Heat Treatment Oven

One doesn't want to use a 1n400X-type diode on spikes.  This is a power supply diode.  Its fastest intended application would be to rectify French line power.  It is not intended to be used upwards of a KHz.  Another way to say it is its capacitance is way to high.  The diode, provided our currents our sub-Ampere, to use is a 1n914 or 1n4818 because they are gold-doped to minimize minority carrier lifetime.  Shottkys are fast, low-drop, but their BV is limited.  So if we are wrestling in the open class, we need UF diodes.  The degradation on power Qs  by hot electron comes on slowly.  So people who clamp with inappropriate diodes on their bench and proclaim 'it works' don't seem to 'get it.'  Also, no benefit from a fast diode will ensue unless the far end is connected to a fast capacitor through a low-Z route.  Margin for capacitor BV, probably a resistor across it.

Here is a useful circuit idea:  Get  a small line transformer, output around 6-0-6.  Connect this to a tiny bridge rectifier.  Connect this to an opto-isolator, insert R for current-limit.  Connect opto output to a resistor.   Connect this to a schmidt-trigger.  [Connect this to a %2 circuit?] Connect this to an interrupt line on your processor.  Now your uP knows when the zero-crossings are.

One doesn't want to use a 1n400X-type diode on spikes.  This is a power supply diode.  Its fastest intended application would be to rectify French line power.  It is not intended to be used upwards of a KHz.  Another way to say it is its capacitance is way to high.  The diode, provided our currents our sub-Ampere, to use is a 1n914 or 1n4818 because they are gold-doped to minimize minority carrier lifetime.  Shottkys are fast, low-drop, but their BV is limited.  So if we are wrestling in the open class, we need UF diodes.  The degradation on power Qs  by hot electron comes on slowly.  So people who clamp with inappropriate diodes on their bench and proclaim 'it works' don't seem to 'get it.'  Also, no benefit from a fast diode will ensue unless the far end is connected to a fast capacitor through a low-Z route.  Margin for capacitor BV, probably a resistor across it.

Here is a useful circuit idea:  Get  a small line transformer, output around 6-0-6.  Connect this to a tiny bridge rectifier.  Connect this to an opto-isolator, insert R for current-limit.  Connect opto output to a resistor.   Connect this to a schmidt-trigger.  [Connect this to a %2 circuit?] Connect this to an interrupt line on your processor.  Now your uP knows when the zero-crossings are.

Don, experience and simulation show that the 1N4001 is more robust and works BETTER than a 1N4148. Other diodes may work better than either but fast or fancy ones will cost more. Using a passive RC network works fine and does not result in ringing of the load current.

I've attached a rather huge screenshot of the three options simulated in LTSpice.

The netlist for the RC simulation follows:

* C:\Docs\Rabbits\relay_zobel.asc

L1 N001 N002 .47

R1 N002 N004 288

V1 N001 0 12

M1 N004 N006 0 0 NDC7002N

V2 N005 0 PULSE(0 5 1m 50n 50n 20m 40m 1)

R3 N006 N005 1k

R2 N003 N004 288

C1 N001 N003 4.7µf

.model NMOS NMOS

.model PMOS PMOS

.lib C:\Program Files (x86)\LTC\LTspiceIV\lib\cmp\standard.mos

.tran 50m

.backanno

.end

The relay is an OMRON G5V-2 type, 12V coil, 288R, 0.47H off, 0.74H on. The simulation makes no attempt to model the effect of the armature moving whe the relay releases.

In case it's not clear from the picture the 1N4001 ciruit rings for about 0.2mS at about 29kHz, the IN4148 for about 0.5mS at 42kHz and the initial amplitude of the ringing is about twice as large for the 1N4148. In either case the frequency and amplitudes are so low that there would not normally be any EMC issues.

The passive network works better with no HF ringing at all.

If you have any other data, measured or simulated, to suggest otherwise, I would be interested to see it.

MK