Richard, You could use a Schottky diode. They usually have much lower Vf. I like the CDBA320 to CDBA380 series, up to 3 A of If and from 20V to 80 V Vrrm, with a Vf of approx. 0.25 V. They are not very cheap though. The SD2114S040S8R0 supports currents up to 8 A and has a Vf of approx. 0.125V for small currents, a tough guy. But there are many other Schottky diodes, with various If, Vf and Vrrm ranges. Some of them are very affordable. By the way, my friends call me Isaac. Cheers, Isaac Em 17/09/2015 08:57, Richard R. Pope escreveu: > Marino, > These are some really good points. I didn't put in a diode because=20 > of the forward voltage drop. I'm using a 5 volt regulated supply and 4.5= =20 > volts would be right at the limit of what a 628A will tolerate. I'm=20 > going to put these suggestions away for another day. I appreciate this. > Thanks, > rich! > > On 9/17/2015 6:34 AM, Isaac Marino Bavaresco wrote: >> Richard, >> >> >> It is a good idea to always provide some sort of reversal polarity >> protection to circuits. It is very common for equipment to be connected >> with the wrong polarity or a wrong power adapter. >> >> There are several approaches, suitable for various circuit requirements. >> >> 1) Just use a diode in series with the power input. Suitable when your >> circuit consumes a moderate current and you have a voltage regulator in >> the input or can tolerate a small voltage drop. >> >> 2) Use a fuse in series with the power input and a powerful diode >> connected cathode after the fuse and anode to ground. Your diode must be >> strong enough to ensure the fuse will blow before the diode is damaged. >> The advantage is that you don't have the Vf loss from the diode when the >> circuit is operating. >> >> 3) Use a power P-Channel MOSFET with its Drain pin connected to the >> power supply, Gate to ground and Source as output to the circuit. This >> circuit can be used for voltages up to approx. 20V, which usually is the >> Gate-Source breakdown voltage. With the addition of a Zener diode and a >> resistor this limit can be raised. >> This circuit can be used for really high currents with very little >> energy loss. If you add another MOSFET in series in the opposite >> direction plus a TL431, another smaller MOSFET and some resistors, you >> have overvoltage protection also. >> >> 4) Use a relay with its coil with a diode in series connected to the >> power input. Use the normally-open contact to power your circuit. This >> method can be used for any current and voltage ranges and the only loss >> is the relay's coil current. >> >> Cheers, >> >> Isaac >> >> >> Em 17/09/2015 03:43, Richard R. Pope escreveu: >>> Bob and et al, >>> Well I just make a goof! I was very fortunate. I hooked the power >>> to my control board up the wrong way. The PICs are tough little >>> monsters. Even though the power was hooked up the wrong way for almost >>> twenty minutes all of the PICs are fine. It looks like all that I >>> damaged were the tantalum capacitors. Wow! Good news. I'll be more >>> careful from now on. I appreciate all of the help that everyone has >>> given me. >>> Thanks, >>> >> --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .