Adding Shutdown when LT3083 in parallel

Hi,

When using two LT3083 regulators in parallel, the shutdown circuit can be implemented in a similar manner as the single-device example.

For the SET pin, follow the same approach as the single LT3083 shutdown circuit. Since the SET pins of the paralleled regulators are tied together, a single shutdown transistor (Q1) can be used to pull the common SET node low and force the programmed output voltage to 0V.

For the output clamp transistor (Q2), it is recommended to use one Q2 connected to the final VOUT node after the ballast resistors, rather than using a separate Q2 on each LT3083 output. This is because the purpose of Q2 is to clamp the load output to ground and ensure VOUT remains at 0V during shutdown. Once the common output node is pulled low, both regulators are effectively disabled through the shared SET network and common output connection.

Therefore:

• Q1: One transistor on the common SET node.
• Q2: One transistor connected to the final VOUT node (after ballast resistors).
• No need for two separate Q1 and Q2 transistors on each LT3083 output in a standard parallel configuration.

Best Regards,
Tech Support

Hi Harshal,

Thank you for the reply.  From LTspice simulations, using one Q2 transistor after ballast resistors, I can't get true zero Vout when in shutdown, especially for low loads.

In my application, since LT3083 VControl is separate from VIN, I decided to use reed relay to disconnect supply to VControl when shutdown is required.  Using this method, Vout is truly zero in shutdown.

Regards,

Anwar