W
Watson A.Name - \"Watt Su
Guest
The file (posted in ABSE) was posted here recently, I don't know who posted
it. I built it, but changed the Q2 to a BC338, and I added a 47 uF across
the supply lines. The problem I have is that it's balky, sometimes it
doesn't want to start up, and sometimes it will. It usually won't start if
I turn on the PS, but if the PS is on and I hook it up, then it'll start. I
think it needs to have a faster risetime for the supply voltage, if it's
slow, then it won't start. I thought that if someone had this modeled in
their spice prog, then they could try slowly ramping up the supply voltage
and see what causes it to be so snotty.
I compared it to Stepan's boost circuit, and I find that it's a lot simpler
and going by the column on the right, it's a very efficient circuit. But
somehow I doubt that it could be that efficient, 75 to 80%. It regulates
the LED current by robbing the output transistor of its base bias. That
seems to me to be wasteful. I like Stepan's circuit a lot better, the one
on the right of URL
http://members.shaw.ca/novotill/LedSupplyRegAA/index.htm
because it works by reducing the bias current, not by robbing it from the
output transistor. But that makes it more complicated, and of course it's
more difficult to fit more parts into the limited space inside of a
flashlight.
But I think both circuits waste power across the current sensing resistor in
series with the LED. And Stepan's circuit wastes more power across the
schottky rectifier; it may be better to just run the LED directly off the
choke, and let it do the rectifying - after all, it _is_ a diode.
I remember a circuit that was better at sensing the current, and used a much
lower voltage and a lower resistor, 10 or 6.8 ohms. I'll have to come up
with that circuit.
it. I built it, but changed the Q2 to a BC338, and I added a 47 uF across
the supply lines. The problem I have is that it's balky, sometimes it
doesn't want to start up, and sometimes it will. It usually won't start if
I turn on the PS, but if the PS is on and I hook it up, then it'll start. I
think it needs to have a faster risetime for the supply voltage, if it's
slow, then it won't start. I thought that if someone had this modeled in
their spice prog, then they could try slowly ramping up the supply voltage
and see what causes it to be so snotty.
I compared it to Stepan's boost circuit, and I find that it's a lot simpler
and going by the column on the right, it's a very efficient circuit. But
somehow I doubt that it could be that efficient, 75 to 80%. It regulates
the LED current by robbing the output transistor of its base bias. That
seems to me to be wasteful. I like Stepan's circuit a lot better, the one
on the right of URL
http://members.shaw.ca/novotill/LedSupplyRegAA/index.htm
because it works by reducing the bias current, not by robbing it from the
output transistor. But that makes it more complicated, and of course it's
more difficult to fit more parts into the limited space inside of a
flashlight.
But I think both circuits waste power across the current sensing resistor in
series with the LED. And Stepan's circuit wastes more power across the
schottky rectifier; it may be better to just run the LED directly off the
choke, and let it do the rectifying - after all, it _is_ a diode.
I remember a circuit that was better at sensing the current, and used a much
lower voltage and a lower resistor, 10 or 6.8 ohms. I'll have to come up
with that circuit.