Hi all,
I'm using a 220V - 24V transformer as a supply of 24V AC - 18V DC converter which is my own design. Since I cannot control the output of the transformer I put a crowbar circuit in the DC converter circuit as a precaution for the high voltages and it triggers around 42-43V DC. So the whole system is as described below.
220V AC -- Transformer -- 24V AC --> Full rectification -- Crowbar Circuit (42-43V) -- DC-DC Boost Converter -- 18VDC
However I'm observing high voltage spikes on the output of the transformer which sometimes triggers the crowbar circuit and blows up the protection fuse. Here is a scope analysis.
Green line is 24V AC input, and the yellow one is the input of the crowbar. These spikes are captured at the exact moment of turning off the transformer. There are also some other minor spikes captured when I turn it on.
As you can see from the measurements, crowbar input can jump up to 49-50V level, which causes it to be triggered and resulting in a blown-up fuse.
So my questions are;
1 - What is the root cause of those spikes? (actually I'm curious about this one more than the second question)
2- How to prevent them from happening?
I already read about zener transition suppression circuits and MOVs that can prevent such things, and will try to test them in this week. I wanted to get some ideas before ordering the components.
Thanks in advance,
bh
I'm using a 220V - 24V transformer as a supply of 24V AC - 18V DC converter which is my own design. Since I cannot control the output of the transformer I put a crowbar circuit in the DC converter circuit as a precaution for the high voltages and it triggers around 42-43V DC. So the whole system is as described below.
220V AC -- Transformer -- 24V AC --> Full rectification -- Crowbar Circuit (42-43V) -- DC-DC Boost Converter -- 18VDC
However I'm observing high voltage spikes on the output of the transformer which sometimes triggers the crowbar circuit and blows up the protection fuse. Here is a scope analysis.
Green line is 24V AC input, and the yellow one is the input of the crowbar. These spikes are captured at the exact moment of turning off the transformer. There are also some other minor spikes captured when I turn it on.
As you can see from the measurements, crowbar input can jump up to 49-50V level, which causes it to be triggered and resulting in a blown-up fuse.
So my questions are;
1 - What is the root cause of those spikes? (actually I'm curious about this one more than the second question)
2- How to prevent them from happening?
I already read about zener transition suppression circuits and MOVs that can prevent such things, and will try to test them in this week. I wanted to get some ideas before ordering the components.
Thanks in advance,
bh