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QUICK START GUIDE

The pre-regulator can also be disabled in a similar manner as the

oscillator using JP50. However, note that this connection is floating

with respect to the ground so removing the jumper for external

connection requires a floating switch to correctly control this function.

Refer to the datasheet of the controller IC and the schematic in this

quick start guide for specific details.

The ZVS timing adjust circuits for the ZVS class-D amplifiers are each

independently settable to ensure highest possible efficiency setting

and includes separate ZVS tank circuits.

Additional protection features

An undervoltage-lockout circuit has been implemented for the input

voltage (V

). The amplifier board will not start unless V

minimum required value specified in table 1.

A clamp diode also protects the board from V

brief period and accidental reverse polarity connection with up to

11 A current protection.

On-Off-Key (OOK) modulation

On-Off-Key (OOK) modulation (as illustrated in figure 6) can be

implemented by applying the modulation signal at J76. It is

compatible with 5 V logic only. When the signal is high, the power

stage functions normally; when the signal is low, the gate drive signal

of one half-bridge is shut off. Therefore, for optimal performance,

the signal should be synchronized with the oscillator signal. The

modulation signal should also change state between the oscillator

states and must complete an even number of clock cycles. Failure

to follow this will lead to DC voltage shift on the ZVS capacitor (C

and other harmonic generation issues in the amplifier output. The

OOK modulation frequency will also become present and thus could

lead to radiated emission violations if the frequency exceeds what is

allowed in the ISM band.

When not using OOK modulation, J76 should be left open – an on-

board pull-up resistor keeps the level high.

Single ended or Differential Mode operation

The EPC9512 amplifier can be operated in one of two modes; single-

ended or differential mode. Single ended operation offers higher

amplifier efficiency but reduced imaginary impedance drive capability.

If the reflected impedance of the tuned coil load exceeds the capability

of the amplifier to deliver the desired power, then the amplifier can be

switched over to differential mode. In differential mode, the amplifier

is capable of driving an impedance range of 1 Ω through 56 Ω and

±35j Ω and maintains either the 1.375 A

33 W of power. The EPC9512 is set by default to differential mode and

can be switched to single ended mode by inserting a jumper into J75.

When inserted the amplifier operates in the single-ended mode.

Using an external pull down with floating collector drain connection

will have the same effect. The external transistor must be capable of

sinking 25 mA and withstand at least 6 V.

For differential mode only operation, the two ZVS inductors L

can be replaced by a single inductor L

ZVS2

and C

ZVS2

4 |

reaches its

over-voltage for a

zvs

coil current or deliver up to

RMS

and

ZVS1

and by removing C

ZVS12

ZVS1

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ZVS Timing Adjustment

Setting the correct time to establish ZVS transitions is critical to

achieving high efficiency with the EPC9512 amplifier. This can be

done by selecting the values for R71, R72, R77, and R78 or P71, P72,

P77, and P78 respectively. This procedure is best performed using a

potentiometer installed at the appropriate locations 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 initially be set WITHOUT the source coil connected to the

amplifier. The timing diagrams are given in figure 12 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:

1. With power off, remove the jumper in JP1 and install it into JP50 to

place the EPC9512 amplifier into Bypass mode. Connect the main

input power supply (+) to JP1 (bottom pin for bypass mode) with

ground connected to J1 ground (-) connection.

2. With power off, connect the control input power supply bus (19 V)

to (+) connector (J1). Note the polarity of the supply connector.

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

of the half-bridge and the ground post.

4. Turn on the control supply – make sure the supply is approximately

19 V.

5. Turn on the main supply voltage starting at 0 V and increasing

to the required predominant operating value (such as 24 V but

NEVER exceed the absolute maximum voltage of 80 V).

)

6. While observing the oscilloscope adjust the applicable

potentiometers to achieve the green waveform of figure 12.

7. Repeat for the other half-bridge.

8. Replace the potentiometers with fixed value resistors if required.

Remove the jumper from JP50 and install it back into JP1 to

revert the EPC9512 back to pre-regulator mode.

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 capacitors C

to have a very small ripple voltage component and are typically

around 1 µF. The amplifier supply voltage, switch-node transition

time will determine the value of inductance for L

to be sufficient to maintain ZVS operation over the DC device load

resistance range and coupling between the device and source coil

range and can be calculated using the following equation:

ZVS

Where:

Δt

= Voltage Transition Time [s]

= Operating Frequency [Hz]

= Charge Equivalent Device Output Capacitance [F]

OSSQ

= Gate driver well capacitance [F]. Use 20 pF for the LM5113

well

Demonstration System EPC9129

ZVS

and C

ZVS1

ZVS2

ZVSx

∆t

8 f

+ C

)

OSSQ

well

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are chosen

which needs

(1)