Monday, August 06, 2012

Front End Security for SMPS

Now we have smps in most everything. AC Adapters and CFL lamps and many Home Consumer Electronics. The Failures of these units are on the rise. The Cooper transformers are out, but the SMPS reliability is falling.

Designing and manufacturing a SMPS facing a 230V input constantly, is not easy. You cannot Mutz your way in this, in a cost-cutting spree of this Vital Organ, just to have a competitive advantage of 'a lower cost product' (read cheap).

Now 230 V AC 50 Hz is not what you think it has, it has EMI-RFI, Inductive Kickback Spikes from the neighborhood, resonating and ringing with the RLC network that your home wiring forms. Lightning and Atmospheric Static that may strike at the weakest part on the SMPS. Wrong wiring, 3 phase mess ups. short circuits, falling tree branches, thunderstorm. Your SMPS is facing the Real Harsh Cruel world and the best part, they left off the Security Department to keep costs low. The critters in the box get zapped for no fault of theirs.

Front End Security for SMPS

There is one difficult way out of this, we move to a 24V DC standard within the house, it is safe and the Box outside the house faces all the Electrical Environment Variables and Unpredictability. This box that charges the battery and steps down the mains voltage can be protected well. Protection on this one unit, protects all the equipment in the Home or office. This is the Civilized way electricity should be used in Homes and Offices. Easy to integrate with Alternative energy. Factories can have all the High Voltage they want.

When a good technical collaborator is involved, quality is given due respect, the products are affordable yet robust. Some firms cut off vital circuitry (these happen in mechanical, electrical and chemical field too) to keep the product cost low. These products will work well in a Mains conditioned environment which is only affordable in some companies and never at homes.

The Security system consists of something that a Surge Protector from Belkin has. Let us see the traditional way, We need Gas Discharge Tube Lightning Arrestors. Then Varistors, Thermistors, X and Y caps and the Common Mode Choke Coils. A high voltage and high current fast acting fuse or trip circuit. Overrating of Mosfet and caps that face the high voltages. Using HV Back-to-Back zeners with fuses. Snubber Plastic HV self healing caps and Fast Switching diodes to absorb the inductive spikes.

Do it within the budget you have. SMPS should withstand 1.2KV microsecond pulses. 600V millisecond pulses and 400V for a few seconds. 300V AC for many minutes. Else let us go 24V Standard.

Other Protection devices your house or lab may needs to have. CVT - Constant Voltage Transformer, 1:1 Isolation Transformer, Servo Motorized Auto-transformer Stabilizer, Earth Leakage Circuit Breaker, HV-Relay Trip Circuit, Overload Current Relay Trip Circuit, MCB, Switched Triac or Relay, Copper Transformer Stabilizer with Layer or Layer Primary Insulation to protect against high voltage. This transformer should have earth shield, guarded terminals, primary windings should not slip layers, Vacuum Impregnated. 

May the Earth be good to you ! - Means - the earthing in your Home of Office should be excellent and do not compromise on Wiring Insulation and Switchgear. Let the wires outside have concrete gutters which are closed so that water or rodents do not get to the cables.

Read more at my Power Electronics Section