KV9U wrote: > As long as you are going down in voltage, there are relatively simple > analog circuits that can drop the voltage to anything you might > want. While you can use a simple dropping resistor, this only works > if there is a known steady current draw and you design for that draw > and you have some risk under no load where the voltage could damage > the device.
I do not TRUST a resistor to be GENERALLY good enough. I would use a regulator if I don't wan't to see aluminum confetti inside the guts of my radios... > You could use a standard 78xx series three terminal regulator design. > This would only require a couple of capacitors and a resistor or > two. For example, when HT's first became popular, they often did not > work directly on 13.8 VDC and had to have some kind of controller. > The ICOM IC-2AT actually used a slide on pack, which looked like a > small battery pack, but was a simple controller to drop the voltage > down to a safe 9.6 VDC for proper operation of the HT. I built one inside one battery case for my old and still functional IC-2A using a TO-3 7805. It happily stands 24 volts at 1 ampere load current, delivering 9.6 V regulated. There is a series diode that allows recoverable silence from the radio. Without the diode it might not be recoverable after it first goes silent... > You are probably aware that you will have to dissipate the current > from the voltage drop that you don't want. This would mean some > substantial inefficiencies when you have to drop quite low as you > would with 1.5 or 3 volts. The only reason that I would do this is so > that I could operate on battery power. It might be better to run > those devices on a separate battery pack at their native voltage > requirement. I still have an old PC using a 5 to 3.3V linear regulator. Really, it does not make much sense and it better uses a switching regulator. I believe I read somewhere there is a trend for some motherboards to be powered only by 12 V and generate all the needed lower voltages on the MB. So, the current at 12 V is lower and false contacts a 3.3V at 10 amps are a very serious concern that simply you may forget this way. > James Wilson wrote: > > > Is there a noise free 12 volt to lower volt circuit that can be > > built? Maybe one that would handle 9,5,3 and 1.5 volts. I would be > > willing to build cords to remove all ac/dc converters from my radio > > area. Noise free....would mean well shielded and filtered. There are some loads that do not make sense to be fed from a linear regulator. 73 de Jose, CO2JA
