CERAMIC CAPACITORS

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Page revised 06/20

POWER CAPACITOR ENDURANCE TESTING

ULTRA-LOW ESR, HIGH RF POWER

I. FOREWORDS

I.1. Concept

Figure 1 shows the general concept. The setup contains a direct digital synthesizer

(DDS) that generates an RF signal with a variable frequency. Its signal is amplified by a

driver stage followed by a power amplifier stage. The gain of the PA stage is controlled

by varying its supply voltage. For that purpose a variable power supply is provided. The

directional coupler measures the forward and the reflected power. The latter is a value

that describes the quality of the matching condition. The role of the matching network is

to match the capacitor to a 50W load. The capacitor under test is mounted on a separate

printed circuit board and is encapsulated by a small cabinet. This cabinet isolates the

capacitor from the ambient temperature. A temperature sensor is integrated into the

cabinet to measure the capacitors temperature.

DSC

Oscillator

20-100MHz

Variable

Power

Supply

RF

Driver

Resistive

load

RF-PA

Match

Match Controler

Micro Controler

LC Display

RS-232

Capacitor

under

test

Temp.

Sensor

Temp. Controler

Directional

Coupler

Figure 1

With a microcontroller, there are two control loops realized. The temperature of the

capacitor is measured at the beginning of the 5 seconds off time with a temperature

sensor. The sensor’s signal is used to control the variable power supply which

influences the power amplifiers gain and as a consequence, the output power or the

current through the capacitor under test.

The ground plane improves the heat spread between the capacitors. This is further

supported by a copper bar that is directly pressed on the ground plane of the PC board.

On the front side of the copper bar, a NTC is mounted. Tests have shown that this heat

coupling is very critical for the overall performance. The NTC is screwed directly and by

that the heat coupling is both tight and reliable.

Capacitors under test (x9)

Ground plane

PC board

PC board

Copper bar

PTFE insulation

with vias

NTC

Figure 2

I.2. Test Cycle

The complete test cycle is shown in figure 3. The test starts with a tuning procedure

at low power. As soon as the matching condition is achieved the RF power is set to the

value that is necessary to heat the capacitors. During the ON time, the frequency is

continuously adjusted to minimize the reflected power. After 5 seconds ON, the RF is

switched off for the next 5 seconds. Then the RF is switched on again. Because the

capacitors have cooled down during the OFF time, the test generator needs to re-tune.

The re-tune procedure takes 500ms. After that, the RF is ON for the next 5 seconds. That

way a complete cycle takes 10 seconds.

Pforwarded

Preflected

5 sec.

Retuning

Tuning

at

Start

5 sec.

5 sec.

5 sec.

Retuning

Figure 3

The following conditions have been used:

• HiQ multilayer ceramic capacitors operated at 27MHz;

• 2 complete test sets are done, one for B size (1111) and another for X size

(2225);

• a complete test set represents 1 million cycles (4 months of continuous RF

power).

I.3. Data Acquisition

The test generator measures continuously: the frequency, the forward power, the

reflected power and the three temperatures. The test generator stores these values

always at the end of the 5 seconds ON time. The remote computer gathers the data at

least once each cycle and writes these records to a log file. Each file collects the record

of one day and is automatically sent by email once a day.

II. RESULTS

All the tests have been performed by an external independent company named Barthel

HF Technik located in Aachen, Germany.

II.1. HiQ Capacitors – B Size (1111) – Solderable Nickel Barrier

The CHB series RF/Microwave capacitors offer both extended operating temperatures

up to 175°C and extended voltages up to 1500 VDC. These components are based on

our well-known P100 HiQ dielectric, a low loss material, which is ESA and MIL qualified

- ITAR free.

On May the 9th 2011, the test set was completed without any problem to report.

!

II.2. HiQ Capacitors – X Size (2225) – Non Magnetic Solderable Barrier

The CLX series High RF Current/Voltage capacitors offer both ultra stability over

temperature and extended voltages up to 3 600 VDC. These components are based

on our well-known NP0 HiQ dielectric, a low loss and ultra stable material, which is

MRcertified® and MIL qualified - ITAR free.

General Information