Galvanically separated current probe
For needs of servicings of screens and TVs have made current probe. Consists from current transformer and amplifiers also additional amplifier for correction falls amplifications on short frequencies. For observation current through switching drivers shows up excellent because of separated masses amplifiers at all do have not disturbance in output signal.
fd = 2 Hz (-3dB)
fg = 100 kHz
Di / dt = 90 A / us
output = 0,1 V / A
Imax = 30 A peak
Warning: Upper border frequency relationship on period the observed signal (usually sawtoothed forms) i.e. real upper border frequency (for sinus harmonics) is over 1MHz.
Although scheme of complex seems substantial simple and has been realized with low cost elements, the frequency range which has attained more than sufficient for quality analysis of waveform current. Lack of complex is the change DC of level during flexions current (consequence AC connection). However, for periodic signals this is not problem. Anyway, probes of the such AC characteristic are rare and usually expensive.
Dimensions: 154 * 33 * 20mm (L * W * H)
Price of finished complex (without box): 370 HRK (50 euro)
Example: oscillogram of voltage and current on transistor 2SD2539 (TV Sony KV-29X5D). Has been presented the exit from the conduction when grows voltage on the colector (100V / cm) and fall current (2A / cm). The time base is 1us / cm. Shown oscillogram is oscillogram of good work of transistors. Are measured tf = 250ns (time for fall current with 90 % on 10 %). Warning: for measurement of voltage has been used probe 15kV / 1:1000, and for current probe 1:10.