Graetz Bridge Questions

[kacernator]

Hi,

I am little confuse about graezt (diode) bridge rectifier circuit.
Lets say I have 0-20V 1A secondary winding. If I rectify that with graetz bridge cap input filter I will get voltage of 1.4*20V. But how about current?
I read somewhere that graetz is only 60 percent efficient, so that means I can only draw 600mA from secondary max? If I do draw the 600mA from graetz bridge will the actual load on transformers secondary be too 600mA?

Thanks.

[janneman]

Originally posted by kacernator
Hi,

I am little confuse about graezt (diode) bridge rectifier circuit.
Lets say I have 0-20V 1A secondary winding. If I rectify that with graetz bridge cap input filter I will get voltage of 1.4*20V. But how about current?
I read somewhere that graetz is only 60 percent efficient, so that means I can only draw 600mA from secondary max? If I do draw the 600mA from graetz bridge will the actual load on transformers secondary be too 600mA?

Thanks.

The 1A spec is an RMS spec. It's not exacrtly the average current, but somewhat similar.The 20V is also an RMS voltage and that gives you 20Watts RMS capability. So if your rectified voltage is 26V (you lose about 2V in the rectifier diodes) and you would want to take 1A out of it you try to take 26Watt! So in this case you can only take say 0.6 or 0.7A to keep within the xformer spec.
And indeed, that 0.65A DC from the rectified voltage translates to about 1A RMS from the secondary!
You CAN take 1A from the rectified DC but probably the xformer sec will drop too much and the xformer will become too hot...

Jan Didden

[kacernator]

Thank you very much!