toxicmouse
Senior Member
Thanks to a great post by MikeyBoo on isolated power supplies (http://www.picaxeforum.co.uk/showthread.php?30096-Isolated-power-supplies&highlight=isolated+power) , I have decided to upgrade my power supplies for picaxe projects. Seeing as most of my projects use motors and relays which have significant back EMF and really noisy supply lines, it is probably worth putting in filters and all sorts of other goodies.
Question 1: if I use an isolated power supply, is it worth putting in the usual precautions as I would for regulators (LM2937 regulator) like:
- fuse, well upstream, then within your box
- forward biased diode in supply line
- MOV in supply line
- low value resistor in supply line
- TVS/varistor/zener across supply line
- inductor in supply line immediately before regulator
- large and small caps upstream of regulator
- reverse biased diode across regulator output and input
- large and small caps downstream of regulator
- 5v1 zener on output of regulator
Question 2: if an MOV is placed accross the supply lines, then as I see it there are 2 modes:
1 - high resistance when the MOV is below is threshhold voltage
2 - low resistance mode when the MOV is above the threshhold voltage.
but surely in mode 2 this means that the supply lines are short circuited by the MOV. How is that a good idea? It would save the circuit but short circuit the power supply until the power supply is switched off?
Thank you in advance for any advise.
Question 1: if I use an isolated power supply, is it worth putting in the usual precautions as I would for regulators (LM2937 regulator) like:
- fuse, well upstream, then within your box
- forward biased diode in supply line
- MOV in supply line
- low value resistor in supply line
- TVS/varistor/zener across supply line
- inductor in supply line immediately before regulator
- large and small caps upstream of regulator
- reverse biased diode across regulator output and input
- large and small caps downstream of regulator
- 5v1 zener on output of regulator
Question 2: if an MOV is placed accross the supply lines, then as I see it there are 2 modes:
1 - high resistance when the MOV is below is threshhold voltage
2 - low resistance mode when the MOV is above the threshhold voltage.
but surely in mode 2 this means that the supply lines are short circuited by the MOV. How is that a good idea? It would save the circuit but short circuit the power supply until the power supply is switched off?
Thank you in advance for any advise.