 Description This circuit provides a fully protected, 100% automotive proof, low voltage and low consumption proposal for driving additional (or existing) 2x55W bulbs (high beams). Superior ruggedness and reliability is offered by means of a pure Solid State Switches solution. The advantages of using semiconductors are manifold:
• They are substantially more reliable and durable than mechanical relays.
• They are smaller and lighter.
• They incorporate self-diagnostic capabilities.
• They offer self-protection and external protection capabilities.
• You can find practically any functionality you need.
| Special thanks to author Giovanni TORRISI, who sent us this project. | Electromechanical relays are constantly being replaced by high-side drivers, which are also known as intelligent power switches or IPS. These devices are commonly made in a monolithic technology in which a vertical Power MOSFET (power output) is integrated with a low-voltage control circuitry based on NMOS components. The availability of the low-voltage control circuitry allows the implementation of standard protections require for driving automotive loads. These protections include current limiting, voltage clamp, thermal protection, open-load, current sense, and electrostatic discharge. These protections allow the device to operate in harsh automotive environments and to survive abnormal (but not so rare) conditions such as reverse battery and load dump. In this specific circuit, the used IPS is VND5012AK: most valuable features, for this application schematic, are the current limitation and thermal shutdown that, in case of short circuit of the load, come to protect the device, the bulbs and the module. The High Side is supplied by the regulator L4979D: the latter is typically off (enable pin is low, tied to gnd through the R2 resistor), except when the mechanical switch is turned-on and the resistive partitioning is activated (Enable pin is high).
Some words on the workaround circuitry:
- • Resistors R3, R4 and R7 are needed to tie to ground unused pins.
- • The RD network R8-D2 protects the High Side Driver when a reverse battery occurs.
- • D1-C1 protect the regulator during negative transients and reverse battery
- • D3 helps in protecting the device if the pulses on the Battery line are higher than 41V (maximum rating of the HSD).
- • R1, R2 represent a resistive partioning that enable (once the mechanical switch is in its closed position) the voltage regulators
- • R5, R6 represent a resistive partioning that turn on the HSD
- • The 100nF Capacitor on the Regulator Output is needed for stability
In case of different bulb wattage (27W, 21W, 10W or 5W) it is simply needed to change only the High Side Driver All the resistors are low wattage ones. The circuit was designed to work with an ambient temperature in the range -40°C-85°C; the module, in stand-by mode, sinks less than 10A. Giovanni TORRISI
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