much higher current. (Only body-temp at 750 mA) The bipolar version achieved 73% eff at 750 mA and should be capable of 1 amp continous. For smaller planes the bipolar is thus best suited. For large planes, I'd reccommend using a FET.
Another side-note:
The Bipolar seems to keep the oscillations going at lower voltages while the FET stops. This can be very bad for flights... I suggest testing the BEC thouroughly to find what pont it will become unreliable with your parts. The oscillations dissappear when it reaches a too low input voltage. This is best checked with a scope, but I suppose one can measure the frequency over the coil with a DVM...
Basically it's a regulator using a LM circuit (linear regulator) as a stabelizer instead of as the actual regulator. It basically does the job of a zener voltage reference and error amplifier/fet-driving circuitry with feedback filter. In essence it thus reduces partscount to 7.
The schematic looks like this:
(see attached image)
Depending on if one needs more current, or low input voltage capability one can use a lov threashold FET or a high current capable bipolar transistor.
There are now two different layouts. One for non-passthrough and another for passthrough of the RXchannel. You'll see wich is wich.
The two green pads are for the coil wich is mounted on the back of the board.
Parts-list is as follows:
Part Value
C1 47u (30v capable)
C2 470u (minimum 5v capable)
D1 SM6T30A (30 V capable transient diode)
FET1 IRF7404 (0.7v threshold 20v capable. This limits max V-in to 20v.)
L1 Coil. Preferably toroid, atleast 5-600 uH, mounted on back of board.
R1 30 to 100 Ohm, 0805 size
REG LM340MP-5,0 (Or any pin-compatible 5v linear reg.)
I will be posting the PCB mask when I get home.
Some tests I've done with this setup include 750 mA continous load with both FET and bipolar transistor. The FET only resulted in 60-65% eff possibly due to the fact that it has max eff at a much higher current. (Only body-temp at 750 mA) The bipolar version achieved 73% eff at 750 mA and should be capable of 1 amp continous. For smaller planes the bipolar is thus best suited. For large planes, I'd reccommend using a FET.
Another side-note:
The Bipolar seems to keep the oscillations going at lower voltages while the FET stops. This can be very bad for flights... I suggest testing the BEC thouroughly to find what pont it will become unreliable with your parts. The oscillations dissappear when it reaches a too low input voltage. This is best checked with a scope, but I suppose one can measure the frequency over the coil with a DVM...