Hi all
I had a circuit that powered some IR leds directly, but redesigned it with the O/P (pin 3) going into the base of an npn transistor, via a 2k2 resistor. For some reason, the frequency 'dissapears' on the base end of the 2k2.. Any Ideas?
Hi all
I had a circuit that powered some IR leds directly, but redesigned it with the O/P (pin 3) going into the base of an npn transistor, via a 2k2 resistor. For some reason, the frequency 'dissapears' on the base end of the 2k2.. Any Ideas?
Are you checking this with a scope? I think going larger on the base resistor may be the wrong way to go, you are trying to drive a whole bunch of IR devices.
Your meter probably will not do the trick. If I get your circuit, your trying to drive a bunch of IR leds off the collector circuit. Just as a test, try using a couple regular visable leds on say two jumper blocks, short out the remainder jumpers and see if that works, ie leds should light up. I could not read the part number of the transistor on your schematic so I hvae no idea of its beta.
The circuit works OK, the problem was in the batch of IR leds. The leads were cropped the wrong way round! (long lead on the cathode side)
Thanks for all the help though!
Your meter probably will not do the trick. If I get your circuit, your trying to drive a bunch of IR leds off the collector circuit. Just as a test, try using a couple regular visable leds on say two jumper blocks, short out the remainder jumpers and see if that works, ie leds should light up. I could not read the part number of the transistor on your schematic so I hvae no idea of its beta.
Mike, did you consider that the LEDs or the transistor might be destroyed by running this test? If the transistor saturates (which it probably will), the collector (and LED) current could be over 200mA. If the transistor doesn't saturate, the power dissipation could destroy it, if the LEDs survive long enough.