Practical - 19 :- Testing High-Frequency Transformers

To identify a high-frequency transformer and determine its Inductance and Turns Ratio.

S. No.	Equipment	Function
1	HF Transformer	The component to be tested (usually small with a black/gray core).
2	Digital Multimeter (DMM)	To measure Resistance (for continuity and winding identification).
3	LCR Meter	To accurately measure Inductance ( $L$ ) at a specific frequency.
4	Function Generator	To create a high-frequency AC signal for functional testing.
5	Digital Storage Oscilloscope (DSO)	To measure the input ( $V_1$ ) and output ( $V_2$ ) voltages.
6	Connecting Wires & Probes	To connect the equipment.

Core Material: HF transformers use ferrite cores (a type of ceramic) instead of laminated iron cores. Ferrite minimizes energy loss when AC current switches direction very quickly (high frequency).
Inductance ( $L$ ): This property is directly related to the transformer's ability to store energy. An LCR meter measures it by applying a test frequency (e.g., 10 kHz or 100 kHz).
Turns Ratio ( $a$ ): This is the ratio of the number of turns in the primary winding ( $N_1$ ) to the number of turns in the secondary winding ( $N_2$ ). It determines the voltage change:

Visual Check: A high-frequency transformer is small and has a dark gray/black ferrite core.
Continuity Check: Use the DMM in resistance ( $\Omega$ ) mode.
- Test continuity between all pins to identify which pins belong to the same winding (resistance value close to zero). Pins from different windings should show Open Loop (OL).
- Label the input winding as Primary ( $P$ ) and the output winding as Secondary ( $S$ ). Tip: The primary usually has more turns, so it might have a slightly higher resistance.

Set the LCR meter to Inductance ( $L$ ) mode at a test frequency of around 10\text{ kHz}.
Connect the probes across the Primary Winding ( $P$ ) and record the value ( $L_P$ ).
Connect the probes across the Secondary Winding ( $S$ ) and record the value ( $L_S$ ).

Winding	Inductance (L) (mH)	Measured Voltage (V peak-to-peak) (V)
Primary ( $P$ )	$L_P = $	$V_1 = $
Secondary ( $S$ )	$L_S = $	$V_2 = $

Practical- 16 :- calculate inductive reactance at different input signal frequency using function generator lab manual