While the injection transformer used for Bode plots is a very wideband transformer, it is not useful for measuring ripple rejection (PSRR) of a power supply or even an opamp. Doing so could permanently damage the transformer. This is because the attributes that make the injection transformer perform so well also result in a transformer that is intolerant of DC current. Even very small DC currents (5mA or less) can greatly reduce the signal capacity or even totally saturate the transformer. For this reason, the Picotest line injector (J2121A) is another essential test adapter for power supply testing.
The J2121A is especially suited to high power applications such as those associated with military and satellite busses. It can be used with input bus voltages up to 400V and supply up to 20A at 1MHz. The line injector allows the input DC supply voltage to be modulated by the network analyzer source signal (oscillator). The J2121A line injector output is DC regulated and provides a fixed voltage drop of 750mV from the input bus voltage fed into the injector in addition to the AC modulation signal.
The J2121A can be connected to the power supply input under test and, depending on the test probe connection points, can be used to measure either PSRR or the power supply’s input impedance The line injector can also be used to measure the impedance/inductance of an inductor under bias.
While a current probe can be used as part of a test setup, the J2121A includes a current sense monitor output that can be connected to the VNA.
The J2121A comes with the J2171A power supply and connecting cable, used to power it, and a 1-ohm calibration fixture.
應用範圍
- Measurement of PSRR
- Measurement of DC Bias
- Measurement of DC-DC Converter Input Impedance Testing
The J2121A includes a 1 ohm shunt calibration device
A 3.3uH shunt mounted inductor is connected to the output of the J2121A in order to measure the inductance change with bias. The measurement is setup as an impedance test (Voltage/Current) with voltage out of the J2121A voltage port and current from the J2121A’s Current Sense Monitor Output (BNC).
The input impedance of a DC/DC converter can also be measured using the J2121A. The J2121A output is connected to the DC/DC converter input and a scope probe is connected to CH2 of the VNA and used to measure the input.
The J2121A setup for measuring an inductor under DC bias
Line Injector Comparison - J2121A vs. J2120A
- J2121A supports much higher voltage and current applications
- J2120A has ultra-low noise output, 50V/5A max 10MHz bandwidth, passive, variable voltage drop (1.5V-3.5V) based on the load impedance
- J2120A favors PSMR and low current, low voltage, PSRR measurement applications
- The J2121A has a much higher voltage range, much higher current rating and integrated Hall current monitor
- The J2121A favors high voltage, high current PSRR testing and DC/DC and Inductor impedance measurement
What's included :
1. J2121A High Power Line Injector
2. 1 ohm Calibration Fixture
3. J2171A 200mA Low Noise Power Supply
4. User manual
5. 1 Year Warranty
