Archive for the ‘Power Supplies’ Category:

2021-07-29 Heathkit IP-18 Power Supply Re-Cap

Last week I saw an old Heathkit IP-18 power supply on eBay for $50 OBO, free shipping. I don’t really need another PS, but I’m a Heathkit builder and a big fan. So I offered $30, thinking the seller would not take it. But a few hours later the message came that the seller had

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2021-06-12 Switch Mode Power Supply Items To Check

From FB group electronics parts Joshua E. Hrouda There also is a high value resistor from the rectified and filtered DC to the base of the power transistor. This can change value. After this resistor bootstraps the transistor into oscillation, there js a winding, a rectifier diode and filter capacitor that powers the base. Make

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2021-05-11 Power Supply Protection Diodes

First off, *all* power supplies should have what this one has. A high current diode across the output jacks, cathode or banded end to positive. This is to protect the output from reverse voltage. A high current diode across the 2N3055 pass transistor, cathode or banded end towards the collector. This protects the transistor from

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2020-09-05 Capacitive Dropper Failures In 240 VAC countries

From a comment I left in Big Clive’s youtube video https://youtu.be/jgaCYRc1-og In the past I’ve seen Clive having to replace “used up” capacitors in the ‘capacitive dropper’ circuits of low cost line operated devices. The problem seems to be common in other countries but here in the US I haven’t seen any problems with the

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2020-09-03 Distributed Generation And Islanding

There is a lot of concern for safety when DGs (distributed generators) are connected to the power grid. The grid operators must ensure that none of the DGs feed back into the grid when the grid generator is not operating. They go through several scenarios in this article. https://electrical-engineering-portal.com/protection-impacts-intentional-islanding-distributed-generation From what I see the DG

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2018-07-20 My Digital Dice Were Loaded!

From FB group Building Transistor Radios, Jul 27 Rolando Fernández I bought a kit for a digital die (one die of a pair of dice). I assembled it and then I rolled the die many times and wrote down the values to see if it was random. I was shocked! It was loaded! It was

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2017-09-23 Cellphone Charger Secret Circuit

Posted to FB Arduino group Sep 23 Mbihi Oliver Four hours is twice as long as 2 hours with the correct charger.  Here is a secret many don’t know:  Smartphones don’t necessarily charge at maximum, especially if they’re charged by a charger not made for their phone. Smartphones often have a sensing circuit that checks

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2017-06-15 Capacitor Leakage Tester Ideas

I was asking about very old capacitors and their shelf life on FB vintage test equipment group.  The guys tell how good the old capacitor testers are because they have the “magic eye” to check for leakage. I was thinking that it would be easy to test any capacitor for leakage.  All that’s needed is

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2017-06-01 How To Disable 5V Regulator?

I’ve been getting PC boards that have all the chips operating at 5 volts, but the input voltage has to be between 7 and 12 volts.  The board has a 5 volt regulator on the board, and often it is a surface mount chip.  But I have dozens of 5 VDC, 1/2 amp AC adapters,

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2017-05-04 Interrupting The Supply V to the Oscillator

I was working on the 27 MHz oscillator for testing the regens, and I thought it would be a good idea to turn the carrier off for a small fraction of a second every 1 or so seconds.  So I built a two transistor flasher with a third transistor to invert the pulses.  Instead of

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