Lundahl Splitting transformer, LL7904

High Level Splitting Transformer, LL7904

In many splitting applications, the splitting transformer must have a high immunity to input common mode signals, to stray magnetic fields from e.g. power transformers and to large ground potential differences in receiving systems. The LL7904 is developed to handle those types of problems. When designing the LL7904, we have used our well established two-coil structure to create a transformer with a high degree of symmetry. The transformer is built up from two primary windings (which should be used in parallel) and two secondary windings. Each secondary winding is built up from two sections, one from each coil and is surrounded by it own electrostatic shields. The symmetric structure results in an internal cancellation of noise signals caused by external magnetic field (humbucking). It also increases immunity to ground noise between secondary systems and reduces the effects of input common mode signals. The transformer is housed in a mu-metal can and is impregnated in solventless epoxy resin.

Turns ratio: 1 + 1 : 1 + 1

Dimensions (Max. L x W x H above PCB(mm)): 66 x 32 x 21
Weight: 155 g
Static resistance of each primary: 55 ?
Static resistance of each secondary (Pins 14 - 22 and pins 16 - 13 resp.): 43 ? and 66 ?
Distortion: 0.1% @ +16 dBU, 50 Hz; < 1 % @ +23 dBU, 50 Hz
Frequency response (Ref: 0 dBu, 1kHz): 10 Hz -- 80 kHz +/- 0.5 dB
Test arrangement: Parallel input - parallel output. Source 150?, load 10 k?
CMRR at 20 kHz (Source 600 ohms, load 2 x 10k): > 60 dB
CMRR at 20 kHz from sec. to sec. (Source 600 ohms, load 2 x 10k): > 40 dB
Isolation test primary - secondary / secondary - secondary / 18 - (15+17): 4 kV / 2 kV / 1 kV RMS