I designed a relatively simple +30V PSU. Output current can be adjusted via Rsense resistor. A -30V PSU can be build by use of complementary transistors and LM337.
**broken link removed**
I was thinking of adding a DPDT relay. One contact will be wired to high power low Ohm resistor that will be in series with the circuit right after the bridge. This is to limit the inrush current. Once the capacitors are at their peak voltage, a timer circuit will toggle the relay and bypass the series resistor.
That won't work, the n-channel MOSFETs on the output will never turn on because they're permanently biased off as the gate will always be below the source.
That won't work, the n-channel MOSFETs on the output will never turn on because they're permanently biased off as the gate will always be below the source.
The circuit also will have poor regulation because you can not use a remote sense connection (as you show) to eliminate the drop from the Rsense and output transistors (see the 317 data sheet section about "Load Regulation" ). The 317 adjusts the output to get a 1.2V drop between the output pin and the ADJ input. If you connect the adjust resistor to the load point and not the 317 output pin, any voltage drop on the output line will just be subtracted from the reference voltage, degrading the regulation.
I agree with Hero999. Place all the current limit circuitry at the LM317 input.
But you can't have any resistors or circuitry on the output or you will degrade the regulation, so you need to also remove the emitter follower booster from it's location. Use the "High Current Adjustable Regulator" configuration shown on page 17 in the National LM117/317 data sheet.
I agree with Hero999. Place all the current limit circuitry at the LM317 input.
But you can't have any resistors or circuitry on the output or you will degrade the regulation, so you need to also remove the emitter follower booster from it's location. Use the "High Current Adjustable Regulator" configuration shown on page 17 in the National LM117/317 data sheet.
Thanks for your suggestion. However I am abandoning this design. I am working on a +/- 40V supply design that does not rely on LM317 for regulation. 317 will only be used to set a voltage reference. The rest will be taken care by an op-amp circuitry. I will try to upload the new design within two hours
Oh and if I cascade several LM317 in series, will that increase noise rejection? My goal is 30V reference. Input is 55V with less than 100mV input ripple.
The LM317 is fine providing the input-output differential is below 40V. A 39V zener can be connected across it to protect it from transient short circuits. If over current protection is still required then it can be done before the LM317.
I don't see any need to cascade a load of LM317s unless you've got no choice in voltage you want to drop. In this case since you have a choice, make the voltage drop as low as you possibly can.