ENERGY AMPLIFICATION

[Magluvin]

MarkE


Can you post a good source of information step by step how to build snubber circuit to protect mosfets/transistors from inductive kickback ? I knew that in relay coils it is usually used diode across coil terminals. Funny thing with that diode (is it called freewheeling diode?) - when I added it to my circuit current consumption from battery rised from 200mA to 4A !!! Just that is interesting....but the snubber would help really I think. Another strange issue is my IR1405 mosfet survive 80V spikes, hmm.....

Hey Forest
200ma to 4a ?   sounds as if the diode is backwards of normal snubbing and conducting forward when the transistor is on.  Can you show the circuit?

Other than that, it could be the diode is keeping the load(coil, primary?) freewheeling and each time the transistor turns on, the field in the coil has not fully collapsed yet and yes, will take on more current from the transistor being that the transistor doesnt have to wait for the field to build. When the coil has max flux per input, the more current that will flow through the coil.

In some circuits, the snubber keeps the field of the coil going beyond the off time, which may not be what you want. 

The snubber could be used to send the spike to a cap and that energy used for something else.  Just be sure to keep the cap loaded with and output(charge battery, lights, etc), if V gets close to spike peak, it wont take much more and the spike has to go elsewhere.

Mags

[TinselKoala]

MarkE


Can you post a good source of information step by step how to build snubber circuit to protect mosfets/transistors from inductive kickback ? I knew that in relay coils it is usually used diode across coil terminals. Funny thing with that diode (is it called freewheeling diode?) - when I added it to my circuit current consumption from battery rised from 200mA to 4A !!! Just that is interesting....but the snubber would help really I think. Another strange issue is my IR1405 mosfet survive 80V spikes, hmm.....

It sounds like you put the diode in "backwards" from the way it should go. That is, you put it in "forward biased" instead of reverse biased.
Check the data sheet for the IRF1405 mosfet and note the polarity of the body diode.  Note particularly Figure 12a.

[MarkE]

forest and markE
You can also  use an NE2 bulb between collector and emitter if your transistor can stand 100 volts.
You can use 2 ne2 bulbs in series if your transistor can take 200 volts etc, etc, etc.


Done it loads of times.

That depends on how much energy that you need to clamp.

[MarkE]

MarkE


Can you post a good source of information step by step how to build snubber circuit to protect mosfets/transistors from inductive kickback ? I knew that in relay coils it is usually used diode across coil terminals. Funny thing with that diode (is it called freewheeling diode?) - when I added it to my circuit current consumption from battery rised from 200mA to 4A !!! Just that is interesting....but the snubber would help really I think. Another strange issue is my IR1405 mosfet survive 80V spikes, hmm.....

The list of application notes posted by lost_bro covers the subject fairly well.  Your diode is backwards.  When the MOSFET turns on the supply conducts through the diode and the MOSFET.

[forest]

Tinsel


I have EXACTLY that setup from Figure 12a except pnly one mosfet. I found that diode from schematic  does nothing in my case. However when I placed diode across coil terminals directly (of course against the current flow) then current consumption rised to 4A.