Hey this one's for the real geeks,
I have a circuit I'm working on that has a 5v power supply (which powers digital IC's such as gates etc.). Also, I have a 24v power supply which supplies power to solinoids (Such as relays and motors). The two sepertate supplies share the same Ground (RTN).
I have been noticing that the digital circuitry is susceptible to line transients, such as unpugging loads on the same AC supply line (the supply line before rectification).
I have thought about using a 5V Zener Diode, but am not able to locate one that can supply enough current to my digital Circuitry. I need one that can regulate @ 1 Amp (output current, not breakdown current).
I have also considered geting a Transient supressor on the AC side to avoid my digital circuitry from "Changing State" when transients are present.
What do you think is a good solution for this? Do you think bypass capacitors across the IC's Will prevent this nonsense from occuring?
I think it might be Ground Bouncing because it occures when I switch off the 24v DC supply
Thanks in advance!
I have a circuit I'm working on that has a 5v power supply (which powers digital IC's such as gates etc.). Also, I have a 24v power supply which supplies power to solinoids (Such as relays and motors). The two sepertate supplies share the same Ground (RTN).
I have been noticing that the digital circuitry is susceptible to line transients, such as unpugging loads on the same AC supply line (the supply line before rectification).
I have thought about using a 5V Zener Diode, but am not able to locate one that can supply enough current to my digital Circuitry. I need one that can regulate @ 1 Amp (output current, not breakdown current).
I have also considered geting a Transient supressor on the AC side to avoid my digital circuitry from "Changing State" when transients are present.
What do you think is a good solution for this? Do you think bypass capacitors across the IC's Will prevent this nonsense from occuring?
I think it might be Ground Bouncing because it occures when I switch off the 24v DC supply
Ground Bounce: defines a condition when a device's output {really a number of outputs} switches from High to Low and causes a voltage change on other pins. The problem is cause by the large current flow through the ground pin which develops a voltage drop over the lead inductance. This voltage drop on the ground line creates two main problems; first it rises the chip off ground [0 volts] potential which increases the devices input threshold level, and increases the voltage level on an output pin which is not switching. Because a quiet output is effected by the other switching outputs, this is also called Simultaneous Switching Noise. It's really a question of loss of noise margin which is listed below. The faster the slew rate of the logic family, the worse the problem becomes. With glue Logic, the ground pins may have been moved around to reduce the inductance. Using a surface mount device instead of a Through Hole will reduce the lead inductance. For FPGA's with hundreds of possible output pins the situation may change, and it's more up to the designer. Start a noise budget to determine if the ground bounce [rise in ground potential] effects the design. The voltage developed over ground lead is proportional to the rate of change in current, so the faster the logic family the worse the problem becomes: V = L * [di/dt]. The more outputs switch at the same time, the larger the current value, and the greater voltage bounce. Also occur when the outputs switch from a 0 to a 1 but to a much smaller degree. Series termination of the line is one method of reducing ground bounce. Series termination resistors slow the rate of change of the output, and so reduce the instantaneous current on the ground line. Also Resistor Pull-Ups on the line cause the ground bounce voltage to increase. The pull-up resistor allows the load capacitor to charge to it's flow value, so as the line switches maximum current is delivered back to the driver. Eliminate pull-up resistors on devices with an issue, use pull-down resistors or series resistors if possible. Reducing the loading on the driver also reduces ground bounce.
Thanks in advance!