# FLYBACK DESIGN, PSR, BCM Mode, Constant current output design, Calculations

#### aja_augus

Joined Aug 25, 2020
5
Hi,

Can anyone help with materials for the designing of LED drivers (Home applications). Transformer design values such as Primary inductance....etc. I referred so many equations, each of them looks different and as there are different modes, DCM,CCM, and different ICs, I am totally confused with the calculations.

#### aja_augus

Joined Aug 25, 2020
5
I have got a transformer design with equations for PSR, DCM transformer design. I don't know what are the parameters different from DCM from BCM design. As my IC is working with Critical Conduction Mode(It is also called BCM I guess).

#### DickCappels

Joined Aug 21, 2008
7,540
Attached is documentation for a small line powered LED lamp I made a few years ago. I think you might find the Supertex HV99-10B controller is very flexible. This power supply is not isolated from the power line so keep one hand in your back pocket!

https://www.microchip.com/wwwproducts/en/HV9910B

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#### aja_augus

Joined Aug 25, 2020
5
Attached is documentation for a small line powered LED lamp I made a few years ago. I think you might find the Supertex HV99-10B controller is very flexible. This power supply is not isolated from the power line so keep one hand in your back pocket!
Thanks for the reply, This is Buck converter right?. But I want to do it with a flyback, standalone converter. 18-36V DC, 0.500A at max voltage.

The design is in BCM mode. I have calculations for DCM mode, I am confused with the Lp values and all, what is the difference compared to DCM.

#### Marc Sugrue

Joined Jan 19, 2018
216
Thanks for the reply, This is Buck converter right?. But I want to do it with a flyback, standalone converter. 18-36V DC, 0.500A at max voltage.

The design is in BCM mode. I have calculations for DCM mode, I am confused with the Lp values and all, what is the difference compared to DCM.
DCM & BCM are pretty much the same in terms of magnetics. Both willl have their worst case at low line voltage and maximum load. The big difference is around control method and its EMI signature.

To ensure DCM you effectively design around a small dead (say 45% Duty cycle) and control the output by changing the duty cycle which ensure it remains discontinous. For BCM you assume 50% duty at low line max load which means theres no dead time.

The big differency with a BCM controller is how it fundamentally works. It typically uses a fixed duty cycle (normally monitoring the peak current) which means that depending on the line voltage the time to reach the peak current will change. This changes the Ton based on the line voltage. The controller also normally monitors the output voltage from the transformer via a Zcd line which identifies when the energy in the transformer starts to collapse, when it starts to collapse the mosfet is switched back on to recharge the transformer.

This means that the frequency of operation at low line and max load will be lower than at high line and light load as opposed to DCM which uses fixed frequency and changable duty cycle

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#### DickCappels

Joined Aug 21, 2008
7,540
I apologize for the post. I though you were looking for ideas for a DIY led lamp, rather than a training vehicle for a particular power supply topology. Have to been to the Power Integrations website yet? https://www.power.com/