On Tue, 31 Mar 1998 16:00:25 -0800 Bob Blick writes: >> I have a PIC controlled circuit that also includes an LM386 audio >> amplifier. When I put the PIC into sleep mode, I'd like to eliminate >the >> power drain of the amp. I can use a relay to do this but I figure >that >> there is probably some very clean solid state way to accomplish >this. > >Hi John, >Let me rush in here before several other people tell you to replace >that >useful inexpensive LM386 chip with some expensive unavailable chip >just >because it includes a powerdown pin. Many chips, including probably the LM386, can be "powered down" by feeding DC into one of the audio inputs to bias the chip way out of the normal linear range. This often reduces the power draw considerably. An open-collector PIC pin or a diode can be used to apply the upsetting DC bias. Some experiments are in order to see which polarity of bias works best. If you decide to cut the power off, it may be easier to switch the ground (- supply) pin instead with a NPN transistor or N-channel FET. The AC grounds should be returned to the + supply in that case. Depending on where the audio comes from, it may not be practical, too much noise will result. Of course cutting and restoring the power to the chip or applying a DC bias usually causes the speaker to "pop" or "thump" (depending on how good the low-frequency response of the speaker is). The effect can be minimized by using a small capacitor to couple the speaker and applying the power or bias slowly. If the effect is really objectionable, it may be a reason to go to a newer chip designed to minimize it. Two LM386's could be used in a bridge configuration which would offer the ability to power on and off without sending DC through the speaker. _____________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com Or call Juno at (800) 654-JUNO [654-5866]