We disign products for educational purpose, "student proof" is our main difficulty. We test a step down +5 V supply (Vin from a regulated +24V PS) with a LM2675M-5.0. If a student apply the 24 vcc to the +5V output, does the LM2675 or other components will be damaged ? If we add a diode series after the inductor L1, is-it a good solution ?
Thank you for help.
Applying 24V at the output of LM2675M-5.0 will not damage the IC. However, you would need to use an output capacitor (C8 in your schematic) which is rated for the 24V.
If you don't want to use an output capacitor rated for 24V, you can consider adding the diode you described. Connect the diode anode at the +5V like shown below. In this configuration the capacitor C8 does not need to be rated for 24V. Note that the voltage at VOUT in the schematic below will be equal to 5V - the diode forward voltage drop. Please be sure that the output diode is rated for 24V and the maximum load current (1A for LM2675). You can probably use the same diode as D1.
before to receive your answer we tested to insert a diode in serie with L1 (and C8) in the feedback loop... very bad effect on the C8 and the LM2675.
The simplest solution you suggested is the best one. Upgrade C8 to 35V. You're right, the LM2675 is not damaged with 24 Vcc.
To protect the other circuits on the +5vcc line, we will add a low resistance PTC and a 5.2V zener diode.
Like this, we should have a "student proof" supply.
Groupe MFT Inc.
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