DPA-Switch at Vin = 12V?

Posted by: pmillett on 05/12/2014

Hello -

The DPA-switch datasheet mentions that the device can start and run at voltages "much lower than 16V". Also that a current can be sourced into the control pin to help accomplish this.

Can anybody provide a little more detail, background, and/or a suggested imnplementation?

I need a flyback converter that will operate from a 12V regulated supply (say, 11V - 13V) at about 18 watts.

Thanks!

Pete

Comments

Could you tell me which page in the datasheet claims “the much lower input voltage”？

Thanks

Note D on page 25:

"D. It is possible to start up and operate DPA-Switch at DRAIN voltages well below 16 V. However, the CONTROL pin charging current is reduced, which affects start-up time, auto-restart frequency, and auto-restart duty cycle. Refer to Figure 45, the characteristic graph on CONTROL pin charge current (IC) vs. DRAIN voltage for low voltage operation characteristics. "

And note 3 on page 17:

"3. Reduced input voltage decreases the available output power for the same device dissipation. Tables 3 to 6 are the power tables for 16 VDC and 24 VDC input voltages. Input voltages below 16 V are possible, but since the internal start-up current source is not specified at voltages below 16 V, an external chip supply current should be fed into the CONTROL pin approximately equal to but less than ICD1."

Pete

For input voltage above 16V, the internal shunt regulator is good enogh for start up bias. For input voltage below 16V, an external start up bias is needed to make sure that the C pin voltage is high enough to start up the power supply during power up. But the load capability of the start up bias must be lower than Icd1, or the DPA will not be fully controlled by the feedback and thus results in problems.

For your application, try a 5.8V linear regualtor with zenner and NPN transistor for start up, and use a resistor on the emitter to limits the load capability of the linear regulator. You have to try the circuit in your lab, and I believe you will find th esweet point of theresistor valaue.

Regards