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HTB28XXS

(185°C, 28V Input, Single Output)

4. Measuring Output ripple of HTB:

The HTB converter’s output ripple should be measured per prescribed procedure to get reliable values.

Figure 4 shows how an oscilloscope and associated external R-C components should be connected to get

true value of output ripple at full load.

+ Vout

Return

DUT

R

0.1 µF

50

Ω Coax

50

Ω

Oscilliscope or Equivalent

with 10 MHz Bandwidth.

Multiply readings by 2.

1 µF

50

Ω

Termination

Figure 4. Measuring O/P noise+ripple of HTB Converter

Figure 3. Pictorial Definition of O/P noise+ripple of any Converter

Because of the high frequency content of this ripple, special measurement techniques must be employed

so that correct measurements are obtained. First, a 10 MHz bandwidth oscilloscope is normally used for the

measurement so that all significant harmonics of the ripple spikes are included. Otherwise on a 200 MHz or

500 MHz oscilloscope, one can limit the bandwidth of measurement to 10 MHz.

The actual ripple voltage measurement must be carefully made in order not to induce error voltages in the

test equipment. Therefore, the conventional ground clip on an oscilloscope probe (see Figure 5) should

never be used in this type of measurement. This clip, when placed in a field of radiated high frequency

energy, acts as an antenna or inductive pickup loop, creating an extraneous voltage that is not a part of the

output noise of the converter.

Figure 5. Oscilloscope probe

Figure 6. Correct method to use Oscilloscope

Probe