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I’m trying to ‘hack’ a LED Fire-effect light bulb to work on a 9v battery.

Using a multimeter I can see that the bulb converts mains voltage to 5v. I’ve got my hands on a 9v-to-5v voltage regulator (spec sheet - https://dm-components.com/eBay%20pdf/AMS1117.pdf) and did some experiments.

When I plug my multimeter into a simple battery circuit I get 7v (the battery I’m using must be a little flat).

Battery

However, when I put the multimeter into the voltage-out part of the regulator, I get 6.3v…not the 5v I’m expecting.

Volt Out

What am I missing? And any advice for a newbie to electronics on how to convert 9v battery to 5v?

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    \$\begingroup\$ I want you to understand that taking these pictures was a really smart move on your part. Good job. \$\endgroup\$ – Harry Svensson Oct 22 '18 at 21:43
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A three terminal voltage regulator requires a ground (or for adjustable regulators, divided output voltage) connection.

Your pictures clearly show that you have none.

You must provide this connection, otherwise the regulator has no way to monitor its own output voltage, so its feedback loop cannot requlate.

Many regulators also require capacitors on the input and output for stability.

Please see the regulator's data sheet for the recommended connections and required capacitors.

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    \$\begingroup\$ @bluefrog: Also, many regulators require a minimum load current to produce the correct output voltage - too little load current may cause the output voltage to be higher than spec. \$\endgroup\$ – Peter Bennett Oct 22 '18 at 21:53
  • \$\begingroup\$ Thanks for your responses, it’s really helped kick me in the right direction. I moved to LM7805 regulators and now get 5v outputs - super! As Peter has expertly predicted,I’ve come to another problem. the 9v battery drains to a point that is out of the volt tolerance,killing the circuit with juice in the battery. Are there components/tools that output 5v, and allows the battery to continue powering the circuit once it’s drains below the rvolt tolerance (or boasts the output to 5v until the battery is dead)? I’ve seen the name Buck Converter flowing round, am I on the right track? \$\endgroup\$ – BlueFrog Nov 5 '18 at 0:25
  • \$\begingroup\$ The problem had nothing to do with the choice of regulator, and everything to do with not wiring it up properly. A 9v battery is almost certainly not what you want to use for your project. \$\endgroup\$ – Chris Stratton Nov 5 '18 at 13:58

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