I rebuilt my power supply the last few weeks. I had a couple of LED panel meters (Volt and Ammeter) and thought I would convert my old single output lm350T regulated supply to a 3 output (5,12, var) supply. Transformer is a 26.2 Center tapped. I used the full windings and feed three regs (7805, 7812, 350K) after the large (enough) bridge rectifier. Variable works fine. 7812 output appears OK
Problem is that the 7805, supplies the +5 for the digital meters. This voltmeter is to display the variable output value. With the voltmeter connected, it draws about 40 mA. It causes the 7805 to immediately shut down to ~2 volts, thus wreaking havoc on the meter. I know the meter is OK as I temporarily connected it to the var output at 5 volts and it is fine. Anyone have experience with this? I thought I popped the 7805 so replaced it but same thing next time. The input voltage is quite high....38 volts after rectification and filtering, no load, but at such a low current draw, power dissipation in the 7805 is just over 1 watt and the shut down is immediate so I do not think it is a heat issue.
Any suggestions? Input just too high?
Problem is that the 7805, supplies the +5 for the digital meters. This voltmeter is to display the variable output value. With the voltmeter connected, it draws about 40 mA. It causes the 7805 to immediately shut down to ~2 volts, thus wreaking havoc on the meter. I know the meter is OK as I temporarily connected it to the var output at 5 volts and it is fine. Anyone have experience with this? I thought I popped the 7805 so replaced it but same thing next time. The input voltage is quite high....38 volts after rectification and filtering, no load, but at such a low current draw, power dissipation in the 7805 is just over 1 watt and the shut down is immediate so I do not think it is a heat issue.
Any suggestions? Input just too high?
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