Demonstration board description

UM0727

4/18

Doc ID 15906 Rev 1

1

Demonstration board description

The STEVAL-ISA018V1 board is based on an LLC resonant converter, and employs the

5

Ω, 500 V STF21NM50N power MOSFET as the primary switches in the half-bridge. The

STF21NM50N is produced using STMicroelectronics’ proprietary high voltage MDmesh™ II

gate charge and high switching performance. The device is available in different packages,

i.e. the TO-220, TO-247 and TO-220FH.

The demonstration board has been designed based on the specifications listed in Table 1.

The electrical schematic of the board is shown in Figure 2. The input section is provided

with a connector for line input and a jumper for voltage double operation for a 110 Vac input

voltage.

The output voltage is available on the CN3 connector. The converter is controlled by the

L6599, a double ended primary controller for resonant half-bridge ZVS (zero voltage

switching). The IC controls the output power, changing the switching frequency and

controlling the half-bridge with a constant 50% duty cycle by means of a dedicated pin,

connected to the output feedback through an optocoupler. Light load conditions are

managed, with optimized consumption, thanks to burst mode operation. The IC also

includes a disable function and two-level over-current protection with programmable delay.

In order to properly run the half-bridge devices and guarantee high efficiency, the IC

switching element to avoid the use of a bootstrap capacitor.

During normal operation the IC is powered by the auxiliary winding of the transformer via the

D9 diode. A discrete linear voltage regulator is connected in order to stabilize the auxiliary

voltage fluctuations. The circuit consists of Q4, C42, R38, D3, D12, C32 and C33.

Table 1.

Main specifications

Parameter

Value

Input voltage range

a. 185 to 265 Vac - b. 85 to 185 Vac (with voltage double)

Input frequency range

50/60 Hz

Output voltage

24 V ± 2%

Output power

150 W (240Wpk)

Safety

EN60950

EMI

EN55014