STMicroelectronics - High Voltage Converters | VIPer53 Smart Off-Line Primary Switch for Flyback Converters

Built using the chip-to-chip approach it takes advantage of both the successful MDmesh (Multiple Drain Mesh) and VIPower technologies. The Power stage is an MDmesh Power MOSFET: this technology combines a new vertical drain structure with ST’s Mesh Overlay horizontal layout. MDmesh uses a vertical p-strip structure consisting in an array of partitions that reduce the resistivity of a conventional lightly doped drain.

The control part is built with high voltage M0-3 VIPower technology. This smart technology allows the design of the control circuit with protection features and an easy assembly process using a single package frame.

VIPer53 Smart Off-Line Primary Switch for Flyback Converters

VIPer53: A New Approach

VIPer53 encloses in the same package an enhanced current mode PWM controller and a high voltage MDmesh Power MOSFET. The minimum breakdown voltage between drain-source pins is 620V and the R_DS(on) at 25°C is 1 ohm. A thermal sensor is integrated inside the Power MOSFET for the over temperature protection. The maximum switching frequency can be set externally up to 300kHz by an RC (Resistor Capacitor) Network attached to the OSC pin.

At the converter start-up, the internal high voltage current source, placed between the drain pin and the VDD pin supplies the device and charges an external capacitor connected to the V_DD pin. When the voltage of V_DD reaches the V_DD(on)threshold, the internal high voltage current source turns off, and the transformer auxiliary winding supplies the device.

The feedback control system is the current mode control and is implemented via the comp pin. It is possible to adjust the converter dynamic characteristics using a simple external network connected to the above pin.

Overload Protection: A New Feature

The new important feature implemented with VIPer53 is the “delaying of the over-load protection and this feature is implemented through an appropriate pin: the TOVL.

The overload protection is enabled if the voltage on the Comp pin exceeds 4.4V (Typ. value) but to discriminate between a temporary over-voltage or an abnormal condition, a delay is introduced by an external capacitor connected on TOVL pin.

This capacitor is charged during the over-load condition and in the meantime the MOSFET switches. If the over-load is maintained and the capacitor reaches the VOVL threshold, the MOSFET turns off. The delay is the capacitor charging time that the designer can set accordingly to the time needed by the output voltage to become establish it.

Features

	Switching frequency up to 300kHz
	Overload control
	Current mode control with adjustable limitation
	Soft start up and shut down control
	Automatic burst mode for very low consumption in standby condition (< 300mW)

	Over-temperature, over-voltage protection
	Integrated high voltage start up current source
	Auxiliary undervoltage lockout with hysteresis

When Every milliWatt Counts

Flyback topologies are most commonly used for small and medium size power supplies when the output has to be electrically isolated from input, and when the electrical equipment operates from 85 to 230 Volt mains supply.

These converters are found primarily in set-top boxes, DVDs, VCRs, auxiliary power supplies for TVs and PCs and travel adaptors.

Nowadays these applications require higher power densities and better thermal efficiencies without the use of heatsinks. Furthermore the minimal stand-by consumption allows power supply manufacturers to comply with the more stringent new Eco Norms such as the Energy Star Program.

Thanks to the MDmesh characteristics The VIPer53 can typically provide 30W output power in DIP-8 and 40W in PowerSO-10, from 85 Vac to 230 Vac without using any heatsink; in addition the five pins of VIPer53 have the same functionalities as those of the VIPerXX0 devices such as VIPer50 and VIPer50A.

The VIPer53 can easily be applied in all the AC/DC converters already designed with VIPer50 and VIPer50A, saving even more board space (heatsinks are no longer needed) and giving the same output power of VIPer50 and VIPer50A.

VIPer53 - The output power is limited until the Power MOSFET is turned off by the overall protection.

The output power is limited until the Power MOSFET is turned off by the overall protection.

Applications

	SMPS solutions for: set-top-boxes, DVDs, VCRs, printers, TVCs and monitors
	External AC/DC power supply

General block diagram



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