EPC EPC9508 Snelstarthandleiding - Pagina 3

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QUICK START GUIDE

DETAILED DESCRIPTION

The Amplifier Board (EPC9508)

Figure 1 shows a diagram of the EPC9508 ZVS class-D amplifier with pre-

regulator. The pre-regulator is set to a specified current limit (up to 1.5 A)

by adjusting P49 and operates from 6 V through 36 V input. The output

voltage of the pre-regulator is limited to approximately 2 V below the in-

put voltage. The pre-regulator can be bypassed by moving the jumper

(JP60) over from the right 2 pins to the left 2 pins. To measure the current

the amplifier is drawing, an ammeter can be inserted in place of the jumper

(JP60) in the location based on the operating mode (pre-regulator or bypass).

The amplifier comes with its own oscillator that is pre-programmed to

6.78 MHz ± 678 Hz. It can be disabled by placing a jumper into J70 or can

be externally shutdown using an externally controlled open collector / drain

transistor on the terminals of J70 (note which is the ground connection).

The switch needs to be capable of sinking at least 25 mA. An external os-

cillator can be used instead of the internal oscillator when connected to

J71 (note which is the ground connection) and the jumper (JP70) is moved

from the right 2 pins to the left 2 pins.

The pre-regulator can also be disabled in the same manner as the oscilla-

tor using J51. The pre-regulator can be bypassed, to increase the operating

voltage (with no current or thermal protection) to the amplifier or to use

an external regulator, by moving the jumper JP60 from the right 2 pins to

the left 2 pins. Jumper JP60 can also be used to connect an ammeter to

measure the current drawn by the amplifier (make sure the ammeter

connects to the pins that correspond to the mode of operation either

bypass or pre-regulator).

Single Ended Operation

The amplifier can be configured for single ended operation where only

devices Q1 and Q2 are used. In this mode only L

establish ZVS operation. If Q11 and Q12 are populated, then the following

changes need to be made to the board:

1) Remove R76 and R77

2) Short out C46 and C47

3) Short the connection of JMP1 (back side of the board)

4) Remove LZVS11

5) Check that CZVS1 is populated, if not then install.

6) R74 and R75 may need to be adjusted for the new operating

condition to achieve maximum efficiency (see section on ZVS timing

adjustment).

ZVS Timing Adjustment

Setting the correct time to establish ZVS transitions is critical to achiev-

ing high efficiency with the EPC9508 amplifier. This can be done by

selecting the values for R74 and R75 respectively. This procedure is best

performed using potentiometer P74 and P75 installed that is used to

determine the fixed resistor values. The procedure is the same for both

single ended and differential mode of operation. The timing MUST initial

be set WITHOUT the source coil connected to the amplifier. The timing

diagrams are given in Figure 4 and should be referenced when following

this procedure. Only perform these steps if changes have been made to

the board as it is shipped preset. The steps are:

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1. With power off, connect the main input power supply bus to +V

2. With power off, connect the control input power supply bus to +V

3. Connect a LOW capacitance oscilloscope probe to the probe-hole J2

4. Turn on the control supply – make sure the supply is between 7 V

5. Turn on the main supply voltage to the required predominant oper-

6. While observing the oscilloscope adjust P74 for the rising edge

7. Check that the setting remains optimal with a source coil attached.

8. Replace the potentiometers with fixed value resistors.

Differential Operation

The amplifier can be configured for differential operation where all the

devices are used; Q1, Q2, Q11 and Q12. In this mode either L

Determining Component Values for L

The ZVS tank circuit is not operated at resonance, and only provides the

necessary negative device current for self-commutation of the output

voltage at turn off. The capacitance C

ripple voltage component and is typically around 1 µF. The amplifier

and C

are used to

ZVS1

ZVS

supply voltage, switch-node transition time will determine the value of

inductance for L

tion over the DC device load resistance range and coupling between the

device and source coil range and can be calculated using the following

equation:

Where:

Note that the amplifier supply voltage V

equation as it is accounted for by the voltage transition time.

The charge equivalent capacitance can be determined using the

following equation:

To add additional immunity margin for shifts in coil impedance, the

value of L

of the devices (which will increase device losses). Typical voltage

transition times range from 2 ns through 12 ns. For the differential case

the voltage and charge (C

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(J50). Note the polarity of the supply connector.

(J90). Note the polarity of the supply connector.

and lean against the ground post as shown in Figure 3.

and 12 V range (7.5 V is recommended).

ating value (such as 24 V but NEVER exceed the absolute maximum

voltage of 36 V).

of the waveform so achieve the green waveform of figure 4.

Repeat for the falling edge of the waveform by adjusting P75.

In this case it is important that the source coil is TUNED to resonance

WITH an applicable load. Theoretically the settings should remain

unchanged. Adjust if necessary.

or L

only is used to establish ZVS operation.

ZVS

ZVS12

which needs to be sufficient to maintain ZVS opera-

ZVSx

ZVS

8 ∙ f

Δt

= Voltage transition time [s]

fsw = Operating frequency [Hz]

= Charge equivalent device output capacitance [F].

OSSQ

∫

V AMP

∙

OSSQ

AMP

can be decreased to increase the current at turn off

ZVS

) are doubled.

OSSQ

Demonstration System EPC9508

, L

ZVS1

ZVS

is chosen to have a very small

ZVS

∆t

(1)

∙ C

OSSQ

is absent from the

AMP

(2)

(v) ∙ dv

OSS

and

ZVS11

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