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# Power Supply Universal Front End

IP.com Disclosure Number: IPCOM000037084D
Original Publication Date: 1989-Nov-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 2 page(s) / 45K

IBM

## Related People

Celenza, N: AUTHOR

## Abstract

Disclosed is a circuit topology which enables a Power Supply (PS) circuit to operate from 110VAC or 220VAC without any manual intervention. It uses a Triac (TR1), some compare circuitry, and a latch to double the input AC low voltage and not double the input AC high voltage as it is being rectified.

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Power Supply Universal Front End

Disclosed is a circuit topology which enables a Power Supply (PS) circuit to operate from 110VAC or 220VAC without any manual intervention. It uses a Triac (TR1), some compare circuitry, and a latch to double the input AC low voltage and not double the input AC high voltage as it is being rectified.

To cover an AC input voltage range from 70VAC to 137VAC for a 110VAC PS and 140VAC to 259VAC for a 220VAC PS, one usually has two part numbers which are costly to manufacture and keep inventory. At times a manual switch is used to change a PS from 110VAC to 220VAC, but this has the disadvantage of damaging a PS if the switch is in 110VAC input position and 220VAC is applied.

The figure shows the standard diode bridge (D5 - D8), the dual capacitors (C3 and C4), and the switch represented by TR1 which is needed to double or not to double the rectified AC input voltage at Vbto Vb-.

The novel circuitry shows how two comparators and a latch are used in making the double or not to double decision. When the AC input voltage is applied, C1 charges up faster than C2. If VinAC is higher than 160V, the SCR latch Q1Q2 is triggered on and Q3 is prevented from turning on. If VinAC is lower than 160V, the Q1Q2 latch does not turn on, but C2 charges up high enough to turn Q3 on. When Q3 turns on, it turns on triac TR1 which causes the rectifier circuit to double VinAC at Vb+ or Vb-.

Once the decision not to double (220VAC input) is made, Q3 cannot tur...