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IRISMPS3

Circuit Description

The IRISMPS3 reference design is a complete tested power supply circuit. It is designed for a universal AC

line input and will provide a 15V, 4A full load DC output.

The design uses a flyback converter topology, with an IRIS4013K as the main switch and control device. The

initial start-up current for the IRIS4013K is provided by a dropper resistor from the DC bus. Once the circuit is

started the Vcc power for the IRIS4013K comes from the bias winding of the main transformer. The primary

current control circuit consists of a current sensing resistor which feeds a voltage proportional to the transformer

primary current into the feedback (FB) pin of the IRIS4013K. The secondary voltage control loop uses an LM431

precision shunt regulator as the reference and an optocoupler to feedback the information across the transformer

galvanic isolation boundary back to the control circuit of the IRIS4013K.

Test Circuit Set-up

The circuit is designed for a universal AC line input. To safely test and evaluate this circuit it is recommended

that an isolation transformer or a synthesized and isolated AC source (such as a Pacific Power Source 115-ASX)

is used to power the board, with a voltage in the range of 90-265VAC, with a frequency of 50/60Hz. The AC input

signal is applied to the pins at P1 and P3 marked on the board.

For the output the best load to use is an electronic load which will allow easy changes in the output load, e.g.

something like a Chroma 63102. Another simple alternative is to use a High power resistor for the load. The output

connection are as follows: P2 is the Positive output voltage connection, P4 is the negative(or return) output con-

nection.

Circuit Operation

The front end of the circuit consists of an EMI Filter, a diode bridge rectifier, and a DC bus filter capacitor.

These are all fairly common circuit components used to create a DC voltage at the top end of the transformer.

At power up the DC voltage is applied to the top of the transformer, and the top of resistor R2. R2 and R3 allow

Fig 1) Connections to the board viewed from the top board layout